Ndt-liquid Penetrant Testing - General Dynamics.pdf

PI-4-2

FOURTH EDITION

PROGRAMMED INSTRUCTION HANDBOOK

NONDESTRUCTIVE TESTING liquid penetrant

GENERAL DYNAMICS

Convair Division

PI·4·2

FOURTH EDITION

PROGRAMMED INSTRUCTION HANDBOOK

NONDESTRUCTIVE TESTING liquid penetrant Copyright

©

1977

GENERAL DYNAMICS ConI/air Division

TABLE OF CONTENTS

Preface

v

Acknowledgements

vi

Introduction

vii

Instructions .

viii

Chapter I - Introduction to Liquid Penetrant Testing

I-I

Description . . . . . . . . . Detectable Discontinuities . . . Review of Possible Discontinuities Oil and Whitmg Method Review Chapter 2 - Surface Preparation. Need for Cleaning Methods of Cleaning Selection of Cleaning Method(s) Review Chapter 3 - Penetrant Application Capillary Action . . . Properties of Penetrants Fluorescent Penetrants Visible Dye Penetrants Dual Sensitivity Penetrants Methods of Application Penetration Time. Temperature Review Chapter 4 - Excess Penetrant Removal Precautions . . . . Types of Penetrant . Methods of Removal

I-I 1-2

1-6 1-8 1-15

2-1 2-2 2-4 2-10 2-14

3-1 3-1 3-2

3-6 3-6

3-9 3-14

3-16 3-26 3-32

4-1 4-1

4-3 4-3

Review Chapter 8 - Practical Applications Material Combinations Process Description. . Selection of Penetrant . Surface Preparation. . Penetrant Application . Selection of Dwell Time Excess Penetrant Removal Selection of Developer Developer Application. . Development Time . . . Operation of Black Light. Use of Post-Emulsified Penetrants Use of Solvent-Removed Penetrants Use of Dual Sensitivity Penetrants . Chapter 9 - Test Equipment and Special Purpose Materials Stationary Test Equipment. . . . . . Automatic Processing . . . . . . . . PrecIeaning and PostcIeaning Equipment. Portable Test Equipment. . Special Purpose Materials Liquid Oxygen Compatibility Other Special Purpose Materials Review

7-\7

8-1 8-1 8-2 8-8 8-23 8-28 8-29 8-40 8-42 8-44

8-50 8-53 8-54

8-70 8-81 9-\

9-1 9-7 9-8

9-9 9-12 9-\2 9-22

9-25

Self-Test

A-\

Glossary

B-\

iii

PREFACE

This Fourth Edition of PI4-2, "Liquid Penetrant Testing." has been considerably revised over previous editions. As was the case with the earlier issues, several years of use in hundreds of training situations has produced many recommendations for changes ahd improvements. All such recommendations were carefully screened and where they fell within the scope of coverage and where it was felt they would improve the teachability or understanding of the subject matter, they were Incorporated. The material has been further expanded to cover the recent developments in hquid penetrant testing. Other programmed instruction handbooks in the Nondestructive Testing series include: PI4-1 PI4-3 PI44 PI4-5 PI4-6

Introduction to Nondestructive Testing Magnetic Particle Testing Ultrasonic Testing Eddy Current Testing Radiographic Testing

It is recommended that PI4-1, "Introduction to Nondestructive Testing." be com-

pleted before starting this book in order to have the benefit of certain basic metallurgy information that will make this program on liquid penetrant testing more understandable and easier to master.

v

INTRODUCTION

This handbook will teach you how and why a liquid penetrant test works, the materials required for a liquid penetrant test, liquid penetrant indications and their meaning, and the limitations of liquid penetrant testing. When you have completed this study, you should be ready for practical demonstration sessions and on-the-job training to fully qualify you as a liquid penetrant test technician. Do not rush through the book. Take whatever time you need to get the most from the material presented. Depending on your background knowledge, reading speed, etc., the reading time it takes you to complete this book may vary from 2 hours to 6 hours or more. At the back of the book is a set of self-test questions that will help you in evaluating your newly-gained knowledge. Also included is a glossary of terms relating to liquid penetrant testing.

vii

CHAPTER 1 - INTRODUCTION TO LIQUID PENETRANT TESTING

I-I

Liquid penetrant testing is one of several methods used in nondestructive testing to locate discontinuities. Discontinuities, you'll recall from our "Introduction to Nondestructive Testing," are simply breaks in the continuity of a material or structure. Examples of discontinuities are laminations, cracks, forging laps, folds, seams, inclusions, and porosity. In short, liquid penetrant testing is a method used to find breaks in continuity. Virtually any material, except those considered "overly" porous, can be tested with liquid penetrants. Metallic materials that can be tested include aluminum, magnesium, titanium, iron, copper, brass and bronze, as well as most alloys. Non-metallics include ceramics, plastic, and glass. Briefly, the method works like this: A dye carrying liquid (penetrant) IS spread over the surface of the specimen or article to be tested. Time is allowed for the liquid to seek out and enter discontinuities. The liquid remaining on the surface is then cleaned off and a powder (developer) is applied. This powder acts like a blotter. It draws the dyed liquid remaining in the discontinuities back to the surface, producing an indication. Oversimplified? Yes, but that's basically all there is to liquid penetrant testing. But since we're going to be required to use the method, we'll have to tackle the subject in a great deal more detail. So, let's get at it. Tum to page 1-2.

From page I-I

1-2

A liquid penetrant inspection is One of several methods used in nondestructive testing to locate discontinuities. Typical applications include the detection of cracks, porosity, and "through" leaks - leaks that pass from one surface to another. In locating discontinuities, however, a liquid penetrant test will find only those discontinuities that are open to the surface' Think about it for a moment and you will see that this simple point is mighty important. If penetrant cannot enter the discontinuity, no indication can be produced. Below are two pictures of example specimens. Each shows the specimen cut to reveal a cross section of the material. Each includes an exaggerated and enlarged discontinuity - but only one of the discontinuities is detectable with liquid penetrant testing before the cross section was cut. Whlch view has the discontinuity that you could find with a liquid penetrant test?

View A View B

Page 1-3 Page 1-4

From page 1-2

1-3

Another look at the two pictures is in order.

Although View A has a discontinuity, this discontinUity is not open to the surface and therefore cannot be reached by a liquid penetrant. The very first point to remember in this program is that in a liqUid penetrant test, you can expect to learn the location of only those discontinuities that are open to the surface. View A couldn't be the an,wer since a liquid cannot reach the discontinuity, but look again at View B. That discontinuity could be reached with our liquid penetrant, couldn't it? View B is the correct choice. Turn to page 14.

From page 1-2

1-4

Good. You've spotted the picture of the surface discontinuity (View B). This program will show you how a surface discontinuity such as this can be found with a liquid penetrant test.

VIEWB

As we take a close look at liquid penetrant testing, you will learn the answers to such questions as: WHAT CAN BE LEARNED FROM A LIQUID PENETRANT TEST? HOW DOES LIQUID PENETRANT TESTING WORK? WHAT MATERIALS ARE REQUIRED FOR A LIQUID PENETRANT TEST? WHAT ARE THE LIMITATIONS OF LIQUID PENETRANT TESTING?

In fact, we've already begun to provide the answer to the first of these questions! Which one of the following statements is true? Using liquid penetrant testing, I can detect all discontinuities. Using liquid penetrant testing, I can locate those discontinuities that are open to the surface

Page 1-5 Page 1-6

From page 1-4

1-5

Sorry but your selection is incorrect. For discontinuities to be detected by liquid penetrant testing, they must be open to the surface. The penetrant must be able to enter the discontinuity. If the penetrant cannot enter the discontinuity, no indication will be produced. The discontinuity remains undetected. With this in mind, tum to page 1-6 and continue.

From page 1-4

1-6

Right! With a liquid penetrant test, you can fmd only those discontinuities that are open to the surface. To detect subsurface discontinuities, another method of testing such as radiographic or ultrasonic testing must be used. By now you are also well aware that there are many, many types of discontinuities. And many of them are or can be made open to the surface. Here are just some of the discontinuities that you could encounter. nonmetallic inclusions porosity stringers seams

forging laps heat treat cracks

forging bursts, or cracks cold shuts shrink cracks blow holes grinding cracks fatigue cracks

And when welding ... crater cracks shrink cracks

porosity nonmetallic inclusions

The question is - which of them can be detected with liquid penetrant testing? Turn to the next page.

From page 1-6

1-7

Some discontinuities formed during rolling, forging, or casting are always open to the surface. They are detectable with penetrants from the time they are formed. Forging laps, grinding cracks, and crater cracks are examples of this type of discontinuity. Some of the others, however, are not always open to the surface. Examples of thiS type of discontinuity are nonmetallic inclusions, stringers, and porosity. Nonmetallics, for example, are formed when the ingot is poured. They could very well be subsurface in the mgot and even if the entire surface of the Ingot was subjected to liquid penetrant tests, no indications of nonmetallics would be found. The ingot is then cropped. The top of the ingot is removed, and a billet is formed. Would the nonmetallics now be detectable? If the cropping cut through them, those exposed by the cut ... or "brought to the surface" by the cut, could be located with penetrants; those still within the billet would not be detectable. During rolling, forging, or casting (the next operation) the same possibilIty exists. If the operation brought discontinuities to the surface, a subsequent penetrant test would reveal their presence. And, to carry the example one step further, subsurface discontinuities might yet be exposed during finishing operations such as grinding or machimng. A liquid penetrant test conducted after grinding or machining could then reveal the presence of a discontinuity that had been hidden during earlier tests. I would like to know more about the development of discontinuities during the processing of metals . . . . . . . . . . . . . . I understand why discontinuities that are subsurface at one stage in production could be open to the surface at another and am ready to continue. . . . . . . . . . . . . . . . . . . . . .

Page 1-9

Page 1-8

From page 1-7

1-8

Fine. Discontinuities that are subsurface at one stage in production could very well be open to the surface at another. When they are, they're detectable with liquid penetrants. This means a penetrant test could be performed successfully following any operation that might cause or expose surface discontinuities. In fact, many of the controlling specifications and standards make in-process inspections mandatory. We now have the answer to "WHAT CAN BE LEARNED FROM LIQUID PENETRANT TESTING?". We can learn the location of discontinuities that are open to the surface at the time penetrants are applzed. HOW DOES A LIQUID PENETRANT TEST WORK? The answer to that can best be seen in a brief look at the "Oil and Whiting" method - the forerunner of modern liquid penetrant testing. The oil and whiting method was used in the early 1900's by the railroads in testing locomotive parts, etc., such as axles, crank pins, and couplers.

It worked like this: First, the parts were prepared for test by removing as much dirt, grease, rust and scale, etc., as possible. This often involved bOiling the parts in a caustic soda solution and then drying. Following drying, the parts were dipped in a heavy, dark colored lubricating oil that had been thinned WIth kerosene or some other thin oil. This served as the "penetrant." Frequently, a used oil was employed because it provided an even darker color. A time interval of up to several hours was then allowed for the diluted oil to soak into possible cracks. What occurred can be seen in this picture.

Turn to page 1-14.

From page 1-7

1-9

Good for you. Let's consider again the steel making process as presented in the first programmed text in this series. Here are the first few steps taken in the process as shown in the flow chart from that book.

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TOP CROPPED (CUTOFF) TO FORM BILLET

INGOT

Although thus far in the steel making process only a few of the many possible discontinuities could have been created, those that the process has brought to the surface could be examined with liquid penetrants. Thus, if ingot cropping cuts through an area of porosity or nonmetallic inclusions, examination of the cropped ingot with a liquid penetrant test would reveal the location of those discontinuities. Turn to the next page.

1-10

From page 1-9

As the steel making process becomes a production process, the flow chart shows that additional types of discontinuities (such as stringers, seams, forging laps, and cold shuts) can be created by roIIing, forging, or casting.

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USABLE BOTTOM PORTION OF INGOT (BILLET) CONTAINS SOME INCLUSIONS AND POROSITY. FORMING BEGINS HERE

,...

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SHEET METAL PARTS OR PLATE MATERIAL

, ... FORGED PART

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CASTING

CAST PART

Discontinuities created by the forming of metals are called "formed discontinuities" and many are always open to the surface. They, and any other discontinuities that have been opened to the surface during the production process, are detectable with liquid penetrants. Turn to the next page.

1-11

From page 1-10

Now let's carry the flow chart one step further to show a later stage in development that can reveal discontinuities, which may be found with liquid penetrant testing. That stage is the "fimshing" stage where the materials developed from rolling, forging, and casting are further worked to form finished products. The finishing stage may include welding, grinding, and machining.

BAR STOCK ...

SHEETMETAL PARTS OR PLATE MATERIAL

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Two examples of new discontinuities that may develop during finishing operations are grinding cracks and crater cra-cks. The finishing stage may also expose subsurface discontinuities, such as nonmetallic inclusions, which can now be located by liquid penetrant testing. Turn to the next page.

From page 1-11

1-12

It is possible to expand the flow chart one step further and include the one other time that liquid penetrants can be used to locate discontinUities that would not have been detectable in the various stages we've discussed so far. This final stage occurs long after steel making, forming, and finishing. It occurs during operational use of the article. Fatigue cracks are a good example of this type discontinuity. Such discontinuities may occur: 1) as the article is weakened through repeated use, or 2) as the result of overloading. Inspections are performed at predetermined time intervals throughout the service life of the article, or when there is reason to suspect the article has been damaged. Liquid penetrant testing of large valve bodies on a periodic basis would be an example of the former, while testing of the same valve after an extreme system pressure would illustrate the latter.

During these inspections, often previously subsurface discontinuities as well as service created discontinuities might now be open to the surface and could be located with penetrants. (Fatigue cracks are sometimes traceable to subsurface discontinuities that have weakened the article during its use.) Adding the example used here to illustrate this point, the flow chart will now give us the overall picture and show us when we can expect liquid penetrant evidence of various discontinuities. This has been done on the following page. Turn to the next page.

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1-13

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In summary, a discontinuity that is not detectable with liquid penetrants in early production stages, could be detected with liquid penetrants at later stages. Turn to page 1·8 and continue.

1-14

From page 1-8

Continuing with the oil and whiting method, the oil remaining on the surface was then wiped off with rags or swabs usually moistened with kerosene. The kerosene was the "excess penetrant remover."

~;::~::--~R~::;:~RAG (MOISTENED WITH KEROSENE)

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When surfaces had dned, a coating of powdered chalk or whiting was applied. The whiting served as the "developer." WHITING (DEVELOPER)

01 L FILLED CRACK

If there were discontinuities, the oil in them would begin "creeping" back to the surface and appear as a dirty brown stain in the whiting. Discontinuities became visible. WHITING (DEVELOPER)

N

The parallel between the oil and whiting method and modem day liquid penetrant testing becomes most obvious when compared to the "visible dye" penetrants used today - as you'll see later on in this program. But first, a quick review. Tum to the next page.

I-IS

From page 1-14

I.

The next few pages are different from the ones that you have been reading. There are arrows on this page. (Write in the correct number of arrows.) Do not read the frames below. FOLLOW THE ARROW and turn to the TOP of the next page. There you will find the correct word for the blank line above.

5.

open

6.

Crater cracks, because they are open to the , (can/ cannot) be located by liqUid penetrant inspection.

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10.

liq uid penetrant

II.

Even after production is completed on an article and the article is in use, dis may develop.

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remover

16.

When surfaces had dried, a coating of whiting (chalk) was applied. This whiting was the dev

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1-16

This is the answer to the blank in Fra e number I. fo Frame 2 IS nex

~ These frames will provide a review of the matenal you have covered

2.

to this point. There will be one or more blanks in each -'.f_ __ Turn to the nex t page. Follow the arrow.

6.

surface can

7.

Forging laps are a type of "formed" dIscontinuity that will always be _______ tothe _ _ _ __

II.

discontinuities

12.

An example of a postproduction discontinuity is a fatigue crack. If .____ to the it can be detected with lIquid penetrant testing.

16.

developer

17.

The oil and whiting method, though it was quite crude, set the stage for modern liqUId penetrant testing. We still use a ~ __________ , ,anda~d~_ _ _ _ __ a

1-17

2.

frame

3.

By following the arrows or instructions you will be directed to the frame that follows in sequence. Each frame presents information and requires the filling in of

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open surface

8.

Other types of discontinuities, such as porosity and nonmetallic inclusions may not always be detected by liquid penetrant testing. When they can not be detected, they will be sub discontinuities.

12.

t

open surface

13.

An early test method used by the railroads to locate fatigue method. cracks was called the - - and

t 17.

penetrant remover (cleaner) developer

18.

However, there is a little more to today's liquid penetrant testing. Today there are Six Basic Steps to accomplishing the test. We'll now study each of them in some detail. Tum to page 2-\'

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1-18

3.

blanks (spaces, words)

4.

Liquid penetrant testing is one of several nondestructIve testing methods used to locate dis

t 8.

subsurface

9.

However, if they are open to the surface, discontinuities such as non inc can be located with liquid penetrant testing.

t 13.

oil whiting

14.

In the "oil and whiting" method, a diluted oil was used as the lL

t Disregard this frame. The instructions were to turn to page 2-1.

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1-19

4.

discontinuities

5.

It is important to note that liquid penetrant testing will locate only

those discontmuihes that are

"'0_ _ _ _

to the surface. Return to page 1-15, frame 6.

9.

10.

nonmetallic inclusIOns

In many cases, a discontinuity that is subsurface in an early stage of production will be exposed in a later production stage. It may then be detected by testing. Return to page 1-15, frame 11.

14.

penetrant

15.

After the diluted oil has been allowed to penetrate discontinuities, the excess was removed with rags usually moistened with kerosene. The kerosene was the excess penetrant r,.,e'-_ _ __ Return to page 1-15, frame 16.

2-1

CHAPTER 2 - SURFACE PREPARATION

We are about to take the first of the Six Steps required in a liquid penetrant test. It is necessary that the sequence of the steps be learned. To help you in this learning, we will not only explain each step, but will also show each step on a flow diagram, As each step is introduced, it will be added to the flow diagram In solid lines. Here is Step One entered on the flow diagram. ,---------,

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From page 2-1

2-2

To be adequately prepared for any liquid penetrant test, anything that could block the entry of penetrants must be removed. Right away this bnngs CLEANING to mind. You can readily imagine how dirt and grease could prevent penetrants from entering discontinuities. Both are "contaminants" and must be removed. The list of contaminants also includes oil, rust, scale, weldmg flux, acids, and chromates just to mention a few. Even water is considered a contaminant and must be removed in Step One - Surface PreparatIOn. It will also be apparent that paint and metallic plating would block penetrant entry. In most cases you will be required to conduct tests before such coatings are apphed. But not always. When such a coating is encountered, adequate surface preparatIOn requires that it be removed before any further action is taken.

Therefore, if you received a finished article that had been painted, and you are required to give It a liquid penetrant test, your first action would be to ... apply a penetrant carefully over the surface remove the paint. . . . . thoroughly wash the article. . . . . . .

Page 2-3 Page 2-4 Page 2-5

From page 2-2

2-3

"Apply a penetrant carefully over the surface"....717? Hold on a minute. Think over the basic principle of liquid penetrant testing again-

"The penetrant must enter the discontinuity. " Here's a picture of the procedure you've chosen .... • A'·nll~U' • • NETRANT

DISCONTINUITY

See our point? The paint blocks the entry of penetrant. Return to page 2-2 and pick an answer that will give our penetrant a chance to go to work!

From page 2-2

2-4

Right! Before you took any other action (such as washing or cleaning) that paint would have to go. The same would be true of any plating. Paint can be effectively removed by solvent paint removers, or by "hot tank" alkaline paint strippers. Plating and inorganic soils such as rust and scale can be removed with inhibited acid pickling solutions. Hot alkaline cleaners are also employed for descaling and rust removal. No attempt will be made here to teach you how to use these various cleaning methods; but do remember, you must be down to bare metal if you plan to use liquid penetrants on metals ... down to bare ceramic if testing ceramic materials... down to bare plastic... down to bare glass. Test surfaces - as well as discontinuities - must be dry and contaminant-free before penetrants can be applied. Turn to page 2-6.

From page 2-2

2-5

"Thoroughly wash the article" was your choice. Not correct. Why? Here's the article before washing.

DISCONTINUITY

Here's the article after washing.

See, no change! Penetrant still couldn't enter the discontinuity. Return to page 2-2 and select another answer.

2-6

From page 2-4

More cleaning methods commonly employed in Step One - Surface Preparation are solvent cleaning, vapor degreasing, detergent cleaning, and steam as well as ultrasonic cleaning. But how do we decide on what method to use? (Assuming we have a choice.) Solvent cleaners are often used to dissolve and flush away the various oils and greases found on test articles. In selecting a solvent cleaner, remember that it must be volatile (readily vaporized) so it will easily evaporate from tight discontinuities and not leave any residue to dilute or prevent the entry of penetrant. Typical solvents that will do the job include naphtha, mineral spirits (paint thinner), acetone, perchlorethylene, isopropl alcohol, and methylene chloride - all of which evaporate readily at room temperature.

Solvent cleaners, however, are not recommended for removing rust and scale, welding flux or spatter, and in general, inorganic soils. Also a word of CAUTION! MOST SOLVENT CLEANERS ARE TOXIC! MOST OF THEM ARE FLAMMABLE! THEY BURN. This means they could injure you or make you sick. Avoid breathing their fumes. Avoid skin contact. Avoid open flames. And never smoke while handling them! Turn to the next page.

From page 2-6

2-7

Vapor degreasing is the preferred method for removing organic contaminants such as oil and grease. The method not only thoroughly cleans test articles, the resultant heating helps to drive off and evaporate moisture in discontinuities. The chlorinated solvents employed, however, can be harmful to certain materials such as nickel, stainless steel, and titanium. The method should not be used in cleaning articles made of such materials. Detergent cleaning involves the use of nonflammable, water-soluble compounds mixed with water. It is also an effective method for removing surface soils, particularly when employed as a "hot tank" process. Since the solutions used, however, may be either acidic or alkaline in nature, precautions must be taken to ensure that the selected detergent is noncorrosive to the article being cleaned. Following cleaning, a thorough rinsing and drying is necessary. Methods of drying include the use of hot air blowers, heat lamps, and ovens. Steam cleaning is particularly adaptable to the cleaning of large unwieldY items. It removes inorganic soils as well as many organic contaminants. But it may not reach to the bottom of deep discontinuities. A followup solvent soak is often recommended. Ultrasonic cleaning is often combined with a solvent or detergent bath to improve cleaning efficiency and reduce cleaning time. The method works best with water and detergent cleaning when contaminants to be removed are inorganic, and with solvents when contaminants are organic. Following cleaning, it is recommended that test articles be heated to aid the evaporation of cleaning fluids.

What this all "boils" down to is that a number of cleaning methods are available. But the one, or ones, selected will depend on ... the type of contaminant or soil to be removed. the composition of the test article both of the above. . . . . . . . . . . .

. Page 2-8 . Page 2-9 Page 2-10

From page 2-7

2-8

Well, you're "half right." The cleaning method or methods selected will depend on the type contaminant or soil to be removed. But what about composition? Didn't we also learn that vapor degreasers can harm certain materials ... that detergents may be corrosive? Sure did. This means you must also consider composition in selecting a cleaning method for doing the job in Step One - Surface preparation. With this in mind tum to page 2-10.

From page 2-7

2-9

That's right. Some cleaning methods can be hannful to certain materials. The composition of test articles must be considered. But didn't we also learn that some cleaning methods may do a better job than others relative to a specific contaminant? Didn't we learn that solvents and vapor degreasing are better for removing organic contaminants such as oily films and grease? Sure did. An acidic or alkaline cleaner is likewise better for removing inorganic soils such as rust, scale, and dirt. In selecting a cleaning method to do the job, you must consider both the composition of the test articles to be cleaned as well as what type of contaminant is to be removed. Tum to page 2-10.

From page 2-7

2-10

Good. Both the type of contaminant (soil) to be removed and the composition of the test articles must be considered in selecting the cleaning method(s) for preparing articles for test. Other considerations are the "practicality" of the cleaning method (e.g., are test articles too large to be cleaned by a particular method), and possible health hazards, if any. Keep in mind that specific requirements are spelled out in the controlling specifications and standards to which you will be working. Mechanical cleaning methods such as wire brushing, abrasive blasting, emery cloths, and metal scraping are not generally recommended. But there are times when they must be used. When they are, the risk is run that a discontinuity, otherwise open to the surface, might be closed. This is shown in the examples below.

BEFORE MECHANICAL CLEANING

AFTER MECHANICAL CLEANING

When mechanical cleaning must be used, discontinuities can be reopened with a chemical etch that removes a very slight amount of material from the surface. Which of the statements below best states the risk involved in using mechanical cleaning? Discontinuities might be closed Contaminants could be sealed in discontinuities Peening of test surfaces may occur . . . . .

Page 2-11 Page 2-12 Page 2-13

From page 2-10

2-11

Right! Discontinuities might be closed. If mechanical cleaning must be used, a chemical etch is generally recommended to reopen discontinuities. This, however, can be an extremely delicate operation and usually does not involve the liquid penetrant testing technician. Remember, proper cleaning is the key to Step One - Surface Preparation. Without it, penetrant tests will be unreliable. Vapor degreasing is usually the preferred method for removing organic contaminants such as oil and grease. Detergent cleaning is preferred in removing inorganic soils. But whatever the cleaning method used, it must not harm the articles to be cleaned, and it must result in a test surface that is dry and contaminant-free ... free of residue. Again, hot air blowers, heat lamps, and ovens are often recommended to expedite drying. Before we proceed to Step Two, turn to page 2-14 and check yourself on the major points with a short review.

From page 2-10

2-12

You're right. Contaminants could be sealed in discontinuities as a result of mechanical cleaning. But, the real problem is much more basic. If penetrant can't enter the discontinuities, no indications will be produced. Return to page 2-10, take another look at the pictures, and then choose the simple, basic statement that best states the risk involved in mechanical cleaning.

From page 2-10

2-13

Yes, peening of test surfaces may occur but that by itself isn't the best choice. In many instances, a peened surface may be actually desired - but not in a liquid penetrant test. The real problem with mechanical cleaning is that discontinuities might be sealed and thereby prevent the entry of penetrant. Should this occur, no penetrant indication is possible. Why not return to page 2-10, look at the pictures again, and choose once more when you're ready.

2-14

From page 2-11

1.

Step One in any liQuid penetrant test is Surface

t 4.

contaminants

5.

Although surface coating such as paint or metallic plating are not considered contaminants, they must be re any cleaning.

prior to

t 8.

discontinuities

9.

Unlike abrasive blasting or wire brushing, chemical cleaners such as cleaning solvents and detergent solutions will not discontinuities.

t 12.

harm (damage)

13.

Test surfaces, as well as discontinuities, must be left dry and free of following cleaning.

t

2-15

I.

Preparation

2.

During Step One, any contaminants that might block the entry of ________ into discontinuities must be removed.

5.

removed

6.

If paint or plating were not removed, the penetrant inspection results could be thought to indicate mistakenly that the article is free of _ _ _ _ _ _ _ _ _ _---'i"'e"s .

9.

close (seal)

I O.

Of the chemical cleaning methods, vapor de is preferred for removing 0 contaminants such as oily films or grease.

13.

contaminants (residue)

14.

And use of hot air blowers, heat lamps, or ovens is often recommended following cleaning operations to expedite _ _ _ __

2-16

2.

penetrant

3.

Step One involves two considerations. First, any surface coating such as paint or metallic plating must be removed. Second, all con (s) must be removed with proper cleaning.

6.

discontinuities

7.

Mechanical cleaning methods such as abrasive blasting, wire brushing, emery cloths, and metal scraping are not generally recommended because they could a discontinuity that might otherwise be open to the surface.

I o.

degreasing organic

II.

... 0,--_ _ _ _ _ _ cleaning is recommended in removing ino

soils.

14.

drying

15.

This completes the review of Chapter 2. Let's now turn to page 3-1.

2-17

3.

con taminan ts

4.

Water, dirt, grease, oil, scale, and rust are all considered

Return to page 2-14, frame 5.

7.

close (cover, seal, conceal)

8.

When mechanical cleaning is employed, it should be followed by a chemical etch to reopen ___________ that may have been closed. Return to page 2-14, frame 9.

I I.

Detergent inorganic

12.

Whatever the cleaning method employed, it must not _ _ _ _ __ test articles. Return to page 2- I 4, frame 13.

Whoops. Your instructions were to turn to page 3-1.

CHAPTER 3 - PENETRANT APPLICATION

3-1

Penetrant application is Step Two in the procedure. What materials are required in this step? A penetrant, obviously. But what makes a "good" penetrant? Basically, any liquid could be considered a penetrant. The so-called "penetrating power" is gained from a force in nature called capillary action. This force is available to any liquid. Capillary action is the force that causes sap to rise in trees. It's the force that causes oil to rise in a lampwick, a towel to soak up water, and a blotter to clean up spilled ink. The "penetrant" in each case is the liquid. . . the force is capillary action. A liquid penetrant placed on a surface does not merely seep into discontinuities. It is pulled into them by capillary action. Remember a penetrant does not depend on gravity to enter discontinuities. Capillary action is the reason you can cover the under surface of an item with a penetrant and have it work its way upward into a crack while all the time working against gravity. /PENETRANT

Turn to the next page.

From page 3-1

3-2

For liquid penetrant testing, however, we require much more from our penetrants than simply the ability to capitalize on nature's gift, "capillary action." Today, even the oil and kerosene used as the penetrant in the "oil and whiting" method is considered crude and outmoded. Although most penetrants are still oil based, chemists have been working with them until they seem to have combined the uncombinable. No single property makes a penetrant a "good" penetrant. It requires a combination of properties. The penetrants used in liquid penetrant testing must have the right viscosity, wetting ability, and surface tension. They must have "fluidity" so they will flow over the test surface and penetrate the smallest of discontinuities.They must have "body" (the exact opposite of fluidity) so they will stay put. They must not drY or evaporate too rapidly. And the flash point must be high enough to minimize the possibility of a rITe or explosion. Having a low specific gravity also has its advantages (most commercial penetrants today have a specific gravity of less than one). Water - a common contaminant - thus tends to settle or separate, making penetrant contamination easier to control. We, however, need not learn the chemistry involved in obtaining these properties. The proper compounding, fortunately, has been done for us. Turn to the next page.

From page 3-2

3-3

Here are five abilities - properties - that today's penetrants must have to help us as testers.

I. 2. 3. 4. 5.

The ability to hold a dye material in suspension. The ability to spread the dye evenly over the surface. The ability to carry the dye into any discontinuity open to the surface. The ability to bring up the dye as it is "coaxed" back to the surface. The ability, when desired, to be easily removed.

Notice the first four properties have something to do with a dye. The dye's the thing! Tum to the next page.

From page 3-3

3-4

New penetrants and the addition of dyes have given us the liquid penetrant methods used today. There are two dyes used:

FLUORESCENT

VISIBLE OR COLOR CONTRAST

A DYE THAT EMITS VISIBLE LIGHT RAYS WHEN VIEWED UNDER BLACK LIGHT.

1

A BRILLIANTLY COLORED DYE THAT IS HIGHLY VISIBLE UNDER NORMAL LIGHTING CONDITIONS.

1

When either a fluorescent or visible dye is combined with a suitable liquid, a dye penetrant is formed. Liquid penetrant testing requires, as Step Two, the spreading of one of these dy penetrants over the surface to be tested. We then rely on a natural force to get the dye penetrant into discontinuities. That force is called ... gravity. . . . capillary action

Page 3-5 Page 3-6

3·5

From page 3-4 Ooops! Hold on a minute.

We can't count on gravity to get the dye into a discontinuity. We often work on the under surfaces during penetrant application. Gravity certainly wouldn't help then, would it? Remember this picture? /PENETRANT

In order for the dye penetrant to fill the discontinuity it had to be drawn up into the discontinuity against the downward pull of gravity. Capillary action can do this.

Turn to page 3-6.

From page 3-4

3-6

Rightl We count on capillary action to get the dye into discontinuities. Again, we have two different dyes to work with - fluorescent and visible. Fluorescent penetrants contain dyes that are visible only under black light - black light being a special light of wavelengths between visible and ultraviolet light (3200 to 4000 angstroms). Almost invisible, black light causes many materials such as the fluorescent dye to glow in the dark. This fluorescence is normally a brilliant yellowgreen glow that "catches" the eye and magnifies. For special applications, there are fluorescent dyes that glow red or blue. Visible dye penetrants, as the name implies, contain dyes that can be seen in visible (white) light. They are also known as color contrast or nonfluorescent penetrants. The dye is usually bright red. but here again, there are special colors for special applications.

Of the two dye penetrants, the visible or color contrast penetrants are the simplest to use. No darkened area is required to view indications and neither is black light. The primary limitation is in getting enough contrast - enough dye into a discontinuity to form an indication. Best sensitivity (seeability) is obtained with fluorescent penetrants. Which of the following statements is true? Most fluorescent dyes produce a red discontinuity image. Visible dyes require the use of black light to be seen . . Yellow-green fluorescent indications appear only under black light

Page 3-7 Page 3-8 Page 3-9

From page 3-6

3-7

Color-wise you should have selected another answer. The fluorescent dyes usually appear as a brilliant yellow-green glow under black light. It is the visible or color contrast dyes that, in their commonest form, provide a red discontinuity image. Return to page 3-6 and select another answer.

From page 3-6

3-8

Since we evidently have not made this clear enough, we will take time here for a restatement of the characteristics of fluorescent and visible dyes. FLUORESCENT DYES - Fluorescence refers to the ability of certain materials to absorb light at one wavelength and return it at another. The light used is black light - an almost invisible light in the near ultraviolet range of wavelengths (3200 to 4000 angstroms). Fluorescent dyes absorb the black light and in turn emit light at a wavelength visible to the human eye. VISIBLE OR COLOR CONTRAST DYES - These dyes for the most part do not respond to black light. They are nonfluorescent, and they are viewed under normal (daylight or electric bulb) lighting. Remember, it is the fluorescent dyes that require special lighting. With this in mind, return to page 3-6 and make another selection.

From page 3-6

3-9

Correct. Because of the nature of the fluorescent dyes, yellow-green fluorescent indications can be seen only under black light. Again, the visible dye penetrants are the simplest to use, but best "see ability" is obtained with fluorescent penetrants. A third type of penetrant in use today is the "dual sensitivity" penetrant.

DUAL SENSITIVITY

{

A DYE PENETRANT THAT COMBINES THE CHARACTERISTICS OF FLUORESCENT AND VISI BLE DYEPENETRANT5.

DUBI sensitivity penetrants contain a combination of visible and fluorescent dyes. The visible color is generally a bright red; the fluorescent color, a yellow-to-orange red. The combination permits penetrant tests to be made under visible light, and questionable indications to be resolved under black light. Hence the term "dual sensitivity."

From what you now know, determine whether the following statement is true or false. All dye penetrants used in liquid penetrant testing depend on capillary action for penetration into a discontinuity. True False

Page 3-10 Page 3-11

From page 3-9

3-10

True. All dye penetrants depend on capillary action to get the penetrant into discontinuities., That is, they do once we've properly applied them to the surface we want to examine. Which of the following dye penetrants allows us to look for gross discontinuities using visible light, then check forvery fme cracks, porosity, etc., with black light? Fluorescent. . Visible dye . . Dual sensitivity

Page 3-12 Page 3-13 Page 3-14

From page 3-9

3-11

You do not yet believe that all dye penetrants depend on capillary action for penetration into a discontinuity? But, they do! Let's again see if we can convince you. Penetrants (liquids) would have to depend on one of two forces to enter a discontinuity - gravity or capillary action. If gravity were the only force, penetrants would seep into discontinuities only in a downward direction. Remember, however, that penetrants will also work their way into a discontinuity from the underside of an article. Capillary action is the reason. We again ask the question - do all dye penetrants depend on capillary action for penetration into a discontinuity? You bet they do. Tum to page 3-10 and your answer is ...

From page 3-10

3-12

Sorry but discontinuity indications produced by fluorescent penetrants can't be seen with visible light (unless of course the discontinuities are large). They require black light to make them visible. Visible dye penetrants likewise won't do the job because indications can be seen only with normal lighting (daylight, electric light bulb). That leaves us with the dual sensitivity penetrants. Dual sensitivity penetrants employ a combination of fluorescent and visible dyes. This means indications can be seen in normal light as well as black light. Neither the fluorescent or the visible dye penetrants have this capability. With this in mind ... Turn to page 3-14.

From page 3-10

3-13

A visible dye penetrant would do the job in locating gross discontinuities under visible light but does not respond to black light. A fluorescent penetrant likewise wouldn't work because the indications would be invisible under normal lighting. Dual sensitivity penetrants, however, employ a combination of fluorescent and visible dyes. What this means is that indications can be seen in normal light as well as black light. Neither the fluorescent or visible dye penetrants have this capability. With this in mind, tum to page 3-14.

3-14

From page 3-10

That's correct. Using a dual sensitivity penetrant will allow us to inspect for gross discontinuities with visible light, then under black light, check for extremely fme cracks, porosity, etc., without having to change penetrants. This has its advantages as you'll see later on. Since Penetrant Application is Step Two in the process, let's add it to our flow diagram and continue with the methods of penetrant application.

STEP I SURFACE

PREPARATION

0

SlEP2

~

PENETRANT APPLICATION

f+l.

0

~

1

Dye penetrants can be applied by anyone of the following means: Dipping (or immersion) Spraying Brushing Flowing In dipping test articles, the article is generally lowered into a tank containing the

dye penetrant, then raised and allowed to drain. Spray methods involve the use of conventional spray guns or pressurized spray cans. Brushing is accomplished with brushes or swabs. Flowing simply requires pouring the penetrant over the test specimen and allowing it to drain. Regardless of which method is chosen, the area to be tested must be adequately covered. As minimum coverage, keep this fIgure in mind: Cover all surfaces at least I inch (2.5 centimeters) around the area (e.g., a weldment) to be tested.

Is the following statement true or false? Applying a dye penetrant under pressure, such as with a spray gun, is done because it will more effectively force the solution into small discontinuities than will dipping. True False

Page 3-15 Page 3-16

From page 3-14

3-15

Not so. You think that applying dye penetrant with pressure from a spray gun will more effectively force the solution into small discontinuities than will dipping of the article. While the spray gun (or spray can) is popular for applying penetrants, it is not used for this reason. The spray method has merely proved itself convenient in application. The real work is accomplished by capillary action regardless of the method of penetrant application used. Turn to page 3-16.

From page 3·14

3·16

Right. It is capillary action that causes the penetrant to enter discontinuities. The spray gun is merely one means of applying penetrant. Sufficient time must then be allowed for the penetrant to enter discontinuities for capillary action to do its job. This time is called the penetration or "dwell" time. How long a time is required? Controlling specifications and standards, as well as the penetrant manufacturers' recommendations, provide us with penetration time charts to help in determining the correct time. In using these charts, however, remember, they suggest the minimum times that should be used. Here is a typical example. Minimum Dwell Time (Minutes)"

Material

Form

Type Discontinuity

Aluminum

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 5 10

Magnesium

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 10 10

Steel

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

10 10 20 20

-Temperature range 60 to 125° F (16 to 52°C) What do the times on the above chart represent? The maximum time penetrant can remain on an article for good test results . . . . . . . . . . . . . . . . . . . . . The time an article must remain submerged in a penetrant tank . The minimum time necessary for penetrant to enter a discontinuity

Page 3·17 Page 3·18 Pa~e 3·19

From page 3-16

3-17

Hold on a minute! The penetration times suggested on the charts aren't maximums, but minimums! They tell us the least time that can be used to expect valid test results. These times should never be considered maximums. It would be too easy to fall short of the required time. The result? Penetrant would not have enough time to enter all discontinuities! Return to page 3-16 and select another answer.

From page 3-16

3-18

Your answer is not correct. Here's why. Dipping (or immersion) is just one of the four methods suggested for penetrant application. There is also flowing, spraying, and brushing. The penetration time charts are equally useful when these methods are used. The times shown on the charts therefore cannot suggest, as you have chosen: "The time an article must remain submerged in a penetrant tank." Dipping is momentary. It merely applies the penetrant. After you have reexamined the selections on page 3-16 you'll see that there is a much better answer. Reread page 3-16 and make another selection.

3-19

From page 3-16

Correct. The times suggested on the chart reflect the minimum times necessary for the penetrant to enter a discontinuity. It is the time - duration - the penetrant must remain on test surfaces. The basis for determining the correct penetration or dwell time is a simple one. It simply takes longer for the penetrant to enter fme tight discontinuities than it does their larger cousins. Minimum Dwell Time (Minutes)'

Material

Form

Type Discontinuity

Aluminum

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 5 10

Magnesium

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 10 10

Steel

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

10 10 20 20

0

0

·Temperatu re range 60 to 125 F (16 to 52 C)

Looking at the chart again you'll notice that different times are specified for different types of discontinuities. Besides the type of discontinuity, we must also consider "form;" for example, is the test article a casting, forging, or weldrnent, etc.? There is one remaining variable shown on our example chart. Can you spot it? The type of penetrant used. . . The type of material being tested

Page 3-20 Page 3-21

From page 3-19

3-20

Ooops. You must be seeing something we don't. No place on the example chart was the type of penetrant mentioned (though some charts do include the type of penetrant as another variable). Why not Teturn to page 3-19, look again at the headings on the time chart and select the correct response.

From page 3-19

3-21

Good for you. The type of material being evaluated is the remaining variable shown on the chart (though some charts do include the type of penetrant as another variable). Again, the purpose of the penetration time charts is to help us in determining minimum dwell time. There will be instances when you might be asked to look for more than one type of discontinuity. There are a couple of ways you may determine the penetration time when looking for all discontinuities. They are: 1. 2.

• Use the applicable penetration time chart. Use a predetermined time as specified during design of the article.

Let's take a look at how the chart may be used to determine penetration time (or dwell time) when inspecting for all discontinuities with one test. Remembering the content of the chart we showed you (or referring back to it on page 3-19), which of the actions below would you take to determine the penetration time for all possible types of discontinuities in anyone article? I would use an average time by taking an average of the longest and shortest times on the chart . . . . . . . . . . . . . . . I would use the shortest recommended time to expedite the test I would use the longest suggested time to be on the safe side . .

.Page 3-22 .Page 3-23 .Page 3-24

From page 3-21

3-22

You must have been guessing. If you take an average of the shortest and longest chart times and use this time to test for all possible discontinuities, you will not be reaching the required minimum time for some of them. Remember, if you are checking for all discontinuities, penetrant dwell time must be long enough to penetrate all of them. Think about it again and return to page 3-21 for another selection.

From page 3-21

3-23

Wait just a minute! Consider again that the penetration times are the minimum times allowable. If you used the shortest time on the chart when asked to pick up all discontinuities, you would most certainly miss those needing the longer minimums. Return to page 3-21, look over the selections and select again.

From page 3-21

3-24

Very good. Be on the safe side. Use the longest suggested time. Since the times on the chart are minimums, this is the only way to be sure that penetrant will enter all discontinuities. Now let's take a look at the other method of obtaining penetration time for testing an article to fmd all discontinuities. This method requires the use of a predetermined time as specified during design of the article. This simply means that you are told the penetration time. This time is determined by design and quality control engineers. The reason for this is that the people who design the article are best qualified to determine the quality level desired. They know what it is to be used for and can therefore determine what degree of quality must be achieved. It all "boils" down to this: 1) You obtain the penetration time from the applicable penetration time chart; or 2) you use a predetermined penetration time given to you.

Turn to the next page.

From page 3-24

3-25

There are a couple of other points to consider when using penetration time charts. First, the minimum times recommended on the charts are based on the assumption that the penetrant will remain wet throughout the entire dwell period. This means that the penetrant must initially be applied liberally to the test surface. Also, additional penetrant may have to be applied during the dwell if it appears that the initial coat is drying. This will assure full penetration into discontinuities. If dwell time exceeds 30 minutes, the penetrant will have to be reapplied to assure that the penetrant remains wet. While there is no maximum penetration time recommended, the penetrant must be wet prior to starting the next step. Because of this, once the required dwell time is reached it is best to get right on with the rest of the procedure while the penetrant is still wet. We will talk more about this when we get into Step Three. Turn to the next page for one fmal consideration to keep in mind when using penetration time charts.

From page 3-25

3-26

The fmal point we want to make concerning the use of penetration time charts is that the times given refer to "normal" temperatures. By normal temperature we mean that the penetrant and the article being tested are between 60 and 1250 F (16 to 52 0 C). And that temperature remains within this range during the entire dwell period. Our example chart establishes the temperature range for minimum dwell time by a footnote. Most charts handle it in this manner. Minimum Dwell Time (Minutes)'

Material

Form

Type Discontinuity

Aluminum

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 5 10

Magnesium

Castings Forgings Weldments All Forms

PorOSity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 10 10

Steel

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

10 10 20 20

eTemperature range 60 to 125°F (16 to 52°cD Tum to page 3-27.

From page 3-26

3-27

The upper temperature limit generally does not present too much of a problem since test articles simply become too hot to handle.

Besides burnt fmgers, the penetrant may vaporize. Its ability to produce indications is adversely affected. Sensitivity suffers. If test must be performed at high temperatures (e.g., in testing hot weldments, etc.) special high temperature penetrants must be used.

Turn to the next page.

From page 3-27

3-28

The low temperature limit presents somewhat more of a problem. It may be common practice in some areas to apply penetrants at temperatures near or below freezing. But below 60 0 F (16 0 C), conventional penetrants become increasingly sluggish. Sensitivity decreases. Time charts become useless since they are based on a known sensitivity at normal temperatures. In extremely low temperatures, the penetrant may become so sluggish that it will not enter discontinuities regardless of the time allowed. Special low temperature penetrants must be used.

Normally, for charts to be useful, the penetrant as well as the test article must remain between 60 and 125 0 F (16 to 520 C) for the duration of dwell period. Which of the following statements is correct? Recommended dwell times are affected by temperature. . . . Temperatures above 1250 F (52 0 C) will restrict penetrant entry . Penetrants become useless below 600 F (16 0 C) . . . . . . .

.Page 3-29 .Page 3-30 .Page 3-31

Prom page 3-28

3-29

Correct. Recommended dwell times are affected by temperature. Testing at temperatures below 60 0 P (J 6 0 C) or above 12S oP (S2°C) requires special qualification of the penetrant and test procedure. It may even require the use of a penetrant specifically formulated for testing at high or low temperatures. Briefly, here are the steps we've covered thus far and what they encompass.

STEP 1

SiE'2

SURFACE

PENETRANT

PREPARATION

APPLICATION

II

Step One, Surface Preparation Anything that can hinder the application and/or entry of penetrant into discontinuities is removed. This includes surface coatings such as paint and plating as well as contaminants. Cleaning methods employed range from wiping with rags soaked in solvent to vapor degreasers and alkaline baths. Step Two, Penetrant Application In this step, penetrant is applied to test specimen and allowed sufficient time to seek out and enter possible discontinuities. Basic types of penetrant are fluorescent, visible or color contrast, and dual sensitivity. The methods of application include dipping, spraying, brushing, and flowing. Turn now to page 3-32 for a review.

From page 3-28

3-30

Watch out now. This is a hot one! Penetrant temperatures above 125 0 F (52 0 C) will not restrict penetrant entry but, these temperatures might cause the article to become heated. The heated article, in turn, could become hard to handle. Additionally, penetrants will lose some of their effectiveness if heated excessively. Their chemical consistency can be changed adversely. If you will now return to page 3-28, the correct answer will probably be obvious.

From page 3-28

3-31

Your answer is not entirely correct.

It is true only in a sense. It would be more accurate to say that penetrant becomes increasingly sluggish - less sensitive - as the temperature drops below 60°F (16°C). Whether the penetrant becomes useless depends on how far the temperature drops. Take another look at page 3-28 and choose the statement that is entirely true.

3-32

From page 3-29

1.

Step One of a liquid penetrant test is Surface Preparation. Step Two is _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

6.

fluorescent visible (color contrast)

7.

When a fluorescent or visible dye is combined with a suitable liquid, a dye _ _ _ _ _ _ _ is formed.

12.

fluorescent visible (color contrast) dual sensitivity

13.

The simplest to use but least sensitive of the dye penetrants are the penetrants.

18.

surfaces (articles, specimens, areas)

19.

After penetrant has been properly applied, it must be allowed enough time to seek out and enter discontinuities. This time is called the penetration or _ _ _ _ time.

3-33

2.

In Step Two, a liquid _ _ _ _ _ _ _ is applied to the clean dry surface of the article under test.

7.

penetrant

8.

The fluorescent dyes used in liquid penetrant testing usually appear as a brilliant yellow-green glow under _ _ _ _ _ _ _ _ __

13.

visible dye (color contrast)

14.

Greatest sensitivity, "seeabiJity," is obtained from _ _ _ _ _ _ __ penetrants.

19.

dwell

20.

Suggested (maximum/minimum) _ _ _ _ _ _ _ dwell times are contained in controlling specifications and standards.

3-34

2.

penetrant

3.

What makes a penetrant a "good" penetrant is not a single physical property but a combination of _ _ _ _ _ _ __

8.

black light

9.

Black light refers to light ra in the near ultraviolet range of wavelengths (3200 to 4000 angstroms).

14.

fluorescent

15.

Penetrants that combine the advantages of fluorescent and visible dye penetrants are called penetrants.

20.

minimum

21.

Penetrant must be kept ___ during the entire penetration or dwell time.

3-35

3.

properties (abilities)

4.

Penetrability can at best be measured in terms of wetting ability and surface tension. The penetrant must also have the right viscosity. "Penetration power," however, is obtained from a force in nature called _ _ _ _ _ _ _ _ __

9.

radiation (rays)

10.

"Color contrast" is another name for _ _ _ _ _ dye.

15.

dual sensitivity

16.

Dual sensitivity penetrants generally appear a bright red color in _ _ _ _ _ light; fluoresce a yellow to orange red under ______ light.

21.

wet

22.

The minimum dwell times indicated on penetration time charts are applicable only when penetrant and test article temperatures are held within a particular temperature range. That range in most cases is (temperature in degrees) to _ _ _ __

3-36

4.

capillary action

S.

Capillary action refers to the tendency of a liquid penetrant to travel or enter small openings even while working against _ _ _ __

10.

visible

II.

Visible or color contrast dyes usually appear bright red under _ _ _ __ light.

16.

visible (white, normal) black

17.

Penetrants can be applied by anyone of four methods. They are: I. dip 3.b "r'--_ _ __

2.s'!JP~r~_ __

4.

!Jfl""'o_ _ __

22.

60°F (16°C) 12SoF (S2°C)

23.

Testing outside the normal range requires special _ _ _ _ _ _ _ __ of penetrants and test procedures.

3-37 5.

gravity

6.

Two different dyes are used in liquid penetrants. They are f and _ _ __ Return to page 3-32 frame 7.

II.

visible (white, nonnal)

12.

The three basic types of dye penetrant are "'f_ _ _ _ _ _ __ V ):._ _ _ _ ,and\!.d_ _ _ ~s_ _ _ _ _ __

Return to page 3-32, frame 13. 17.

18.

Regardless of which method of application is used, test _ _ _ _ __ must be adequately covered with penetrant.

Return to page 3-32, frame 19.

23.

qualification (approval)

24.

You are now ready for Step Three. Turn to page 4-1.

CHAPTER 4 - EXCESS PENETRANT REMOVAL

4-1

Excess penetrant is the penetrant that remains on the surface of test article at the end of the required dwell period. It is the penetrant that has not entered discontinuities. In Step Three, we are going to remove this excess. But before we begin, you'll recall that near the end of the discussion in Step Two we stated that the penetrant must still be wet prior to starting Step Three. If penetrant has dried, you cannot just rewet the penetrant. You must start over beginning with Step One, Surface Preparation. The same applies if you encounter delays in later steps of the procedure. To do otherwise can result in an unreliable test. Select the correct completion to the following statement. If you notice that excess penetrant has dried before starting Step Three ... you may rewet the test specimen and continue with excess penetrant removal . . . . . . . . you must return to Step One . . . . . . . . . . . . . . . .

Page 4-2 Page 4-3

From page 4-1

4-2

You've indicated that you can rewet the test specimen and continue. Not correct. You must retum to Step One. To continue with excess penetrant removal after you notice that excess penetrant has dried can only produce unreliable test results. Tum to page 4-3.

From page 4-1

4-3

Correct. You must start over with Step One. You may apply new penetrant only if the existing penetrant has not dried. You also learned in Step Two that there are three basic types of dye penetrant. They are: Visible (Color Contrast) Fluorescent Dual Sensitivity Liquid penetrant processes are further classified by the method of penetrant removal used. They are: Water Washable Post Emulsified (P.E.) Solvent Removed The water-washable method employs "self-emulsifying" penetrants. Excess penetrant is removed by simply washing with water. The post-emulsi[ied method is generally a two-step removal process employing penetrants that do not contain an emulsifying agent. Excess penetrant is removed by applying a separate emulsifier to make the penetrant water washable, then following with a water wash. The solvent-removed method also employs post-emulsification type penetrants. But instead of using an emulsifier and a water wash, excess penetrant is removed by a solvent. Turn to the next page.

From page 4-3

4-4

Let's add the three penetrant removal methods, plus Step Three to our flow diagram.

KJ1'l.

WATER WAStlABLE

STEP I SURFACE

PREPARATION

r.

STEP 2 PENETRANT APPLICATION

A,

STEP 3

EXCESS APPLICATION PENETRANT REMOVAL EMULSIFIER

SOLVENT REMOVEO

+[}

In review, here are the three basic dye penetrants:

Visible (Color Contrast) Fluorescent. . Dual Sensitivity . . .

Viewed Under Visible Light Viewed Under Black Light Viewed Under Visible and/or Black Light

Here are the methods ofremoval: Water Washable. . Excess Removed With Water Post Emulsified . Excess Removed With Separate Emulsifier Plus Water Wash Solvent Removed. Excess Removed With Solvent Cleaner Water-washable penetrants contain their own "built-in" emulsifier making them water washable. The post-emulsified and solvent-removed penetrants are one and the same. They require a separate emulsifier to make them water washable, or they can be removed with solvent. Taking the last method first, turn to the next page and see how excess penetrant is removed using a solvent.

From page 44

4-5

In the solvent-removed method, as much excess penetrant as possible is wiped from the test surface with a clean dry, lint-free cloth (or absorbent paper). This is followed with another clean, lint-free cloth dampened with a solvent cleaner or "penetrant remover." Example penetrant removers include commercial solvents such as naphtha and mineral spirits (paint thinner) in addition to special proprietary removers. In selecting a solvent remover keep this in mind: Only those removers recommended by the penetrant manufacturer may be used. Additionally, flushing of surfaces with solvent is not permitted! When using visible (color contrast) dye penetrants, a check is made to ensure excess penetrant has been removed in the following manner: A clean lint-free cloth is wiped over the surface. If it shows no traces of dye (usually pink or red) the surface has been properly cleaned of excess penetrant. When using solvent-removed fluorescent penetrants, penetrant removal is performed under black light. This allows you to easily tell when the excess penetrant has been removed. Wiping is stopped when surface fluorescence disappears. Is the following statement true or faIse? The incomplete removal of excess penetrant could result in the formation of nonrelevant or false indications. True. False.

Page 4-6 Page 4-7

From page 4-5

4-6

Good. You are correct. Incomplete removal of excess penetrant can result in the formation of nonrelevant or false indications. The complete removal of excess penetrant is very important. Remember, when using solvent removers: 1. 2. 3.

4.

Remove as much excess penetrant as possible with dry, lint-free wipes. Remove the remaining excess with remover-dampened, lint-free wipes. When using visible dye penetrants, check for complete removal by noting that the last remover-dampened wipe is "color-free." When removing fluorescent penetrants, check progress with black light and stop when test surface no longer fluoresces.

Again, excess penetrant must be thoroughly removed to avoid nonrelevant or false indications that might result in the rejection of acceptable articles. However, there is also a defInite taboo - something you must not do!

EXCESS PENETRANT SHALL NOT BE FLUSHED FROM SURFACE WITH SOLVENT. The object is to remove only the excess penetrant from the surface of the specimen without removing the penetrant from discontinuities. Now that you're familiar with the materials and techniques used in the solventremoved method, let's move on to the water-washable method of penetrant removal. Turn to page 4-8.

From page 4-5

4-1

Your answer is not correct. Excess penetrant, if not completely removed, can cause nonrelevant or faIse indications. These indications could in turn result in the rejection of acceptable articles. They could even hide or obscure true discontinuity indications. The complete removal of excess penetrant is therefore very important. With this in mind, turn to page 4-6.

From page 4-6

4-8

Water-washable penetrants you'll recall have a "built-in" emulsifier. TIlls emulsifier is what makes the penetrant water soluble. The penetrant can be washed off with water. But haphazard washing, called "overwash," may remove penetrant from discontinuities as well as from the surface! In removing water-washable penetrants, a coarse forceful water spray is found to work best - the action being limited to the time it takes to remove only the surface penetrant. If the penetrant is visible dye, the surface is washed until "color-free." If penetrant is fluorescent, the wash is conducted under black light and the wash continued until the surface no longer fluoresces. As was the case with solvent-removed penetrant, this allows you to tell when excess penetrant has been removed. Only the possible glow of discontinuities remains. There is one recommendation to keep in mind when using a water wash to remove excess penetrant. The temperature of the water should be held between 60 and I100 F (16 to 43OC). Higher water temperatures tend to increase the removal of penetrant from discontinuities, and some of the penetrant's power to produce vivid images of discontinuities may be lost. On the bottom end of the scale, low temperatures tend to reduce the effectiveness of the water wash in removing excess penetrant. Select the best completion for the following statement. Excess water-washable penetrant is best removed with a ... coarse forceful water spray not exceeding 60 0 F (l6 0 C). . coarse forceful water spray between 60 and 1100 F (16 to 43 0 C) coarse forceful water spray of at least 1I00 F (43 0 C) . . . . .

. Page 4-9 .Page 4-10 .Page 4-11

From page 4-8

4-9

Slow down a bit. You have indicated that water temperature mustn't exceed 600 F (16 oC). This is incorrect. Remember, low water temperatures can reduce the effectiveness of the water wash. Removal of excess penetrant becomes more difficult. The result could be an unreliable test. Best results are obtained with a water wash temperature between 60 and 11 OOF (16 to 43 0 C). With this in mind turn to page 4-10 and continue.

4-10

From page 4-8

Right. The recommended water wash temperature is 60 to 1100 F (16 to 43 0 C). The best wash again is a coarse forceful spray. The one remaining method of penetrant removal is the post-emulsified method. As we stated earlier, the penetrants used do not contain a "built-in" emulsifier. Emulsification is accomplished by applying a separate emulsifier to break the penetrant down and make it water washable. The emulsifier is usually dyed orange to contrast with penetrant. Emulsifiers may be either "lipophilic," or "hydrophilic." Granted these are impressive looking words but they simply mean the emulsifier is either oil or water based. Lipophilic. . Hydrophilic .

Oil Base Water Base

Lipophilic or oil-based emulsifiers are what we call "contact" emulsifiers. They begin emulsifying or breaking the penetrant down on contact, making the penetrant water washable. The speed of emulsification will depend on the particular emulsifier used. Some emulsifiers are relatively fast acting; others are slow. Hydrophilic or water-based emulsifiers may also be used as "contact" emulsifiers. But more often they are diluted to the point that simple contact with penetrant does not make the penetrant water washable. Application must be accompanied by some form of mechanical agitation or scrubbing. Hence the term "hydrophilic scrubber." Usually, the emulsifier is added to the water wash and sprayed under pressure. By controlling the strength and duration of the spray, we can control the amount of penetrant removed.

Turn to page 4-12.

From page 4-8

4-11

You have selected the answer that states the temperature of the water wash must be at least II00F (43 oC). You apparently feel the temperature could be even higher. This is incorrect. If the temperature of the wash is too high, the heat of the water will tend to vaporize penetrant right out of any discontinuities that may exist. In a tight crack, for example, there is only a very small amount of penetrant available. We mustn't take chances on losing any of it. The best overall water wash temperature is between 60 and II00F (16 to 43 oC). With this in mind turn to page 4-10.

From page 4-10

4-12

Emulsifiers are applied in the same manner as penetrants... with one exception. Never apply an emulsifier by brush. Brushing makes emulsification more difficult to control. We'll get into the importance of this later; but for now, remember that emulsifiers can be applied by...

DIPPING

EMULSIFIER SPRAYING

~

Note the one exception and turn to the next page.

BUT NEVER BY BRUSHING

From page 4-12

4-13

In review, the additional operation required with "post emulsification" is the addition of an emulsifier. Before its addition, the penetrant is not water washable. After its addition, the penetrant becomes water washable. Here is a surface coated with a post-emulsification penetrant. Notice that sufficient penetration time has been allowed for penetrant to enter the discontinuity. PENETRANT

Here is the same article after the addition of the emulsifier. ,1~I"UIL.liI.'ER

MIXING (DIFFUSION) ZONE PENETRANT

Notice that the emulsifier starts to work from the penetrant's surface, diffusing into the penetrant as it works toward the article. Turn to the next page.

From page 4-13

4-14

With post emulsification, the most critical operation during the entire liquid penetrant process begins when the emulsifier is applied to the penetrant. The critical factor is time. How long a period should be allowed for this action? The emulsifier should be allowed to remain on the surface until it has mixed with the surface penetrant, but not long enough for it to mix with the penetrant in discontinuities. Following are two situations. In View A, time has been allowed for mixing. In View B, a longer time has elapsed. Study them both with the following thought in mind: You do not want to remove penetrant from the discontinuity. Further, the penetrant cannot be removed until the emulsifier has mixed with it. EMULSIFIED PENETRANT PENETRANT IN DISCONTINUITY NOT EMULSIFIED

VIEWB

Which of the above represents the proper emulsification time? ViewA. ViewB.

Page 4-15 Page 4-16

4-15

From page 4-14 Good. View A illustrates the proper emulsification time.

You can see that with post emulsification, the emulsification time is critical. In fact, emulsification time is considered more critical than the penetrant dwell time! What then is the advantage in using a post-emulsification penetrant? Proper control of the emulsification period will prevent the removal or "overwash" of penetrant from shallow discontinuities! Let's see how. Below is a comparison of water-washable and post-emulsification penetrants on two identical parts with shallow discontinuities. Let's call them Part A and Part B. For Part A, we'll use a water-washable penetrant ... for Part B, a post-emulsification penetrant. WATER WASHABLE ~--:SH)'LL.OW

PART A

POST EMULSIFICATION DISCONTI NUlTY - - - , .

PARTB

Note: The size of the discontinuities in the above parts is exaggerated for teaching purposes. They are not intended to represent the typical shallow discontinuity. Turn to page 4-1 7.

From page 4-14

4-16

Let's take another look at the two pictures to solve this difficult problem. EMULSrFIED PENETRANT ~..PENE·rRJ'NTIN

1K\0::~7J.H

DISCONTINUITY NOT EMULSI FI ED

EMULSIFIED PENETRANT

VIEWA

VIEWB

Now the trick is to determine which surface has experienced the proper emulsification time. Study the pictures in terms of the following: View A - This view shows that the emulsifier has had time to work its way from the surface of the penetrant down through the body of the penetrant until it is exactly

at the surface of the article. The emulsifier has not worked its way into the penetrant inside the discontinuity. Remember these important considerations: I) You do not want to remove penetrant from the discontinuity; and 2) excess penetrant cannot be removed with water spray until it has mixed with the emulsifier. By applying a water rinse to View A as it is shown above, you would be rinsing away only the penetrant from the surface of the article and would not remove any penetrant from the discontinuity. This represents the ideal emulsification time. View B - This view shows that the emulsifier has had time to work its way from the surface of the penetrant down into the discontinuity. So what happens when a water spray is applied to remove excess penetrant? Excess penetrant is removed alright, but so is some of the penetrant from the discontinuity. This condition will not make for a very effective test. Turn to page 4-15.

4-17

From page 4-15

The penetrants are applied to the parts and allowed sufficient time to penetrate discontinuities. Our pictures show that the discontinuities have filled with penetrant. WATE R WAS;:...H::.A::B::L:.E_ _ _ _ PEN
:TfIA~IT _ _ _..:.P.:O:.5T:..;:.E:::M.:U:LSI FICATI ON

PART A

PARTB

We then apply a coarse forceful water spray to Part A ... an oil-based (lipophilic) emulsifier to Part B. WATER SPRAY

EMULSIFIER

Turn to the next page.

From page 4-17

4-18

After careful control of emulsification time, Part B is washed in the same manner as Part A. A coarse forceful water spray is used. Even the same water temperature is recommended - 60 to 1100 F (16 to 43 oC).

"

Remember, with water-washable penetrants, it is the wash time that is critical; with post-emuisification, it's the emulsification time. Turn to the next page.

From page 4-18

4-19

WATER """'HAB,Lt

PENETRANT

PARTA

PART A AFTER "OVERWASH," PART A WOULD LOOK JUST THE WAY IT DID BEFORE PENETRANT APPLICATION. NO PENETRANT REMAINS IN DISCONTINUITIESI

EVEN WHEN MOST CAREFULLY WASHED, SOME PENETRANT WI LL BE LOST, AS SHOWN ABOVE

POST EMULSIFICATION

BUT AFTER CAREFUL EMULSIFICATION CONTROL AND THE WASH, PART B LOOKS LIKE THISI

PARTB

If you were required to use a fluorescent penetrant to locate suspected shallow discontinuities, which of the following would be your course of action?

I'd use a post-emulsification fluorescent penetrant I'd use a water-washable fluorescent penetrant. ,

.Page 4-20 .Page 4-21

From page 4-19

4-20

Fine! Post-emulsification penetrant has advantages that make it a good choice in locating shallow discontinuities. Correct emulsification will depend on the test article's surface condition and the type discontinuities sought. Under normal circumstances, average times will range from I to 3 minutes. . . seldom exceed 5 minutes. Correct time is determined by experiment (Steps One through Three are repeated, using different emulsification times, until the desired wash is obtained.) There is one important difference between emulsification time and penetration time that you must remember. Whereas the penetration times are minimum and no maximum time is insisted upon, this is not the case with emulsification times. Emulsification time is a specific time and must be carefully controlled. If too short a time is used, not all of the penetrant on the surface will be removed and the remaining penetrant will obscure discontinuity indications. If too long a time is used, penetrant within the discontinuities will become water washable and be washed a way along with the excess penetrant. Which of the following would be the best reason for selecting a post-emulsification penetrant to test for shallow open discontinuities? The water wash is less critical . . . . The penetrant dwell time is less critical

.Page 4-22 .Page 4-23

From page 4-19

4-21

1his is not the best choice. When a water-washable penetrant is used it is very easy to wash the penetrant from shallow discontinuities. Excess post-emulsification penetrant, however, does not become water washable until it has had time to mix with the emulsifier. By carefully controlling the emulsification time, the penetrant in discontinuities remains insoluble. Therefore, whenever you are looking for shallow discontinuities, we would recommend a post-emulsification penetrant over water-washable. Turn to page 4-20 and continue.

From page 4-20

4-22

Good for you! Since the wash is less critical with post-emulsification penetrants, there is less chance of removing penetrant from shallow discontinuities. When water-washable penetrants are used there is always this possibility, even when the utmost care is observed to avoid "overwash."

Both the water-washable and post-emulsification penetrants you'll recall carry a dye in suspension. If that dye is a visible or color contrast dye, it can be seen in normal (white) light. Excess penetrant can be removed under visible light. If the dye is fluorescent, however, it is visible only with the aid of black light. This suggests a washing technique that will assure the surface has been cleaned of excess penetrant. The technique is stated below. Can you spot it? Consult a chart for the proper wash time . Use a solvent cleaner in place of water. Wash under black light. . . . . . . .

.Page 4-24 .Page 4-25 .Page 4-26

From page 4-20

4-23

Remember now, both water-washable and post-emulsification penetrants require a specific minimum dwell time. But the penetrant dwell time for post-emulsification penetrants is not any more critical than the dwell time for water-washable penetrants. Turn to page 4-22 and let us show you a better reason for using post-emulsification penetrant in this case.

From page 4-22

4-24

You say we would consult a chart for proper wash time. This would be a logical method if there were such a chart - but there isn't. Your choice in this instance was incorrect. Keeping in mind that you are looking for fluorescent indications, return to page 4-22 and select another alternative.

From page 4-22

4-25

To ensure removal of all excess fluorescent penetrant from the surface of an article you would use solvent cleaner in place of water. This is not correct. Remember that you are using a penetrant that is designed to be effectively removed with water. Keeping in mind that you are looking for fluorescent indications, return to page 4-22 and select another alternative.

From page 4-22

4-26

Washing under black light will indeed facilitate the removal of excess fluorescent penetrant. Good for you! You made the correct selection. Washing under black light is the recommended procedure when removing excess fluorescent penetrant. By washing under black light, you can easily tell when excess penetrant has washed away. Only the possible glow of discontinuities will remain. Let's now turn to the next page for another quick review before proceeding to Step Four.

4-27

From page 4-26

1.

So far we've covered the first three steps of a liquid penetrant test. Step One is _ _ _ _ _ _ _ _ _ _ _ _ __ Step Two is ________________ Step Three is E!i.-_ _ _ P f.. _ _ _ _ _ R~_ _ __

7.

water washable

8.

Excess post-emulsification penetrant may also be removed by a

14.

oil (lipophilic) water (hydrophilic)

15.

Lipophilic emulsifiers are ___ based and hydrophilic emulsifiers are based.

21. Post-emulsification

(-ed)i

solvent

22.

Solvent removers used must be approved by the _ _ _ _ _ __ manufacturer.

4-28 I. Surface Preparation Penetrant Application Excess Penetrant Removal 2.

Excess penetrant is that penetrant which (has!has not) _ _ _ _ __ entered discontinuities at the end of the recommended penetration or "dwell" time.

9.

Liquid penetrant processes are further classified by the method of penetrant removal used. The three basic processes are: 1) w w , 2) P "'e_ _ _ _ _ __ and 3) "-s_ _ _ _ ~r_ _ _ _ __

15.

oil water

16.

Oil-based emulsifiers begin emulsifying on contact with _ _ _ _ _ _ __

22.

penetrant

23.

With solvent-removed processing, excess penetrant is removed by wiping the test surface with a clean, lint-free cloth (saturated! dampened) _ _ _ _ _ _ _ _ with remover.

4-29 2.

has not

3.

Prior to beginning Step Three, the penetrant remaining on test article surfaces must be (wet/dry) _ __

9.

water washable post emulsified (-able) solvent removed (-able

10.

With water-washable processing, the penetrant remover is

16.

penetrant

17.

Water-based emulsifiers are usually diluted and _ _ _ _ __ under pressure. Washing action stops when spray is _ _ _ __

23.

dampened

24.

Flushing of surface with solvent remover (is/is not) _ _ __ permitted.

4-30

3.

wet

4.

If penetrant has dried, procedure must be repeated beginning with Step _ __

10.

water

II.

The best water wash is obtained with a coarse forceful _ _ _ _ and a water temperature of (temperature range) _ _ _ _ _ _ _ __

17.

sprayed stopped (turned off)

18.

Control of penetrant removal is important. With water-washable time that's critical. With postpenetrants, it is the emulsified penetrants it's the time.

24.

is not

25.

Proper wash is obtained with (type of dye) _ _ _ _ _ _ __ penetrants when surface and lor wipe appears "color-free."

4-31

4.

One (Surface Preparation)

5.

In addition to the type of dye,liquid penetrants are classified as either w

w

or p

e

II.

spray 60 to 11q,°F (16 to 43 C)

12.

Using post-emulsified processing, excess penetrant is also removed with water. But first an must be applied to make the penetrant water washable.

t t

18.

wash emulsification

19.

Too long a wash time with water-washable penetrants, and the penetrant is washed away. in

t 25.

visible dye (color contrast)

26.

With fluorescent penetrants, proper wash is obtained when surface of test article no longer fluoresces under b

,

4-32

5.

water washable post emulsified (-able)

6.

Water-washable penetrants contain a "built-in" "'e_ _ _ _ _ __ making them water washable.

12.

emulsifier

13.

Emulsifiers can be applied by dipping, spraying, pouring or flowing but never by _ _ _ _ _ __

19.

discontinuities

20.

Use too long an _ _ _ _ _ _ _ _ _ _ time with post-emulsified penetrants and the penetrant in discontinuities becomes _ _ __

26.

black light

27.

Tum to page 5-1.

4-33

6.

emulsifier

7.

Post-emulsification penetrants require the application of a separate emulsifier to make them w -"w'--_ _ _ __ Return to page 4-27, frame 8.

I3.

brush (-ing)

14.

Emulsifiers may be either _ _ or _____ based.

Return to page 4-27, frame 15. 20.

21.

emulsification water washable (water soluble)

P,--_ _ _ _ _ _ _ _ _ _ _ type penetrants are also employed in the solvent-removed process. The remover is a _ _ _ _ __ Return to page 4-27, frame 22.

5-1

CHAPTER 5 - DEVELOPER APPLICATION

Some discontinuities, depending on their size, location, etc., may produce images at the conclusion of Step Three. Some dye penetrants used today are specifically formulated for use without a developer. But generally, a developer is required. This is what Step Four is all about - developers and their application. This is how our flow diagram looks with Step Four added. WATER WASHABLE

m"

SURFACE

PREPARATION

.

STEP 1 PENETRANT

APPLICATION

STEP 3

~,

EMULSifiER

EXCESS

APPLICATION PENETRANT

SOLVENT REMOVED

REMOVAL

STEP"

DEVElOPER

0

~

APPLICATION

,---I

In the "oil and whiting" days, powdered chalk or whiting served as the developer. It was used to draw the oil from discontinuities to form indications. Today's developers are applied to test surfaces for this same purpose - to get the dye in discontinuities back to the surface so it can form an image of the discontinuity from which it came. Turn to the next page.

From page 5-1

5-2

The essential ingredient of today's developers is a highly absorbent, whitish powder. When applied to test articles (following excess penetrant removal) this powder acts as a blotter... absorbing the dye carrying penetrant from discontinuities and spreading the dye in the powder to form indications. The blotting action is capillary action at work again - only this time in reverse! The penetrant is actually drawn from discontinuities by the powder. When we see a discontinuity indication, we are actually seeing the dye that has diffused in the developer. Therefore, we can expect to see an indication that is one of the following: Smaller than the discontinuity . Larger than the discontinuity . Same size as the discontinuity •

. Page 5-3

Page 54 . Page 5-5

5-3

From page 5-2 Remember our goal in liquid penetrant testing! To make the discontinuities easy to see.

Now, for a moment reconsider your answer to the question about the size of the discontinuity images which you'll see. You were given three choices (smaller, larger, the same size). You chose "smaller." We feel certain that, with our liquid penetrant goal in mind, you can make the correct choice now. Here's the question again, followed by the remaining two choices. Choose again! When we see a discontinuity indication, we are actually seeing the dye which has spread in the developer. Therefore, we can expect to see a discontinuity image that is one of the following: Larger than the discontinuity The same size as the discontinuity

Page 54 Page 5-5

From page 5-2 (or 5-3)

5-4

Right. The developer tends to enhance or make discontinuities easier to see. They appear larger than actual size. A typical discontinuity indication might look something like this: DISCONTINUITY INDICATION DISCONTINUITY

Moving on, there are four basic developers that will get the job done. They are: Water-m1spended Particle Water Soluble Dry

Nonaqueous Wet Notice that the fIrst two have something to do with water... the last two do not. Primary differences are in the liquid "carrier" used (or not used), their sensitivity,

and the manner in which they are applied. Let's look at the water-based wet developers fmt. Tum to page 5-6.

From page 5-2 (or 5-3)

5-5

Your choice was the "same size as the discontinuity." This is incorrect. Perhaps a picture will best show you why. DISCONTINUITY INDICATION DISCONTINUITY

The shaded area in the picture represents the penetrant that has been drawn from discontinuity and spread through the developer. Keeping this picture in mind, return to page 5-2, and select the correct answer.

From page 54

5-6

There are two types of water-based wet developer. In one, the developer particles are held in suspension in water and require continuous agitation to keep them in suspension. In the other, the developer powder is dissolved in water, forming a solution. Once mixed, they remain mixed. It is the latter developer that provides the greater sensitivity in detecting fine discontinuities. Water-suspended particle and water-soluble developers are generally used with waterwashable or post-emulsified penetrants, and rarely with solvent-removed penetrants. They're applied while test article is still wet from the water wash. Methods of application include:

Dipping (or immersion) Pouring (or flowing) Spraying Articles may be dipped or immersed in the wet developer, raised and allowed to drain. The developer may be poured or flowed over the specimen. Or a spray gun may be used. A point to remember with dip tanks is that excessive amounts of water must not be carried over from the water wash and added to the developer. This can alter the developer's consistency, making it less predictable. Best results are obtained with a thin and even coating with no pools of wet developer remaining on the test article's surfaces. Thickness of coating is controlled by bath strength. Specific gravity is measured with a hydrometer, and powder or water added as needed. For greatest sensitivity, a thin and even spray is preferred. You were told which of the water-based wet developers was the more sensitive. Which then is the less sensitive? WateHuspended particle. Page 5-7 Water soluble . . . . . . . Page 5-8

From page 5-6

5-7

Right! The water-suspended particle developers are the less sensitive. In fact, they are the least sensitive of all the developers in detecting fme discontinuities. When a water-based wet developer is applied to an article, a short time must then be allowed for the test surface to dry - the water to evaporate. Evaporation is often accelerated using a recirculating hot air dryer or oven. Depending on test specimen thickness, the drying temperature used for most applications is between 150 and 225 0 F (66 to 1070 C). Drying time also should be just long enough to dry test surfaces. Why must we control drying temperature and time? To prevent the evaporation a/penetrant from discontinuities. Select the best completion for the following statement. Dryer maximum temperature is restricted to 225 0 F (I 07 0 C) so that... penetrant does not dry out • . . • critical articles will not be damaged. developer does not evaporate . • .

• Page 5-9 .Page 5-10 .Page 5-11

From page 5-{j

5-8

You selected "water soluble" as being the less sensitive. This is incorrect. Water-soluble developers are more sensitive . .. not less sensitive! The developer powder dissolves in the water and once mixed it stays mixed. Water-suspended particle developers, on the other hand, require continuous agitation to keep the developer particles in suspension ... to keep them from settling. As a result, the developer is said to be less sensitive. With this in mind, turn to page 5-7.

From page 5-7

5-9

Correct. Dryer temperature is restricted to less than 225 0 F (1070 C) to prevent the penetrant in discontinuities from drying out. Again, the recommended drying temperature for most applications is between ISO and 225 0 F (66 to 107OC). The time in the dryer should be just long enough to dry the test surfaces and not the penetrant in discontinuities. Many of the controlling specifications and standards also limit the test article's maximum surface temperature to 125 0 F (52 0 C) to further control penetrant evaporation. Here's a note of warning. There will be conditions or situations in which even the above temperatures could be harmful, depending on the test article's material and thickness. For this reason, the temperature used must be established for each particular job. Care must also be observed in keeping wet developers in covered containers when not in use. If not, the consistency or balance between the water and powder could be altered by evaporation, causing the powder coating to crack during drying. Developer could become contaminated.

Tum to page 5-12.

From page 5-7

5-10

Your concern that critical articles may suffer damage is commendable, but limiting dryer temperature to "less than 225 0 F (107 0 C)" will not necessarily guarantee safety of the test article without being more specific. What about delicate plastics, etc.? The upper limit of 225 0 F (107 0 C) might well be too high for them. (Naturally, when materials are unusually sensitive to temperatures, special temperature restrictions will apply.) The object in restricting dryers to temperatures below 225 0 F (1070 C) is to protect the one material that we know will always be present, and which is always subject to adverse effects should the temperature get too high. What is this material? Penetrant. What can happen to it? The answer to that is included in the proper choice on page 5-7. Turn to page 5-7, reread the page, and select the answer!

From page 5-7

5-11

We'd better run through our introduction to dryer use again. We didn't make our point on the first go-around. You have indicated that dryer temperature is restricted to 225 0 F (l07oC) maximum so that... "wet developer will not evaporate." That answer is not correct. We want the developer to evaporate! The dryer is used after water-based wet developer application to help evaporate the water, leaving only the powder ItIm thinly spread over the article. Dryer temperature is restricted to temperatures below 225 0 F (l07oC) for another reason. Return to page 5-7, reread the page and give it another try.

5-12

From page 5-9

Here's how our flow diagram looks with the proper sequencing of water-based wet developer application and use of dryer. Notice the dryer is used after developer application. WET

WATER

WASHABLE

~ DRYER

STEP 1

SURFACE PREPARATION

STEP 2 PENETRANT ~ APPLICATION

STEP 3

f+j,

EXCESS EMULSIfiER APPLICATION PENETRANT REMOVAL

STEP 4

DEVELOPER APJIliCATION

I

I I I

,, ,

,,

, I

SOLVENT REMOVED

I

Let's turn our attention to dry developer. Dry developers are used for the same purpose as wet developers - to blot penetrant

back to the surface... their sensitivity being about the same as that of the watersoluble developers. The difference between wet and dry developers is ••• dry developer is not carried in a liquid. . . . . . . . . dry developer is applied in powder form. . . . . . . . the surface must be dry before dry developer can be applied all of the above. . . . . . . . . . . . . . . . . .

.Page 5-13 .Page 5-14 .Page 5-15 .Page 5-16

From page 5-12

5-13

You are right in that dry developer is not carried in a liquid (as is the wet). But ... did you read all the choices you had? Here they are again: · .. dry developer is not carried in a liquid. (Your selection) · .. dry developer is applied in powder form. · .. the surface must be dry before dry developer can be applied. · .. all of the above. Take a moment and study the remaining choices. Since dry developer is not carried in a liquid (your choice), it must be applied in powder form. Right? Similarly, if developer is to be applied in a thin and even layer - the same end sought with wet developer - the test surface must certainly be dry before developer can be applied. This leaves you, " •.. all of the above." Turn to page 5-16.

From page 5-12

5-14

Right. Wet developer is applied in liquid form, as one might guess from its name. And no more surprising, dry developer is applied in powder form. Turning to this page however was not the best choice. Three of the statements were legitimate differences between wet and dry developers! Here they are again; see if you agree. · .. • .. · .. · ..

dry developer is not carried in a liquid. dry developer is applied in powder form. the surface must be dry before dry developer can be applied. all of the above.

The last choice, "all of the above," then has to be the best choice. Right? Turn to page 5-16.

From page 5-12

5-15

Yes - your choice, "the surface must be dry before dry developer can be applied," is an important difference between wet and dry developers. But why is this dry surface necessary? Because: .•. dry developer is not carried in a liquid, and ... dry developer is applied in powder form. These statements also mark differences between wet and dry developers. Do the statements seem, perhaps, familiar? Return to page 5-12 and try again.

5-16

From page 5-12 Correct. "All of the above" was the best choice.

Dry developer is supplied as a fIne grained, fluffy powder. Methods of application

include the use of low air pressure such as that from a rubber squeeze bulb or a spray gun. A soft brush may sometimes be used. Or, since the developer is a very fme powder, articles may be simply dipped in the {!eveloper, raised, and the excess powder removed by gently blowing, shaking, or tapping the article. Dust chambers, particularly where there is automatic processing, are also frequently used in applying dry developer. SPRAY GUN

SOFT BRUSH

DIPTANKOR DUST CHAMBER

SQUEEZE BULB

The requirement that test article surfaces be dry before developer application is very important. A wet surface would result in an uneven layer of powder, or even worse - too thick a powder buildup as the powder forms a "mat" in wet areas. Discontinuity indications would be obscured. This suggests a different drying sequence than that used for water-based wet developer. The new sequence is listed below. Spot it? Use the dryer before penetrant application . Use the dryer before developer application . Use the dryer after developer application

Page 5-17 Page 5-18 Page 5-19

From page 5-16

5-17

Step One was surface preparation. Step Two was penetrant application. You are quite correct that the dryer oven is sometimes used as a part of Step One. When? When water, which is considered a "contaminant," must be removed from a surface. However, the question asked was, "when are dryers used during developer application?" You've learned that these dryers are used after water-based wet developer has been applied. They are used to speed the evaporation of the liquid part of that wet developer. A thin deposit of developer remains covering the article. Are these dryers used in a different sequence when dry developer is used? You bet they are! In order to get a thin, even deposit of dry developer over the article, the article must be thoroughly dry prior to developer application. Dryers are used to do this job. With this information you should have no difficulty in spotting the dryer sequence necessary when dry developers are used in Step Four. Return to page 5-16 and see how you do.

From page 5-16

5-18

Good for you. You are correct. We use the dryer before developer application. The dryers and ovens used to speed up the evaporation of water-based wet developers may also be used to dry test articles prior to dry developer application, and thus assure the necessary dry surface. But, keep these temperatures in mind to prevent the drying out of penetrant in discontinuities: Maximum dryer temperature - 225°F (107°C) Maximum test article surface temperature - 125°F (52°C) Minimum dryer temperature - 150°F (66°C) And again, you must limit the length of drying time to the time necessary to just dry test surfaces. Turn to page 5-20

From page 5-16

5-19

Evidently we have not clearly distinguished between water-based wet and dry developers. When we do so, you'll have no further difficulty fitting the dryer into the picture. Here, let's try again! In a water-based wet developer, the powder is mixed with water. When this wet developer is used, the article is usually dipped into the developer, removed and a short time allowed for the water to evaporate, leaving a thin f:tlm of powder. The evaporative process is often hurried by the use of a recirculating, hot air dryer after the developer has been applied. Dry developer is applied dry ... in powder fonn. It too can be applied by dipping,

but to avoid layers of developer that are too thick or uneven, the article must be dry prior to developer application. Dryers are used prior to developer application to accomplish this objective. Now then, if the question were asked, "How can danger from a wet surface be eliminated when dry developer is used?" You could answer .. Use the dryer before penetrant application . Use the dryer before developer application .

Page 5-17 Page 5-18

5-20

From page 5-18

Here's the flow diagram with the proper sequencing of dry developer application and use of dryer added. Notice this time the dryer is used before developer application. w"

DEVELOPER

WATER

STEP I

STEP 2

SURfACE

PENETRANT

PREPARATION

APPLICATION

..

~

sm, EMULSIFIER

EXCESS REMOVAL

I I I I I

STEP 4

DEVElO1'ER APPLICATION

APPLICATION PENURANT

SOLVENT REMOVED

II I

WASHABLE

,

II

'"

DEVELOPER

I

.n L-.J

One basic developer remains that we haven't yet discussed. That's the developer in which the powder particles are held in suspension in a rapid drying solvent (nonaqueous) carrier instead of water. It's called nonaqueous wet developer. Nonaqueous wet developer is most often employed with solvent-removed penetrants and less often with water-washable or post-emulsified penetrants Gust the opposite of water-based wet and dry developers). But like dry developer, it is applied only to dry test surfaces. Application is usually by conventional spray gun or pressurized spray can. The nonaqueous wet developer is also the most sensitive of all the developers in detecting fme discontinuities. Evaporation of the solvent carrier helps draw penetrant from discontinuities. The best results are obtained when developer is applied as a thin and even film (the test surface is not soaked). Turn to the next page.

From page 5-20

5-21

Now, see if you can specify the proper sequence for dryer use with a water-based wet developer. Study the procedure below and select the correct sequence for dryer use. Step One. Surface preparation. Step Two. Apply penetrant. Step Three. Remove excess penetrant. USE DRYER Step Four. Apply developer. USE DRYER

Page 5-22 Page 5-23

5-22

From page 5-21

Evidently we have not clearly distinguished between water-based wet and dry developers. When we do so, you'll have no further difficulty fitting the dryers into the picture. Here, let us try again!

REMOVE EXCESS PENETRANT

APPLY WET DEVELOPER

USE DRYER

In a water-based wet developer, water is the carrier. The test article is usually dipped into the developer, removed and a short time allowed for the water to evaporate, leaving the article coated with a thin film of powder. The evaporative process is often hurried by the use of a recirculating hot air dryer - but only after the developer has first been applied.

REMOVE EXCESS PENETRANT

USE DRYER

APPLY DRY DEVELOPER

Dry developer is applied dry ... in powder form. It too can be applied by dipping or spraying, but to avoid layers of developer that are too thick or eneven, the article must be dry prior to developer application. The dryer is therefore used prior to dry developer application to accomplish this objective. Return to page 5-21, study the sequence presented and make the correct selection.

From page 5-21

5-23

OK! Fine. How about dryer use with dry developer? Do you have that procedure down pat? Choose the correct sequence. 1.

2.

3. 4.

Clean surface. Apply penetrant. Remove excess penetrant. USE DRYER Apply developer. USE DRYER

Page 5-24 Page 5-25

From page 5-23

5-24

Excellent. You've recognized the need for using the dryer at a different point in the inspection process depending on whether a water-based wet or dry developer is used. TIIis brings up another point! What should the test article's surface condition be when a nonaqueous wet developer is used? Dry

Wet

Page 5-26 Page 5-27

From page 5-23

5-25

Evidently we have not yet clearly distinguished between water-based wet and dry developers. When we do so, you'll have no further difficulty fitting the dryers into the picture. Here, let us try again!

I

REMOVE EXCESS PENETRANT

APPLY WET DEVELOPER

USE DRYER

In a water-based wet developer, the powder is mixed with water. The article is usually momentarily dipped or sprayed with the developer. A short time is then allowed for the water to evaporate, leaving the article thinly coated with a layer of powder. When water-based wet developers are used, the evaporative process is often hurried by the use of a recirculating hot air dryer after the developer has been applied.

REMOVE EXCESS PENETRANT

USE DRYER

APPLY DRY DEVELOPER

Dry developer is applied dry ... in powder form. It too can be applied by dipping

or spraying, but to avoid layers of developer which are too thick or uneven, the article must be dry prior to developer application. Dryers are used prior to dry developer application to accomplish this objective. Return to page 5-23, study the sequence presented there, and make the correct selection.

From page 5-24

5-26

Right. The test article's surface must be dry before applying nonaqueous wet developer. Should drying time require speeding up, blowing with compressed air is usually sufficient. Now you might ask what governs the choice of developer for a given situation. Here are some guidelines. WATER-BASED WET DEVELOPER APPLICATIONS

1. 2.

3.

On very smooth surfaces where a dry developer will not adhere. When testing large numbers of small irregularly shaped articles (production testing). When wide, shallow discontinuities are sought, wet developer tends to leave a more even fIlm of developer than does dry developer.

DRY DEVELOPER APPLICATIONS

I. 2. 3.

On rough surfaces, dry developer gives far better results than wet developer. On sharp fillets, holes, and threaded articles where wet developers tend to leave too much developer. On very large articles where it might be difficult to apply wet developer.

NONAQUEOUS WET DEVELOPER APPLICATIONS

1. 2. 3.

On spot checks or when conducting tests in the field. On vertical surfaces, a uniform film of developer is more easily obtained.

When greatest sensitivity is needed in showing borderline indications.

Again, these are only guidelines. There will be exceptions. Some specifications permit the use of only one type of developer. And as mentioned earlier, there are a number of penetrants that do not require a developer. The penetrant alone provides sufficient indication. Turn to page 5-28.

From page 5-24

5-27

Incorrect. The test article's surface must be dry •• _not wet. This generally presents little problem however. If you'll remember, nonaqueous wet developer is most often employed with "solvent-removed" penetrants. The penetrant remover is a solvent . . . not water. This solvent readily evaporates, leaving a dry test surface for developer application. In those few instances when water is used as the penetrant remover, it must also be removed before developer is applied. Water and nonaqueous wet developer don't mix. Developer action becomes unreliable. Just remember, like dry developer, nonaqueous wet developer is applied after test surfaces dry. With this in mind, turn to page 5-26.

From page 5-26

5-28

You might also ask if there is a "development time" for developers similar to the penetration or dwell time for penetrants. There is but it should present no problem. Development or developing time is defmed as the time from developer application to the time article is inspected. If a dryer is used, it includes the time in dryer. But how long a time do we use? We use a time that is long enough for indications to develop . . . but not so long that they become blurred or distorted. When using water-based wet developers, the time in the drying oven is usually sufficient. With dry or nonaqueous wet developers, the accepted norm is 7 to 30 minutes (A "rule of thumb" is to use a time equal to one-half the penetration or dwell time used). That's all there is to it! For a quick review before we proceed to the interpretation of indications, turn to the next page.

5-29

From page 5-28 1.

Step One is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Step Two is _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Step Three is _ _ _ __ Step Four is _ _ _ _ _ _ _ _ _ _ _ _ _ __

5.

dry

6.

There are three basic types of wet developer used in liquid penetrant ~part",-,-_ __ testing. They are: I) water-sus 2) wa solu , and 3) nonaq wet.

10.

larger

II.

When dryers are used to speed up drying time, they are used (before/after) application of a water-based, wet developer.

IS.

16.

The period from developer application to inspection of disconn t time. tinuity indications is called _ _ _ _ _.J.m,..,e"'....

5-30

I. Surface Preparation Penetrant Application Excess Penetrant Remova Developer Application 2.

If test is interrupted or delayed, allowing penetrant to dry out, you must return to Step _ __

6. water-suspended particle water soluble nonaqueous 7.

Two of the wet developers are _____ based; in the third, the developer particles are suspended in a rapid drying _ _ _ _ __

II.

after

12.

The recommended drying temperature range for most applications is between (temperature) and _ _ _ __

16.

development

17.

Development time is the time allowed between application of developer of test article. and the

5-31

2.

One

3.

The one ingredient that all developers used in liquid penetrant testing have in common is a highly absorbent ______

7.

water solvent

8.

Dry developers are said to have about the same level of sensitivity

as the water soluble developers. The least sensitive of all the devel-""'a"te"'rcc-s"'us"'--_ _ _ _ _ "p'-____ developers; opers are thew most sensitive are the non developers.

12.

ISO and 225°F (66 and 107°C)

13.

Test article surface temperature, however, should be limited to (temperature) _ _ maximum.

17.

18.

With water-based wet developer, the time in dryer is usually sufficient development time. (True - False) _ __

5-32

3.

powder

4.

When the powder is suspended in a liquid, the developer is said to be a ___ developer.

B. water-5uspended particle

9.

Developers are used to blot penetrant from _ _ _ _ _ _ _ __

14.

When using dry developer, dryer must be used (before/after) _ _ _ _ _ developer application.

lB.

True

19.

With dry or nonaqueous wet developers, the accepted norm for to minutes. development time is

5-33

4.

wet

5.

When the developer is applied in its natural powder state, the developer is considered a ___ developer. Return to page 5-29, frame 6.

9.

10.

discontinuities

The dye penetrant drawn from discontinuities diffuses into the developer, forming an image of the discontinuity that is usually (larger/smaller) that the actual discontinuity size. ... Return to page 5-29, .,. frame II.

14.

before

15.

When using a nonaquenous wet developer, test surfaces must be (wet/dry) ___ before applying developer. Return to page 5-29, frame IS.

19.

7t030

20.

You are now ready for Step Five. Please turn to page 6-1.

CHAPTER 6 - INSPECTION AND POSTCLEANING

6-1

INSPECTION Next in the sequence of operations is Step Five - Inspection - the searching out of penetrant indications and detennining their cause.

e . WH

WATER

WASHABLE

DRYER

STEP T SURFACE PREPARATION

r.

sm,

STEP 2 PENETRANT

APf'L1CAlION

EXCESS EMULSIFIER APf'UCATlON PENETRANT REMOVAL

A·

SOLVENT

REMoveD

STEP 4

DEVELOf'EA

STEP S

INSPECTION

APf'LICATION

B

DRY DEVELOPER

II I I I

:

I I I

I I

~

Proper lighting should be our frrst consideration in the inspection of an article. If fluorescent penetrant is used, a room or booth equipped with black light is essential. Black light intensity should measure at least 800 microwatts per square centimeter at the test surface. You should also allow at least 5 minutes for the light to warm up and your eyes to become accustomed to the dark. The lighting when viewing visible dye indications should be at least sufficient to ensure no loss of sensitivity. As a minimum, the lighting at the test surface should measure at least 32.5 footcandles (350 lux). In searching out indications, inspection may reveal indications that are either "true" indications or "nonrelevant" indications. True indications are indications caused by penetrant bleeding from actual discontinuities in the test article. These indications are the ones we set out to fmd when we started the test. Nonrelevant indications (also sometimes called "false" indications) are indications that do not stem from actual discontinuities, and are therefore not relevant to the determination of the acceptability of an article. However, they can present problems. Turn to next page.

I

I

From page 6-1

6-2

Improper cleaning in Step One and poor or incomplete washing of penetrant from test surfaces in Step Three are common causes of nonrelevant indications. The resultant streaks and patches can hide true indications. The only acceptable corrective action is to repeat the process beginning with Step One. Dirt and lint often produce indications similar to discontinuities. Penetrant may also be trapped by rough surfaces, sharp fillets, and blind holes. Other sources of nonrelevant indications are threads, keyways, and press-fits or joints. Following are typical examples of nonrelevant indications you may encounter.

Fluorescent Streaks and Patches Due to Incomplete Wash

Tum to the next page.

From page 6-2

6-3

Nonrelevant Fluorescent Indications Due to Rough Surfaces and Poor Wash Again, the problem with nonrelevant indications is that they sometimes look like true indications (e.g., the indications caused by dirt and lint). They sometimes hide or obscure true indications (e.g., fme cracks at an interface between assembled parts, or at fasteners such as bolts and rivets). If there is doubt about the source of a particular indication, the test should be repeated and indications carefully watched as they develop. Test materials used also should be checked for possible contamination. Select the correct completion for the following statement. True indications are indications caused by ... penetrant retained in test article's features . . penetrant bleeding from actual discontinuities

Page 6-4 Page 6-5

From page 6-3 Sorry but your selection describes possible nonrelevant indications. indications.

6-4 . not true

By true indications we mean indications resulting from penetrant bleeding from actual discontinuities; for example, a fatigue crack, forging lap, or surface porosity. They are the indications we set out to fmd when we started the test. With this in mind, turn to page 6-5 and continue.

From page 6-3

6-5

Correct! True indications are indications caused by penetrant bleeding from actual discontinuities. They are the indications we set out to fmd. Learning to identify indications is one phase of the test that takes much practice. For example, cracks, cold shuts, seams, and forging laps all show up as continuous line indications. These same discontinuities may appear as an intermittent or broken line - the discontinuity being partially closed at the surface. Small dots and rounded indications generally indicate porosity, small inclusions, or blow holes. The size of the indications, their intensity, and the amount of bleeding can sometimes give us a rough estimate of discontinuity size. Fine cracks and porosity for example, produce faint indications. The wider or deeper the crack, or the larger the porosity, the larger and brighter or more rapidly spreading the indication. There are many types of discontinuities that you will be working with and we cannot possibly cover them all here. But, no course in liquid penetrant testing could be considered complete until the student has had the opportunity to see discontinuities as they would appear on actual test articles. The next few pages therefore contain photographs that show you just a few of the discontinuities you will be faced with in your further training and job performance. In examining these photographs you must realize that the discontinuities were not

visible prior to the liquid penetrant test. They have become visible only as the result of the liquid penetrant process. The dye spreading through the developer has given us a "larger-than-life" indication of the discontinuity. Turn to the next page.

6-6

From page 6-5

•

•

'-

.r" ,.;

--

,

"

"

,

,,

,

,

•

•

•

,

---

.';

,

Visible Dye Indications of Surface Bursts in Steel Forging

•

/;'

.

Visible Dye Indications of Fatigue Cracks Plus Nonrelevant Indication at Rivet

Turn to the next page.

.,

.:,'

From page 6-6

6-7

Visible Dye Indication of Seam

Visible Dye Indication of Lamination

Visible Dye Indication of Forging Lap

Tum to the next page.

6-8

From page 6-7

Visible Dye Indication of Forging Lap

Visible Dye Indication of Forging Burst

Turn to the next page.

6-9

From page 6-8

Visible Dye Indications of Weldment Shrink Cracks

Visible Dye Indications of Cracks in Aluminum Forging

,

I

'

" - j, '

,

,

''b

Visible Dye Indications of Unhealed Porosity in Aluminum Plate Turn to the next page.

6-10

From page 6-9

Now you are ready to start back through the book and read those upside-down pages. TURN OR ROTATE THE BOOK 1800

-

LIKE THIS.

6·11

U-g

Look at the fluorescent indications on page 6-11 and continue as before.

A-I SELF-TEST

1. Water-washable liquid penetrants differ from post-emulsification penetrants in that they: a. Can only be used on aluminum alloys. b. Need not be removed from surfaces prior to development. c. Have an oily base. d. Contain an emulsifier. 2. Minimum penetration or dwell times can be detennined with the aid of prepared time charts. a. True b. False 3. With post-emulsified processing, penetration times are: a. Not so important as emulsification times. b. More important than emulsification times. c. Equal to emulsification times in importance. 4. Uquid penetrant tests can be used to detect: a. Internal porosity in castings. b. Corrosion wall thinning in pipes and tubes. c. Fatigue cracks in magnesium alloy parts. d. Carbon content of steels. 5. Which of the following substances on test articles can interfere with liquid penetrant testing? a. Oil or grease c. Traces of water b. Acids or chromates d. All of these 6. Fluorescent penetrants produce indications that are visible only under: a. Visible light c. Fluorescent light b. Black light d. Infrared light 7. Which of the following are commonly-accepted methods for applying penetrant? a. Dipping c. Spraying b. Flowing d. All of these 8. Visible dye penetrant indications become visible under black light. a. True b. False

A-3

18. The length of time the emulsifier remains on the test article is very important if detection of shallow discontinuities is desired. a. True b. False 19. Washing excess fluorescent penetrants from a surface is a critical operation and should be conducted under black light. a. True b. False 20. A thick coat of wet developer is better than a thin coat of developer for the detection of small discontinuities. a. True b. False 21. Penetrant tests will show discontinuities open to the surface, which are free from oil, grease, dirt, water, and other contaminants. a. True b. False 22. Glass and ceramics, as well as metals, can be inspected with liquid penetrant testing. a. True b. False 23. If too long an emulsification time is used, which of the following would most likely result? a. Nonrelevant discontinuity indications would appear. b. Shallow discontinuity indications would be lost. c. Excess penetrant would remain after the wash. 24. Subsurface discontinuities are detectable with liquid penetrant testing. a. True b. False 25. The function of the solvent cleaner when used with a post-emulsification penetrant is to: a. Render surface penetrant water washable. b. Remove excess penetrant from test surfaces. c. Remove penetrant from discontinuities. d. Speed up emulsification of penetrant. 26. Which of the follOWing is not a generally-accepted method for cleaning test articles prior to penetrant application? a. Solvent cleaner c. Alkaline cleaner b. Vapor degreasing d. Wire brushing

A-5 35. A red discontinuity image is most apt to be seen when which of the following occurs? a. Dry developers are used. b. Fluorescent penetrants are used. c. Visible dye penetrants are used. 36. Which of the following is the one true limitation of liquid penetrant testing? a. It cannot be used on ferromagnetic materials. b. It cannot locate subsurface discontinuities. c. It cannot be used on porous materials. d. It cannot be used on nonmetallic surfaces. 37. The penetrant and test article temperature, at time of penetrant application, should be: c. Atleast 125 0 F (52 0 C). a. No more than 600 F (l6 0 C). b. 175 to 225 0 F (79 to 1070 C). d. 60 to 125 0 F (16 to 52 0 C). 38. Penetrant diffusion into the developer is necessary in order to make the penetrant water washable. a. True b. False 39. A water wash that is too hot is detrimental to test results because: a. It may remove some of the penetrant from discontinuities. b. It may remove fluorescent dyes from penetrant. c. It may form water contaminants in smaller discontinuities. 40. The dryer temperature setting for drying test articles either before or after developer application should be: 60 to 125 0 F (16 to 52 0 C). c. ISO to 225 0 F (66 to 1070 C). a. b. 110 to 175 0 F (43 to 79 0 C). d. 225 to 325 0 F (107 to I 63 0 C). 41. In applying a wet developer, greatest sensitivity is obtained by: c· Dipping. a. BruShing. b. Swabbing. d. Spraying. 42. An emulsifier must be applied before a post-emulsification type penetrant can be removed by the solvent-removed method. a. True b. False

A-7

51. Which of the following is the best method for detecting shallow discontinuities? a. Post-emulsified processing b. Water-washable processing c. Solvent-removed processing 52. Development time is defined as the time period from: a. Penetrant application to penetrant removal. b. Penetrant application to developer removal. c. Emulsifier application to emulsifier removal. d. Developer application to inspection. 53. When a water-based wet developer is used, the time in drying oven is usually considered sufficient to develop indications. a. True b. False 54. The time duration that test articles must remain in drying oven, following water-based wet developer application, should be long enough to: a. Dry penetrant in discontinuities. b. SuffiCiently heat test articles. c. Just dry test surfaces. d. Assure maximum bleedout of penetrant. 55. When a dry or nonaqueous wet developer is used, test articles should be inspected: a. Immediately following developer application. b. Within 7 to 30 minutes after developer is applied. c. At least 3 hours after developer application. d. Within 24 hours of developer application. 56. Number the actions below using numbers I through 6 in the order they would occur when performing a penetrant test with water-washable penetrant and a dry developer. _ _ Inspect _ _ Dry in dryer _ _ Apply developer _ _ Prepare surface _ _ Apply penetrant _ _ Remove excess penetrant

A-9

64. Approved LOX compatible penetrant materials do not contain any: a. Fluorescent dyes. b. Cleaning materials. c. Combustible materials. 65. When LOX compatible penetrant materials are used, the equipment must be: a. Cleaned prior to use. b. Cleaned after use. c. Approved by specifications. 66. The sulfur and chlorine found in common penetrant materials can be detrimental to: a. Stainless steel. c. Nickel alloys. d. All of these. b. Titanium.

67. In detecting fine discontinuities, greatest sensitivity is obtained with: a. Visible dye penetrants. b. Fluorescent penetrants. c. Dual sensitivity penetrants. 68. A brilliant yellow-green glow is a characteristic of: a. Visible dye penetrants. b. Fluorescent penetrants. d. Dual sensitivity penetrants. 69. In using a diluted "hydrophilic" emulsifier to remove excess post-emulsified penetrant, application is generally accompanied by some form of mechanical agitatIOn or scrubbing. b. False a. True 70. The penetrant indication of a forging lap will normally appear as a: a. Round or nearly round indication. b. Cluster of indications. c. Continuous line. d. Dotted indication.

A-ll

79. Which of the following safety precautions must be observed when handling penetrant materials? a. Avoid contact or splashing of penetrant materials on skin and clothing. b. Avoid inhaling vapors and powder particles. c. Never conduct tests near spark emitting equipment or open flames. d. All of above. 80. Retests, when required, shall be conducted only with fluorescent penetrants. a. True b. False

A-13

Question

Page No. Ref.

Question

Page No. Ref. Prepare surface 6-1 Apply penetrant Remove excess penetrant Dry in dryer Apply developer Inspect

39. a

4-8

40. c

5-7,5-18

41. d

5-6

42. b

4-3

43. d

4-12

57. c

6-1

44. b

5-20

58. c

4-5

45. c

5-6

46. a

3-19

59. 1. 2. 3.

47. c

3-1

48. c

3-26

49. a

7-8

60. d

8-53

50. b

3-14

61. b

9-9

51. a

4-15

62. b

9-1

52. d

5-28

63. a

9-9

53. a

5-28

64. c

9-12

54. c

5-7

65. a

9-19

55. b

5-28

66. d

9-22

56. 1. 2. 3. 4. 5. 6.

4. 5. 6.

Prepare surface Apply penetrant Remove excess penetrant Apply developer Dry in dryer Inspect 6-1

GLOSSARY

B-1

Angstrom Unit A unit of length equal to 10-8 em and used to express wavelengths of light; i.e., electromagnetic radiation. Aqueous Developer

See Wet Developer.

Background The surface upcn which an indication is viewed. It may be the natural surface of the test article, or it may be the developer coating on the surface. This background may contain traces of unremoved penetrant (fluorescent or visible), which if present, can interfere with the visibility of indications. Background Fluorescence Fluorescent residues observed over the general surface of the test article during fluorescent penetrant inspection. Bath Term used colloquially to designate the liquid penetrant inspection materials into which test articles are immersed during inspection process. Black Light Light radiation in the near ultraviolet range of wavelengths (3200 to 4000 angstroms), just shorter than visible light. Black Light Filter A filter that transmits black light while suppressing visible light and harmful ultraviolet radiation. Bleedout The action of the entrapped penetrant in spreading out from surface discontinuities to form an indication. Blotting The action of the developer in soaking up penetrant from a surface discontinuity, so as to cause maximum bleedout of penetrant for increased contrast and sensitivity. Capillary Action The tendency of liquids to penetrate or migrate into small openings, such as cracks, pits, or fissures. Carrier Fluid A fluid in which liquid penetrant inspection materials are dissolved or suspended. Oean

Free of interfering solid or liquid contamination.

Color Contrast Penetrant

See Visible Dye Penetrant.

B-3 Drain Time That portion of the penetrant inspection process during which the excess penetrant, emulsifier, detergent remover, or developer is allowed to drain from the test article. Dry Developer

A fine dry powder developer that does not employ a carrier fluid.

Drying Oven

An oven used for drying rinse water from test articles.

Drying Time

The time allotted for a rinsed test article to dry.

Dual Sensitivity Penetrant fluorescent dyes.

A penetrant that contains a combination of visible and

Dwell Time The total time that the penetrant or emulsifier is in contact with the test surface, including the time required for application and the drain time. Also see Emulsification Time. Electrostatic Spraying A technique of spraying wherein the material being sprayed is given a high electrical charge, while the test article is grounded. Emulsification Time The period of time that an emulsifier is permitted to combine with the penetrant prior to removal. Also called Emulsifier Dwell Time. Emulsifier A liquid that combines with an oily penetrant to make the penetrant water washable. Also see Hydrophilic Emulsifier and Lipophilic Emulsifier. Evaluation The process of determining the severity of the condition after the indication has been interpreted. Evaluation leads to determining whether the article is acceptable, salvageable, or rejectable. False Indication An indication due to improper processing. Distinct from nonrelevant indication. Family The complete series of materials necessary to perform a specific process of liquid penetrant inspection. Flash Point The lowest temperature at which a volatile flammable liquid will give off enough vapor to make a combustible explosive mixture in the air space surrounding the liquid surface.

B-5

Penetrant A liquid (sometimes gas) capable of entering discontinuities open to the surface, and which is adapted to the inspection process by being made highly visible in small traces. Fluorescent penetrants fluoresce brightly under black light while the visible penetrants are intensely colored to be noticeable under visible light. Penetration Time Post-Emulsification emulsifier.

See Dwen Time. A penetrant removal technique

employing a separate

Post-Emulsification Penetrant A penetrant that requires the application of a separate emulsifier to render the surface penetrant water washable. Also can be removed by applying a solvent remover. Precleaning The removal of surface contaminants or smeared metal from the test article so that they cannot interfere with the penetrant inspection process. Quenching of Fluorescence The extinction of fluorescence by causes other than removal of black light (the exciting radiation). Rinse The process of removing liquid penetrant inspection materials from the surface of an article by washing or flooding with another liquid - usually water. Also called Wash. Seeability The characteristic of an indication that enables the observer to see it against the conditions of background, outside light, etc. Self-EmuIsul3ble Sensitivity

See Water Washable.

The ability of the penetrant process to detect surface discontinuities.

Solvent Developer

See Nonaqueous Wet Developer.

Solvent Removed A penetrant removal technique wherein the excess penetrant is washed or wiped from the test surface with a solvent remover. Solvent Remover A volatile liquid used to remove excess surface penetrant from the test article. Sometimes called Penetrant Remover.

B-6

Surface Tension That property of liquids which, due to molecular forces, tends to bring the contained volume into a form having the least superficial area. Viscosity The state or degree of being viscous. The resistance of a fluid to the motion of its particles. Visible Dye Penetrant An inspection penetrant that is characterized by its intense visible color - usually red. Also called Color Contrast or Nonfluorescent Penetrant. Wash

See Rinse.

Water-Soluble Developer A developer in which the developer powder is dissolved in a water carrier to form a solution. Not a suspension. Water-Suspended Particle Developer A developer in which the developer particles are mixed with water to form a suspension. Water-Wash A penetrant removal technique wherein excess penetrant is washed or flushed from the test surface with water. Water-Washable Penetrant making it water washable.

A type of penetrant that contains its own emulsifier,

Water Tolerance The amount of water that a penetrant, emulsifier, or wet developer can absorb before its effectiveness is impaired. Wet Developer A developer in which the developer powder is applied as a suspension or solution in a liquid - usually water or alcohol. Wetting Ability solid surfaces.

The ability of a liquid to spread out spontaneously and adhere to

B-4

Flaw

See Defect.

Fluorescence The emission of visible radiation by a substance as a result of, and only during, the absoprtion of black light radiation. Fluorescent Penetrant An inspection penetrant that is characterized by its ability to fluoresce when excited by black light. Hydrophilic Emulsifier A water-based agent that, when applied to an oily penetrant, renders the penetrant water washable. Can be used as a Contact Emulsifier, but more often the emulsifier is added to the water rinse and accompanied by some form of mechanical agitation or scrubbing to remove excess penetrant. Sometimes called a Hydrophilic Scrubber. Indication That which marks the presence of a discontinuity, as the result of detectable bleed out of penetrant from the discontinuity. Inspection The visual examination of a test article after completion of the penetrant processing steps. Interpretation The determination of the significance of indications from the standpoint of whether they are relevant or nonrelevant. Leak Testing

A technique of liquid penetrant testing in which the penetrant is applied to one side of the surface, while the other side is inspected for indications that would indicate a through-leak or void. lipophilic Emulsifier An oil·based agent which, when applied to an oily penetrant, renders the penetrant water washable. Usually applied as a Contact Emulsifier. Nonaqueous Wet Developer A developer in which the developing powder is applied as a suspension in a quick..Irying solvent. Also called Solvent Developer. Nonfluorescent Penetrant Nonrelevant Indication discontinuity.

See Visible Dye Penetrant. An indication that is not or cannot be associated with a

Penetrability The property of a penetrant that causes it to find its way into very fine openings, such as cracks.

B-2

Comparative Test Block An intentionally cracked metal block having two separate but adjacent areas for the application of different penetrants so that a direct comparison of their relative effectiveness can be obtained. Can also be used to evaluate penetrant test techniques and test conditions. Contact Emulsifier An emulsifier that begins emulsifying penetrant upon simple contact with the penetrant. Usually oil based (lipophilic). Contrast The difference in viSibility (brightness or coloration) between an indication and the surrounding surface. Dark Adaptation darkened area.

The adjustment of the eyes when one passes from a bright to a

Defect A discontinuity that interferes with the usefulness of an article. A fault in any material or part that is detrimental to its serviceability. Detergent Remover A penetrant remover that is a solution of a detergent in water. Also see Hydrophilic Emulsifier. Developer A material that is applied to the test article surface after excess penetrant has been removed and that is designed to enhance the penetrant bleedout to form indications. The developer may be a fine powder, a solution that dries to a fine powder, or a suspension (in solvent, water, alcohol, etc.) that dries leaving an absorptive mm on the test surface. Developing Time The time between the application of the developer and the examination of the test article for indications. The elapsed time necessary for the applied developer to bring out indications from penetrant entrapments. Also called Development Time. Discontinuity An interruption in the normal physical structure or configuration of an article, such as cracks, forging laps, seams, inclusions, porosity, etc. A discontinuity mayor may not affect the usefulness of the part. Dragout The carryout or loss of penetrant materials as a result of their adherence to the articles being processed.

A-14

Question

Page No. Ref.

67. b

3-6

68. b

3-6

69. a

4-10

70. c

6-5

7J. d

6-5

72. c

6-5

73. d

7-12

74. d

7-12

75. a

6-16

76. c

7-12

77. a

4-1

78. b

6-1

79. d

7-16

80. b

8-81

A-12

Question

Answers for Self-Test Page No. Ref.

Question

Page No. Ref.

I. d

4-3

20. b

5-6

2. a

3-16

21. a

2-2

3. a

4-14

22. a

I-I

4. c

1-6

23. b

4-14

5. d

2-2

24. b

7-1

6. b

3-6

25. b

4-5

7. d

3-14

26. d

2-10

8. b

3-6

27. b

24

9. a

1-7

28. a

4-8

10. d

4-10

29. a

7-1

II. b

4-14

30. a

4-8

12. b

4-15

31. a

44

13. a

3-9

32. c

3-6

14. d

2-7

33. c

4-5

15. b

5-16

34. a

3-9

16. c

6-2

35. c

3-6

17. b

5-2

36. b

1-6

18. a

4-14

37. d

3-26

19. a

4-22

38. b

4-10

A-1O 71. Round or nearly round indications on the surface of a test article are indications of: a. Cracks. b. Nonmetallic inclusions. c. Seams. d. Porosity. 72. An intermittent or broken line is indicative of: c. A partially closed crack. a. An open crack. d. A subsurface defect. b. A blow hole. 73. What is the most common contaminant that will be found in penetrant tanks? Oil c. Metal filings a. b. Detergents (from cleaning) d. Water 74. Which of the following contaminants will be found in developer tanks? c. Penetrant a. Dlft or lint d. All of these b. Water 75. In general, the cleaning methods employed in the postcleaning of test articles are the same as those recommended for pre cleaning. a. True b. False 76. The specific gravity of water-based wet developers should be routinely checked with a: a. Densitometer. c. Hydrometer. b. Centrifuge tube. d. Hygrometer. 77. It is difficult to remove penetrant from discontinuities once it has dried. a. True b. False 78. When viewing fluorescent indications in a darkened area, the generally-accepted time period for becoming accustomed to the dark is: a. I minute. c. 10 to 15 minutes. b. 5 minutes. d. None of these.

A-8

57. In viewing fluorescent indications, black light intensity at the test surface should be at least: a. 3000 microwatts per square centimeter. b. 600 microwatts per square centimeter. c. 800 micro watts per square centimeter. d. 1000 microwatts per square centimeter. 58. When solvent-removed processing is used, which of the following is a must? a. Use only cloths and towels recommended by penetrant manufacturer. b. Excess penetrant must be removed indoors. c. Cloths used to wipe off excess penetrant must be lint free. 59. Number the actions below using numbers I through 6 in the order they would occur when performing a penetrant test with water-washable penetrant and a water-based wet developer. __ Inspect _ _ Dry in dryer _ _ Apply developer _ _ Prepare surface _ _ Apply penetrant _ _ Remove excess penetrant 60. Which of the following statements concerning the use of mercury vapor black lights is not true? a. Light may extinguish because of excessive line voltage fluctuations. b. It takes about 5 minutes for light to warm up to maximum output when fIrst turned on. c. Light will not immediately respond if an attempt is made to relight bulb right after it has been turned off. d. Operation of light without a fIlter is safe. 61. Extremely large articles are usually tested with: a. Stationary test equipment. b. Portable test equipment. c. LOX compatible materials. 62. The arrangement of stationary liquid penetrant test equipment depends on: a. the equipment available. b. the test procedure to be used. c. the judgment of the operator. 63. Portable test kits must contain all the materials and equipment required for a complete test. a. True b. False

A-6

43. Which of the following is not permitted? a. Application of emulsifier by dipping b. Application of developer by spraying c. Removal of penetrant with water d. Application of emulsifier with a brush 44. Which of the following developers is rated highest in sensitivity? a. Dry c. Water suspended particle d. Water soluble b. Nonaqueous wet 45. Which of the following developers is rated the least sensitive? a. Dry c. Water suspended particle b. Nonaqueous wet d. Water soluble 46. When small discontinuities are sought, the penetration times will be: a. Longer than when only larger discontinuities are sought. b. Shorter than when only larger discontinuities are sought. c. The same as when larger discontinuities are sought. 47. The natural force relied upon to the greatest extent in liquid penetrant testing is called: a, Gravity. c. Capillary action. b. Boyle's Law. d. Penetrant attraction. 48. Penetrant and test article temperature will affect: a. The penetration time chosen. b. The usefulness of the time charts. c. Both of the above. 49. On which of the following would liquid penetrant testing be the least successful? a. Unfired ceramic d. Glass b. Steel e. Aluminum c. Plastic 50. It is necessary for the test article to remain submerged in the penetrant throughout the penetration period. a. True b. False

A-4 27. Which of the following contaminants is best removed by an alkaline cleaner? a. Grease c. Oily films b. Rust or scale d. Water

28. Removal of excess water-washable penetrant is best accomplished with a coarse forceful water spray. a. True b. False 29. Liquid penetrant testing is effective on nonmagnetic materials. a. True b. False

30. When water is used to remove excess penetrant, the water temperature should be: a. 60 to I 100F (16 to 43 0C). b. No more than 60 0 F (l6 0C).

c. d.

At least 125 0 F (52°C). 110 to J75 0 F (43 to 79 0 C).

31. Solvent-removed processing involves the use of post-emulsification type penetrants. a. True b. False 32. Which of the following is an advantage of visible dye penetrant over fluorescent penetrant? a. They are highly visible under black light. b. They can be used reliably at temperatures below 60 0 F (l6 0C). c. They are more portable in that they do not require a source of electrical power nor a darkened area to view indications. d. They are more sensitive in detecting fine discontinuities.

33. When excess penetrant is to be removed by solvent-removed processing, the best a. b. c. d.

method is to: Flush or swab test surface with the solvent. Use a soft bristled brush to apply solvent. Wipe test surface with a solvent-dampened, lint-free cloth or wipe. Apply solvent directly to test surface, then wipe off with a clean rag or cloth.

34. Dual sensitivity penetrants permit liquid penetrant tests to be made under visible light and questionable indications to be resolved under black light. a. True b. False

A-2

9. A discontinuity. undetectable with liquid penetrants at one stage in production, could be detected with liquid penetrants at a later stage in production. a. True b. False 10. The function of the emulsifier when used with a post-emulsification penetrant is to: a. Drive the penetrant into tight cracks more rapidly. b. Add fluorescent dye or pigment to the penetrant. c. Provide a coating to which dry powder developer can adhere. d. Render surface penetrant water washable.

I I. With post-emulsified processing, timing is most critical during the: c. Excess penetrant a. Penetration time. removal. b. Emulsification time. d. Dwell time. 12. To detect shallow discontinuities with post-emulsification methods, the emulsification time should be long enough to: a. Mix emulsifiers with penetrant in the discontinwties. b. Mix emulsifiers with excess penetrant. c. Mix emulsifiers wi th all penetrant. 13. Dual sensitivity penetrants contain visible as well as fluorescent dyes. a. True b. False 14. Which of the following is the preferred method for removing oily ftIms or grease from test articles prior to testing? a. Wire brushing c. Abrasive blasting d. Vapor degreasing b. Alkaline cleaner 15. Articles do not need to be completely dried before application of dry developers, since the powder will dry them anyway. a. True b. False 16. Liquid penetrant indications of a press-fit are considered a: a. discontinuity indication. c. non-relevant indication. b. defect indication. d. relevant indication. 17. Fluorescent dyes are added to developers to enhance discontinuity indications. a. True b. False

6-11

From page 6-10

Fluorescent Indications of Porosity in Machined Aluminum Plate

Fluorescent Indications of Blow Holes and Random Porosity in Aluminum Casting Turn to the next page.

From page 6-11

6-12

Fluorescent Indications of Laps in Aluminum Die Forging

Fluorescent Indications of Radius Cracks in Machined Steel Fitting

Turn to the next page.

From page 6-12

6-13

Fluorescent Indications of Porosity

Fluorescent Indications of Tears in Stretch Formed Aluminum Angle Turn to the next page.

From page 6-13

6-14

Photographs, as you're now well aware, provide excellent permanent records. Both black-and-white and color fIlm can be used - the self-developing fIlms providing the ultimate in convenience. We fmd that inspection today increasingly involves the recording of indications for test reports and inspection records. In addition to photographs, there are special wax and plastic fIlm developers that absorb and fix penetrant indications to provide permanent records. Or the recording of indications can be done with a "strippable" lacquer. Several coats of lacquer are applied over the indication and allowed to dry. The coating is then lifted, bringing the indication with it. Another method sometimes used is to spray the indication with a "fixer," and when dry, lift the indication with a piece of transparent tape. The tape, with the indication, is then transferred to the appropriate test document. But whatever the method used to record indications, time is of the essence. Delays will cause indications to become blurred or distorted through the continued bleeding of penetrant. They will not be representative of the discontinuities from which they came. Is the following statement true or false? Prolonging development time can adversely affect penetrant indications. True False

Page 6-15 Page 6-16

From page 6-14

6-15

True! Prolonging of development time can adversely affect penetrant indications. Again, the time in drying oven is usually sufficient for wet developers, and 7 to 30 minutes is the accepted norm for dry or nonaqueous wet developers. POSTCLEANING

The fmal step in the liquid penetrant process is postcleaning. Here it is added to our flow diagram as Step Six. WET WATER WASHABLE

fi

..... DISCONTINUITIES

DRYER

STEP t

SURFACE PREPARATION

STEP 2

~

PENETRANT

APPLICATION

f+I.

sm.

"'" 3 EXCESS

DEVELOPER

EMULSIFIER APPLICATION PENETRANT REMOVAL

SOLVENT REMOVED

INSPECTION

APPLICATION

~

FOR EVALUATION

STEP 5

sm. POST

DRY DEVELOPER

DISCONTINUITY fREE

CLEANING

Notice that only those articles, surfaces, weldments, etc., that have been found discontinuity free are directed to Step Six on the flow diagram. This has been done to stress the point that when discontinuities are discovered, they require evaluation. Naturally this would be done before removing the indications with a postcleaning! In fact, after evaluation, Step Six could be eliminated entirely when evaluation determines that the discontinuities present are such that the specimen tested is no longer useful and must be scrapped. When test articles tum up "discontinuity-free" Step Six is usually required. A thorough postcleaning is necessary because penetrant and developer residue tend to attract moisture, which may cause corrosion. Or it can interfere with subsequent processing or usage. In general, the cleaning methods employed in postcleaning are the same as those recommended for precleaning. Tum to page 6-17.

From page 6-14

6-16

Sorry but prolonging the development time does adversely affect penetrant indications. The statement was true. You'll recall that in Step Four, Developer Application, we established a developing time before indications can be viewed. You learned that the time in drying oven was usually sufficient when water-based wet developers were used ... that with dry or nonaqueous wet developers, the accepted norm was 7 to 30 minutes. You learned that longer times would result in blurred or distorted indications ... that indications would not be representative of the discontinuities from which the penetrant came. For the correct answer, tum to page 6-15.

6-17

From page 6-15

Detergent cleaners generally work best in removing water-base materials while vapor degreasers are best in removing oil-base materials. Developers are often simply washed off with plain water. Here again, the cleaning methods to be used are spelled out in the controlling specifications and standards. Here's one last look at the completed flow diagram - our study now having taken us through all six steps of a liquid penetrant test.

."

WATER

WASHABLE

H'''''}

~ 01SCOtHiNUITlES FOR EVALUATION

DRYER

STEP 1

SURfACE PREPARATION

STEP 2

~

PENETRANT

APf>lICATION

STEP]

A

EMULSIFIER

EXCESS

APPLICATION PENETRANT

SOLVENT

REMOVEO

Tum to the next page.

STEP 4

REMOVAL

a

STEP S

D£VEtOPEfI

INSPEcnON

APPLICATION

STEP 6

POST

OR'

O15tONTINUITY

DEVELOPER

FREE

CLEANING

6-18

From page 6-17 1.

Step One is _ _ _ _ _ _ _ _ _ _ _ _ __ Step Two is _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Step Three is _ _ _ __ Step Four is _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Step Five is _ _ _ _ _ _ __ Step Six is

3.

5 (five)

4.

The intensity ofvisible light when perfonning visible dye penetrant examinations should be at least _____________

7.

A nonrelevant indication that appears as large splotches of penetrant indicates that Step 3, _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ has been poorly done.

9.

line

rounded 10.

Proper development time is very important when it comes to interpreting indications. It should be long enough for indications to develop but not so long that they become blurred or distorted! For wet is usually sufficient; for dry or developers, the time in nonaqueous wet developers, the accepted nonn is to minutes.

6-19

I. Surface Preparation Penetrant Application Excess Penetrant Removal Developer Application Inspection Postcleanin 2.

4.

When inspecting fluorescent penetrant indications in Step Five, examinations are conducted in a darkened area with black light. The intensity of the black light used should measure at least _ __ microwatts per square centimeter at the test ______

32.5 footcandles (350 lux)

5.

When conducting Step Five, you must be on the lookout for indications that are - for testing purposes - meaningless! In liquid penetrant testing such indications are calledn ""o"n_ _ _ _ __ indications.

7.

Excess Penetrant Removal

8.

Dirt and lint often produce indications that can be mistaken for ____ indications.

10.

dryer 7 to 30

II.

Step Six, _ _ _ _ _ _ _ _ _ , isn't always needed. But when it is, the same cleaning methods as employed in Step ____ are generally recommended.

6-20

2.

800 surface

3.

Before actually conducting examinations of fluorescent indications, you should allow at least minutes for the black light to warm up and your eyes to become accustomed to the dark.

~

Return to page 6-18, frame 4.

s.

nonrelevant

6.

When a penetrant test shows indications of press-fitted articles and/or a poor excess penetrant wash, both indications are considered to be Return to page 6-18, frame 7.

9.

true (relevant)

10.

True indications are indications of actual discontinuities. Cracks, cold shuts, seams, and forging laps generally appear as continuous ___ indications? while porosity, small inclusions, and blow holes, are seen as _ _ _ _ _ _ indications or dots. Return to page 6-18, frame 10.

II.

Postcleaning One

12.

Turn to page 7-1.

CHAPTER 7 - LIMITATIONS AND PROCESS CONTROL

7·1

UMITATIONS

In Chapter I we gave you four questions to which you would learn the answers in this program. They were:

WHAT CAN BE LEARNED FROM A LIQUID PENETRANT TEST? HOW DOES LIQUID PENETRANT TESTING WORK? WHAT MATERIALS ARE REQUIRED FOR A LIQUID PENETRANT TEST? WHAT ARE THE LIMITATIONS OF LIQUID PENETRANT TESTING? Only the last of these questions remains unanswered - WHAT ARE THE LIMITA· TIONS OF LIQUID PENETRANT TESTING? When you get right down to it, this testing process we've been discussing has, for all practical purposes, only one limitation: Discontinuities must be open to the surface! However, this doesn't mean that liquid penetrant testing is always used when you

are looking for discontinuities open to the surface. In two situations there is def· initely a better choice, and liquid penetrant testing generally becomes second choice if it is used at all! Here are the two situations where other testing methods have proved better able to handle the job.

I. 2.

When it is necessary to examine fe"omagnetic material. When the surface you must examine is extremely porous.

Let's take these situations one at a time. But fIrst - before we see what method is fIrst choice for ferromagnetic materials - are you sure you understand what is meant by the term "ferromagnetic"? No Yes

Page 7·2 Page 7·3

From page 7-\

7-2

Before we proceed here's a working defInition of the term ferromagnetic. By defInition ferrous means, "pertaining to or derived from iron." So ferrous materials are those materials derived from iron (steel) or of the same family as iron (cobalt and nickel). Ferromagnetic materials, then, are those ferrous materials which are strongly attracted by magnetism and include the above mentioned metals and their alloys. Keeping this defmition in mind, turn to page 7-3.

From page 7-1

7-3

OK. Let's continue. When testing a ferromagnetic material there will be instances when another test method, such as magnetic particle testing, may be used. Details of magnetic particle testing will not be covered here. However, one point should be made - magnetic particle testing is not limited to the search for surface discontinuities. Here's the significance of that statement. After a magnetic particle test has been applied, it is sometimes desirable to use liquid penetrant testing to determine whether a discontinuity detected by the magnetic particle test method is, or is not, a surface discontinuity. Liquid penetrant testing will fill the bill because ... it will show only those discontinuities not already located by magnetic particle testing. . . . . . . . . . . . . . . it will show only those discontinuities that are open to the surface. it is an older and far more reliable test method

Page 74 Page 7-5 Page 7'{;

From page 7-3

7-4

Here's a point we may not have stressed strongly enough. A magnetic particle test is not limited to the detection of surface discontinuities (as is the liquid penetrant test). It will also detect "near-surface" discontinuities. Note carefully the word "also" in the preceding sentence. It's a reminder thaUhe magnetic particle process will show both surface and subsurface discontinuities (discontinuities that lie just below the surface). Return to page 7-3, and give it another try.

From page 7-3

7-5

Exactly! If our second carefully conducted test, this time with liquid penetrant, came up with a blank, the discontinuities located by magnetic particle tests would be known to lie beneath the surface. The second situation where our liquid penetrant test is apt to be no more than a second choice occurs when the surface that needs examination is extremely porous. In this case, as before, liquid penetrant testing will work but there is a better method. It is called filtered particle testing. Its name gives us a clue to the peculiarities, which make it fIrst choice. Keep this name in mind as we examine the problem faced in testing porous surfaces. First of all, a porous surface is full of small cavities that will hold liquids. When such a surface is undesirable, it becomes a discontinuity called ... an inclusion . porosity . a cold shut .

Page 7-7 Page 7-8 Page 7-10

From page 7-3

7-6

Your answer: " . it (liquid penetrant testing) is an older and far more reliable testing method (than magnetic particle testing)." You are going to be directed to try that last batch of questions again. When you state that you feel our liquid penetrant testing is an older method, you are correct. We can't honestly state, however, that is is a far more reliable testing method than magnetic particle testing. However, one of the selections on page 7-3 does state a very sound reason for using our liquid penetrant test after a magnetic particle test has been completed. Return to page 7-3, and select one of the other choices.

From page 7-5

7-7

An inclusion is described as a particle of foreign material that has been caught in the

hardening of metal into an ingot state. Inclusions are always subsurface unless they have been machine cut and exposed to the surface. This is not common, but even a surface that reveals inclusions will not be one that is full of small cavities "that will hold liquids," a surface described as porous. Your answer was not correct. Look again for a name that could be used to describe such a surface from among those offered on page 7-5.

From page 7-5

7-8

Good. When unwanted, such a porous condition is called porosity and is a surface discontinuity sought with the liquid penetrant method. However, in such things as unftred ceramics, porosity is the normal condition. In these materials, the porous surface is accepted, even desirable, and is not a discontinuity! These normally porous materials, however, don't escape nondestructive testing. They are still subject to flaws and must be checked for those things that are considered discontinuities. A crack, for example, may be just as serious in a ceramic insulator as in a gas pipeline. If the insulator is to be examined, indications of cracks would be sought while indications of its porous nature (or porosity) would not. The liquid penetrant testing procedures we've been studying would reveal both conditions. In a liquid penetrant test, indications of a porous nature are often so strong that other discontinuities may be overwhelmed and remain undetected. With porous materials, a test method is needed that will not show porosity but will show cracks and other legitimate discontinuities. Filtered particle testing accomplishes this objective. Tum to the next page.

From page 7-8

7-9

Filtered particle testing is similar to liquid penetrant testing. However, instead of using fluorescent or visible dyes, small particles are found in the penetrant liquid. These particles in most instances are fluorescent. When testing a porous surface with filtered particles, you will fmd that all of the liquid penetrant will be absorbed. There will be no "excess" requiring removal (as in our liquid penetrant processes). Where a discontinuity such as a crack is present, a peculiar phenomenon occurs, which provides us with indications of the crack. The increased area created by a crack (its walls, etc.) will cause more of the penetrant to be absorbed there than elsewhere. The crack will "filter" the penetrant, leaving the particles on the surface. Since more penetrant will be absorbed there, a greater buildup of particles will be found at the site of the crack. This buildup of particles provides a visual indication of discontinuities open to the surface. Is the following statement true or false? Liquid penetrant testing must never be used on a porous surface. True. False

Page 7-11 Page 7-12

From page 7-5

7-10

A cold shut is described as an imperfect joining of two metals, as when casting and chilling prevents one stream of metal from fusing with another stream in the same mold. The result is seen as a crack-like discontinuity called a cold shut. It is not a surface that can be described as "full of small cavities which will hold a liquid." Such a surface is considered porous and is called by another term than cold shut. The term is listed among the choices on page 7-5. See if you can spot it now.

From page 7-9

7-11

Looks as if we've understated liquid penetrant's role and overstated the role of mtered particle testing relative to porous surfaces. We did not mean to imply that liquid penetrant testing cannot be used on porous surfaces. All that was intended was to inform you that liquid penetrant testing may be second choice when testing such surfaces. Turn to page 7-12.

From page 7-9

7-12

Good for you. You recognize that liquid penetrant testing can be used on porous surfaces (though it may not necessarily be the best choice). Again - the primary limitation of liquid penetrant testing is that it will detect only

those discontinuities open to the surface. To fmd subsurface discontinuities, another method of testing such as ultrasonic or radiographic testing must be used. PROCESS CONTROL In previous chapters we have stressed the importance of test articles being dry and free of contaminants before proceeding with tests. Contamination of penetrant materials likewise should be held to a minimum. Excessive amounts of water, for example, can reduce the penetrating qualities as well as the washability of penetrants. Too much water can adversely affect emulsifier and developer characteristics. The quality of penetrant test materials may also deteriorate as a result of oil, dirt, and solvent contamination. Adequate steps must be taken to minimize contamination. Several factors should be considered in minimizing contamination. The dip tanks used in applying penetrants, emulsifiers, and developers should be kept covered when not in use to prevent the entry of dirt or dust and to reduce evaporation. Care should be taken to prevent rinse water from splashing over and contaminating the different materials. And to reduce the "drag-out" or "carry-over" of materials from one tank to the next, test article pockets and recesses should be allowed to drain before proceeding with subsequent steps. Test materials in open tanks should be routinely checked for sensitivity and possible contamination. The quality of penetrants is usually determined by a check of penetrant sensitivity and water content. Water-washable penetrants are checked for water washability. Emulsifiers are tested for water washability and water content. Water-based wet developers are checked for proper density with a hydrometer. Dry powder developers are checked for fIuffmess and freedom from lumps. Turn to the next page.

From page 7-12

7-13

Overall system performance is often determined by taking material samples and comparing them with control samples using artifically cracked test blocks. Materials are discarded when quality requirements of the controlling specifications or standards are not met.

As you've probably guessed, contamination of penetrant test materials is less of a problem with ... solvent-removed processing. . . . . . . . water-washable and post-emulsified processing

Page 7-14 Page 7-15

From page 7-13

7-14

Right. Contamination of penetrant materials is less of a problem with solventremoved processing. The reason being that materials are usually dispensed from pressurized (aerosol) spray cans and are not normally recovered or reused. Inspection of test articles having excessive background because of inadequate penetrant removal should never be attempted. Such articles should be recycled beginning with Step One - Surface Preparation. Retests, when required, likewise should be performed using the same type penetrant. Reprocessing with a different penetrant should be avoided. Visible dyes, for example, will quench the fluorescence of fluorescent penetrants. Fluorescent penetrants may dilute or prevent the entry of visible dyes. Even with a thorough recleaning, some of the original penetrant may remain in the bottom of discontinuities. Fluorescent dyes respond most actively to radiant energy of approximately 3650 angstroms. For fluorescent inspection, the area to be examined should be masked from as much visible light as possible. Black light should be checked routinely to determine if line voltage fluctations are detrimentally affecting light output. Routine checks also should be made to determine if aging, dust or dirt have reduced light intensity below minimum standards. Light intensity should measure at least 800 rnicrowatts per square centimeter at the test surface. Again, these requirements will be found in the controlling specifications and standards. In performing liquid penetrant tests, you must also be aware of possible health hazards and safety precautions. Turn to page 7-16.

•

From page 7-13

7-15

Sorry but your guess was incorrect. Contamination of water-washable and postemulsified processing is more of a problem - not less. Both usually involve the use of bulk materials and frequently the use of open dip tanks. The same materials are used to test many articles. This means more chances for contamination. Solvent-removed processing on the other hand usually involves the use of materials dispensed from pressurized (aerosol) spray cans. The materials are not recovered and reused. Thus the less chance for contamination. Tum to page 7-14

From page 7-14

7-16

Liquid penetrant testing for the most part does not introduce any hazards that are uncommon to other manufacturing operations. However, it would be well to point out those protective measures that should be taken. Continual exposure to penetrant materials can be injurious. Fumes can create a fire hazard. Safety precautions usually begin with good housekeeping practices. A clean work area and well-kept equipment are requisites to the conduct of any penetrant test. For protection, oil-resistant gloves and apron should be worn. Face and eyes should be protected by wearing a face shield. And inhaling of fumes and dust and the splashing of materials on clothing should be avoided. Should materials come in contact with the skin, they should be washed off with soap and water as soon as possible. And because of the possible fire hazard, tests should not be performed near spark emitting equipment or open flames. Finally, black lights must never be operated with missing, cracked, or broken filters because of possible exposure to harmful ultraviolet radiation. With this background in liquid penetrant testing, you're now ready for another short review. Turn to the next page.

7-17

From page 7-16

l.

When you consider the liquid penetrant process in its entirety, you can see that it has but one limitation. The discontinuity sought must be

2.

filtered

3.

And when ferromagnetic materials are tested, a method that will show subsurface as well as surface discontinuities is commonly chosen instead of liquid penetrant testing. This nondestructive testing method is called _______ particle testing.

4.

subsurface

5.

From this you can see that it is often worthwhile to use liquid penetrant tests in combination with other -"n",o",n~_ _ _ _ _ _ _ tests.

6.

specification (standard'i directive) .

7.

You should also be aware of possible health hazards reletive to liquid penetrant testing. Penetrant test materials can be "in"'i-=ur"-_ __ fumes can create a f_ _ "'h_ _ __

7-18

\.

open to the surface

2.

Even though liquid penetrant testing has but one limitation (discontinuities sought must be open to the surface), it is not always the first method chosen in every situation. For example, when a surface is quite porous in

~::~;~~e:t~:;:se:::ec=~~ testing

first choice.

lhod c;~;:

.,.

to page 7-17,

frame 3.

3.

magnetic

4.

When a magnetic particle test produces indications of discontinuities that do not appear when the same article is then subjected to a liquid penetrant test, the discontinuities are known to be _ _ _ _ _ __ Return to page 7-17, frame 5.

5.

nondestructive

6.

Improper usage, contamination, and deterioration of penetrant test materials adversely affect reliability. This means there must be checks and controls. You will fmd these in the controlling _ _ _ _ _ _ __ to which you will be working.

Return to page 7-17, frame 7.

7.

injurious fire hazard

8.

Steps should be taken to avoid contact with penetrant materials, and never perform tests near spark emitting equipment or open flames. This completes the review of Chapter 7. For some practical applications of liquid penetrant testing, turn to page 8-\.

8-1

CHAPTER 8 - PRACTICAL APPLICATION

In this, the second part of this program, you'll be supplying answers to questions

that arise in typical situations requiring nondestructive testing with liquid penetrants. In supplying these answers, you'll be asked to apply different combinations of penetrant, penetrant remover, and developer. As each combination is applied, the reason for its selection and the action you must take will be discussed. The different material combinations that are possible can be seen in this block diagram. VISIBLE

FLUORESCENT

I

I

PENETRANT

•••••••••••••• •••••••••••••••• •••••••••••••••

DUAL SENSITIVITY

• •••••••••••••• ••••••••• • ••••• SOLVENT

REMOVER EMULSIFIER

WATER

SOLVENT

WATER

WATER

•••••••••••••• •••••••••••••••• ••••••••••••••• ••••••••••••••••••••••••••••••••• DEVELOPER

DRY

WET

I WATER SUsPENDED PARTICLE

I WATER SOLUBLE

Turn to the next page.

NONAQUEOUS WET

From page 8-1

8-2

Here are typical examples of the different penetrant processes used. Notice the PENETRANT/REMOVER/DEVELOPER combinations. Visible dye, water-washable penetrant/dry developer Fluorescent, post-emulsified penetrant/emulsifier/wet developer Visible dye, solvent-removed penetrant/solvent remover/nonaqueous wet developer Dual sensitivity, water-washable penetrant/nonaqueous wet developer Each process is self-descriptive. For example, the type of penetrant dye will be indicated in the process description. The words ''visible dye," "fluorescent," or "dual sensitivity" will always be in evidence. In your judgment, is the following statement true or false? The type of lighting needed in a liquid penetrant test will be indicated by the process description. True. False.

Page 8-3 Page 84

From page 8-2

8-3

True is correct. The type of lighting needed will be indicated by the process description. The process description also provides a quick reminder of how to go about conducting the test. For example, if the description includes the term "fluorescent" instead of "visible dye," you know that black light will be used during ... Steps Three and Four Steps Two and Five. Steps Three and Five

Page 8-5 Page 8-6 Page 8-7

From page 8-2

84

Here is the statement again: ''The type of lighting needed in a liquid penetrant test will be indicated by the process description." Although you judged this a false statement, it is actually true. Look at it this way. You know that when a fluorescent dye penetrant is used, indications are usually seen as a yellow-green glow under black light. This tells you that a black light is needed to view indications. If the process you plan to use employs a visible dye or color contrast penetrant, you know that the dye produces brightly colored indications that can be seen under ordinary light. You know that black light isn't needed.

You can now see that your choice could have easily been true. OK? Turn to page 8-3.

From page 8-3

8-5

It looks as if a review of the steps outlined in the previous chapters is in order. Here they are:

Step One - Surface Preparation Step Two - Penetrant Application Step Three - Excess Penetrant Removal Step Four - Developer Application Step Five - Inspection Step Six - Postcleaning You've stated by your answer that you'd expect to use the black light during Step Three and Step Four. You are partially correct. During Step Three's excess penetrant removal you will be frequently using a water wash, and with fluorescent dyes washing under black light is recommended. There is no place for black light use during developer application, however. With a review of the steps above, you'll have no difficulty locating an answer that provides two ideal places for use of black light. Return to page 8-3 and give it another try.

From page 8-3

8-
Your answer, "During Steps Two and Five," is only partially correct. Black light is used during Step Five, aIright. That's the point in the test when our efforts should bear fruit! Step Two, however, is penetrant application. It would be difficult to apply penetrant in the darkened area necessary for black light use. But black light will come in handy when removing excess penetrant. Return to page 8-3 and try again.

From page 8-3

8-7

Fine! If you got here on your first pick, you must have the steps mentioned in the previous chapters down pat. In Step Three, Excess Penetrant Removal, your chances for an adequate wash are definitely improved if the washing is done under black light. And when you look for evidence of discontinuities in Step Five, Inspection, you wouldn't have much luck without the black light that fluorescent dyes require. The point to remember is this: If you get stuck, or are puzzled at any time during your work with liquid penetrant testing, stop and take a look at the words used to describe the process you want to use. It can tell you quite a bit, and might just solve your problem. Here again are the example processes we showed you earlier. But keep in mind they're only a sampling. Many more combinations are possible... some of which do not require a developer. Visible dye, water-washable penetrant/dry developer Fluorescent, post-emulsifled penetrant/emulsifier/wet developer Visible dye, solvent-removed penetrant/solvent remover/nonaqueous wet developer Dual sensitivity, water-washable penetrant/nonaqueous wet developer Turn to the next page.

From page 8-7

8-8

The penetrant and processing used will depend on the discontinuities sought and material being tested - the test article. Factors to consider include the level of sensitivity required; test article size, shape and surface condition; number of articles to be tested; and available equipment and facilities. In selecting a penetrant, visible dye penetrants are the simpler to use. No electrical power is required nor is a darkened area to view indications. But they are limited by their marginal ability in detecting [me discontinuities. They have a relatively low sensitivity . Fluorescent penetrants are much more sensitive to fme discontinuities. Depending on the penetrant formulation and processing used, they can be classified as having a medium, high, or superhigh sensitivity. Dual sensitivity penetrants have the advantage of providing two levels of sensitivity a low sensitivity as well as a medium sensitivity. They allow you to look for gross discontinuities under visible light, then resolve questionable indications under black light. They permit you to change sensitivity without changing penetrants. Again, there are penetrant processes that provide sufficient sensitivity without using a developer. All liquid penetrant processes, however, have one of the following characteristics in common. Can you spot it? All require the use of a water wash between 60 and II OaF (16 and 43 0 C) . . . . . . . . . . . . . . . . . . . . . . All require cleaning of test article before penetrant application All require dryer use

Page 8-9 Page 8-10 Page 8-11

From page 8-8

8-9

You've indicated that all liquid penetrant processes require use of a water wash between 60 and lIOoF (16 and 43 oC). This is not entirely true. Solvent removed penetrants you'll recall use a solvent to remove excess penetrant. Water isn't needed. You are correct, however, on water wash temperature. When a water wash is used, the temperature should be 60 to lIOoF (16 to 43 oC). Return to page 8-8 and try again.

From page 8-8

8-10

Good enough! Each process does require cleaning of test articles prior to penetrant application. What else is disclosed by the process description? Let's look at two of the processes: ... Water washable, and ... Post emulsified.

''Water washable" tells us more than just the fact that excess penetrant is removed with water. And "post emulsified" or "P.E." implies more than the requirement of an additional step! Water-washable processing, for example, is particularly valuable for testing parts having rough surfaces or parts containing blind holes, threads, or keyways. You know why from your reading in previous chapters. One of the following states that reason pretty well. The penetrant's composition makes it easily washed The penetrant itself contains solvents to clean out surface contaminants in rough surfaces. . . . . . . . . . .

.Page 8-12 .Page 8-13

From page 8-8

8-11

Hold on a minute. Dryer use is not always required. We can't say that all liquid penetrant processes will require the use of a dryer. A dryer is used, when possible, to speed up the drying process. But it is not required in all instances. With this in mind, return to page 8-8 and try again.

•

From page 8-10

8-12

Fine. You are defInitely on the right track! Water-washable penetrant has a "built-in" emulsifIer that speeds up the process makes it easy to wash away excess penetrant from rough surfaces. The advantage of having a "built-in" emulsifIer becomes a disadvantage when we face a somewhat different situation, a situation expressed in one of the statements below. Water-washable penetrant processing requires an "extra step" before penetrant removal . . . . . . . . . . . . . . . . . . . . Water-washable penetrant is not satisfactory for shaI10w discontinuity detection because of its built-in emulsifIer . . . . . . . . . Water-washable penetrant is not good for use on rough surfaces because of its emulsifying agent . . . . . . . . . . . . .

Page 8-14 Page 8-15 Page 8-16

From page 8-10

8-13

Incorrect. Water-washable processing is particularly valuable for testing articles having rough surfaces, etc., but the penetrant used does not contain any "solvents" to clean away surface contaminants. Nor do the penetrants used in post-emulsified processing. Again, water-washable processing is recommended for rough surfaces. Return to page 8-10, reread it, and choose again.

From page 8-12

8-14

Let us clear up one point right now! It is the post-emulsified penetrant that requires the "extra step," not water-washable penetrant. Water-washable penetrant has what can be thought of as a "built-in" emulsifier. The addition of the emulsifier is the extra step mentioned in the answer you selected. Why is it used? To make the postemulsified penetrant water washable. But, why isn't water-washable penetrant used in the first place? Because when carefully used, post-emulsified penetrant is much more satisfactory for use when checking for shallow discontinuities. Please return to page 8-12 and select another answer.

From page 8-12

8-15

Right again! You are demonstrating a grasp of the material presented in previous chapters. The water-washable penetrant has a major limitation; its built-in emulsifier makes it too easily removed from shallow, scratch-like discontinuities. Therefore, it is unwise to use this penetrant when you are interested in detecting discontinuities of this nature. One of the other penetrant processes is better suited for this job. It is the ... solvent-removed process post-emulsified (P.E.) process

Page 8-17 Page 8-18

From page 8-12

8-16

We goofed it! Your answer was not correct and it tells us we should stress our point again. Water-washable penetrant has a "built-in" emulsifier that speeds up the liquid penetrant process and makes it easy to wash away excess penetrant from rough surfaces. Since it washes easily from rough surfaces, how will it work on surfaces we want to inspect for shallow discontinuities? With this question in mind, return to page 8-12 and take another crack at the selections listed there.

From page 8-15

8-17

You have indicated that, given a choice between post-emulsified and solvent-removed processing, you'd choose the latter. It is not the answer we'd hoped you'd select. But we can't say that you are entirely wrong. There are many situations when it will be specified that solvent-removed processing be used and the excess be removed with a solvent designed for that purpose. There can be many reasons for this. The greater mobility provided by solventremoved processing may require its use. The need to avoid using water-based materials on the article might likewise demand it. But, in our example, we made no specific mention of any special consideration.

We simply wanted to stress the advantage found in using the extra step of postemulsification. That it is more reliable for use when shallow discontinuities are sought because, with careful control of the emulsifier, penetrant will not wash from discontinuities. Return to page 8-15 and select the other answer.

From page 8-1 5

8-18

Excellent! Chalk up another correct one. Selecting the post-emulsified process would be a good move. Its extra step permits reliable inspection for shallow discontinuities, but there's a price to pay for this safeguard. Items with blind holes, threads, or keyways present a problem. It is sometimes difficult to determine the correct emulsification time. Too little time and you will have poorly emulsified penetrant in a hard-to-reach location. The result: excess penetrant may not be removed from those areas during wash. If you allow enough time for penetrant to emulsify in these blind holes, etc., penetrant will also emulsify in the shallow surface discontinuities you seek. The result: shallow discontinuity indications are lost. Which of the penetrants listed below would you select to examine this bolt?

Water washable P.E. . . . . .

Page 8-19 Page 8-20

From page 8-18

8-19

Water Washable. Fine! And which for this keyway?

Water Washable

P.E.

. ...

Page 8-21 Page 8-22

From page 8-18

8-20

Ooops! You know that water washable is preferred for use when articles are rough surfaced or contain threads or keyways. The bolt had threads. Come on now, you'd use water washable, wouldn't you? Turn to page 8-19.

From page 8-19

8-21

Good for you. Water-washable processing is recommended for testing articles with rough surfaces, blind holes, threads, or keyways. Post-emulsified processing is better for locating shallow discontinuities. Let's look now at the third process - solvent-removed processing. It must not be forgotten because it has characteristics that make it especially attractive for some penetrant testing jobs. It, you'll recall, also involves post-emulsification type penetrants. But instead of using a separate emulsifier and following with a water wash, excess penetrant is removed with a solvent-dampened, lint-free cloth. The most important characteristic of solvent-removed processing is portability. It can be used in the field without the need for heavy complex equipment to perform tests. And it is excellent for spot tests and in examining such items as weldments. Here's a chance to put one of the penetrants to work. Let's say we've been called on to test sixty steel screws with rolled threads. We want at least a "medium" level of sensitivity. Which one of the following processes would you choose? Fluorescent water-washable. Fluorescent post-emulsified .

Page 8-23 Page 8-24

From page 8-19

8-22

Hold on a minute. Your answer was not correct. Remember, water washable is preferred for use when articles are rough surfaced or contain threads or keyways. That article shown had a keyway! Tum to page 8-21.

From page 8-21

8-23

Right. Fluorescent water-washable processing is the best choice for use on the sixty steel screws - the fluorescent dye providing a medium-to-high sensitivity for detecting fine cracks, etc. Now that you have the best penetrant for testing the screws, you are ready for Step One - Surface Preparation. You will want to clean as many of the screws as possible in one operation. The contaminant let's say is an oily film. If the following cleaning methods were available to you, which would you select to clean the screws? Vapor degreasing . Sandblasting Water wash . . .

Page 8-25 Page 8-26 Page 8-27

From page 8-21

8-24

You must have missed the key word "threads" when reading over the description given for the items we want to examine. Here it is again: Sixty steel screws with rolled threads. Remember that water-washable processing is recommended when you have rough surfaces, threads, or keyways. If sensitivity is also a factor, a fluorescent dye is recommended. For the sixty steel screws, you'd select fluorescent water-washable processing. Right? Turn to page 8-23.

From page 8·23

8-25

Correct! Vapor degreasing would be the best choice for removing the oily film from the example screws.

VAPOR DEGREASER

Proper cleaning is the key to liquid penetrant testing. Without it, penetrant tests can be unreliable. Again, vapor degreasing is preferred for removing organic contaminants such as oil and grease. An alternate method would be to wipe or flush test surfaces with a solvent cleaner. Alkaline cleaners are recommended for removing inorganic contaminants such as dirt, scale, and rust. Steam cleaning is useful in cleaning large unwieldy items. And when appropriate, ultrasonic cleaning can be employed in combination with a solvent or detergent to improve cleaning efficiency and reduce cleaning time. But whatever the cleaning method used, it must not harm test articles, and it must result in a test surface that is dry as well as free of residue. Detergent cleaning must be followed with a thorough rinsing and drying. And to expedite drying, heat lamps, hot air blowers, or ovens are often recommended. Tum to page 8·28.

From page 8-23

8-26

No. You are not correct. Sandblasting is one of the cleaning methods we generally do not recommend! Why? Because it is apt to close discontinuities that would otherwise be open to the surface. One method that is widely used is listed on page 8-23. Return to that page and see if you can spot it.

From page 8-23

8-27

Water washing is occasionally the only method available for cleaning articles in surface preparation, but that's about the only time it will be used. Water will not cut through fIlms such as those that oil leaves, etc. When you have the opportunity to use vapor degreasing to remove oily fIlms or grease, by all means, use it! Since sandblasting (the other choice) in most instances isn't recommended, there is no reason for you to return to page 8-23. You'd use vapor degreasing now, wouldn't you? Tum to page 8-25 and continue.

From page 8-25

8-28

You are now ready for Step Two - Penetrant Application. Penetrants you'll recall can be applied by dipping or immersing test articles in the penetrant, spraying or brushing them with penetrant, or by pouring or flowing the penetrant over them and then allowing the penetrant to drain. Which of the penetrant application methods listed below do you think would be the most ideal for applying penetrant to our sixty steel screws? Dipping Spraying Brushing

Page 8-29 Page 8-30 Page 8-31

From page 8-28

8-29

Good for you. Dipping is an ideal method for applying penetrant to our sixty steel screws. It's fast, and it assures complete coverage.

PENETRANT

The next consideration will be to determine how much time should be allowed for the penetrant to do its job before removing the excess penetrant. We have called this the penetration (dwellJ time. To help determine this time, charts have been prepared; but to effectively use them, three things must be known: Type of material Material "form" Type discontinuities sought So far, we've covered two of the requirements. Which one remains that you must know before you will have enough information to correctly select the penetration time from charts? Type of material . Material "form" . . . . . Type discontinuities sought.

Page 8-32 Page 8-33 Page 8-34

From page 8-28

8-30

You selected "spraying" as being the most ideal method for applying penetrant to our sixty steel screws. Sorry but spraying would not be the best choice in this case. We find that spraying is excellent for applying penetrant to large test surfaces and when performing spot checks, etc. But there is another method that will assure a more complete coverage of small test articles such as our sixty steel screws. Why not return to page 8-28, look again at the choices you have, and make another selection.

From page 8-28

8-31

Sorry but brushing would not be the best choice for applying penetrant to the sixty steel screws. It would not only be time consuming, it would be difficult to adequately cover the screws. There is another method, however, that will do the job quite nicely. Return to page 8-28, look at the choices you have, and make another selection.

From page 8-29

8-32

Remember now, we are going to conduct a test of sixty steel screws. That tells us what material we'll be examining - steel. Why not return to page 8-29, and look those other selections over again? One of them contains the missing fact.

From page 8-29

8-33

We know two of the required three facts necessary to use the penetration time charts successfully. What do we lack? Not as you've suggested ... "material form." We are testing steel screws, remember? Return to page 8-29 and make another selection.

8-34

From page 8-29

''Type discontinuities sought" is correct. Some charts, you should remember, also base penetration times on the type penetrant used. One time, for example, may be given for water-washable penetrants - another for post-emulsified penetrants. If told to seek indications of cracks (a common surface discontinuity), we now have the necessary information to use the following chart.

Minimum Dwell Time (Minutes)"

Material

Form

Type Discontinuity

Aluminum

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 5 10

Magnesium

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 10 10

Steel

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

10 10 20 20

"Temperature range 60 to 125°F (16 to 52°C) Just for drill, what is the minimum dwell time recommended for the steel screws? 5 minutes 10 minutes 20 minutes

Page 8-35 Page 8-36 Page 8-37

From page 8-34

8-35

Nope. Your answer: "5 minutes" is incorrect.

Minimum Dwell Time (Minutes)"

Material

Form

Type Discontinuity

Aluminum

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 5 10

Magnesium

Castings Forgings Weldments All Forms

Porosity, Cold Shuts Laps Lack of Fusion, Porosity Cracks

5 10 10 10

Castings Forgings Weldments

Porosity, Cold Shuts Laps Lack of Fusion, Porosity

10 10 20

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"Temperature range 60 to 125° F (16 to 52°C)

Here's the chart again. The screws are steel, and we are looking for cracks. The correct minimum penetration time taken from this sample chart is 20 minutes. The correct use of the chart for this example is shown by circles drawn around the correct items. Turn to page 8-37.

From page 8-34

8-36

Ooops! Your answer (10 minutes) was not correct. Remember, we are testing steel screws for cracks. Turn back to page 8-34 and check the chart again before choosing another answer.

From page 8-34

8-37

Good show. Twenty minutes is the minimum dwell time recommended by the chart for testing the steel screws. In using dwell time charts, however, a word of caution! Penetrant and test article temperatures must be held within the temperature range specified on the charts. Otherwise, suggested minimum dwell time will be unreliable. Penetrant may even become useless. What temperature range was recommended to avoid this problem? 32 to nOF (0 to 22 oC) . . 110 to 22s oF (43 to 107°C) 60 to 12s oF (16 to S2°C) .

Page 8-38 Page 8-39 Page 840

From page 8-37

8-38

Now think about your answer, "32 to nOF (0 to 22 0 C)." We have stated in previous chapters that penetrant and test article temperatures that are too low can make the penetrant sluggish. Any temperature below 60 0 F (l6 0 C), in most instances, is too low. Obviously then, 32 0 F (OOC) would be much too low. Return to page 8-37 and select the moderate temperature limits which will best allow our penetrant to do its job.

From page 8-37

8-39

Think back a bit. Penetrant and test article temperatures must be held within moderate limits to best accomplish our purposes. A range of 110 to 22s o F (43 to 1070 C) is not moderate. You were probably thinking of drying temperature when you selected this answer. Remember that penetrant and test article temperatures above l2S o F (S2°C) can adversely affect penetrant properties and thereby reduce sensitivity. This we do not want! Return to page 8-37 and select another answer.

From page 8-37

8-40

Correct. The recommended temperature range for applying most penetrants is 60 to l25 0 F (16 to 52 0 C). Temperatures above or below this range require special qualification of the procedures and materials used. Having monitored penetrant for correct temperature and having allowed for correct penetration time, it's time to remove the excess penetrant. This you'll recall is Step Three in the procedure. Here's where we capitalize on the water washable feature of our penetrant. Water, at 60 to llO oF (16 to 43 0 C), will be used to rinse off the excess penetrant. How would you suggest this wash be done? Use a wire basket to hold the screws and quickly dip them in a tank of water . . . . . . . . . . . . . . . . Use a coarse forceful spray . . . . . . . . . Brush on a water rinse using brush of correct size

Page 8-41 Page 8-42 Page 8-43

From page 840

841

You have chosen to use a basket and dip the screws into a tank of water to remove excess penetrant. If you were applying penetrant, or if you were applying developer, this would be a good method. Penetrant removal, however, has been found most easily accomplished with the aid of a coarse forceful water spray! Try using a coarse forceful spray to remove the excess penetrant and turn to

page 842.

From page 8-40

8-42

Good. The best wash would be a coarse forceful spray. And since we are using fluorescent penetrant, this wash should be conducted under black light. . . the object being to remove only the excess penetrant and not the penetrant in discontinuities.

Following excess penetrant removal, next comes Step Four - Developer Application. Unless of course you are using a penetrant that requires no developer. In that case, the next step would be to dry the screws. But let's suppose a developer is required. For the developer, we have a choice of wet or dry. . . a choice of water-based wet or nonaqueous wet. But what governs our choice? For the most part, developer selection will depend on test article size, shape, and surface condition. Are test articles large, small, simple, complex, smooth or rough surfaced? You might also want to consider the number of articles to be tested; for example, is this a production run or simply a spot test? What equipment is available? Returning to the steel screws, which of the developers do you think is best suited for the task? Water-based wet Dry . . . . . Nonaqueous wet

Page 8-44 Page 8-45 Page 8-46

From page 8-40

8-43

In answer to our query about washing off excess water-washable penetrant you have stated that you would accomplish this by using a brush. A brush would not prove very effective in the case of the screws and, in any event, is not recommended for use in removing excess penetrant. A coarse forceful water spray, however, is recommended and is effective. Having decided to use this method, you are ready to tum to page 8-42.

8-44

From page 8-42

Right. A water-based wet developer is a good choice. It works well in covering small items such as the sixty screws. Water-based wet developer is applied immediately following the water wash. It is not necessary to ftrst dry the screws - as would be the case if a dry or nonaqueous wet developer were used. We also want to apply the developer so that it evenly coats the screws.

WET OEVELOI'ER

Momentarily dipping the screws in the developer does the job nicely. The next action will be to ... dry the screws. . . . . . inspect the screws under black light

Page 8-47 Page 8-48

From page 842

845

Yes - a dry developer could be used but the screws would have to be dried flISt. Dry developer could then be applied by dipping the screws or using a dust chamber. But more often, the developer used would be a water-based wet developer. It's not only convenient to apply, it assures complete coverage of our screws. Tum to page 844.

From page 8-42

8-46

A nonaqueous wet developer would be a good choice for conducting spot checks, etc., or when examining larger test articles, or when maximum sensitivity is of primary importance. But here we are testing sixty steel screws in what could be considered a production job. We want a developer that's convenient and easy to apply. We want a developer that guarantees complete coverage of the screws. There is just such a developer in one of the other choices you had. Why not return to page 8-42, evaluate the remaining choices, and make another selection.

From page 8-44

8-47

Correct. We dry the screws next. And in drying the screws, we would probablY use a recirculating hot air oven or dryer and a drying temperature between 150 and 225 0 F (66 to 107 0 C). Why limit drying temperature? Because higher temperatures can cause wet developer to evaporate. Because higher temperatures may adversely affect the penetrant in discontinuities. . . . . . . . . . . . . . . . . . . . .

Page 8-49 Page 8-50

From page 844

848

You answer, "inspect the screws under black light," indicates that you are getting a little overanxious for the payoff. Before inspecting the screws, there fIrst must be allowed suffIcient time for the screws to dry and discontinuity indications to develop. The clue to your next step is in the word "wet." Return to page 844 and select the action required after application of developer.

From page 8-47

8-49

Your selection, "Because higher temperatures can cause wet developer to evaporate," is not what we wanted. Although care certainly must be taken to limit dryer temperature, wet developer evaporation is not the reason. We want the water in the developer to evaporate so that only a thin film of dry powder remains. Return to page 8-47, reconsider the statements given, and try again.

From page 8-47

8-50

Good for you. That's the point we hoped to make. Dryer temperatures above 225 0 F (107 0 C) are apt to dry out the penetrant in discontinuities and thereby reduce sensitivity. For best results, dryer temperatures should be held between 150 and 225 0 F (66 to 107 0 C), and the drying time limited to that required to just dry test surfaces. No longer. Our next consideration is the development time needed to develop indications. Development time you'll recall is the flme from developer application until article is ready to inspect. In previous chapters, a guide was mentioned for determining correct development time when a water-based wet developer was used. Remember what it was? Our guide will be the developer time charts found in the testing area Our guide will be to experiment using samples containing the type of discontinuity we seek . . . . . Our guide will be the time in dryer . . . . . . . . . . . . . .

Page 8-51 Page 8-52 Page 8-53

From page 8-50

8-51

You chose the statement: " ... will be the developer time charts... " In selecting this answer you are probably remembering the penetration time charts mentioned earlier; there are no charts for determining development time. A guide has been mentioned, however, that we can use in obtaining correct development time. Return to page 8-50 and select the guide which was stated earlier.

From page 8-50

8-52

Experimentation is used in determining emulsification time, NOT IN DETERMINING DEVELOPMENT TIME. It is probable that you were remembering this experimentation when you selected your answer. To determine development time, we use something a little less scientific. A guide was given to you earlier in the program. Return to page 8-50 and see if you can spot it.

From page 8-50

8-53

Good thinking. Since we are using a water-based wet developer, the time in the dryer is usually sufficient to fully develop indications. The point to remember here is that enough time is allowed for the indications to develop, but not so much time that they become blurred or distorted. In using a fluorescent penetrant, remember that inspection must be performed under black light. Bulbs and fIlters should be kept clean and the black light intensity measure at least 800 microwatts per square centimeter at the test surface. For maximum sensitivity, inspection should be performed in a darkened area such as a black light booth. Also, on entering the booth you should allow at least 5 minutes for the black light to warm up and your eyes to adjust to the dark before attempting to view indications. You should avoid looking directly at the light as this can cloud your vision. You should also keep in mind that though black light is harmless, the mercury vapor arc bulbs used to produce black light also emit harmful ultraviolet rays. Never operate the lights with missing, cracked, or broken filters! You should also realize that black lights may go out because of excessive voltage fluctuations or if line voltage should drop below 90 volts. If lights should extinguish because of an interruption in current, they may not respond immediately when turned back on. It may take up to 10 minutes for bulb to cool sufficiently to reestablish an arc. Turn now to the next page and we'll tackle a somewhat different test situation.

From page 8-53

8-54

In which of the following situations would you choose to use a post-emulsified (P.E.) penetrant? Precision castings for shallow discontinuities A weldment for shrink cracks . . . . . .

Page 8-55 Page 8-56

8-55

From page 8-54

Excellent! The clue is " ... shallow discontinuities." P.E. penetrant will fill the bill nicely. It will ailow a close check for it serves particularly weII in detecting shallow discontinuities. Which of the following will be your course of action when testing the precision castings with post-emulsified penetrant? Procedure A I. Prepare surface a. Clean article 2. Apply penetrant a. Dry article b. Apply emulsifier

Procedure B I. Clean article 2. Apply penetrant a. Apply emulsifier 3. Remove emulsifier a. Dry article

3. Wash article Page ... 8-57

Page ... 8-58

Procedure C

I. Prepare surface a. Clean article 2. Apply penetrant a. Apply emulsifier 3. Remove excess penetrant Page ... 8-59

Turn to the page number at the bottom of the procedure you have selected.

From page 8-54

8-56

You think you can examine a weldment for shrink cracks with post-emulsified penetrant. We feel that you would have better luck with this penetrant if you had chosen to use it on the precision castings where you were requested to check for shallow discontinuities. P.E. penetrant is specially designed for detecting shallow discontinuities, such as we seek in the precision castings. It is not recommended for use on relatively rough surfaces. Weldments are often considered rough and post-emulsified penetrants are denied them. Of course, which penetrant you use may depend on what's available to you, or required by the controlling specifications or standards. But for the purposes of this program, assume post-emulsified penetrant is available for use on the precision castings. It will make your job of testing them easier. Turn to page 8-55 and we'll continue.

From page 8-55

8-57

You have selected the following sequence for applying the P.E. penetrant process to precision castings. I.

Prepare surface a. Clean article 2. Apply penetrant ~Dry art§§> - - - - - incorrect b. Apply emulsifier 3. Wash article 'This is incorrect. Notice that in Step Two (apply penetrant), the next action was to dry the article. 'This is not the case. Prior to penetrant application the article may have been dried as a part of surface preparation if water were present. But, the next action after the application of penetrant should be the application of the emulsifier. 'This in tum should be followed by the water wash used to remove the penetrant excess. Return to page 8-55 and choose a sequence that better represents the P.E. penetrant process.

From page 8-55

8-58

The following was your choice representing the sequence of actions necessary when P.E. penetrant is used on precision castings.

1. 2.

Clean article Apply penetrant a. Apply emulsifier 3. (!emove emulsifiV - - - - incorrect a. Dry article Your choice was not correct. Step One, the first action, was better represented with ... I.

Prepare surface a. Clean article, ... but we have no real quarrel with your choice in this instance.

However, you've chosen to remove the emulsifier as Step Three and then dry the article. In real practice, the emulsifier must be allowed to mix with the penetrant excess for the proper time. It is then that penetrant excess is removed in Step Three. If a dry developer is to be used in Step Four, your next action was correct ... the article would be dried. If, however, we decide to use a water-based wet developer, it would be applied next - prior to dryer use. There is a better sequence of actions on page 8-55. Please return to that page and select it.

From page 8-55

8-59

Good. You have chosen the proper sequence for post-emulsified penetrant processing. You are aware that the most critical part of a test using P.E. penetrant will be the emulsification time. Proper timing here is even more critical to testing success than the timing of penetrant dwell and development. Can you remember how proper emulsification time is determined? Prepared charts Rule of thumb. Experiment. .

Page 8-60 Page 8-61 Page 8-62

From page 8-59

8-60

You'd be very lucky if your answer were true! You've stated that you would be able to determine the proper emulsification time from prepared charts. This is very seldom possible. The reason being that there are so many variables that emulsification times must be determined for each particular test situation. If you have such a chart, it means that someone else has conducted the tests

necessary to give you the emulsification time for your particular task. The process used to fmd the correct emulsification time is well named by the correct answer on page 8-59. Return to that page and see if you can spot it.

From page 8-59

8-61

Your answer indicates that you feel emulsification times are determined by some "rule of thumb." Evidently we have confused the issue. Emulsification times are a "horse of a different color." They must be determined indiVidually for each and every test situation. What might be the ideal emulsification time in one situation might be completely inadequate in another. The process used to determine the correct emulsification time is well named by the correct selection on page 8-59. Return to that page and see if you can pick it out!

From page 8-59

8-62

Experiment is correct. It would be nice if there were a less time consuming method for determining correct emulsification times but there isn't. When P.E. penetrant is selected, the proper

emulsification time must be determined for each test situation faced. Use too little time and excess penetrant will not be completely removed from test surfaces. Use too much time and the penetrant in discontinuities also becomes water washable. Indications are lost. To determine the correct time, you must repeat the surface preparation, penetrant application, and excess penetrant removal steps (Steps One through Three) - using different emulsification times - until the desired wash is obtained. Depending on the emulsifier used, average times range from I to 3 minutes, and seldom exceed 5 minutes. Again, the correct time is determined by experiment. One method of applying emulsifier was prohibited. Remember it? Never apply emulsifier by dipping . Never apply emulsifier by spraying . Never apply emulsifier by brushing .

Page 8-63 Page 8-64 Page 8-65

From page 8-62

8-63

"Never apply emulsifier by dipping" was your answer. This is not correct. Dipping is in fact the prefe"ed method of applying emulsifier. Why this is so can best be explained by considering once again why we are using P.E. penetrant - a penetrant that requires a time consuming extra "step." It is this extra step that will make the penetrant water washable. We have avoided this to the last moment, and carefully controlled the process because penetrant might be mistakenly removed from shallow discontinuities. When we have to test articles for such discontinuities we are likely to use P.E. penetrant to do the job. However, if we are not careful in applying the emulsifier we could prematurely remove some of the penetrant, and thereby lose the advantage we've gained in conducting the extra step. Return to page 8-62 and look again at the selections. One of them is quite unreliable when it comes to controlling emulsification times. It is the forbidden application method. See if you can spot it.

From page 8-62

8-64

Hold on a minute. There is nothing wrong with spraying on the emulsifier. (Your answer has indicated you feel there is.) On the contrary, this is an acceptable, and often used, method. Look at the situation again. We have used P.E. penetrant because we want to make sure we do not miss any shallow surface discontinuities. Using water-washable penetrant we run the risk that penetrant will be too easily washed away from these shallow discontinuities. It stands to reason then, that we must be just as concerned with the possibility of removing penetrant from these areas by any other means such as scraping, for example. If we were to apply our emulsifier by a means that could do that, we would certainly run the risk of missing the shallow discontinuities. We would have lost the advantage gained in using the P.E. penetrant in the first place! One of the methods suggested on page 8-62 is prohibited because, using it, you would run that risk. Can you spot it now?

Prom page 8-62

8-65

Good for you. We never apply emulsifier with a brush. Dipping, spraying, or flowing may be used - but never brushing! The preferred method is dipping. Conventional oil-based (lipophilic) emulsifiers begin emulsifying on contact, diffusing into the penetrant and making it water washable. The action continues until water is applied. By controlling the length of emulsification time we can control the amount of penetrant removed. We sometimes have the option of substituting a hydrophilic "scrubber." Here, you'll recall, the emulsifier is mixed with the water wash and usually sprayed under pressure. By controlling the strength of the wash and the duration of spray, we can control the amount of penetrant removed. Which of the following actions would get your informed OK for removal of excess fluorescent P.E. penetrant in Step Three? Maximum allowable water wash temperature will be 900 p (32°C) Excess penetrant may be wiped from test surface Washing should be accomplished under black light . . . . . .

Page 8-66 Page 8-67 Page 8-68

From page 8-65

8-66

Wait a minute now, we said your infonned OK. The maximum allowable water wash temperature is not 90°F (32°C); it is 110°F (43°C)! Remember? Return to page 8-65 and choose the correct statement for use with Step Three, removal of excess penetrant.

From page 8-65

8-67

You say "Excess penetrant may be wiped from test surface." That statement is not the one sought. To do so, you would probably run the risk of removing penetrant from shallow discontinuities. A water wash is the recommended method for removing emulsified penetrant. Return to page 8-65 and select the action that correctly goes with Step Three, the removal of excess penetrant.

From page 8-65

8-68

Good for you! Complete and adequate wash is more certainly obtained when excess fluorescent penetrants are washed under black light. Although some discontinuities might be visible at the completion of Step Three, more often than not we would still have another step to go before we are ready to inspect the precision castings (our example). That would be Step Four, application of the developer. (Unless of course we are using a penetrant that does not require a developer.) Somewhere about here in the process, we will want to dry the castings. When do you think we might want to use the drying oven? Before application of the developer. . . It would depend on the type of developer After application of the developer . . .

Page 8-69 Page 8-70 Page 8-71

From page 8-68

8-69

You've jumped the gun. It is mighty important to use the dryer before the application of developer ... if dry developer is to be used. But, are we going to use dry developer in this case ... or wet developer? You can see that we'll have to decide this point before we can decide when to use drying oven. The time to use dryer therefore will depend on the type of developer used. Right? Turn to page 8-70.

From page 8-68

8-70

Right. The point in the process that drying oven would be used depends on the type developer used. In this particular situation, a water-based wet developer would be a good choice because of the smooth surfaces generally found on precision castings. Drying would follow developer application. For greatest sensitivity, however, we would select a nonaqueous (solvent base) wet developer. Castings would then have to be dried before developer application. Again, the accepted "norms" for development time are: the "time in the drying oven" for water-based wet developers, and "7 to 30 minutes" for dry or nonaqueous wet developers. (A rule of thumb for determining development time for dry or nonaqueous wet developer is to use a time equal to "one-half the penetration or dwell time used.") Let's tum our attention to the examination of a weld on a large tank.

-=.=----=-

To check the weldment, a visible dye penetrant, solvent remover, and nonaqueous wet developer is suggested. Why do you suppose a visible dye? Because, as yet, we haven't used it as an example Because it is more practical for this situation . .

Page 8-72 Page 8-73

From page 8-{)8

8-71

Yes - you would use the dryer after the application of developer ... if water-based wet developer is used. But, are we going to use wet developer in this case? So far, we have not decided. You can see that we'll have to do just that before we can decide when to use drying oven. The time to use the dryer will therefore depend on the type of developer used. Right? Turn to page 8-70.

From page 8-70

8-72

Well, how 'bout that! True. We haven't used "nonfluorescent" penetrants as an example, and - you guessed it - we're going to do so right about now. By the way, if you selected this page because of curiosity ... good for you. It may be dangerous for the feline cat, but for inspector type cats, it's a valuable attribute! So, another point: If you're curious about the other selection choice, it was also correct! You'd use visible dye penetrant because it provides for greater mobility than the other penetrants. And that's why we will use it. So, let's do it. Turn to page 8-73.

From page 8-70

8-73

Right. A visible dye penetrant is more practical for examining the example weldment. Look again where we must go to conduct the test. With visible dye penetrant, no electrical power is needed ... and neither is a darkened area to view indications.

A solvent-removed penetrant likewise was suggested because of its versatility. Excess penetrant is removed simply by wiping with a solvent-dampened cloth. A source of water is not needed. The first step is to clean the weldment. This is generally accomplished with the same solvent that's used to remove excess penetrant. After cleaning, time is allowed for the weldment to dry, and then penetrant is applied. To apply the penetrant, let's spray it on; but remember brushing would do fme too. Dipping or flowing you'll admit would be a bit awkward. Earlier we gave you a dimension relative to minimum coverage. Remember what it was? Apply penetrant at least 0.25 inch (0.64 centimeter) each side of weldment. . . . . . . . . . . . Apply penetrant at least I inch (2.5 centimeters) each side ofweldment Apply penetrant at least 2 inches (5 centimeters) each side ofweldment

Page 8-74 Page 8-75 Page 8-76

From page 8-73

8-74

You've selected the statement, "Apply the penetrant at least 0.25 inch (0.64 centimeter on either side of the weldment" as representing coverage recommended in this program. This is not correct. We have recommended at least I inch (2.5 centimeters) on each side of a weld. This was done because several of the specifications and standards use this figure. Obviously, if you were testing a very small object, the entire object would be coated with penetrant. And, in some stiuations, 0.25 inch (0.64 centimeter) might (we stress again ... might) be adequate. It is recommended here, however, that you use at least I inch (2.5 centimeters) on either side of the weldment you want to test unless you are told to do otherwise. Turn to page 8-75.

From page 8-73

8-75

Good. With penetrant applied at least I inch (2.5 centimeters) each side of the weldment, we are off to a good start. During our work with this penetrant, which of the following would be of particular concern to do a really good job on the example weldment? Excess penetrant must not remain on test surface longer than the time recommended by penetration time charts. . . . . . . . . . . Penetrant must be drained from all pockets and recesses before the next step. . . . . . . . . . . . . . . . . . . . Temperature of penetrant and weldment should be between 60 and 1250 F (16 to 52oC). . . . . . . . . . . . .

Page 8-77 Page 8-78 Page 8-79

From page 8-73

8-76

You evidently did not remember the I inch (2.5 centimeters) dimension we specified earlier. You have chosen to cover the weldment 2 inches (5 centimeters) on either side. In this situation, I inch (2.5 centimeters) would have been OK, but you are to be commended. When in doubt, cover it well. Again, I inch (2.5 centimeters) minimum coverage is usually recommended by the controlling specifications and standards. Use it unless directed to do otherwise. And remember, you are quite correct. When in doubt, cover it well. And that means more than I inch (2.5 centimeters) if you think it is necessary. Turn to page 8-75 and continue.

From page 8-75

8-77

Your concern for strict adherence to the penetration time charts is praiseworthy. But remember, the times suggested are minimums. The time duration that penetrant can be allowed to remain on an item after the minimum has been met is primarily an economic consideration (provided the penetrant isn't allowed to dry). You shouldn't be overly concerned with leaving the penetrant on longer than recommended as long as it remains wet. But using a longer time than necessary costs money. As a rule, the minimum suggested time will do the job - and cost less. Why not return to page 8-75 and make another selection. There is a better one!

From page 8-75

8-78

No curve ball intended, but your answer was not correct. You've stated that " ... penetrant must be removed from all pockets and recesses before the next step." The next step will be developer application. And, as you can readily imagine, we're not going to dip this one in a tank of wet developer.

When dipping was done, we were concerned with carrying penetrant over into the tank of wet developer. That won't be our problem here. Please return to page 8-75, look over the selections again, and choose one that will be of particular importance to us in this testing situation.

From page 8-75

8-79

Right. Temperature of the penetrant as well as the weldment should be between 60 and 12SoF (16 to S2°C). Again, applications outside of this range require special qualification of the penetrants and procedures used. After allowing enough time for the penetrant to enter possible discontinuities, the next step is to remove the excess penetrant. Since we've selected solvent-removed processing for testing our weldment, penetrant removal will be accomplished by wiping with a soIvent-dampened cloth. A couple of points to remember here are: I. 2.

Never apply solvent directly to test article. Use only those solvents recommended by the penetrant manufacturer.

For developer, you'll recall a nonaqueous wet developer was suggested. Common sense explains its choice. Two important reasons are its convenience and ease of application. The developer is usually applied as a spray from a pressurized spray can. Which of the following techniques do you recall will provide the best sensitivity? Apply enough developer to thoroughly soak the test surface Apply just enough developer to provide a thin and even film

Page 8-80 Page 8-81

From page 8-79

8-80

Sorry but you did not make the best choice. To thoroughly soak the test surface as you suggest would result in an excessive buildup of developer. This would make it difficult for fine discontinuities to be seen. Best results are obtained when developer is applied as a thin and even film without soaking the test surface. With this in mind, turn to page 8-81 and continue.

From page 8-79

8-81

Very good. Best sensitivity is obtained when the developer is applied as a thin and even fIlm and does not soak the test surface. Following inspection, the next step would be to remove the penetrant and developer residue. Here again, removal would probably be accomplished by wiping with the same solvent remover used to remove excess penetrant. As a fInal step, the application of a rust or corrosion inhibitor may be recommended. This would complete the test. Suppose now we must repeat a liquid penetrant test. What would be required to obtain reliable results? First, remember that dried penetrant residue left in discontinuities can adversely affect test sensitivity. This means a thorough precleaning is essential. Secondly, retests, when required, should be conducted with the same type penetrant originally used. Visible dye residue left in discontinuities, for example, would quench the fluorescence of fluorescent penetrants. Fluorescent penetrants similarly could block the entry of visible dye penetrants, causing a reduction in sensitivity. The switching from visible dye to fluorescent, or vice versa, is not recommended. But suppose we want to conduct a liquid penetrant test in which two different levels of sensitivity would be desirable. There is one penetrant that fIts the bill quite nicely. Remember what it is? Dual sensitivity penetrant Fluorescent penetrant . Visible dye penetrant . .

Page 8-82 Page 8-83 Page 8-84

From page 8-81

8-82

Yes - a dual sensitivity penetrant would fit the bill nicely. Gross discontinuities could be located under visible light, and examinations for rme cracks, porosity, and penetrant residue carried out under black light. In conclusion, remember, the reliability and effectiveness of liquid penetrant testing depends on your knowledge of the penetrant processes and the thoroughness with which you conduct tests. It requires familiarity with manufacturing processes and a knowledge of discontinuities likely to occur, and their appearance. It requires a knowledge of how different materials fail and where. Only then can determinations be made as to test article acceptability or the seriousness of defects found. For a study of the equipment used in liquid penetrant testing, turn to page 9-\.

From page 8-81

8-83

Yes - fluorescent penetrants are capable of providing different levels of sensitivity. Some, for example, are classified as having a medium sensitivity. Others, depending on their fonnulation and the combination of processing used, provide high or even superhigh sensitivity. But, none of them can provide two different levels of sensitivity while using just one penetrant. Only one penetrant has that capability, and that's the "dual sensitivity" penetrant. Right? Turn to page 8-82.

From page 8-81

8-84

Ooops. Sorry but you're way off base with this selection. Visible dye penetrants are capable of producing only one level of sensitivity - and a relatively low sensitivity at that. But there is one penetrant that does provide two different levels of sensitivity depending on the type lighting used. Why not return to page 8-81 and see if you can spot it.

CHAPTER 9 - TEST EQUIPMENT AND SPECIAL PURPOSE MATERIALS

9-1

In the previous chapters we discussed the different materials and procedures used in liquid penetrant testing. We are now going to look at some of the test equipment as well as special purpose materials used. STATIONARY TEST EQUIPMENT The equipment used in liquid penetrant testing may be either stationary or portable. Stationary equipment is that equipment which is normally located in one place. It is too bulky to be easily moved, which means that test articles must be brought to the equipment. The various items of stationary equipment - called stations - are: Precleaning station (usually remote from the penetrant test station) Penetrant station (tank) Drain station (used with penetrant tank) Emulsifier station (tank) Rinse station (tank and spray equipment) Dryer station (usually an oven type) Developer station (tank, dust chamber or spray equipment) Inspection station (enclosed black light booth or a table with visible lighting) Postcleaning station (usually remote from the penetrant test station) Notice that stations coincide with the steps required in performing a liquid penetrant test. The actual number of stations and their arrangement will depend on the penetrant (visible dye or fluorescent), the penetrant process or method of penetrant removal used, and the type of developer (if used). Turn to the next page.

From page 9-1

9-2

Here we show a typical stationary arrangement. DEVELOPER STATION

INSPECTION STATION INCANDESCENT LIGHT

DRYER RINSE STATION EMULSIFIER STATION PENETRANT STATION

DRAIN STATION

I

-+-=-=.:-

~~!==-:~-=-~--~------- -- --~

--------

~

---

--- -- ----- -----

-----

The stations are arranged in order of use. Notice, for example, in the illustration above that the penetrant station is fIrst (on the left), followed by the emulsifIer station, rinse station, dryer station, developer station, and the inspection station. We can immediately tell that this arrangement is for a visible dye (note the incandescent light) post emulsifIcation penetrant (note the emulsifIer tank ahead of the rinse tank). Can you tell us what type of developer is used in this arrangement? There is a clue in the order of the stations.

Water-based wet developer Dry developer. . . . .

Page 9-3 Page 94

From page 9-2

9-3

You think the arrangement called for a wet developer. Apparently you've forgotten the procedural steps that are required when using a wet developer. If a wet developer were used, the dryer would be placed after the developer station. Let's take a look at that arrangement again. INCANDESCENT LIGHT

DEVELOPER STATION DRYER RINSE STATION EMULSIFIER STATION

INSPECTION

DRAIN STATION

'

PENETF~A~N~T;;~~~~~~~~~~~~~-~-J~~'~=~=~~~

STATION

F~ff~~;;:;ST4ATION

__ _

~ ~.!:::::=--::=::--:: j --

-- --- -

--

--- ---

-- ---

---

---

-----

---

---

----

---

Notice the dryer appears in line before the developer station. Since the dryer is used fIrst, the developer must be dry. Turn to page 9-4

From page 9-2

9-4

Excellent. Since the dryer station is placed before the developer station, the developer must be a dry developer. Now let's look at another arrangement of essentially the same stations. LIGHT

BLACK LIGHT DRYER DRAIN STATION EMULSIFIER STATION

'INSPECTIION BOOTH

PENETRANT STATION

NSE STATION

In addition to changing the arrangement, the lighting has been changed. Which of the following penetrant processes fits this arrangement? Fluorescent, post-emulsified penetrant/dry developer. Fluorescent, post-emulsified penetrant/water-based wet developer . . . . . . . . . . . . . . . .

Page 9-5 Page 9-6

From page 94

9-5

Good. The arrangement called for a dry developer. If a wet developer were used, the developer station would have preceded the dryer. Here are a couple more setups for you to study. INCANDESCENT LIGHT DEVELOPER STATION

RINSE STATION DRAIN STATION

~

PENETRANT STATION

,

___

L~::

ffi} :-

INSPECTION STATION /

.t:;~;;;;;:;;,'l

~

----,.j.---

----

...,

L ------ - -------

Visible Dye, Water-Washable Penetrant/Dry Developer DEVELOPER STATION

REST STATION DRYER

BLACK RINSE ..-rAT"n... HAND·HELDSPflAlrER DRAIN STATION

o

Fluorescent, Water-Washable Penetrant/Wet Developer

Turn to page 9-7.

INSPECTION BOOTH

From page 9-4

9-6

Let's look at that arrangement again. BLACK LIGHT

1 -......".._"""'111. DRVE

BLACK LIGHT

I

DRAIN

EMULSIFIER NSPECTION BOOTH

PENETRANT

UeVEI_OF'ER STATION

STATION

You say the stations are set up for a water-based wet developer. This is not correct. The position of the developer station indicates that a dry developer is used. Test articles are dried before developer application. Turn to page 9-5 and continue.

From page 9-5

9-7

What we have demonstrated is that the arrangement of the equipment is dictated by the process used. Each station will have additional equipment depending on the function of the station. Pumps are installed at penetrant, emulsifier, rinse, and wet developer stations to agitate solutions, to pump drain-<>ff materials into the proper tanks, and to power spray nozzles, etc. Hand-held sprayers and applicators are provided at the required stations. Thermostats and thermometers are provided to control the temperature of drying ovens and penetrant materials. Timers are provided to control penetrant, emulsifier, developing and drying cycles. Exhaust fans are used to facilitate removal of fumes and dust. Hydrometers are used to measure the specific gravity of water-based wet developers. AUTOMATIC PROCESSING

Stationary systems range from the conventional tank systems we've just discussed to fully automatic systems designed for specific applications (e.g., the production testing of such items as bearing races, turbine blades, etc.). Except for inspection, processing is completely automatic. Test articles move along conveyors from one station to the next while materials are applied by dipping, flowing, or spraying. Dust chambers are often employed for applying dry developer. Besides the conventional methods of application, penetrant materials may also be applied electrostatically. In electrostatic spraying, the material (penetrant or developer) being applied is given a high electrical charge while the test article is grounded. This minimizes material buildup, overspray, etc., and prevents materials from entering hollowed passages, which could serve as reservoirs, adversely affecting test results. Again, automatic processing is usually tied to the testing of specific test articles. Tum to the next page.

From page 9-7

9-8

PRECLEANING AND POsrCLEANING EQUIPMENT

Precleaning and postcleaning is usually accomplished in some area other than the test area. Briefly, the equipment and materials used will consist of one or more of the following: Detergent tanks. Most effective in removing inorganic contaminants. When used, they require a suitable means of rinsing the detergent from test articles and drying. Vapor Degreasing Equipment. Most effective in removing oil, grease, and similar organic contamination. In addition, articles are warmed, which tends to drive off moisture in discontinuities. Equipment must not be used to clean materials that can be harmed by the solvents employed. Steam Cleaning Equipment. Particularly adaptable to cleaning large unwieldly articles. Solvent Cleaning Equipment. Solvent cleaners are applied by immersing test articles in solvent tanks or by wipe-on, wipe-off techniques. Rust Removing Equipment. Commercial acid or alkaline rust removers are used with equipment specified by the manufacturer of the remover. Paint Removing Equipment. Paint is effectively removed using chemical removers and strippers. Equipment should be that specified by the manufacturer of the remover. Etching and Neutralizing Equipment. Articles that have been ground or machined often require etching to remove smeared metal. Either immersion or wipe-on, wipe-off techniques may be employed. Turn to the next page.

From page 9-8

9-9

PORTABLE TEST EQUIPMENT

Portable test equipment is available for test situations where it is impractical to use stationary equipment. Both fluorescent and visible dye kits containing all the items and materials necessary for the complete testing process are available. When testing is required at a location remote from stationary equipment, or a spot test of an article is required, portable kits are used. The liquids are usually supplied in pressurized (aerosol) spray cans.

A visible dye kit usually consists of a metal box and at least the following items:

Solvent cleaner or remover Visible dye penetrant Nonaqueous wet developer Wiping cloths and brush Judging from the above list, would you say the kit contains all the materials required to conduct a visible dye penetrant test? Yes No

Page 9-10 Page 9-11

From page 9-9

9-11

We have no idea what you might think is missing from the list. But let's say this - if there is something missing from the kit that you consider to be required to complete the test, then get some and add it to the kit. To be effective, the kit must contain everything that is necessary to perform a complete test. Turn to page 9- I 0 and continue.

From page 9-10

9-12

Right. An incomplete kit can cause considerable loss of time. Always make sure that the kit contains everything needed to complete the test. This is especially important when conducting tests in the field. SPECIAL PURPOSE MATERIALS We have discussed rather thoroughly the use of penetrants under normal situations in previous chapters. Now we want to point out some situations where more specialized materials are required. liquid Oxygen Compatibility Liquid Oxygen (LOX) is used in many modern day applications. By itself, liquid oxygen is nonexplosive; but whenever it comes in contact with a combustible material, an explosive situation comes ir.to play where the slightest spark or jar could set off a violent reaction. In some cases the explosion is spontaneous - nothing else is required to set it off. It is very important then that articles to be ultimately used in a system handling

liquid oxygen be entirely free of combustible substances. For this reason such articles are subjected to extensive cleaning processes. During manufacture and testing of the article, special care is taken not to contaminate the article with combustible materials. A valve, for example, that is to be used to control the flow of Iqiuid oxygen in a LOX handling system must be kept free of materials that burn. During manufacture of the valve no combustible materials should be used. This helps to assure that the valve remains free of such contaminanats. Suppose the above mentioned valve requires a hole to be drilled in its body. Can oil be used to cool the drill? Yes No

Page 9-13 Page 9-14

From page 9-12

9-13

No, no, no. Oil is combustible - it burns. If we used oil to cool the drill we would be contaminating the valve. It would be possible to leave minute traces of oil on the valve in spite of any cleaning procedure used. Then, when the valve was installed in the LOX system, these traces of oil could cause an explosion. To be absolutely certain that the valve is not contaminated, we must avoid using any materials during the manufacture of the valve that are not compatible with liquid oxygen. The same rules apply during LOX system maintenance. Turn to page 9-14

From page 9-12

9-14

Very good. The use of oil on this valve is prohibited since the valve will be used in a LOX system. When such articles are to be tested by penetrant methods, only those penetrant testing materials can be used that do not contain combustible materials. We can use only those penetrant materials that are approved as being compatible with liquid oxygen. To have been approved as being liquid oxygen compatible, each batch of materials must have undergone extensive testing. In brief, a "Liquid Oxygen Compatibility Test" requires that a specimen of the substance be placed in a superclean cup ftl1ed with liquid oxygen. Under carefully controlled conditions this specimen is then given a blow of a specified force by dropping a weight a given distance onto an impact pin. The test operator observes the impact for any reaction between the substance and the surrounding oxygen. You do not need to know the details of this test procedure but you should know when there are requirements for the "Liquid Oxygen Compatibility Impact Sensitivity Test." When using liquid penetrants on the LOX valve we have been discussing, you must be sure that the penetrant testing materials are ... free of combustible materials . . . cleaned from the valve after testing .

Page 9-15 Page 9-16

From page 9-14

9-15

You are absolutely right. The penetrant materials used must not contain any combustible materials. This is always the ftrst consideration. The ftrst step to remember when testing articles to be used in LOX systems is - use only those penetrants, emulsifters, and developers that are currently approved for use on LOX systems by speciftcations and directives. When such LOX compatible materials are used, it is also your responsibility that materials do not become contaminated. Therefore, when using bulk materials, remove only enough material from the original container to test the article immediately at hand. Any material remaining after the test shall be discarded - not returned to the original container. Containers, brushes, spray systems, etc., must be specially cleaned prior to use with LOX compatible materials to avoid contamination. Liquid penetrant testing with LOX compatible materials is identical to the procedures using conventional penetrant materials. Oxygen compatible penetrant materials are usually water washable, and the excess penetrant is removed with water. When liquid penetrant testing articles to be used in LOX systems, the test materials must be ... approved for use on LOX systems by speciftcations applied by a different method than is used in an ordinary situation . . . . . . . . . . . . . . . . . . .

Page 9-17 Page 9-18

From page 9-14

9-16

You are about half right, but half right isn't nearly good enough. Granted, all test materials must be cleaned from the valve after the test and inspection but this is not enough to assure that there are no contaminants remaining on the valve. To ensure that there are no contaminants on the valve, we must take care not to add any. The testing materials used must be free of combustible materials. With this in mind turn to page 9-15.

From page 9-15

9-17

Right. Only those penetrants, emulsifiers, and developers that have been approved as being LOX compatible by current specifications and directives can be used. Special care must be taken to see that the test materials do not become contaminated with combustible materials during their use. The easiest way to prevent contamination of LOX compatible penetrant materials is to use the materials furnished in pressurized spray cans. If bulk LOX compatible materials are to be used, you must ... clean each item of test equipment before use . . use the same equipment used for oridinary testing

Page 9-19 Page 9-20

From page 9-15

9-18

The use of LOX compatible testing materials does not require any change from the ordinary test procedures as you have indicated. Every step is accomplished in exactly the same way. There are only two additional requirements: 1) The materials used must be approved for use on LOX systems; and 2) Care must be taken to ensure that the materials do not become contaminated. Turn to page 9-17 for more information on this subject.

From page 9-17

9-19

You are right. One source of possible contamination is the equipment being used. Therefore, each piece of equipment must be cleaned prior to use with LOX compatible penetrants. After testing, the article must be cleaned with washes that also do not contain any combustible materials. Water is most often used. Extra care must be taken to remove as much penetrant as possible. Whenever LOX compatible materials are suspected of being contaminated with combustible materials, and at other times as may be specified by the applicable directives, they must be retested for compatibility with liquid oxygen. This "Liquid Oxygen Compatibility Impact Sensitivity Test" is extremely complex - hence the need for care in preventing any possible contamination. Any cleaning material may be used in the postc1eaning process. True False

Page 9-21 Page 9-22

From page 9-17

9-20

Well, you are right but this is not the best answer to the question. The same equipment may be used, but when it is to be used with LOX compatible penetrants, it must be cleaned first. Contaminated equipment would contaminate the materials handled by the equipment. The penetrants and cleaning materials used for ordinary penetrant testing do contain combustible substances. Any traces of these substances on the equipment will contaminate the LOX compatible penetrant materials. Therefore, a careful cleaning of the equipment is required. Now with this in mind turn to page 9-19.

From page 9-19

9-21

Slow down a bit. You have selected the answer that says "Any cleaning material may be used in the postcleaning process". This is not correct. Remember - when using LOX compatible penetrants we are trying to avoid using materials that are combustible. Many cleaning materials contain combustible materials - these cannot be used. You must use only those cleaning materials that do not contain any combustible materials. Turn to page 9-22.

From page 9-19

9-22

Right! You can use only those cleaning materials that do not contain combustible materials. In review, there are three facts that you must remember when testing articles that come in contact with liquid oxygen: I.

2. 3.

Use only penetrant materials that are approved as being LOX compatible. Clean the test equipment prior to use. Remove all traces of penetrant materials from the test article after completion of test.

Other Special Purpose Materials In addition to the LOX compatible penetrants, other special penetrants have been developed for specific applications. Nickel alloys, certain stainless steels, and titanium, for example, are adversely affected by sulfur or chlorine - elements present in some penetrant materials. For such usages, penetrant materials are available that are suffiCiently free of sulfur and chlorine.

In your judgment, is the following statement true or false? Penetrants used for testing steel can also be used to test nickel steel. True False

Page 9-23 Page 9-24

From page 9-22

9-23

Your answer indicates that you do not fully understand what an alloy is. An alloy is a mixture of two or more different metals. Briefly, alloys are used because the properties of the alloy - strength, weight, hardness, etc., are different than the properties of the separate metals used in the alloy. Whenever the alloy is a combination of nickel and any of the other metals, special purpose penetrant materials must be used in the penetrant testing process. Therefore, the common penetrants used on steel cannot be used on the nickel steel alloy. Turn to page 9-24.

From page 9-22

9-24

Very good! Since nickel steel is a nickel alloy, testing requires the use of a penetrant that is low in sulfur and chlorine. Plastic and rubber are also sometimes attacked by penetrant materials. When in doubt, tests should be performed first on a piece of scrap. Special formula penetrant materials are likewise available for testing plastic and rubber. The following are more examples of special purpose penetrant materials and their application. Their inclusion here is simply to make you aware of the range of materials available. It is beyond the scope of this book to try and cover them all. There are food compatible penetrants, for example, that combine a harmless dye with edible oils for testing food processing equipment. There are special formula penetrants for testing at high temperatures, and penetrants for testing at low temperatures. There are "gel-forming," slow solubility penetrants that minimize the "wash-away" problem of conventional water-washable penetrants. There are penetrants that provide sufficient contrast and sensitivity without having to use a developer. There are inhibited solvent removers to slow down the washing of solventremoved penetrants and thereby improve reliability. Likewise, there are low energy emulsifiers to slow down the emulsification of post-emulsified penetrants. And there are special wax and plastic fIlm developers that absorb and fix penetrant indications to provide permanent records. There are even processes available that permit the recovery and reuse of penetrant materials, including water, with no sacrifice in performance. Yes - liquid penetrant testing has come a long way since the "oil and whiting" days. For a final review, tum to the next page.

9-25

From page 9-24

I.

The equipment used in performing a liq uid penetrant test may be either "-s_ _ _ _ _ _ _ or "'p_ _ _ __

7.

precedes

8.

Type lighting furnished (fluorescent or visible) will depend on the type penetrant used. Fluorescent systems employ black light at both the _ _ _ _ and _ _ _ _ _ _ _ _ stations.

14.

spray (aerosol) cans

IS.

The penetrant in the portable kit may be either _ _ _ _ _ _ __ or visible dye, while the remover is usually a _ _ _ __

21.

cleaned

22. In cleaning the equipment prior to use with LOX compatible materials, only those cleaning materials that are compatible with _ _ __ _ _ _ _ _ may be used.

9-26 , . . . o:n"..,,'UTOOOO

1.

stationary portable

2.

The equipment shown here is called (stationary/portable) _ _ _ _ _ __

'''''.''',,''''''''''uOMT

.

---

".

-~-

----:---

-~--

while each piece of equipment is called a _ _ _ __

8.

rinse (wash) inspection

9.

Hand-held sprayers/applicators, thermostats, thermometers, timers, and hydrometers are examples of auxiliary equipment used with (stationary/ portable) equipment.

15.

fluorescent solvent

16.

The fluorescent kit also includes a portable _ _ _ _ _ _ __ for viewing indications.

22.

liquid oxygen

23.

Careful postcleaning of LOX handling equipment with LOX compatible cleaners is likewise required. (True - False), ____

9-27

2.

stationary station

3.

The actual num ber of stations employed and their arrangement are , 2) the method of governed by: 1) the type P penetrant removal or "'P_ _ _ _ _ _ _ use,c!, and 3) the type

9.

stationary

10.

In the typical automatic system, processing of test articles may be completely automatic except for _ _ _ _ _ _ __

16.

black light

17.

Pre cleaning and postc1eaning stations frequently employ immersion or wipe-on and wipe-off techniques for cleaning test articles. (True - False) _ _ __

23.

True

24.

Sulfer and chlorine adversely affect certain stainless steels, nickel alloys, and titanium. Their testing requires the use of special purpose penetrant materials that are low in _ _ _ _ _ and _ _ _ _ __

9-28 3.

penetrant processing developer

4.

Equipment stations are arranged in order of use. With post-emulsified processing, the emulsifier station is located between the _ _ __ and stations.

10.

inspection

II.

To minimize material buildup and overspray, etc., a special technique for applying penetrants and developers is sometimes employed. It's called electro

spraying.

17.

True

18.

The presence of combustible materials in an atmosphere of liquid oxygen (LOX) creates an explosive situation. Articles to be used in a LOX handling system must be free of _ _ _ _ _ _ _ __ substances.

24.

sulfer chlorine

25.

Plastic and rubber are sometimes attacked by penetrant materials. Before testing such materials, a compatibility should be performed first on a piece of _ _ __

9-29

4.

drain rinse (wash)

5.

With water-washable processing, an emulsifier station (is/is not) required.

I 1.

electrostatic

12.

When penetrants or developers are applied electrostatically, the material being applied is given a high electrical charge while the test article is _ _ _ _ _ _ __

18.

combustible

19.

Penetrant materials used to test LOX handling articles must be LOX compatible. They must not contain any _________ materials.

25.

test scrap

26.

In conclusion, there are also food compatible penetrants, high and low temperature penetrants, "no developer" penetrants, "inhibited" solvent removers, and special wax and plastic fIlm developers, etc. Since these materials are generally employed for special applications, they're called materials.

9-30

S.

is

6.

When a wet developer is used, the dryer (precedes/follows) the developer station.

t 12. grounded

~

r"' ••,. . '

:,...,."'!

13. When an article is too large to be tested with stationary equipment, equipment may

\

~>.c: ·:B~ .

~r-~ '.:-l' ~ "=

-~

be used.

t

19. combustible

20. When testing articles to be used in a LOX environment, only those penetrant materials that are approved by as being compatible with liquid oxygen can be used.

t 26. special purpose

27. Turn to page 9-32.

t

9-31

6.

fo1!ows

7.

When a dry developer is used, the dryer (precedes/fo1!ows) the developer station.

~ 13.

portable

.... 14.

Return to page 9-25, frame 8.

/~

The "liquids" furnished in the portable kit are usua1!y dispensed from pressurized

~

Return to page 9-25, frame 15.

20.

specification (directive, standard)

21.

Combustible materials on penetrant testing equipment can contaminate LOX compatible penetrant. Equipment therefore must be prior to use with LOX compatible penetrants.

~

Return to page 9-25, frame 22.

t

From page 9-30

9-32

You have just completed the programmed instruction course on Liquid Penetrant Testing. Now you may want to evaluate your knowledge of the material presented in this handbook. A set of self-test questions are included at the back of the book. The answers can be found at the end of the test. We want to emphasize that the test is for your own evaluation of your knowledge of the subject. If you elect to take the test, be honest with yourself - don't refer to the answers until you have fInished. Then you will have a meaningful measure of your knowledge. Since it is a self evaluation, there is no grade - no passing score. If you fmd that you have trouble in some part of the test, it is up to you to review the material until you are satisfIed that you know it. Turn or rotate the book 1800 and flip to page A-I at the back.

INSTRUCTIONS

The pages in this book should not be read consecutively as in a conventional book. You will be guided through the book as you read. For example, after reading page 3-12, you may find an instruction similar to one of the following at tile bottom of the page• Turn to the next page. • Turn to page 3-15. • Return to page 3-10. On many pages you will be faced with a choice. For instance, you may find a statement or question at the bottom of the page together with two or more possible answers. Each answer will indicate a page number. You should choose the answer you think is correct and turn to the indicated page. That page will contain further instructions. As you Will soon see, it's very simple - just follow instructions. As you progress through the book, ignore the back of each page. THEY ARE PRINTED UPSIDE DOWN. You will be instructed when to turn the book around and read the upside-down printed pages. Turn to the next page.

•

viti

ACKNOWLEDGMENTS

This handbook was originally prepared by the Convair Division of General Dynamics Corporalion under a joint arrangement with NASA's George C. Marshall Space Flight Center. Convair's activities in the preparation of nondestructive testing training materials were greatly enhanced and accelerated by the MSFC technical and financial participation. Quality and Reliability Assurance Laboratory personnel at NASA's MSFC were to a large degree responsible for the successful completion of that program. Their understanding of the problems involved in teaching difficult materials by a relatively new technique, their realistic handling of NASA agency reviews, and their efficient transmittal of reviewer comments, made the publisher's task simpler than it might have been. Convair considers itself fortunate to have been associated With NASA on that project. Additional assistance in the form of process data, technical reviews, and technical adVice was provided by a great many companies and individuals. The following listing is an attempt to acknowledge this assistance and to express our gratitude for the high degree of interest exhibited by the firms, thelf representatives, and other individuals, many of whom gave considerable time and effort to the project. Aerojet-General Corp.; Automation Industries, Inc., Sperry Products Division; Avco Corporation; The Boeing Company; Grumman Aerospace Corp.; Lockheed Aircraft Corp.; Magnaflux Corp.; Martin Marietta Aerospace, Denver Division; McDonnell Douglas Corp.; Met-L-Check Co.; Rockwell International, North American Aerospace Group; Rohr Industries, Inc.; Shannon Luminous Matenals Co., Tracer-Tech DIVision; St. Louis Testing Laboratories, Inc.; Turco Products DiviSion, Purex Corp., Ltd.; Uresco, Inc.; X-Ray Products Corp. Our thanks is also extended to the many individuals who assisted in the testing of the materials to validate the teaching effectiveness. Their patience and comments contributed greatly to the successful completion of the handbook.

vi

Solvent-Removed Method Water-Washable Method Post-Emulsified Method Emulsification Times Use of Black Light Review

4-5 4-8 4-10 4-20 4-22 4-27

Chapter 5 - Developer Application.

5-1

Purpose of Developer . . . . Types of Developer. . . . . Application of Water-Suspended Particle Developers Application of Water-Soluble Developers Drying Time and Temperature Application of Dry Developers Application of Nonaqueous Wet Developers Guidelines for Selecting Developer Development Time Review Chapter 6 - InspectJon and Postcleaning Inspection . . . . . . . . . . Lighting Requirements . . . . . True Indications and Nonrelevant Indications. Interpretation of Indications . . Fixing and Recordmg Indications Postcleaning Review Chapter 7 - Limitations and Process Control Limitations. . . . . Ferromagnetic Matenals Porous Surfaces Process Control Contamination Retests Black Light. . Health Hazards ii

5-1 5-4 5-6 5-6 5-7 5-12 5-20 5-26 5-28 5-29 6-1 6-1 6-1 6-1

6-5 6-14

6-15 6-18

7-1 7-1 7-3 7-5 7-12 7-12 7-14

7-14 7-16