Ut P1

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NDT Ultrasonic Testing

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PCN GEN Issue 8 (Based on ISO 9712:2012) Training (PSL 57A) Experience (PSL 30) (randomly verified)

Level I

Level II

40 hrs

80 hrs

3 months

9 months

Vision Requirements (PSL 44): Near Vision – J1/N 4.5 Colour Vision: OK No. of Questions

Pass Percentage

General

40

70%

Specific

36

70%

Practical -

2 plates and 3 pipes – 70% each sample

Pass Percentage: Average mmz 2003

:

80%

NDT NON-DESTRUCTIVE TESTING Definition: Testing of material, component or assembly by means, which do not affect its ultimate use. Non Destructive Testing is the applied use of technologies for inspecting materials to known standards

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Destructive Testing • Small percentage of batches of product tested • Measurement of actual forces applied • Product tested cannot be reused • Product not tested, assumed to have the same properties as product tested mmz 2003

NDT Methods MOST COMMON METHODS     

Penetrant Testing Magnetic Particle Testing Eddy Current Testing Ultrasonic Testing Radiographic Testing

OTHER METHODS     

Visual Testing Acoustic Emission Magnetic Flux Leakage Infrared Testing Other methods

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NDT APPLICATIONS NDT applications are carried out at almost any stage in the production or life cycle of a component: – – –

To assist in product development To screen or sort incoming materials To monitor, improve or control manufacturing processes – To verify proper processing such as heat treating – To verify proper assembly – To inspect for in-service damage mmz 2003

Which is the best NDT method? Depends on many factors and conditions

•Cost •Material type •Equipment availability •Qualified Personnel availability •Types of Defects sought •Sensitivity required •Component location/position •Quantity of components •Condition of component- surface mmz 2003

ADVANTAGES of NDT 

Capable of testing 100% of products



Capable of testing before, during, and after production of components



Capable of testing parts or components in service/ in operation/ on site



Capable of retesting the products



Various materials, sizes, geometries may be tested using specific NDT methods. mmz 2003

Prevention is Better Than Cure

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Mechanical Disasters Costly  May be injurious or deadly  May cause hazards to environment  May cause damage to reputation of the company 

 May

be prevented if NDT and Inspection were carried out properly mmz 2003

Industries involved with NDT: •Oil and Gas

•Construction •Metal Fabrication •Chemical •Aerospace •Power Generation •Transportation Metal Manufacturing •Medical Composite Manufacturing •Electronic Inspection and Testing •Research and Development

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CERTIFICATIONS AND QUALIFICATIONS  NDT personnel should posses

: High Skill, Knowledge, and Integrity

 To achieve these

: Proper training and certification required

 Training

: By qualified training personnel and accredited training centres

 International Certification Schemes available:

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CERTIFICATIONS AND QUALIFICATIONS 

Company Certification Employees are trained and certified in accordance with the requirements of the company. – – –



In-house training Internal Certification issued by company Valid in the specific company only

Central Certification Personnel are trained and certified in accordance with the requirements of independent bodies: – Training conducted by Accredited Training Centres – Examinations issued by Independent Certification Bodies – Certificates issued to personnel mmz 2003

Training & Certification

Any Questions Please ?

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Ultrasonic Testing Part 1

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Basic Principles of Ultrasonic Testing





To understand and appreciate the capability and limitation of UT Most common method used is the PULSE ECHO technique

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Basic Principles of Ultrasonic Testing Sound is transmitted in the material to be tested The sound reflected back to the probe is displayed on the Flaw Detector

probe

Defect

0

2

4

6

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8

10

Basic Principles of Ultrasonic Testing The distance the sound traveled can be displayed on the Flaw Detector The screen can be calibrated to give accurate readings of the distance Signal from the backwall

Bottom / Backwall

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The ability to support sound depends on the DENSITY & ELASTICITY of the medium

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Basic Principles of Ultrasonic Testing The presence of a Defect in the material shows up on the screen of the flaw detector with a less distance than the bottom of the material The BWE signal Defect signal

Defect

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Basic Principles of Ultrasonic Testing

0

10

20

30

40

50

60

60 mm

The depth of the defect can be read with reference to the marker on the screen mmz 2003

Y axis

Peak

Vertical / Amplitude (%) Amount of reflected sound energy

Echo / Amplitude

Division

0 Sub-division

2

4

6

8

10

Horizontal / Time Base / Depth / Distance / Range / Beam Path Length(BPL) mmz 2003

X axis

Calculation:

1

Number of Echoes

=

Range Thickness cal. blocks Range

2

3

Division

Sub-Division

=

=

Number of division (10)

Division Number of sub-div. (5)

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10

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20

30

40

Thickness / depth measurement The closer the reflector to the surface, the signal will be more to the left of the screen

B

C

30

A

46

68

The thickness is read from the screen

C B A mmz 2003

The THINNER the material the less distance the sound travel

Ultrasonic Testing Principles of Sound

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Ultrasonic 

Sound : caused by mechanical vibration

What is Ultrasonic? Very High Frequency sound – above 20 KHz 20,000 cps

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Acoustic Spectrum Sonic / Audible

Ultrasonic

Human

> 20kHz = 20,000Hz

16Hz - 20kHz

0

10

100

1K

10K 100K 1M 10M 100m Ultrasonic Testing

0.5MHz - 25MHz Ultrasonic : Sound with frequency above 20 KHz mmz 2003

ULTRASONIC TESTING Very High Frequency 5 M Hz

Glass High Frequency 5 K Hz DRUM BEAT Low Frequency Sound 40 Hz mmz 2003

 Sound waves are the vibration of particles in solids liquids or gases  Particles vibrate about a mean position  Sound follows a waveform wavelength Displacement

 wavelength

One cycle

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The distance taken to complete one cycle

Properties of a sound  Sound cannot travel in

vacuum  Sound energy to be transmitted / transferred from one particle to another

GAS

LIQUID mmz 2003

SOLID

Sound 

Wavelength :

The distance between successive peak of a wave The time taken for one complete cycle – Measured in Meter or mm



Frequency :

The number of cycles per unit time

– Measured in Hertz (Hz) or Cycles per second (cps)



Velocity :

How quick the sound travels Distance per unit time

– Measured in meter / second (m / sec)



Period: Time taken for one complete cycle Distance per unit time and measured in meter / second (m / sec)

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WAVELENGTH Wavelength is a function of FREQUENCY & VELOCITY Velocity Wavelength

c  f

Frequency

Therefore :

c f 

or

c=λXf

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High Frequency Sound

c   f 5MHz compression wave probe in steel

5,900,000   1.18mm 5,000,000 mmz 2003

Frequency  Frequency

1 second 1 cycle per 1 second = 1 Hertz

: Number of cycles per second

1 second 3 cycle per 1 second = 3 Hertz

1 second 18 cycle per 1 second = 18 Hertz

THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH mmz 2003

Frequency 1 Hz  1 Kilohertz  1 Megahertz 

= = =

1 cycle per second 1 KHz = 1000Hz 1 MHz = 1000 000Hz

20 KHz

=

20 000 Hz

5 M Hz

=

5 000 000 Hz mmz 2003

Frequency

1 M Hz LONGEST

F

5 M Hz

10 M Hz

25 M Hz SMALLEST

=v/f



F



Which probe has the smallest wavelength? Which probe has the longest wavelength? mmz 2003

FREQUENCY OF PROBE

GENERAL APPLICATION

0.5 MHz

Very coarse grained materials like C.I., S. G. Iron, austenitic Stainless Steel, soft plastics, rubber, composites etc.

1.0 MHz

For coarse grained materials like steel castings and those with very high thickness.

2.0 MHz 

For large sized components with fair sensitivity requirement like testing of forgings.

4.0 MHz 

For optimum sensitivity, resolution and penetration. For inspection of fine grained material and those involving low thickness.

6.0 MHz

For very high sensitivity or checking thin walled components used in critical space and nuclear applications.

10.0 MHz

For obtaining exceptionally high sensitivity and resolution. For inspection of materials like titanium, managing steel etc. mmz 2003

Effect of frequency Low Frequency

High Frequency

Long wavelength

Short wavelength

More beam spread

Less beam spread

Shorter near zone

Longer near zone

Better penetration

Less penetration

Less attenuation

More attenuation

Longer dead zone

Shorter dead zone

Less sensitivity

Higher sensitivity mmz 2003

Effects of Diameter Large Diameter

Small Diameter

Less beam spread

More beam spread

Longer near zone

Shorter near zone

Better penetration

Less penetration

Less attenuation (due to beam spread)

More attenuation

Difficult coupling on curved surfaces

Easier coupling on curved surfaces

More coverage on flat surfaces

Less coverage on flat surfaces

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Probe frequency, bandwidth & damping • An ultrasonic probe transmits sound energy at a range of frequencies, not just at the stated frequency which is known as the bandwith. • Bandwith is the width of the frequency spectrum between the high and low cut-off frequency • For example a SMHz probe may produce a frequency range of 4 to 6MHz. • The bandwidth is also an indication of the damping factor.

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Broad Band Probes

Narrow Band Probes

They are highly damped

They have low damping

Have a short pulse length

A longer pulse length

(typically 1 to 2 cycles)

(typically 3 or 4 cycles)

A short ringing time (dead zone)

A long ringing time (dead zone)

Better resolving.power

Poor resolution

Poor penetration

Good penetration

Example : A 4Mhz probe may produce a frequency range of 3 to 5 Mhz which is measured at below -3db point • A – Peak frequency ( Frequency at which the maximum amplitude is observed ) • B & C – Cut-off frequency ( Frequency at which the amplitude of transmitted energy at 3dB below that a peak frequency ) • D – Centre frequency ( Upper and lower cut-off frequency ) mmz 2003

Y

3dB E

X C

D A

B

Wavelength and frequency 







The higher the frequency the smaller the wavelength The smaller the wavelength the higher the sensitivity Sensitivity : The smallest detectable flaw by the system or technique In UT the smallest detectable flaw is ½  (half the wavelength) mmz 2003

What would be the smallest defects that could be found in steel with a velocity of 6km/sec using a 3Mhz probes.

6,000,000   3,000,000

 2mm

Smallest defects can be detected is 1mm mmz 2003

Which of the following compressional probe has the highest sensitivity? 1 MHz 2 MHz 5 MHz 10 MHz

10 MHz mmz 2003

Acoustic Spectrum Sonic / Audible

Ultrasonic

Human

> 20kHz = 20,000Hz

16Hz - 20kHz

0

10

100

1K

10K 100K 1M 10M 100m Testing 0.5MHz - 50MHz

Ultrasonic : Sound with frequency above 20 KHz Very high frequency

= mmz 2003

Very small wavelength

Velocity     

The velocity of sound in a particular material is CONSTANT It is the product of DENSITY and ELASTICITY of the material It will NOT change if frequency changes Only the wavelength changes Examples: V Compression in steel : 5960 m/s V Compression in water : 1470 m/s V Compression in air : 330 m/s

5 M Hz

STEEL

WATER mmz 2003

AIR

Material

Compressional or longitudinal wave velocity (m/s)

Shear or transverse wave velocity (m/s)

Aluminium

6,400

3,130

Brass

4,372

2,100

Cast iron

3,500

2,200

Copper

4,769

2,325

Gold

3,240

1,200

Iron

5,957

3,224

Lead

2,400

790

Oil

1,440

-

Perspex

2,740

1,320

Mild steel

5,960

3,240

Stainless steel

5,740

3,130

Water

1,480

-

Tungsten

5,174

2,380

Zinc

4,170

2,480

Zirconium

mmz 2003 4,650

2,300

Velocity What is the velocity difference in steel compared with in water? 4 times If the frequency remain constant, in what material does sound has the highest velocity, steel, water, or air? Steel If the frequency remain constant, in what material does sound has the shortest wavelength, steel, water, or air? Air Remember the formula mmz = 2003 v/f

Sound Waveforms Sound travels in different waveforms in different conditions

•Compression wave •Shear wave •Surface wave •Lamb wave

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Compression / Longitudinal Vibration and propagation in the same direction / parallel  Travel in solids, liquids and gases 

Particle vibration

Propagation

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Shear / Transverse 

 

Vibration at right angles / perpendicular to direction of propagation and have a whip like action Travel in solids only Velocity  1/2 compression (same material)

Particle vibration

Propagation mmz 2003

Surface Wave Elliptical vibration  Velocity 8% less than shear  Penetrate one wavelength deep 

Easily dampened by heavy grease or wet finger Follows curves but reflected by sharp corners or surface cracks mmz 2003

Lamb / Plate Wave Produced by the manipulation of surface waves and others  Used mainly to test very thin materials / plates  Velocity varies with plate thickness and frequencies 

SYMETRIC

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ASSYMETRIC

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Compression v Shear Frequency  0.5MHz  1 MHz  2MHz  4MHz  6MHZ

Compression  11.8  5.9  2.95  1.48  0.98

Shear  6.5  3.2  1.6  0.8  0.54

The smaller the wavelength the better the sensitivity mmz 2003

Sound travelling through a material 

Velocity varies according to the material

Compression waves

Shear waves

• Steel5960m/sec • Water

1470m/sec

• Steel3245m/sec

• Air

344m/sec

• Water

NA

• Copper

4700m/sec

• Air

NA

• Copper

2330m/sec

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Sound travelling through a material Loses intensity due to

Beam Spread

Attenuation

• Sound beam comparable to a torch beam

• Energy losses due to material

•Reduction differs for small and large reflectors

•Made up of absorption and scatter

Attenuation is defined as the loss in intensity of the ultrasonic beam as it passes through a material and is dependant upon the physical properties of the material. mmz 2003

Scatter 



The bigger the grain size the worse the problem The higher the frequency of the probe the worse the problem

1 MHz

5 MHz

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Beam Spread

The sound beam spread out and the intensity decreases

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Beam spread and Attenuation combined Attenuation and beam spread. 6dB+ reduction

80% FSH

80% FSH

40% FSH

36% FSH

No attenuation,only beam spread. 6dB reduction mmz 2003

Sound at an Interface 

Sound will be either transmitted across or reflected back Reflected

Interface

Transmitted

How much is reflected and transmitted depends upon the relative acoustic impedance of the 2 materials

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Acoustic Impedance 

Definition

Formula

The Resistance to the passage of sound within a material 

Measured in kg / m2 x sec

Z   V  = Density , V = Velocity    

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Steel Water Air Perspex

46.7 x 106 1.48 x 106 0.0041 x 106 3.2 x 106

% Sound Reflected at an Interface 2

 Z1  Z 2     100  % reflected  Z1  Z 2 

% Sound Reflected + % Sound Transmitted = 100% Therefore % Sound Transmitted = 100% - % Sound Reflected mmz 2003

Sound at an Interface 

Sound will be either transmitted across or reflected back Reflected

Interface

Transmitted

How much is reflected and transmitted depends upon the relative acoustic impedance of the 2 materials

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How much sound is reflected at a steel to water interface? 

Z1 (Steel) = 46.7 x 106



Z2 (Water) =1.48 x 106 2

 46.7  1.48   100  % reflected  46.7  1.48  2

 45.22   48.18   100  % reflected   0. 93856 100  88.09% reflected 2

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How much sound transmitted? 100 % - the reflected sound Example : Steel to water 100 % - 88 % ( REFLECTED) = 12 % TRANSMITTED

The BIGGER the Acoustic Impedance Ratio or Difference between the two materials: More sound REFLECTED than transmitted.

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Air

Steel Steel

Large Acoustic Impedance Ratio

Air Large Acoustic Impedance Ratio

Aluminum

Steel Steel

Steel

No Acoustic Impedance Difference

Small Acoustic Impedance Difference mmz 2003

Ultrasonic Displays 

A scan Display of the ultrasonic signal in which the X-axis represents the time and the Y-axis the amplitude. The CRT (Cathode Ray Tube) display The Horizontal axis : Represents time base / beam path length / distance / depth

The Vertical axis : Represent the amount of sound energy returned to the crystal mmz 2003

Ultrasonic Displays B scan -The End View Display 

Image of the results of an ultrasonic examination showing a cross section of the test object perpendicular to the scanning surface and parallel to a reference direction.



The cross section will normally be the plane through which the individual A-scans have been collected.

B

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Ultrasonic Displays C scan-The Plan View Display 

Image of the results of an ultrasonic examination showing a cross section of the test object parallel to the scanning surface.

C

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Ultrasonic Displays D scan - The Side View Display 



Image of the results of an ultrasonic examination showing a cross section of the test object perpendicular to the scanning surface and perpendicular to the projection of the beam axis on the scanning surface. The D-scan will normally be perpendicular to the Bscan.

D

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Advantages of ultrasonic Testing     

Internal defects can be detected and sized Thick specimens take no more time to examine than thin ones Access to only one side of the component is needed There is no radiation hazard in ultrasonic examination, and hence no disruption of work as there is with radiography Planar defects can be detected, irrespective of their orientation

Disadvantages of ultrasonic Testing    

A high degree of operator skill and integrity is needed. Hence, the need for trained and certified NDT personnel In most examinations, there is no permanent record of the inspection as there is in radiography In certain materials, like austenitic steel, the large grain size found in welds can cause attenuation and this may mask defects Spurious indications, and the misreading of signals, can result in unnecessary repairs

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