Radiography Testing

RADIOGRAPHY TESTING

Principle of Radiography

Principle of Radiography • Electromagnetic radiation of certain wavelengths penetrate materials and are absorbed differentially by different materials. • The emergent radiation from the job is recorded normally on a film • The film after processing is called a radiograph and contains the shadow image of the discontinuities which produce differential degree of darkness on the radiograph

ELECTROMAGNETIC SPECTRUM

Characteristics of X rays and Gamma Rays • Capable of Penetrating most of the industrial materials • Travels in straight lines • Can affect photographic films • Can ionize gases • Can affect living cells • Invisible, Odorless

Sources of Electromagnetic Radiation • X Rays – X ray Generator, Linear Accelerator, Betatron

• Gamma Rays – Natural and Artificial Radioactive elements Natural : Radium, Polonium, Uranium, Radon Artificial : Iridium 192, Cobalt 60, Cesium 137 Ytterbium 170, Thulium 169

X RAY • X rays are produced when high speed electrons hit a material target in an evacuated chamber ( 10 ^ -12 to 10^ -13 torr )

CONSTRUCTION OF X RAY GENERATOR

FOCAL SPOT

Parameters in X Radiography • KV – Controls thickness to which can be radiographed • Exposure affects the density of image in the radiographs • Exposure – mA * Mins

X RAY UNIT - CONTROLS

Gamma radiography Gamma rays are produced during radioactive decay of elements – Alpha particles are He ++ – Beta particles are (-) – Gamma radiation is a electromagnetic radiation

Radioactive decay

RADIOACTIVE SOURCE CAMERA

GAMMA RAY CAMERA OPERATION Source in stored position in pig

Source cranked partially out source no longer shielded

Source in exposure position all the way

Source Pencil

Co 60 • Created by Neutron bombardment, • capsuled pellet • 1.17, 1.33 MeV • Penetration 1 - 8 “ steel • Requires thick shielding • Container is bulky and handling difficult

Iridium 192 • Produced by neutron bombardment • 0.31, 0.47 & 0.60 MeV • Capsuled pellet • Easy shielded and less bulky • widely used • 0.25 – 3 inches thick steel

EXPOSURE CHART

Characteristics of sources Isotope Half life Form Energy Practical Ci Rhm Dia, app,

Cobalt60 Ir 192 5.3 yrs 75 days Co Ir

Cs 137c 30 yr CsCl

1.33,1.17

0.45

0.66

Sources 20 27 3 mm

50 60 3 mm

75 30 10 mm

Characteristics of Isotopes • Curie is a measure of disintegration of source 1 Ci = 3.7 x 10 10 disintegrations per sec • In SI System it is 1 Becquerel = 1 disintegrations / sec • Half Life : length of time required for the activity to decay to one half of the original value • Energy is expressed as KeV or MeV • Specific Activity : Ci/ gm of isotope

Parameters in Gamma radiography • Source determines the thickness limit of radiography • Exposure determines the density of radiographic image • Exposure = Curie * min Curie – Strength of source

RADIOGRAPHIC FILM

CHARACTERISTIC CURVE

FILM PROCESSING

ASTM Penetrameters

Hole Type

Wire Type

LOCATION OF PENETRAMETERS – AWS D1.1

Sensitivity Level Equivalent Sensitivity %

Quality Level

T of Penetrameter

Perceptible hole dia

0.7

1-1T

1

1T

1.0

1-2T

1

2T

1.4

2-1T

2

1T

2.0

2-2T

2

2T

2.8

2-4T

2

4T

4

4-2T

4

2T

DIN Wire Penetrameter • DIN 1-7 1- 3.2; 2-2.5; 3-2.0; 4-1.6; 5-1.25; 6-1.00; 7-0.8 • DIN 6-12 • 6-1.00; 7-0.8; 8-0.63; 9-0.5 10-0.4 11-0.32;12 –0.25 • DIN 10-16 10-0.4; 11-0.32; 12- 0.25 13-0.2 14-0.16; 15 - 0.125 16-0.1

ASTM Wire Penetrameter • SET A No 1–0.08 mm, 2-0.1,3–0.13 4-0.16, 5-0.2, 6-0.25 • SET B No 6-0.25,7-0.33, 8- 0.4, 9-0.51, 10-0.64,11-0.81 • SET C No 11-0.81, 12-1.02, 13- 1.27, 14-1.6 15-2.03 16-2.5 • SET D No 16-2.5 17- 3.2 18-4.06 19-5.1 20-6.4 21 – 8

Wire Penetrameter Sensitivity SENSITIVITY S = ( D / T ) * 100 S – Sensitivity in % D - Dia of smallest wire seen in mm T – Thickness of Job in mm

Effect of angle of radiation

RT Techniques

Double wall Single image

Single Wall Single Image Job

Film

Weld

Source

Radiation

RT Techniques

Panoramic Exposure

Double Wall Double Image Job

Film

Weld

Source

Radiation

Radiation Safety • Radiation safety is ensured by – Radiation Protection – Radiation monitoring

Radiation Protection • Radiation Protection is ensured by – Undertaking RT in an enclosure – Maintaining safe distances – Providing local temporary enclosure around the source – Retaining the source in the camera when not in use

Radiation Monitoring • Ensuring that radiation intensity is within limits • Thermo Luminescent Dosage (TLD) badge is used for monitoring the dosage received by the operator • TLD Badges are processed every month by BARC or its authorised agency

AWS D1.1 RT Evaluation Gap between defects w e l d s i z e

* Pl refer to codes for details

AWS D1.1 RT Evaluation

* Pl refer to codes for details

RADIOGRAPHIC INDICATIONS

INTER-PASS SLAG INCLUSIONS

RADIOGRAPHIC INDICATIONS

SLAG INCLUSION

RADIOGRAPHIC INDICATIONS

SLAG INCLUSION

RADIOGRAPHIC INDICATIONS

CLUSTER PORES

RADIOGRAPHIC INDICATIONS

LACK OF PENETRATION

RADIOGRAPHIC INDICATIONS

PORES

RADIOGRAPHIC INDICATIONS

WORM HOLE

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