Radiography Test

3/10/2009

1

Introduction

Radiographic Testing (RT) Radiographic Testing (RT)

Radiation Sources

Attenuation

Recording

ME 538 Welding Design, Fabrication & Quality Control 1

Recording

RT Procedures & Safety

Title Page

Principles of Radiographic TestingPrinciples of Radiographic Testing

Radiation Source

Test Object: Absorbs, scatters and transmits

th di ti

ME 538 Welding Design, Fabrication & Quality Control 2Introduction

the radiation

Recording Film

The shadow of the discontinuity

The shadow of the thin section

Karl DitnerText Box2009/03/11 - Start

3/10/2009

2

Examples Examples

Pores

Transverse &LongitudinalCracks

ME 538 Welding Design, Fabrication & Quality Control 3Introduction

[http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography]

Lack ofPenetration

The Electromagnetic The Electromagnetic Wave SpectrumWave SpectrumIonizing Radiation

(Health Hazard)High

EnergyLow

Energy

ME 538 Welding Design, Fabrication & Quality Control 4The Radiation Source

The energy of a photon (unit [J] or [eV]) is given by : E = h . f = h . c/ =1.24 / (1 eV = 1.602E-19 J) where the number 1.24 has the dimension [eV m] h ... Plancks constant (6.626x10-34 J . s), f ... the frequency of the photon, c ... the speed of light (3.0x108 m/s) and ... the wavelength [m]

3/10/2009

3

Generation of Generation of XX--raysrays

X-ray source from Golden Engineering,

ME 538 Welding Design, Fabrication & Quality Control 5Radiation Sources[ASM Handbook, Vol. 17, Nondestructive Evaluation and Quality Control, 1989]

g g5.4 kg with battery, 36 cm long [www.tedndt.com]

XX--ray ray Radiographic TestingRadiographic Testing

HV Power Supply


X-ray Film

X-ray Generator

3/10/2009

4

XX--ray ray Source SpectraSource Spectra

at max intensity 1.5 min

ME 538 Welding Design, Fabrication & Quality Control 7[ASM, Vol.17, Nondestructive Evaluation and Quality Control, 1989]

min

Radiation Sources

min = 1.24 /E

Effect of Effect of XX--ray ray Tube SettingsTube Settings

Inte

nsity

Inte

nsity

High acceleration voltage

High filament heating current


Wavelength Wavelength

[ASM Handbook, Vol. 17, Nondestructive Evaluation and Quality Control, 1989]

Radiation Sources

3/10/2009

5

Gamma-rays are emitted during the radioactive decay (disintegrating) of unstable atomic nuclei and are at discrete wavelengths.

Commonly used radioisotopes:

--raysrays

Commonly used radioisotopes: Cobalt 60 (emits -rays at 1.17 and 1.33 MeV) Cesium 137 (at 0.66 MeV)

Iridium 192 (at about 0.31 and 0.47 MeV)

There is a continuous reduction in activity (the number of decays in a radioactive isotope sample):


(the number of decays in a radioactive isotope sample): Nt = N0 exp(-t)

where Nt, and N0 are the number of atoms at t = t and 0, is the decay constant. Half-life constant = t (when Nt = 0.5 N0) = - ln 0.5 /

( - ln 0.5 = 0.693 ) Radiation Sources

GammaGamma--ray ray SourceSource

Hand crank

ME 538 Welding Design, Fabrication & Quality Control 10[ASNT CT-6-6, Radiographic Testing] Radiation Sources

3/10/2009

6

100

GammaGamma--ray ray Spectrum of IridiumSpectrum of Iridium--192192Decay of Ir-192

40

60

80

Rel

ativ

e In

tens

ity

[R Nath Yale Univ 2005 AAPM Summer School]


0

20

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Energy (MeV)[L. Cartz, Nondestructive Testing, 1995]

[R. Nath, Yale Univ., 2005 AAPM Summer School]

Radiation Sources

Characteristics of Characteristics of --ray ray SourcesSources

ME 538 Welding Design, Fabrication & Quality Control 12[ASM Handbook, Vol. 17, Nondestructive Evaluation and Quality Control, 1989]

Radiation Sources

3/10/2009

7

Penetrating AbilityPenetrating Ability

X-ray tube X-ray

Thickness limitation of

steel for Approx. -ray yvoltage, kV

ymin, m inspection, mm

pp yequivalent

1002008001000

1.24x10-20.62x10-21.55x10-31 24x10-3

825110125

Ir-192, 0.31 MeVCe-137 0 66 MeV


10002000

1.24x100.62x10-3

125200

Ce 137, 0.66 MeVCo-60, 1.17 MeV

Radiation Sources

Comparison of XComparison of X-- rays and rays and --raysraysX-rays -rays

Advantages: Variable/changeable wavelengths

Fixed wavelengths with high penetrating power

Advantages

Usable for all materials Usable for all materialsGood radiographic contrast & sensitivity

Intensity decays with time

Adjustable Penetration Low initial cost & maintenanceCan turn it on & off Small, portable and provides

access into small cavities

Disadvantages: High initial cost Constant radiation hazard,


Disadvantages

Radiation Sources

g gCan not turn it off, can only shield it

Requires power source Requires intensity calibrationLess portable and more fragile Generally less contrastHigh voltage electrical hazard Penetrating power is not

adjustable[AWS Handbook, 9th ed., Vol. 1, Table 14.4]

Karl DitnerLine

Karl DitnerLine

Karl DitnerLine

Karl DitnerText Box

Karl DitnerText Boxit's a disadvantage

3/10/2009

8

z There is a reduction of intensity of a beam of X-ray or -rays as it passes through matter due to interaction between the beam and the material

Attenuation of Electromagnetic RadiationAttenuation of Electromagnetic Radiation

beam and the material.z Attenuation characteristics of materials depend on:

Type (Electromagnetic? Ultrasonic? ... ) Radiation intensity and energy (frequency) Density and atomic structure of the material

z Decrease in intensity from I0 to I depends on thickness, t ,


Decrease in intensity from I0 to I depends on thickness, t ,of material, i.e., I = I0 exp ( - t )

z Material constants [cm-1] ... linear absorption coefficient of the material

m= / [cm2/g] ... mass absorption coefficient ( ... material density)Attenuation

z Thomson/Rayleigh

Atomic Attenuation ProcessesAtomic Attenuation ProcessesSame energy photon

z The photoelectric effect

z Compton scatteringelectron

electron


z Pair production

[www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/radmatinteraction.htm]

positron

electron

photon

3/10/2009

9

Mass Attenuation CoefficientsMass Attenuation Coefficients


[ASM Handbook, Vol. 17, Nondestructive Evaluation ]and Quality Control, 1989]

Attenuation

Mass Absorption CoefficientsMass Absorption Coefficients

ME 538 Welding Design, Fabrication & Quality Control 18[L. Cartz, Nondestructive Testing, 1995] Attenuation

Karl DitnerText Box2009/03/11 - End2009/03/12 - Start

3/10/2009

10

Mass Absorption Coefficients (cont'd)Mass Absorption Coefficients (cont'd)

ME 538 Welding Design, Fabrication & Quality Control 19[L. Cartz, Nondestructive Testing, 1995] Attenuation

Half-value Thickness (HVT) or half-value layer (HVL): the thickness that decreases the radiation intensity by one-half

HalfHalf--Value Thickness and Subject ContrastValue Thickness and Subject Contrast

one half Subject Contrast:

ratio of transmitted radiation intensities at twolocations of the workpiece

Affected by:


Affected by: nature of the specimen energy of the radiation intensity and distribution of the scattered radiation

Not affected by: time, distance, characteristics of the radiographic film

Attenuation

3/10/2009

11

Experimental and Calculated HVTExperimental and Calculated HVT

ME 538 Welding Design, Fabrication & Quality Control 21Attenuation

Subject ContrastSubject Contrast

I0

Pb Cu Steel Al

It

ME 538 Welding Design, Fabrication & Quality Control 22Attenuation

Film

Contrast due toDifferences in

Specimen Thickness

Contrast due to Differences in

Specimen Composition

3/10/2009

12

Absorption Edges and Subject ContrastAbsorption Edges and Subject Contrast


[L. Cartz, Nondestructive Testing, 1995]

Attenuation



Void Dense Inclusion(e.g., W)

3/10/2009

13



Film Radiography Exposing a sheet of film to unabsorbed radiation

T di i l l t t i f th j t d

Viewing or Recording MediumViewing or Recording Medium

Two-dimensional latent image from the projected radiation

Subsequent development of the exposed film to convert the latent image into a fixed, visible image

Real-time Radiography (radioscopy)


Unabsorbed radiation converted into an optical or electronic signal, which can be viewed immediately or can be processed in near real time with electronic and video equipment

Recording

3/10/2009

14

Thin, transparent plastic base with emulsion Emulsion consisting mainly of grains of

Photographic FilmsPhotographic Films

Cross sectional view of industrial x-ray film

silver bromide (AgBr) dispersed in gelatin Exposure to X-rays or daylight reduces

AgBr to silver, forming a latent image (whichcannot be detected visually or by ordinary physical measurement) D l i th d fil


Developing the exposed film Selective chemical reaction converts the exposed AgBr

grains in the latent image into black metallic silver. The metallic silver remains suspended in the gelatin, blackens (part of) the developed (visible) image.

Recording

Measure of the dose of radiation exposure (E):

the radiation intensity (I)

Film Characteristic CurveFilm Characteristic Curve

Dy ( )

multiplied by time (t) Measure of film blackening

Radiographic density (D)D = log (Iin/Iout)depends on E and film development

D1

D2

G = tan Iin Iout

= dD / d(log E)


development Film gradient (g): slope of

characteristic curve Average gradient (G)

(e.g., for D from 1.5 to 3.5) G = (D1-D2) / log (E1/E2)

Foglevel

Log (E)Film speed

D2

Recording

dD / d(log E)film

3/10/2009

15

CR is determined by the subject contrast I1/I2 and film gradient G

Radiographic Radiographic Contrast, Contrast, CCRR

CR = D1 - D2 = G log (I1/I2) = 0.4343 G ln (I1/I2)

For example, when an inclusion is present of thickness iand with a linear absorption coefficient, i, in a matrix with linear absorption coefficient, M, the contrast due to the presence of the inclusion is C = 0 4343 G ( )


presence of the inclusion is CR = 0.4343 G (M - i)i . A minimum of CR = 0.2 is desired in radiography even

though the eye is sensitive to contrast changes as low as 0.05 of photographic film blackening

Recording

Used to improve image contrast and reduce exposure time, particularly when the radiation intensity is low or when the radiation energy

Intensifying ScreensIntensifying Screens

intensity is low or when the radiation energy (frequency) is high Metal foil intensifying screens (such as lead), when

irradiated by X-rays, emit electrons that affect the silver halide grains.

Fluorescent salt intensifying screens emit visible light photons when irradiated by X-rays. Photographic

l i i h l iti t X h t th


emulsion is much less sensitive to X-rays photons than to visible light photons.

A second lead screen is also added at the back of the film to reduce back-scattered X-rays affecting the film.

Recording

3/10/2009

16

Metal Foil Intensifying ScreensMetal Foil Intensifying Screens


[ASM Handbook, Vol. 17, Nondestructive Evaluation and Quality Control, 1989]Recording

0.05

Factors Affecting Quality of Radiographic ImageFactors Affecting Quality of Radiographic Image[AWS Welding Handbook, 8th ed., Vol. 1, 1987]

ME 538 Welding Design, Fabrication & Quality Control 32Recording

3/10/2009

17

Radiographic Definition is the sharpness of the edge of the image (resolution)

Radiographic DefinitionRadiographic Definition

Geometrical Unsharpness occurs because the radiation source is not a true point source but has a finite size

Spatial Resolution of the image-detecting system Film unsharpness Uf - film grain size, development process, radiation

energy level (worse at higher energy level)


Screen unsharpness - grain size and thickness of the screen, detection efficiency and the energy and intensity of the radiation

Scattered Radiation - back scatter and forward scatter

Recording

Radiographic DefinitionRadiographic DefinitionThe loss of image outline sharpness/definition is a function of focal spot size of the source, source-to-film distance, and specimen-to-film distance. UnsharpnessUnsharpness ( or ( or UUgg) = Source Focal Spot Size ) = Source Focal Spot Size b/ab/a High definition requires a small focal spot size of the radiation source,

the source-to-film distance be as large as practical and specimen-to-film distance should be as small as practical.

ME 538 Welding Design, Fabrication & Quality Control 34[NDT Resource Center]

Karl DitnerText Box2009/03/12 - End2009/03/16 - Start

3/10/2009

18

Maximum Geometric Maximum Geometric UnsharpnessUnsharpness Allowed Allowed

Ug

ME 538 Welding Design, Fabrication & Quality Control 35[CSA W59-M1989 Welded Steel Construction (Metal Arc Welding)]

Recording

Effect of XEffect of X--Ray Voltage on Ray Voltage on UUff

As the radiation strikes the film, free electrons are released which affect

Uf [mm]

the film in the surrounding areas. This type of unsharpness cannot be avoided.

ME 538 Welding Design, Fabrication & Quality Control 36[L. Cartz, Nondestructive Testing, 1995] Recording

X-ray generator voltage [MV]

3/10/2009

19

Three Types of Scattered RadiationThree Types of Scattered Radiation

Internal Scatter Side Scatter


Back Scatter[ASM Handbook, Vol. 17, Nondestructive Evaluation and Quality Control, 1989]

Recording

Effects of Scatter & SolutionsEffects of Scatter & Solutions

Effects ofScatter


Solutions

3/10/2009

20

Scattered X-rays give rise to a general fogging of the film, thereby reducing the sharpness and contrast

Scattered Scattered XX--raysrays

Methods to reduce scattering effects on the X-ray film: Increased object-to-film distance reduces scattered

rays reaching the image Secondary X-rays are of lower energy (frequency) and

can be filtered (absorbed) by a thin metal screen in


( ) yfront of the film

The edges and holes scatter X-rays very badly, fogging the film unnecessary. Blocking materials or masks can be used reduce this problem.

Recording

Image Quality Indicator (IQI) or PenetrametersImage Quality Indicator (IQI) or Penetrameters

ASTM-ASME StandardStandard

Wire Penetrameters


Hexagonal Standard

Recording

3/10/2009

21

Penetrameter Designs Penetrameter Designs

ME 538 Welding Design, Fabrication & Quality Control 41[CSA W59-M1989 Welded Steel Construction (Metal Arc Welding), p. 48]

Recording

Standard Penetrameter ThicknessStandard Penetrameter Thickness


Recording

3/10/2009

22

IQI Location on Approx. Equal Thickness JointsIQI Location on Approx. Equal Thickness Joints


Recording

X-rays X-ray tube voltage

Radiographic ExposureRadiographic Exposure

X-ray tube amperage exposure time source-to-film distance

-raysl th


wavelength radioisotope activity exposure time source-to-film distance

Recording

3/10/2009

23

Provide an estimate of the exposure in terms of X-ray tube current (resp. -ray activity) multiplied by time (e.g., mA-s or Ci-min) for radiographs of aluminum and steel depending on the

Exposure ChartsExposure Charts

min) for radiographs of aluminum and steel, depending on the thickness of the specimen and on the applied voltage (X-ray).

Usually provided for a particular X-ray generator, using specified film-source distance, X-ray film type, film developing-processing.

E f th t i l b d i d i i l t


Exposure for other materials can be derived using equivalent thickness factors.

Intensifying screens are used to shorten the exposure time, but affect the unsharpness.

Recording

Typical Typical XX--ray ray Exposure ChartsExposure ChartsAndrex 160-kV directional X-ray machine, AA film (Eastman Kodak), 2.0 density, no screens, 910mm source-to-film distance, PIX developer (Picker), 7 min manual developing time


Aluminum Steel


3/10/2009

24

Exposure Curves for Exposure Curves for --Ray SourcesRay Sources

A - Iridium-192 source, lead screens, 500 mm source-to-film distance;

B - Cobalt-60, copper screens,500 mm source-to-film distance;

C - Ytterbium-169, lead screens,200 mm source-to-film distance;


Aluminum[ASM Handbook, Vol. 17, Nondestructive Evaluation and Quality Control, 1989]

D.7 film, 2.0 density, 5 min development in Agfa-GevaertVC developer at 20oC,

Recording

Equivalent Radiographic AbsorptionEquivalent Radiographic Absorption



3/10/2009

25

The far-field intensity varies inversely with the square of the distance from the source, mathematically,

Estimated Estimated Exposure if Exposure if Source Distance Source Distance ChangesChanges

Newton's Inverse Square Law

, y,I1 : I2 = (d2)2 : (d1)2

where I is the intensity of radiation at a given distance, d, from a source

Equivalent exposure can be estimated using :

t A t t [www.ndt-ed.org]


t . mA = constant, t ... exposure time, mA ... tube current (X-rays) or source strength (-rays)

Combining the above two equations, we have(mA1 . t1 ) : (mA2 . t2 ) = (d2)2 : (d1)2

Recording

Ionizing Electromagnetic Radiation can damage human blood cells and tissues resulting in acute or

long-term health effects.

XX--rayray, , --ray ray Radiation SafetyRadiation Safety

Licensing The use of -ray inspection is controlled by the Federal

Government through the Atomic Energy Control Board. The use of industrial X-ray machine is controlled by the Provincial

Ministry responsible for the respective Industrial and Occupational Health and Safety Act.

C t lli E


Controlling Exposure Increase distance - doubling the distance from a source reduces the

radiation by four times (inverse square law) Reduce exposure time - using faster film speed Shielding - heavier materials (such as lead or depleted uranium)

absorb more radiationSafety

3/10/2009

26

Detecting and Measuring Radiation Exposure Radiation Survey Meter Personal Dose Meter

Radiation SafetyRadiation Safety

TLDPersonal Dose Meter Thermoluminescent Dosimeter (TLD) traps radiation energy which can

later be released by slow heating and the released energy is measured and recorded.

The monitoring of radiation exposure is controlled by the Federal Government through the Department of Health and Welfare. The TLDs are issued and read and a lifelong history of radiation doses received is maintained by the Bureau of Radiation and Medical Devices

TLD


maintained by the Bureau of Radiation and Medical Devices. Direct Reading Dosimeter (DRD) contains a charged quartz fibre which

moves when struck by radiation.

Warning Signs

Safety

"CAUTION, X-RAYS : NO UNAUTHORIZED USE" "ATTENTION, RAYONS X: UTILISATION NON AUTORISEE"

Advantages Can detect internal discontinuities Provides a physical record of inspection

Radiography: Advantages and Limitations Radiography: Advantages and Limitations

Provides a physical record of inspection Film can be viewed by others for repair, review,

etc., and can be evaluated later Suitable for all weld geometries

Disadvantages Radiation hazard


Less sensitive to cracks Requires highly trained inspectors Relative high capital cost Sensitivity decreased on thicker test pieces Two-side access needed

Summary

Karl DitnerText Box2009/03/16 - End

Documents

Radiography Test