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RADIOGRAPHIC TESTING


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Introduction

•This module presents information on the NDTmethod of radiographic inspection orradiograph!

•Radiograph uses penetrating radiation that isdirected to"ards a component!

•The component stops some of the radiation!The amount that is stopped or a#sor#ed isa$ected # material densit and thic%ness

di$erences!

•These di$erences in &a#sorption' can #erecorded on (lm) or electronicall!


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Detection of internal defects such as porosity, voidsand inclusions

With proper orientation, planar defects can also be

detected.

Also suitable for detecting changes in

• Material composition• Thickness measurement• Locating defective parts or components from

assembled part


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Outline

•ElectromagneticRadiation

•General Principles ofRadiograph

•Sources of Radiation – Gamma Radiograph

– *+ra Radiograph

• Imaging Modalities – Film Radiography – Computed Radiography – Real-Time Radiography

– Direct Digital Radiography – Computed Radiography

• Radiation Safety• Advantages and

Limitations

• lossary of Terms


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The essential difference beteen !"#ays and $amma #ays and

other electromagnetic radiations such as light, %ltra"violet rays and

infrared rays from the testing and evaluation point of vie is that

!"#ay and $amma #ays are able to penetrate matter hich is

opa&ue to light but have a photographic action similar to light.


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General Principles of Radiograph

Top vie! of developed film

X-ray film

The part is placed "et!een the

radiation source and a piece of film#

The part !ill stop some of the

radiation# Thic$er and more dense

area !ill stop more of the radiation#

% more e&posure

% less e&posure

The film dar$ness

'density( !ill vary !ith

the amount of radiation

reaching the filmthrough the test o")ect#


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• 'olumetric (DT method based on differential absorption of

penetrating radiation• )ecause of differences density and variations in thickness of part

*or+

Differences in absorption characteristics caused by variations in

composition and presence of defects

“Different portions of a test piece absorb

Different amount of penetrating radiation”


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General Principles of Radiograph

•The energ of the radiation a$ects its penetratingpo"er! Higher energ radiation can penetratethic%er and more dense materials!

•The radiation energ and1or e0posure time must #e

controlled to properl image the region of interest!

Thin Walled Area

Low Energy Radiation High energy Radiation


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IDL 2001

Radiographyhas sensitivitylimitations whendetecting

cracks.

Xrays !see" a crack as a thickness variation and thelarger the variation# the easier the crack is to detect.

$ptim%m

Angle

2la" Orientation

easy todetect

not easy

to detect

When the path o& the 'rays is not parallel to a crack# the

thickness variation is less and the crack may not (e visi(le.


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IDL 2001

)o *)o +)o

Since the angle "et!een the radiation "eam and a crac$or other linear defect is so critical* the orientation ofdefect must "e !ell $no!n if radiography is going to "eused to perform the inspection#

2la" Orientation ,cont!.


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Radiation Sources

T"o of the most commonl used sources ofradiation in industrial radiograph are 0+ragenerators and gamma ra sources! Industrialradiograph is often su#di-ided into &*+raRadiograph' or &Gamma Radiograph')

depending on the source of radiation used!


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Gamma Radiograph

•Gamma ras areproduced # aradioisotope!

•A radioisotope has anunsta#le nuclei thatdoes not ha-e enough#inding energ to holdthe nucleus together!

•The spontaneous#rea%do"n of anatomic nucleusresulting in the releaseof energ and matteris %no"n asradioacti-e deca!


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Gamma Radiograph,cont!.

•3ost of the radioacti-ematerial used inindustrial radiographis arti(ciall produced!

•This is done #su#4ecting sta#lematerial to a source ofneutrons in a specialnuclear reactor!

•This process is calledacti-ation!


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5nli%e *+ras) "hich areproduced # a machine)gamma ras cannot #eturned o$! Radioisotopesused for gamma radiograph

are encapsulated to pre-entlea%age of the material!

The radioactive +capsule, is

attached to a ca"le to form!hat is often called a +pigtail#,

The pigtail has a specialconnector at the other end

that attaches to a drive ca"le#


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A de-ice called a &camera' is used to store)transport and e0pose the pigtail containingthe radioacti-e material! The cameracontains shielding material "hich reduces

the radiographer6s e0posure to radiationduring use!


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A hose+li%e de-icecalled a guide tu#e isconnected to athreaded hole called

an &e0it port' in thecamera!

The radioacti-ematerial "ill lea-e

and return to thecamera through thisopening "henperforming ane0posure7


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A &dri-e ca#le' is connectedto the other end of thecamera! This ca#le)controlled # theradiographer) is used to

force the radioacti-ematerial out into the guidetu#e "here the gamma ras"ill pass through thespecimen and e0pose therecording de-ice!


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*+ra Radiograph

5nli%e gamma ras) 0+ras are produced #an *+ra generator sstem! These sstemstpicall include an *+ra tu#e head) a high-oltage generator) and a control console.


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*+ra Radiograph ,cont!.

•*+ras are produced # esta#lishing a -er high -oltage#et"een t"o electrodes) called the anode and cathode!

•To pre-ent arcing) the anode and cathode are locatedinside a -acuum tu#e) "hich is protected # a metalhousing!


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*+ra Radiograph ,cont!.

•The cathode contains a small(lament much the same as ina light #ul#!

•Current is passed through the(lament "hich heats it! Theheat causes electrons to #estripped o$!

•The high -oltage causes these&free' electrons to #e pulledto"ard a target material,usuall made of tungsten.

located in the anode!

•The electrons impact againstthe target! This impact causesan energ e0change "hichcauses 0+ras to #e created!

igh .lectrical /otential

.lectrons

-0

1-ray enerator

or Radioactive

Source Creates

Radiation

.&posure Recording Device

Radiation

/enetrate

the Sample


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Imaging 3odalities

Se-eral di$erent imaging methodsare a-aila#le to displa the (nalimage in industrial radiograph8

•2ilm Radiograph

•Real Time Radiograph•Computed Tomograph ,CT.•Digital Radiograph ,DR.•Computed Radiograph ,CR.


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2ilm Radiograph

•One of the most "idelused and oldest imagingmediums in industrialradiograph is

radiographic (lm!• Film contains microscopicmaterial called silver "romide#

• 2nce e&posed to radiation anddeveloped in a dar$room*

silver "romide turns to "lac$metallic silver !hich forms theimage#


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2ilm Radiograph ,cont!.

•2ilm must #e protected from -isi#le light! 9ight) 4ust li%e 0+ras and gamma ras) can e0pose (lm!2ilm is loaded in a &light proof' cassette in adar%room!

•This cassette is then placed on the specimenopposite the source of radiation! 2ilm is oftenplaced #et"een screens to intensif radiation!


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•In order for the image to #e -ie"ed) the (lmmust #e &de-eloped' in a dar%room! The processis -er similar to photographic (lm de-elopment!

•2ilm processing can either #e performedmanuall in open tan%s or in an automatic

processor!


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Once de-eloped) the (lm is tpicallreferred to as a &radiograph!'


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Digital Radiograph

•One of the ne"est forms ofradiographic imaging is &DigitalRadiograph'!

•Re:uiring no (lm) digital radiographic

images are captured using eitherspecial phosphor screens or ;at panelscontaining micro+electronic sensors!

•No dar%rooms are needed to process(lm) and captured images can #e

digitall enhanced for increased detail!•Images are also easil archi-ed

,stored. "hen in digital form!


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Computed Radiograph

Computed Radiograph ,CR. is a digitalimaging process that uses a special imagingplate "hich emplos storage phosphors!


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Computed Radiograph


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Computed Radiograph,cont!.

After exposure:

The imaging plate is read

electronically and erased for re-

use in a special scanner system#

Computed Radiograph


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#otor

$%D

Con&erter

$%D

Con&erter

Imaging

late

'ptical

"canner !oto-multiplier (ube

110010010010110110010010010110

Laser )eam


As a laser scans the imaging plate) light is emitted"here *+ras stimulated the phosphor duringe0posure! The light is then con-erted to a digital-alue!

Computed Radiograph


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Digital images are tpicall sent to a computer"or%station "here speciali


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E0amples of computed radiographs8


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Real+Time Radiograph

•Real+Time Radiograph ,RTR. is a termused to descri#e a form of radiographthat allo"s electronic images to #ecaptured and -ie"ed in real time!

•=ecause image ac:uisition is almostinstantaneous) *+ra images can #e-ie"ed as the part is mo-ed and rotated!

•3anipulating the part can #ead-antageous for se-eral reasons8

– It ma #e possi#le to image the entirecomponent "ith one e0posure! – /ie"ing the internal structure of the part from

di$erent angular prospecti-es can pro-ideadditional data for analsis!

– Time of inspection can often #e reduced!

Real Time Radiograph


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Real+Time Radiograph,cont!.

The e:uipment needed foran RTR includes8•*+ra tu#e•Image intensi(er or

other real+time detector•Camera

• Computer !ithframe gra""er "oard

and soft!are• Monitor • Sample positioning

system 'optional(

R l Ti R di h


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•The image intensi(er is a de-ice thatcon-erts the radiation that passesthrough the specimen into light!

•It uses materials that ;uoresce "henstruc% # radiation!

•The more radiation that reaches theinput screen) the more light that isgi-en o$!

•The image is -er faint on the inputscreen so it is intensi(ed onto a smallscreen inside the intensi(er "herethe image is -ie"ed "ith a camera!

Real+Time Radiograph


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•A special camera"hich captures thelight output of thescreen is locatednear the image

intensifing screen!•The camera is -er

sensiti-e to a-ariet of di$erentlight intensities!

• A monitor is then connectedto the camera to provide avie!a"le image#

• If a sample positioningsystem is employed* the partcan "e moved around androtated to image differentinternal features of the part#


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Direct Radiograph

•Direct radiograph ,DR. is aform of real+time radiographthat uses a special ;at paneldetector!

•The panel "or%s # con-ertingpenetrating radiation passingthrough the test specimen intominute electrical charges!

•The panel contains manmicro+electronic capacitors!The capacitors form an

electrical charge patternimage of the specimen!

•Each capacitor6s charge iscon-erted into a pi0el "hichforms the digital image!


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Computed Tomograph

Computed Tomograph ,CT. uses a real+time inspection sstem emploing a samplepositioning sstem and special soft"are!

Computed Tomograph


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Computed Tomograph,cont!.

•3an separate images are sa-ed ,gra##ed.and complied into >+dimensional sectionsas the sample is rotated!

•>+D images are them com#ined into ?+dimensional images!

Real-Time

CapturesCompiled 4-D

ImagesCompiled 5-D

Structure


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Image @ualit

•Image :ualit is critical for accurate assessment of atest specimen6s integrit!

•/arious tools called Image @ualit Indicators ,[email protected] used for this purpose!

•There are man di$erent designs of I@Is! Somecontain arti(cial holes of -aring si


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Image @ualit ,cont!.

•I@Is are tpicall placedon or ne0t to a testspecimen!

•@ualit tpicall #eingdetermined #ased on the

smallest hole or "irediameter that isreproduced on theimage!


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Radiation Safet ,cont!.

There are man sources of radiation! In general) a personrecei-es roughl BB mrem1ear from natural sources androughl BB mrem1ear from manmade sources!


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1-rays and gamma rays are forms of ioni3ing radiation* !hichmeans that they have the a"ility to form ions in the material that ispenetrated# All living organisms are sensitive to the effects ofioni3ing radiation 'radiation "urns* &-ray food pasteuri3ation* etc#(

1-rays andgamma rays haveenough energy toli"erate electronsfrom atoms anddamage themolecularstructure of cells#

This can causeradiation "urns orcancer#


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Technicians !ho !or$ !ith radiation must !ear monitoring devices

that $eep trac$ of their total a"sorption* and alert them !hen theyare in a high radiation area#

,%rvey -eter ocket /osimeter Radiation Alarm Radiation 0adge



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There are three means of protectionto help reduce e0posure to radiation8


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RadiographicImages


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Radiographic Images

Can ou determine "hat o#4ect "asradiographed in this and the ne0t three slides


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Radiographic Images


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Radiographic Images


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Radiographic Images

Ad-antages of


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Ad-antages ofRadiograph

•Techni:ue is not limited # materialtpe or densit!•Can inspect assem#led components!•3inimum surface preparation

re:uired!•Sensiti-e to changes in thic%ness)corrosion) -oids) crac%s) andmaterial densit changes!

•Detects #oth surface and su#surfacedefects!

•Pro-ides a permanent record of theinspection!

Disad-antages of


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Disad-antages ofRadiograph

•3an safet precautions for the use ofhigh intensit radiation!•3an hours of technician training

prior to use!

•Access to #oth sides of samplere:uired!•Orientation of e:uipment and ;a" can

#e critical!

•Determining ;a" depth is impossi#le"ithout additional angled e0posures!•E0pensi-e initial e:uipment cost!


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Glossar of Terms

•Acti-ation8 the process of creatingradioactive material from stable materialusually by bombarding a stable materialwith a large number of free neutrons.

This process typically takes place in aspecial nuclear reactor.

•Anode8 a positively charged electrode.•Automatic 2ilm Processor8 a machine

designed to develop lm with very littlehuman intervention. Automaticprocessors are very fast compared tomanual development.


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Glossar of Terms

•Capacitor8 an electrical device that stores anelectrical charge which can be released ondemand.

•Cathode8 a negatively charged electrode.

•Dar%room8 a darkened room for the purpose oflm development. Film is very sensitive toexposure by visible light and may be ruined.

•E0posure8 the process of radiation penetratingand object.

•Gamma Ras electromagnetic radiationemitted from the nucleus of a some radioactivematerials.


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Glossar of Terms

•Radioacti-e8 to give o& radiationspontaneously.•Radiograph8 an image of the internal

structure of and object produced using a

source of radiation and a recordingdevice.

•Sil-er =romide8 silver and brominecompound used in lm emulsion to form

the image seen on a radiograph.


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2or 3ore Information

The Colla"oration for

6DT .ducation

!!!#ndt-ed#org

The American Society

for 6ondestructive

Testing

!!!#asnt#org

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