RUANE&TPO.NEILL

RADIOGRAPHIC TESTING -OVERVTEWl.l Principles

Radiography is carried our using x-ray machines oranificial gamma sources (radio-isoropes).X-rays or gamma ravs Dass

thrgugh the object to be radiographed and record an image on a;i:l;ffij:[,11ff1.,*.,:ooo,.:i*ide ri;;dia;io;i.iir,1.c the nrm yilr be dereinineoffi f i;' ilI f Jfr'"t',Tt" ri"* i noffi ffi r r'.

x,ffiwhen rhe film is processed a-negative is produced. The thin areas of an objecr wilr be darterthan rhe-ihicker areas, rherefoie ,nor, *.iJ-J"i"";' *ili' show up dark in reration ro the;Tilii:i::*

**s, excepdons are excess werd miiii.iu,,"r, "opp", incrusions and runssren

1.2 Radiographic qualit-vAn overall.assessmenr of radio-graphic quariiy is made by the use ofr.rna ge quariry indicatorsf '.";il;Ji'i:rlT:ilJ ;il:' :: :IJe+-+\" t+dd"c.eas i n g i n rh i ckness rrrey aremori wires ;itibl ;il#;;s,ffUff1r,il: therefore show on i-t" .uaiog';tmc ril-.'ir,.The derr'sig'- degree of blacknesrJu-lraiogtuph is also measured ro ensure it Iies u,irhina specltted range for oprimum qualiry.

1.3 X.radiography versus gamma radiographyX-radiography requires burky and expensive machinery in comparison with gammaraorography, but x-radiosraohy genera'y produ""i-u"','#q"u,uy radrographs and is safer.x-ray machines can be s;ir;h;din "na irfr, un-rit. iu?ir,u. rou...r,1.4 Capabil i t ies and l imitat ions of radiography

*Jfr3iol l t^"tageofradiographicresringistharapeftnanenrrccordisproduced,i .e.the -

A major limitation of radioeraphy.is rhar it will only detect defects which have significanr Joepth rn relarion to rhe axis 6f rhe x-ny beanro, i... .ia.gr..pny wilr not usuary de6cr prare oramrnarions' lack of inter-run fusion oi cracks'ift;il;rfii ro tne x-rav beam. u2 X AND GAMMA RADIATIoN J

-$2.1 GeneralRadiarion can be either erectrom-agr,tctic energy, e.g. heat, visibre 'ight, infra-red, urtrauiorer. ux-rays'- gamma :.ays: or corpuscrlnr energi'1suu"-aroilic panicle energy), e.g. elecrons,.,-.,ualpna, beta, neutrons. Pdr uurc energy), e.g. elecu

I For x.radiognphy t50-J00 kv isglllcgil. typtcally uscd on stccl wcldmcnts i.rp ro approximarcly 40 mm rool: Cobalr 60 (Co60) has a vcn. hroh *.^,-,;-- ^^...^_,,p ,o zoo ri-,-r]"i j."il;iil'r6!llf*f,9dng Jnwql- vcry shon wqvslgngrh-ard can be uscd on marcrii srtic.crorc p.oouccil;;;;;;";;"tii',:ljj,;"fl.ff|jl#d,mtrt icrdmins urj lo-mm il,9!--;il'I Acuvity is mqlsurcd in Cuncs (Ci) or gi$hxqucrcts (G Bq)..l As I rough guidc: rhc minimum d'.;rtt rlrrcknicsi in ,r,. .",n.'"iiil, ,itjor"-t#.f,.S"*

u"Ori of a dcfccr capabtc of bcing derccrcd is 2% of rhc

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RUANE&TPO,NEILL

2.4 Gamma ray generation' Gamma rays used in industrial radiography arb emittcd from anificial radioactive

isotopest-if a material is radioactive it spontaneousty emits corpuscular andelectromagnetic energy-the gamma radiation is a by-product produced from rhedisintegration of the radioaclive isotope.

The activiry or strength of a radioactive isotope is expressed in curies (Ci) or becquerels(Bq). The hfCheftgJgllIryf4lqe, the greater the intensity of gamma rays produced.

I becque.5el = I disintcgration per second;3.7 x l0'" becquerels = I curie;therefore: 3.7 i 10'0 disintegrations per second = I curie.

For indusrial radiography, it is usually more practical to talk in terrns of gigabecquerels(GBq):

Giga = lOeI glgabecquercl = l0e becquercls37 gigabecquerels = I curie.

Radioactive isotopes are used taking into consideration rheir half-lives; the half-life of aradioactive isotope is the time it14!es for$g rggvp tq qrop ro one half of itsinirial strcngth.The activity of a lsot does not relate to the of the

\

1 ot tne gamma rays producedFor example, cobalr 60 (Co60)

I A radioactive isoopc is an unsublc sarc ofa chcmical elemcnt which has a dilfcrcnt mass to thc normal $atco[ the sarnz elcmenL

2 Thc anode is somedmcs refcrrcd to a:s tha anti-cathode.

raysproduce4[leneEatingpow-rd-epentls.nTh-. � - ' r l - . e l .-Eh-dlhrs

depends on rhe specific radioacrive elemenrhas a very high penetrating power-up to 200 mm of steel-- bEeau-s_e rhe gamr!4--radiationemitted has iviry shon riavelength.

There are three main radioactive isotopes used for industrial radiography: iridium 192(Irl92), coba.lt 60 (Co60) and Yuerbium 169 (Ybt69).

2.5 X-ray generation

X-rays used in indusrial radiography are produced from electrical machines usually referredto as x-ray sersi the x-rays themselves being produced from wirhin an x-rcy tube or insert.

An x-ray tube consists of an evacuated glass bulb, enclosing an anode-rhe positiveelectrodi, and a cathode-rhe nesatittelEmle.

-.The cathode-contains-ifilamEnt wiiFin-

a c[rvd reflecor oipZusing cuplWhen the filament is heated ro a white hot state by a current flow of a few amperes, electronsare emitted and are attracted towards the anode' in a concentrated beam formed by thefocusing cup. The beam sn-ikes a rarget ser into rffifenergy-itrf energy consisrs of appr5ximately 97 to 99Vo heat and I to 37o x-rays forconventional x-ny tubes up to 300 kV.

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Focusing cup

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RUANE&TPO'NEILL

Electrorrs

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4

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Gtoss enveloCe

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Anode nrget 1

X-Ray beam

Because ofthe high amount of heat energy produced, rhe anode is made from coooer roconcluct rhe hear awav. Bur.copperhas a low melting poinr, si rolEiEniTfie-EoppEr niiilTing,EStip-drmeriln-i6'dirigh melting point is recessed if;to rhe anodeat ttre poinr *iicrr i. ,*"roy tne elecron beam.This slip of metal also serves another purpose, because, the higher the atomic number of *" (f

rffiHYJffi'l;:lT'm" y!:lt; and its high atomic numbcr ofJ4. _The area on the_target which is su-uck by the elecrons is ftalied t{foca sG. 41is arca shoutd-,t**:+94-.to avoid local gvelhqnng, although fi.om rh-erad--io-frmc image quatityp:"rlt 91 I,:*' rhe tocal spor should be as smqlljs possible to provide gooa

-aernirio;r(sharpness) on rhe radioggprh.

lggilt:l*Tling is requircd to cool the anode; gas, oil or water normally being emptoyedror rnls purpose.

The cooling system and the inscrt are contained together in an eanhed, lead lined conrainer,Ine complete unit commonly bcing referred to as the x-ray tubehead. The tubehead isconrolled from the contro! panel.

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RUANE&TPO'NEILL

2.6 The x-ray equipment control panel

(20 n di^ituh.dtk L^gth,

The three controls that govern a radiographic exposure using x-rays are the timer, the mAcontrol and rhe kV conrol.

2.6.1 TimerThe timer is usually calibrated in minutes. The exposure time for an exposure is preser;when rhe equipment is acrivared, the timer counis down from the oriset value. Theexposure time will paniallv govern how much radiation is going to rlach rhe film.

2.6.2 Mil l iamps (md):< .ri The mA-controls ,h"l inrr^iryt orlquanrirylof x-rays. When rhe mA is increased. rhe

j SD currenr flow th1ough the filamenr is increased, which causes the Ela4qg41_.lg:gg_hprrcr< ̂ r/ re-su.tttng tn an lngreage in the i4tensity of elecrols released. The greaifi-Fe inrensiryC or erectrons stnlqng the rarger, the greater the intensity of the x_rays produced.

The mA control on convenrional x-ray e4uipment may only allow for a maximum of 6to 12 mA to be used, the value being rireasuied across ihe r,ibe, i.e. berween the carhodeand the anode. Thevalue required fora specific exposurc is usually preset on rhe panel,this value is rrsually at, or close to, rhe ma{imum inA possible with the equipmenr forthe purpose o|n{n,. i4lg.*p*.!- j I I" '

An increase in kV, i.e. a shonening of wavelengrh, has an adverse affect on the contrasrand de finirion of a radiognphic iriage. Cenaii srandard $EatFArions,rtJs-29-t0:l9E6lT hc radio g rap hi.etd mi naiii$fus io tt wclde d circunfere ndal bwr joints in stcel,state ntaximunr kV values for this rcason.

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RUANE&TPO'NEILL

The kv meters on the control parels forconventional x-ray equipment arepeat kV valuesm.eelg!944atess rhe rube, i.e. between the cathole and ihe-anode. The maximum kVy^h_rgh 9an be use-fis-pfimarily govemed by_the tubehead; typicat maximum values are200 kv' 250 kv and 3il0 kv. The value required for a specifii "*pot;;. it ;;u"riyJi"r",on the panel.

2.7 Comparison of x and gamma rays for industriat radiography2.7.1 Safety +Using x-ray machines is, normally .q"{er. tqg using gamma sources because x-raymachines may be swirched off like a light bulb, wherEaithere is a consrant emission ofraqlatlon wlth a garnma source. Gamma sources must always be retumed to their shieldingcontalners when not in use.

2.7 .2 Quality of radiographic imagesAssuming.variables such as test material thickness, film ty^p^e_erc. remains consrant, x-raysproduced.by convenrional I:TI equipT^enr, say up ro j00 tv, p.oaute u.i[.'lu"i,ty:*.i:trt*.1-T3 ̂ :: 1l- trte2 oi cboo iioto'pes, u..uur. ,nlli-!*is;;;; ]ii;erwavelengns than the gamma sources.Ytterbium 169 (Yb 169) may produce radiographs comparable to those produced by usingx-rays.

2.7.3 Handting

Gamma sources are easier ro ̂ handle in comparison with bulky and fragile x_rayequipment. The size also allows for gamma sourcls ro be used in diff,icult and iniccessibteareas for x-ray machines, e.g. on pi-pe racks.

2.7.4 CostCamma sources and containers are much cheaper than x-ray equipment.

2.7.5 Versatitity

l* l:::::ill and wavetengrhs of-x-rays can be adjusred from che x-ray connot panet.

,t_::_1lj:",:tjl and. wavelengtls of gamma radiation cannor be adjusred, although thelnrenstry (acrrvlry) reduces with time_see hajf_lives.cenain gamma sources have a very high penetrating power which enabres them to b€used on very thick material, e.g. !5b mir sieer. Mosiionventionar x-ray machines w lnot penetrate more than 50 mm of steel although there are huge x-ray michines, e.g. thelinear accelerator and the betatron.which can"proauceiuaiaion of i *uueringn irrictrcan penerate as much as, and usually more thdn, gamma radiation.

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3 RADIOGRAPHIC FILM3.1 The make-up of a radiographic film

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RUANE&TPO'NEILL

Radiographic Frlrn is usually madelp ofseven layers: a central base layer and thrce coatingson either side consisting of a subbing layer, emulsion and supercoat.

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Gr.-.IoJ,'D1-. <-oo'bo+e#*wr

bromide,lvitl a.solurign of ielatine. ThEiiiES?t remfiarur€ o-ffirx-rne gouef ifr'l-rain-ur(,rruuc, wlul a suluuon oJ qelaune-ttn t@uces the finest grain sruci-uis, *heieas ilo"sr?ei rapto,mrxtns ar Io uces the finest grain sEumlxrog ar nlgn remperarure produces emulsions with larger grains. en large gra instructures.are required, ro produce a fast emulsion, some silver iodidqis usually inciuded inthe formula.

I In prac(icc thc basc rvill not bc toolly tnnqrarcnt and thcrcforc wilt posscss somc phorographic dcnsiry.

The. sizes of these crysrals and the distribution, effect the find radiographicquality/appearalce; the lergel the crvstal size the greater the sensirivity tn radiarion. Variousshapes of crystals exisr, b e.

/ The reason for two layers of emulsion is to give a faster film speed, i.e. rhe radiographs canI be produced quicker, and higher radiographic colrast.,(

Supercoat (anti-abrasion Iayer)Radiograptric emulsion is s'sceprible to mechanical and chemical damage, so ro pre'enr. orat least reduce this, the emulsion is coated with a layer of hardened gelirine.Although the.supercoar offers some protection againsr chemical attack, e.g. oil fronr rhe skinduring handling, ir musr allorv for chemical readtions to rake place in rhe"processing ranks.

ce lr^ h*-ltuatat'sa'. Pjlc+lef

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BaseThe ptrysical characterisdcs of emulsion do not allow it to be used by itself wirhour suppon.therefore. it.is applied to a subsu-ate known as the base. The basl must be transparLnt'.chemically inen and musr not be susceptible ro e{pgnggnindcallgag!9n. Grass is in idealsubsu-ate to meer rhese req.uiremenrs, but for appticatio-ilwhere rh-SEEGro be radiographedar€ curved, e.g. on.pipes, ir is necessary for a flexible base to be used.

-pg!yg$g1 ang!sg,l,blstg

-u-iacggre, although not quire as stable as glass, are widely employea6iGitr-lliidGii.Subbing layer (substratum)The subbing layers adhere rhe emulsion to the base; the material employed for rhis is gelarineplus a base solvent.

EmulsionThe.layers 9.f nri.rng.n imponance are rhe rwo emulsion layers. These layers consisr ofmillions of silverha^lide crystats-usually silver bromide; theiizes of rhe crysials are usua ll;,between 0.1 and 1.0 micromeres (p.m) and are suspended in a gelarine. binding medium.

'

LEilm emulsion is produced bv-mixinC:plg${4+]{l+riTa!9 ald{allr such as pqrassiur-n€o.ru9g:4!-C-Sg!t&! !fui.laune. l ne rare ano remperature or mrxlns soverns rne srarn

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RUANE & T P O'NETLL

t.rJ

3.2 Film typesRadiographic film may be graded in terms of grain size or speedt:

. Ulra fine grain-excepdonal radiographic qu3!E burygl5!9v/jp9gd. _. Fine grain-slow speeil. ' -::-

. Medium grain-medium speed.. Coarse grain-poor radiogiaphic quatity bur fast speed.Radiographic films are also divided into two types: direct_rype or salt screen type,Di rect-type- films are intended fordirect exposur€ to gammaor x--rays or for exposurc usinglead inrensifying screens. Some of these nh"s ;t 5. ;iraute ro.'uie *i,'t riI.i.-"i"rri.or salt (fluorescent) intensifying screens.

l

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Salt screen tylefikns are designed tobe used exclusively wirh salt (fluoresc.ent) intensifying." F'99nt:' Tney are able to prodqcqraqiqgFptrs with minrmum exposure and are widely usedX_- rn medical radiography.

3.3 Film speedAJilm factor is a number which relates to the speed of a panicular film and is obtained froma Fims charaueristic curve; see Appendix C.

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The SCRAIA scale is a scale ofren used for film factors; the smaller the film facror the fasterthe film. Film manufactufls ma.y have their o*n r"ir" *hi"h ;;t-;;;t'n*i-n."ru.. o,opposire way to the SCRATA scafe.Example to the SCRATA scale:A fllm with a factorof l0 wil be twice as fast compared to a film wirh a factor of 20.This means to say of the film with a ra"ror oiioio6k four minutis ro i*poi.,ln.n tt.tilm with a factoi of l0 witt require t*" -t""t"i i. gl;;;;;;;;;;;i;:""

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Types of filrn with their corrcsponding SCRATA film factors:

l}:l:gl:b.gy uscd forgrain.size an-d spc€d can be misreading. Thc rcrms uscd are usuafly rerarive, e.g. aIrnc g*,n lrlm mav bc considered to be fasior srow dcpending on-what ir is h;,"g ""rp.; #"1;;."-'

DupontKodakKodakAgfa Gevaen

MediumMediumMediumMedium

. FineFineFineFine

202530J )

DupontAgfa GevaenKodak.

Very fineVery fineVery fine

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RUANE&TPO'NEILL

4INTENSIFYING SCREENS4.1 Gcnera lA radiographic firm is normaly sandwiched bctween two inrensifying screens when exposedro x-rays or gamma_rays. Intensifying screens have an exua ihoiographic "ii"ti Jn ,r,.emulsion rhereby reducing the exposurE needed to atrain rhe .equi.ea?erisiryThere are rhree main types of intensifying screens:

l. Lead screensl. !2. Fluorescent (salt) scrcens.3. Fluoromerallicscreens.

closecontacr between screens and film is essenriar in order ro obtain sharp images. Screensmusr be kepr free from dusr.and scrarches, if rhis is not done they miy u"1*" o" in"radiographic image-especially in the case of fluorometallic una n,iores6.nir"i."ni",1.2 Lead screensLead screens consist of a rhin lead foil of uniform thickness, usually stuck onro a rhin basecard in rhe case of reusable screens, or sruck onto a thin sheer odpipi, *n." ,i.J *impre-packed film.L-ead screens inrensify-the image-by emirtijr) berl-radiarion (etecrons) when sruck.by x-rays:l ^s..1*u rays of sufficienr.energy Th.inreniliiaaaioa acron rs only achreved wrrh x-raysaoove approximately l2[lt! and gamma rays above similar energy ievels.

t^r,l-d-,t:l:r"r wilr also improve rhe radiographic image by panially filtering out scatrerr i td I a on '

Ly-:l::.9^,:.::l.are used: rh.e thickne-ss of the fronr screen must be marched ro lhe wavelensrh.,r raora.on berng used, so rhar it wilr pass rhe prinrary radiation while sropping ", ,nuir.,"orthe secondary radiation as possible.The screens are usually between 9.02 ryf and 0. t5 mnr rhick and are commonly borh rhes"anre-thtckness, e.g.9.]l,?5,mm; tnis avoiaitrre pioLi.'ii'.r"""ii"",ry r."irriig i dai,tfi.'i"i r,the screens rhe wrong *ay round!

]he lear screen

1gt5!ywn the effect of back scauered radiadon.

Lead screens are bliable and should be handled wirh care if buckling is to be avoided. IIthcfead screens are io be used more rhan once, ".g. in aoii"rr* as opposed o rollfilm orpre'packedfilm, rhey.become d.usty and should 6. r..qu.ntry dusred *irh a nne u.'ust. trscreens become roo dirrv or splashed wirh riquid, rhey may'be cleaned wirh cotion-wooldamped rvirh a weak deiergeni solurion. whr';';ri. ;;;";; become roo scrarched or dirrycausing the radiographic qria.liry to be impaireJ, in"y ,i,i,.iia be rcplaced bt;;;;;;;.'4.3 Fluorescent (salt) screensFluorescent screens are made up from micro crysrals of a suitable melalric sart. usuan:

dLu-ygJlls$glC applied ro a supponing rt i. u"li-.^ra.

,/ l.nese screens, when subjected to x-rays or gamma ravs, emit lisht radiarion ro which rhr^ t \

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%.<''/ r ',LJe 5Lrccrs' wnen suDJected to x-rays or gamma rays, emit light radiation to which the

0 filrn.is sensitive. This lilhr radiation it i" oli..i proponion to rhe received radiation an6' results in a large increasJof effecrive radiarion_-- ' ' -

I ()rhcr mcullic scrccns cxis! for less commoo applicarions.

:.:t:11:r Ildliuol has a longcr wavelcngth than thc primary bcam Ironr which it is dcrivc-d and is rhcrctbrc tcssf \ - n f l r : l I r r g : . iCc : r l sq Ap to *nd i x B .

' l \ F o r

Therc are two types of fluorescent screen:

l. High definition (fine grain) screens2. High speed or rapid s-reens

The intensification action of high speed screens is ar least twice thar of the high dcfinitionscreens.

A radiograph obtained u-sing fluorcsccnt scrcens will have lowcr definition compared to aradiograph ta-ken using lead screens or no screens, and rhe image produced hai a grainyappearunce due to the screens salt grains.Because of the resuking.loss of image quality, fluorescent screens are only used whereessential, to avoid excessively long exposurc times, e;g. on thick walled specimens.

4.4 Fluorometallic scieensFluorometallic screens are a combination of a sah screin and a Iead screen; they are madeup of from a base card, a lead layer, a salt layer (calcium tungsrare) and a thin protecrivelayer.

There is more than one type of fluorometallic scrcen:Type I -for x-rays up ro 300 kV.Type 2-for x-rays 300- 1000 kV, Ir 192.Type 3-for Co60.

Providing the correcr type of fluorometallic screen and film are used wirh rhe range ofradlatron belng u sed, substantial reducrions in exposure rime or kV can be achieved. Bedauselh:J:{.tll.r yill paniatly fikerout scatterradidtion, the image produced on the radiographwlll be better than one obtained using fluorescent screens, but ihe image will srill reiarn agrainy appearance due to the salt crys-tals.These screens are nor commonly used due to high cost. Their apptication is similar to thoseapplications where fluorescent icreens may be-used, i.e. on thii[ *" J.p""i-Lnr.-

-'

4.5 Comparison of intensifying screens

Screen t.vpe Orderof imagequali ty

Orderof speed

Intensificationfactorr

How intensificationis achieved

Lead I J 2-3 Bera panicles andcharacteristic x-ravs

Fluorescent 4 I 8- 15 Light radiation

Fluorometallic 3 .'5- 10 Light radiation

None 2 4 N/A N/A

I Thc inlensificadon factor rclates to the rcducdon in crposrrc dme, c.g. an inrcnsification facor of 3 willreduce cxposure from say six minutes to two minutcs. '

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RUANE & T P O'NEILL

S IMAGE FORMATION

When radiation passes.through ?n gbjTr ir is differentially absorbed dependins uDon rhethickness. and any.differing materiar densities. rt'";ai;d;;'d;utlil#;e'"]'iii" iiiii .ia.of the object wilr largely determine the nnu cr,.r""t"niu"l-or trre riaiog*'pt: -- -"' "-"

The pordons of rajl"iographic filrn which rec.eive sufficient quantities of actinic radiationr undergominutechanges.Thesechangesaresosmalltheyarei"'i'iur"ioir''-ffiioii"i'iur"when using conventional microscopes; this hidden iilAi; known as ti tareit inai'e.' fnelatentimagecanbedefinedasthehidd'enimag""",i"Ji?e."pr'i"i'r-"iLffi.i"i.radiation bur bcfore developmenr.

Therefore, radiation alone does not conven a radiographic film into a visible readable imeoaThe sequence of processes to artain a radiograpfri"-i?""i"'-" as follows:l' The slvql ialide grystars which have absorbd a sufficienr quantity of radiarion arepanially convened into metallic silver_-rhL is tf," i"r"nt ,.ug".z 1ia5l9"1ea crystals are

*^":":rgil]lr. tgeotrfgd.bt th:,errL; the developercompletely ccinvens the affecred crysrali inro'metallic'suver.3. The radiognph annn:^i1-f,r1"t upry aranceby fi.xation; the fixerremoves rhe unexposedand therefore undeveloped crystats.

J1. : '.--

6 FILM PROCESSING

6.1 GeneralFilm processing may be carried out manually or by using automadc film processors.Manual filrn orocessine rakes place in a darkroorn under the illuminarion of safeltphrs whichusually consist of ordiiarv tigit o"rus #iil;."r;;'d^. other corours for riiters exist,lnJ:*r::,*:

"hosen muit .i,it rigr,i oi;-*"""i1'""g,r,'*ii"r, does not derimenta'y affect

The darkoom should preferabry be divided into two sides, a dry side for roadins andunJoading of.cassenes ind a wei. side f". p;o.;;;;"g;;r,l i, !o tr,Jnlrii J" ".ii,ji!rn.aprior to devcloomenr. The *et siae oirne?;G;;;ii "rualry have five tanks airangedin the followin! sequence:l. Developer unk.? Stopbaih.or rinse ank.J. rlxer tank-4. Final wash tank.

: ,5. Wetring agent tank.when the exposed Frtrnhas bcen unloaded from its cassette, ir is placed inro afrane, or spira!It rrs a long (ilm, and placed into the devclofir.

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6.2 DeveloperDeveloper is usually supplied as.a riquid concenratc and is to bc d utcd wirh water ar a rariogovemed by the minufii:turers rnstrucrions, e.g. I pan developer to 4 pans warer.DeveloPj:r temperature should be -in accordance with the manufacturers recommendation s I : 4-vT^r_ry.:'-F-fiig", but is ryp.ically-20'tf:C. O"""foi-"ni,i.n" is again dependant upon the -_:,,manutacturers recommcndarions or specification; fli --uuL p.o"irsing a'eueiopin/time istypically bctwecn four and five minures. The time should bc raken from when rhe firm hrrsthe developer with a^suitable darlqoo.iii*.i. ii"i""lir""'it'r." rs in the developer ir is aeiraredtorapproximately 20 seconds and then ^g,,."a "pp.ii;;i;ii;;;;#fi.o;;#r"#,.r.Agitadon allows for fresh developer to ijow ovJr'the ntm ana prevents rhe possibiliry of

)

\]ctinic radiauon, in this contexL is rhar which wrllalfccr rhe film cmulsion, i.e. rorm a larcnr i.r*J'.

- - - - � - � . + 4 - . - - - . = - - - . - -

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RUANE&TPO'NEILL

bromide streaklnp,' agitation arso cuts down dcveropment time. The frames or spirars shouldY-'�,ap@ thelt-anks ro prevenrs any air uub'ulesiiitin" on the firm whiih c,n .ar,(.Y]ry?!{.fii1he. tanfs toprevents anyair setding oh the film whi-ch can causelight spots on the finished radi,ograph.Developer is made up as follows:

Constituents Action Chemicals in commonuse

Developingagent(s)

Reduces rhe exposed silver halidcgriuns to metallic silver.

Metol.Hydroquinone.Phenidone.

Accelerator

Preservative

A chcmical which gives - tat*reacrron which spceds upqevelopmenL

Borax.Sodium carbonate.Sodium hydroxide.

Prevents oxidation of the developer. Sodium sulphate.Restrainer

Sequesteringagent

Controls the level of developmentfogging.

Potassium bromide.

Prevents the formation of scale. Sodiumhexametaphosphatc.

ReptenishmentThe activiry of the dcveroper gradu_afly dccreascs with-use and age. Replenishment ensuesthat the acdviw of the developer *a rrt" a"""ioping ume requrrcd remains consranrtfuoughour rhe useful life of rh6 dJ"ld;:

-vlir!n'""pp.o*io,arely l mz of film has becndeveloped' about 400 "rr

I?:.1eri-;iii'r,rl"ii"i":l.ils to be added. Afrer conrinuousreplenishment the oualitvot the.image w'I be. affected and the developer will have to bechanged. A commirn euit*icJthe;ri"ii, #iiSl,lil:|.liiiffg time is when the replenisher addJexceeds

6J StopbathThe stopbath may be:

An acid stopbarh.. A water spray rinsc.

A fresh witei tank.

,t):_n:::,:ln::ent.rype of stopbath is an acid stopbath which is typically madc up of;ffi sstopstt'"'"actlJ["?it'"ai'J.p"11il.1ii,ilJi"""""r6p.,Films should be placed and agita.ted in the stopbatry'rinse urk for at reast l0 seconds; if rhisrs not done properly, the fixei will ,*" Uoo[.,i"Ju*rf rr*.6.4 Fixer

Fixer is supplied as a liquid conccntrare and is to be d uted with water, usuaflv at a rado ofi,l;:"flf;: ro 3 or 4 pans *ater (f"u";-;;i;";;;ilr";; iii.i riiiilii)f i'e,^, i,Fixation is the process *hi:[tf-9:. rhc undevelopcd silver halide crysrals andJtre., rhelt;fr|i;:"t

deviloped crystals, thereby producing ddiograpr,s or " diu'g-"orti. irlla"ur")

' 20 Fcb 92 t2

' !{tiirf . ,s�!fmq$!*....

RUANE&TPO,NEILL

The fixer conains chemica l< . c .h_^_ !

[*T:t!;",:ff:,f"::$1ffi 'Effi ffii.:H:n *:The films musr bc agiu

mlxs':tr"'ft #,ff [:l jxf #i:i:Ti"#:"T,:,:,"i:.i{J:J]f 'l,lr;;:r-,fi f iftiii:H:,"t," ff ff Hk t: :: :lt "i r *i ̂ 'ii', i.::^ ffil?,lflt 1?,'T ? ;fL:ill ",f iH tr::*:l*;.st*m.r*s[:l;it*i,,",U*H:ei j:i;..i{$jui";*:lm6.5 Final wash

ll=_:.p$_* washed preferabry in a rank withzu Jrrnutes. This removfrxineandremov", rh;i::3il 'oruut" siluJ-coiiii"lllrlfi'#n'llff"I#"J;Iff# l?t';ucen"surrciinttJ

- qrL rrxer whrch is an acid' Yeliow rog appears on firrns which have nor6.6 Wetting agent

f:tting agent reduces rhe surface rension of the water aP:,_q"u::',, utact spois oiiiil;:ff,HlT;.Xl':::::j::."rF i" even drying orrhe rlm;is to'be ailutJilil|i;.1':Tt*-s' wetdng agents arewarer. _,,rataradoorrpp,?,"i#iirl"r;"i,#*ffi:,rrJ;i:Jlffi["tra:iFilms are only dipped in and our of the wening agent.6.7 Drying rhe fitmInirially excess water is rcdrvinelauiner, oiiii. jiJi'TfYf^lg the films with a s

fi *i"H;i$Tfi ;?,..lo#"xafl ff "f ;?]ruffi ,f J.f.#Ji,fr..?,1ffi r#::iFjThe drving dme wilr denend on thc remperature, * "o"ir:igr,gd the-rerative humiditv of,T:;*

* Tvpical drving tir.r -" i5 ninii,JJn i'fi,"g ""binet, 45 minures in a &ying7 RADIOGRAPHIC QUALITY

7.1 GeneralRadiographic quality can bc discussed using threc main rerms:

):. ffil:ti*:i:;',",ora radiograph rerares its degree orbrackness.-

rtelds on " r.oiog*pilhit contrast is the degree of difference betwecn densiry

r. Definition _ RadioeIor densicy fields.

' aphic definition is the degree ofsharpness ar rhe boundaries

iflTi"f,UJ;i:ii:n1;:*^,riviry. sensitiviry is a term used to give an indication or'FL ^-- -

,'"5llf._._l*oSualitiesofar"g_,-o-q:?!i:i"ilymeasured:-d.1i_rlV"gasensitivity. Densiryi;.4;1."'"""t"gadensiromererandscnsiriviryis,niiru'.Ia'u'ng animagequariryindicaror

ffi:.*[f;*##s"f,#ffjff #ffij]irr,trff i*:lr^::

O20Fcb92

... l'.qt.rv. , r

RUANE & T P O'NEILL

7.2 Density

7.2.1 Generat :

The density of a radiograph relates its degree of blackness.A high densiry or dark area absorbs more right than a row density or light area. Thegreater the amount of black metalic sitve. g.iins lrcient in an -""'on u ,iJiogrulr,, rt "more light is absorbed and the denser rh;;;';;i;;.More radiation nasses rhrough the thinner sections of a specrmen, e.g. arcas where cracksor lack of fusibn are pr"sinq *,.i"?o;;;r;'il; i,irr ere.t"Eifih.*'rp ." ,i,.radiograph as dense areas.

7.2.2 Measuring density

P:::tjy-gi " p.*essed radiograph is measurcd using an insu-ument c a,ed. a densirometer,tnrs compares the incident fighi.with the transmitid righL ana e*preiies ,h";;;i;;. .logarithmic ratio. Incident'ligtrt is_rignf i.;;-ri.,-; ;i""*"r; traasmitted light is lighrransmined through a filrn whe*n the filfrr is on tti "ie*!r..

Densiry = Lngro incident lighttransmitted light

If the incident light was 316 times greater than the o:ansmiued light:

uensity = LoErc =I

Density - Logro 316

Density - 2.5

Note-: ̂[f the ransmined light was l,/lOthD = 2.0, l /1000th D =3.0eic

of incident tight D = I.0, if it was l/lOOth

Before use, densitometen shouldbe caribrared using a calibrated densiry strip-a stip,o-r.^lll.connining- known densities-on the samE viewer wtrich is to be used forrnterprcung the radiograph.The minimum densitv in the area of interest, i.e. the werd, requircd by specifications istypically betwecn l-jand 2.5- H";;;;rhill;;iAffis pracdcal to derermine whenthe area of intercst has manv rhickn*;."trgeli-"iiJ ,h#|i densiry changes-as is thecase wirh cenain ryoes of m.m.a-, wclds.- i"",hf;i,;;;;",he specification may specifythat the density is i6 be measurea m-eaia't'ei/a;.il;;i" "" werd reinforcemenrThe maximum density stated in a specificadon will typically bi 3.0 or 3.5.7.2.3 Lack of density_causes. Under exposure to radiation.. msutncrent developmenr rime.. uevetoper temperaiurc roo low.. Exnausted developer.. Inconecr developir.. Solurion of deveioper too weak.

,*"jf[tilHltc capable of whitc lighr inrcnsiries suiable for viewhg radiographs up to rhe maximum

o20Rbq2 l4

'"u'ftairo,*iri*,* '

7.2.4 Excessive density-causes. Over exposure ro radiation.. Excessive development time.. Developer- temperature too high.. Incorrect developer.. Solution ofdeveioper roo srong.

7.3 Radiographic con t rast7.3.1 GeneralRa4iographic contrast is the degree of difference betweenradiograph.

I ll a r li()giaph shows a wi(r(: rangc of toncs it is said ro havc *,ide ratitude-

when a radiograph conrains onry blacks and whites and no intermediate tones the conrrastis hrgft,' when onlv tones ofa simirar densiry exist thecont-rsr is t -, tr," op,i.r..r"i."iimay lie between ihese r*o e*r,e"'is, i1a.1d9l'.5g_r!931-d;tgffiil#iili;::If,-an application

,specificarion is not permirting any derected defects in rhe weldwharsoever. rhen rhe contrast should ider[y be a;higli ai possibre, i.e. trigt .onr.usii!ideal for detecting defecrs.

lf however, an aoolicarion specificarion permitted cenain defects, depending on rhedefects through thickness dimensions, as welr as r."gir,-*aloi*i;,h;ffi];';";l;'i;necessary ro have a ranse of tones on the radiograpi,s'io tnat itre ttrio;;ili;il;;;p;;of the defects and rhe hleighr or weld relntorcemenrs can be assessed,Therefore',ro gain. more. informarion about the through thickness dimensions of anydetecrs and rhe werd irserf. we need to have intermediaie lones, r.e. greys rn addition roblack and whites.

Note: We are assumins ,h",_]L:1"_g: rhickness changes or material densiry changespresent in order ro give Is densrry cnanges.The following chart shows rhe crireria which affect radiographic contrast:

!'

density fields on a

, r \ F a :l 5

i .;i

1 '

:

RUANE & Tpo,NErLL . '? . r , : . '

7.3.2 Measuring radiographic contrastRadiographic con'asr is nor usua'y measured excrusivcty; it is normalry assessedsubjectively, but coutd be measurcd 5y;;;;;;;';;,ep *edge type I.e.t..A wire type I.Q.I.-used to measurc sensitivity- primarily gives information abour rheradiographic contrasr, but rhe degree or a"i.niiion

'uiro govems the resurr.

7.3.3 Insuffi cient contrasr_causesRadiation wavelength too shon, i.e. kV/penetrating power too hish.

'i' over exposure to ridiarion, compensatei ro. uy sn?ftinJ ai",,r"io"o.n.n, ,i.... prolonged develoDmenr in ioo c6n "A;i;;i;. "*.uurtJaluXill

.,,,-Unsuitable or wrongly mixed developiInsufficient fixadonl

. Fogt see also Section 7.5.

7.3.4 Excessive contrast_causes. Radiation wavelengh too long_kV/penetrating power too low.. Incorrect develooei. prongly mixed ievelooer.. Under exposu.e, compensated for by a prolonged develoDer.

7.4 Definition

7.4.1 GeneralRadiographic definition is thedegree ofsharpnessat the boundaries of densit,v fields.There are many facrors thllqovem rhe final definition on a radiograph, including rhegeomery of rhe ser-uo during exposure.and the n rtn ivpe used. perfect definirion cannever be obtained due-to the e-xisti "." ori)"ittlii;e;h";1", ;";;;;;;;;h";;'";rr.7.4.2 Measuring radiographic definitionRadiographic definition is not usually measurcd exch,sively; it is normally dlsessedsubjectively, but could ue.eusr.eJ6! tJiri E3_Agl*e r.e.t..Atuplex ryp" I:QJ. is a rype III r.e.t. ,o 95 39[7,refen-ed ro ii a cgli. - io'A' ,, .^^",.,. ^r --:-- ^. ,,Tge q.uality indicators, also

:"ffiitltdm that or rrv-o Goarat. *;,.rinioir,..;;cl;'i;;l::r'l'iifi ;: il:':l,:*:iTi>iliry. The rotal image unsharpness, U. i; F;;;;;;' '" '^'

by:discernabiliry. The total ffi. u"rr,".p".ii,'iii

U,(nm)=/a6 :

where:

d is the widrh of rhe wirea is the spacing bctween thc two wires

Note: Type III I'e'r.s are praced in lhe cenre of thc film adjacent to the werd.

I

;l

OmFcbgZt 6

RUANE&TPO'NEILL

7.4.3 Poor defi nition-causes. Objecr ro film distance (o.f.d.) too Fcat.. Radiation source to film distance ro-o shon.. Dimensions of focal spot or gamma source too large.. KV roo high.. Vibration/movementduringexposure.. Poor contact between fikn and screens.: Salt screens. .6j. Coarse grained filrn.. Fog; see also Section 7.5.

7.4.4 Inherent (film) unsharpness

Ill=j.^l"rjlyn":: i: lh. unsharple.sl on a radiograph caused by sray erecronsL_T"ralI !.,o'n exposed.crystals which have affected- adjacenr cistals. Inherenrunsnarpness always exrsts, rrs magnirude depend.ingon grain iize, grain d.istribution andradlatron energy used; i( increases with a reducrion in wavelenethl

7.4.5 Geometric unsharpnessGeomeo-ic unsharpness or penumbra is rhe unsha.rpness on a radiograph caused by thegeomery of the radiation beam in rerarion ro rhe objecr being raaiogiaphJ."a irr. iirr"Penumbra a.lways exiss and borders all densiry fieids.

--' "

The dimensio-ns of the focal spor,or gamma source, objecr to film distance (o.f.d.) andfocal spor to film disrance 1f.f.d.;' att-affecr p*".6;.'-' "

To minimise penumbra we must adhere ro rhe following condirions:. The source or focal spot should be as small as possible.. O.f.d. should be as small as possible. F.f.d./s.f.d. should be as long as pracricable.

I Sourcc ro t' i lnr rtisuncc (s.ld.) if usinc rarnma ndiation.

:0 | .h .r: t 7

RUANE & T P O'NETLL

Penumbra size can be calculated by the following formula:

size of source x o .f .d,\renlunbraff.d. - o f.d.

The maximum penumbra allowed on radiographs is specifred in cenain standards. Inconractual situarions where the standards do-noi quote ina*i.num pi"r.uo ,"r*i, it "ymay be agreed wirh the clienr; a maximum penumbra of 0.25 mni i, orr.r, ur"J. -'-

The BS 29.10 doe.s not quore a _maximum penumbra value, but recommends that thepenumDra levels do not exceed the maximum levels specified for inherent unsharpness.The minimum f.f.d/s.f.d. chans in BS 2910 are'primarily U"i"O ."' o.",I-U*consideracions, i.e. if rhese chans are being adhered ro ihe penu-b." i, .o"iia'"i.Jio u.acceptable.

7.5 Fog

Fog is unwanted density on a radiograph and may be sub-divided into rhe folowingterms:.

9r9-V fog-often simply termed fog.. Yellow foe.' Dichroic f5e-qreenish corour by reflected righr. pink via rransmitted Iight.. Motrled foel

7.5.2 Causes of fog7.5.2.1 Grey fog. Accidennl eTpgsse to actinic radiation _ light, x-rays, gamma rays. When fogts caused bv lisht leaks, e.g. because of a failty cassitre] ir is oferi termea itgn

foe.. Scatter.. Unsuitable darlcroom lighting, e.g. wrong safelighrs, whire tighr enteringdarkroom.. Bad film storage.

7.5.2.2 Yettow fog. Insufficient final wash.. Exhausted fixer.. Prolonged development in badly oxidized developer.

7.5.2.3 Dichroic fog

: !,ofongeg development in exhausted developing barh.. rum stuck to anorher film in fixer.. Developing rank contaminared wirh fixer.

7.5.2.4 Mottled fog

: Slll badly stored, e.g. in damp surroundings.. l. rlm out of dare.

t .r i

O 20 Fcb 92 l 8

' ' I RUANE&TPO'I.TEILL

7.6 Artifacts

7.6.1 General

An anifact is a spurious indication on the radiographic imagc, e.g. a fault in or on thetrlm usually caused by mishandling or incorrect developing. An anifact may appear tobe a defect in the weld or parent materiat; an anifact may also mask a fault i-n the weld,therefore, ir is essential that anifacts should be avoided.

-

i'l7.6.2 Stat ic discharge

S tatic.discharge marks may occur when rhe film is pulled quickly from between theintensifying screens in a dry atmosphere. The appearance on the ridiograph is usuallylightning like, but ir may also be mottled.

7.6.3 Reticulat ion

Reticuladon is a ner like. smrcture appearing in thc emulsion due to ruprure caused byexcessive lemperarure differences between the processing tanks. k ii a rare anifaitnowadaysfoYo the flexible/plastic nature of modern day eirulsions.

7.6.4 Diffraction mottleDiffracrion motrle. may.occur in a weld area on a radiographic image because of rhe grainstrucrure.and grarn orienration of certain materials mitching the wavelengrh oi rheradiation in acenain way. Austenitic stainless steelsand aluminium welds are pinicularlysusceptable.

Diffraction motrle has rhe appearance of fine porosity throughout the weld area. [r mavbe reduced or eliminared by changing rhe wavelengih of ra-diation, i.e. increasing kVt,or by changing rhe radiarion angle by approximarel! 5..

7.6.5 Causes of ot her artifacts7.6.5.1 Light parches

Film was not agitaredlapped during development or fixation.. Film insufficienrly rinsed afier developmeni.. Drops of fixer fell onro filrn prior to dlveloomenr.. Mechanical demage to emuliion.. Impuriries be rwee-n screen and l-rlm.

7.6.5.2 Dark patches, lines or streaks. Drops of develo-per fallen onro film prior to development.. p-rogs of warer fa.llen onro film prioi ro development.. Mechanical damage ro emulsion after exposurc..' !low and uneven drying of firm, i.e. when there are still droplers of warer on rhe

Frlm.. Uneven drvine.. Scrarches on liad screens.' Bending of film after exposurc (usually berween two fingers causes dark crescenr

shaped marks).

7.6.5.3 tVhitish dcposit. Warer used ro make up processing solurions too hard.

: i

I DiffrJcrion mordc oftcn incrcasqs with a rcduction in kvl

. ' : ( ) t jch 9! l 9

RUANE&TPO'NEILL

7.7 Sensitivity

7.7.1 Generat

l.*^,:gl^"llriuiry., when used in its general sense, is an overail assessment of qualitywnlch relates to the radiographic technique's ability to detect fine defectS 0n aradiograph.

The sensirivity qssociated with a radiograph is direcrly affected by rhe radiosraphrccontrast and definition, therefore all thoie factors whic-h affect contrasr and definiiionwill also affect the sensitivity.

7.7.2 Measuring sensitivitySensitivity is measured by the.use of image quatiry indicators (l.e.Ls),also known as apenelramercrs- Therc are various types of t.e.I.i the type commonly used consiits-of::y:" ili" wires within I pl.a9tic. packaging. r-ni *irei are placed Eansversely acrossllg::'99"u *tngexamined during_exposrrre. The sensitiviryon theresukant ra,iioe.uol,rs then grven a numerical value by dividing the rhickness of ihe smallest *i." "isiu-tetntheradiograph -by rhe thickness oithe spec-imen in ttre atea ueing "iu,nrn"i;ih;i;;;"mu ltiplied by 100 in order to express theiesult as a percentage of ri" ,p;;i;;; ;i;i;k;;;;,.

SensiriviryVo = x 100

:+

The lowcr thc figure obtained, the higtrer the sensitiviry. [t must be nored however, thatthe obtained I.Qll. sensitivity'.raue ?""s noiiii.iiiv i.r.,. ro rhe minimum rhicknesschange or defeci size detectable uy ttri iaaiog.apnii'i"""r'l n iqu" ,r.a.BS 39'1\-lmage qualiry indicators is a standard which specifies three types of I.e.I.:

Type I -wire rype.Iype lt -step wedge/hole typc.Type Irl -!u.i{ex tiire type'for excrusively measuring definition; see Section7.4.2.

li:P-:-{9.4",e type I.Q.t.s ar.e placed adjaccnt to the wetd in the cenre of the film.r ne sensrtrvrrv is assessed in the same way as for wirc types excepr you use the horediamerer insteid of a wire thicxness.

Yill,l::*:"Ogon of duplex.wires, I.e.I.s are made of the same material2 as the specimenoerng examined and are available in a variety of thickness ranges.Technically; the besrposition to place an-I.e.I. is on the source side of the specimen, butforpractical reasons i.e.r.(s) "rdorten fr..ia_-;;;h;;i7;;d;;i;.G;;;;'#i;il'"*itne specimen..It may also b€ sta*d thit_they .ust be poiitioned in tr," -". ,r-n"i" ti"worstsensitivity.is expected.. A specificaiion retatirijit raaiogralhi" iesd;;'hd;olameter plpe welds may state:

"Fo11 pa.noramic exposurc at leastone I.e.l. must be present3, placed at the 6 o,clockpositio.n". Reason:-because this area is more susceltibre to back scatter from theqrarr I n a'l

I somctimes the minimum number of wires which have ro be visible on r}rc radiograph is spccilied insaad.2 Al0rough it is desirabrc for rhc let an-d *re.specimen o be of fre samc marcnar, il is nor arwavs oossible orpmcucabrc ro accom'rish due !o rrt1"1111"11i11i1r, F;;;J;r;ffi;s made fom auoved crehehs, rhe rQrmatcrial choscn should havc similar radiaLion absorptiory'transrirission proprues to fic test spccimen.3 BS 2910 calls for four lel's placcd ar Ute 3, 6, 9, and l2 o,clock positions.

thickness of specimen

O l0 l;cb 92 20

RUANE&TPO'NEILL

"For a.multip-le expc-sure.technique two I.e.r.s musr be used, one ar each end of thentm wlrnln z) mm oI lhe.dtagnosdc film length, with the th innest wire facing towardsthe outside". Reason: the -outside/end of ifilm on a multiple exposure sior is theleast sensitive area due to fade off.

7.7.3 Specific sensitivity terms

Tl9r" g" many specific terms. relating. to sensitivity which may be encounrered; rhefollowing terms are in accordance wirh BS 36g3-Terms usid in non-desrruuuetesting : Part3-Radiological flaw d.eteuion:

Contrast sensitivityThe densiry difference on a radiograph after processing, produced by a smalr changein specimen thickness.Note: It is usuarry expressed as a percentage ofthe toral specimen rhickness.Defect detection sensitivityln a radio€rap.h, the minimum_dimension of a specified defecr thar can be discemed,measured in rhe direcrion of rhe.primary radiarlon beam and usua y e*presseJ "s apercenrage of the specimen rhickness.

-

FIarv sensitivityThe minimum flaw 5126 dgls6lxble under specified conditions usually exoressed asa percenrage of rhe specimen rhickness. (see ilso defect drtrrrio,,t tliiiirrtii.Image quatity indicator sensitivityThe dimension in the direction of the radiation of the rhinnesr step-wirh-hole or wirethar can be clearry idenrified, expressed as a percenrage of rrie rhict<nis.s of rnematerial under eximrnarron.Notc: The duprex;wire image quality indicator is baied on a different principre andglves a measure of unsharpness only.Th ick ness sens i ti vi t_vThe smallest change in rhickness which can be detected by radiography, usua'yexpressed as a percenrage of the specimen thickness.

8 RADIOGRAPHIC TECHNIQ UES8.1 General

,/

l:^*g_lill" techniques for wetds on ,,".Y are lisrcd in BS 2910_R adio,raDttice-ramrltarnn ot rtlsto, wgrdc! circwnferenda! buu joints itt srccT 'and

BS 2600-Rad[ographic exantination of fiio'n-*iiili butt ioints in steer.The radiographic examination of.a prate werd wourd result in a single walr, singrc imagellllTtqu" being used; however, rheie are essentially four *ays to .iaiograptr a'ginn/f,pewetd:

l. Single wall, single image (SWSt)-film inside, source oursrde.t

*gf .::ll'-s11qte ilage (swsl)-film outside' source rnside (internal exposure.usually ru

panoranric ).

3r?:ort""*i""' single image (DwSI)-film outside, source ourside (excernal

.o.:o""orf*;""' double image (DwDl)-film outside' source outside (elliptical

J .

4 .

I | , \ t r o: 2 l

RUANE&TPO'NEILL

;:r.

The panoramic tcchnique is usually the prefcrred rechnique if the equipmcnt is avaitabte,access permits and the minimum f.f.d. reluirements -i .n.t. This is due ro rhe fact rhat rheentlre weld can be examined in one exposure, and girod sensitivity can be achieved becauseof a lower level of scatter and kv in "oo'p*iton-fiih i doubte walred exoosure.

8.2 SWSI: source outside, film insideFor srandard exposures, the radiation beam is positioned at normar incidcnce to the werdface and film paising through the ""n"" oiir,";;il:""

l!i.' tegtliqqe is primariry intended for 100 mm diameter pipe werds and above, whereaccess to the intemal weld area permits. The main disadvaniales of ttris tiitrnique'are rhenumber of exposures reouired dde to a_large amounr oilaoe offi";i ih;;;;;;u'ip""ts orpositioning rhe radiation source at sufficie"nr r.i.a. *r,* a".n";;il'i;#;i;lrl.iuj,rr. r,is a technique more suited to large.diameter pipei, uissets and ranks where the curvarure iscloser to a flat plare and therefori tras a rea u'cfi iire-cr'on rhe amount of fade off.The required minimum number.of exposures to cover the full circumference of the welddepends on the wall thickness, pipe diimeter ana i].J*.r.a.; see table i; BS 2910:"-8.3 SWSI: (panoramic) source inside, film outsideFor standard exposures, the radiation beam is positioned at normal incidence to the weldface and fitm pissing through the c"nte orlli" *"ial *,tt' equal f.f.d./s.f.d. around rhecircumference.- This-rechniq-ue cannot be used if the mrnimum f.f.d./s.f.d. requiremenrscannot be mer.

8.4 DWSI

This technique is commonly applied to all wclds where the use of a panoramic technique isnot possible or practicable,'e.g.-on small diameter pipe welds. . - - -- ---""'!

F_or srandard, exposurcs on any- diameter of pipe weld, the radiation beam is posirioned arapproximarety 85'ro rhe weld'face and film.'\iirtr rhisiicrrnique'il;ff;;t;;Un_l"nno,be posirioned at normar incidence ro rhe weld ponion u"-ing .;;i";-6;;;;r. ,-r.'"'*""ia onthe radiation source side will superimpos";;;iih" F;il,ffi;Jj'i"*rtiii:i" ,"irllituur"radiograph. This problem mainty ap'pties;t;; ;:i;;'*'-."v rubes; the x-ray tube must bemoved approximaiely. 60 *rn. ro it "'siai of rh; ;-ld:r; rhe cenrral line of the x_rav be amsnoots pasr the tube side weld resurting in a diagnosri--;.!;;il"?;ilrio" *"rd 'c-"

must also be raken ro ensure rhat the number rape on the source side do€s not interfere withthe image,.i.e. shoor through rrom rrre ofpositJiii" "i t" werd to that which rhe numbertape is posirioned.

The required minimum numberof exposures !o cover the fu

circumference of the welddepends on the walt thickness, pip. Jii-"ilii"i;i.il ;" table in BS 2910.8.5 DWDI

This technique is only applied to welds on pipe or finings 90 mm diameter or below.The film ca-ssetres are not benr ar. ound the pipe circumfercnce unlike with the orhertechniques; flar.cassettes are used-which "t. ,r,iurjiy "}iri"i to rhe weld to record an e ipticarlruqir pytposelv produced bv ofrsetting *refocat'spoi ai leasr one nrit oitlnlii.a-_"Fro.the eltrprical inrage of rhe weld, rhe tu& siae *itiis lnt"rp.et.d as well as rhe firm sideweld-

I ::irg.:flhree expos ures are usualry.required, offser by 120' to each other: this resultslx119t11o,tj'* t"rerprerabre areas on rhe raariogiaptr *trictriiouta couer rn. rurr.iit;;i;;;"".or tne weld.

I:l::,3".^'llll bore pipework, it is sometimes permitred by specification or crient for rheraorarron to pass rhrough rhe cenrre of the weld'ai n",,""r i'^.io*t" l"iii. 'pip";'inli'*irr

produce a radiograph wirh rhe rube side *"ta sup"rr-poi"d over rhe film side weld.

O I Apr92 22

:'*fi{r.*RUANE & T P O'NEILL

8.6 sandwich rechnique L"ffi /'/t

T.h:::(:.i:!.,,:chnique is a radiographic techniqui sometimes used in order to save time.rt may D€ used on comDonenrs where ihere are su6stantiar ttriitness aiieil";;;;;;;i";';.densirvon a singre radibgraph to be o"t oiip".ilr"uii"" "" "iir,iiiti,hi.;k;;;il;,;; ,;;'";",side or both. Rarher rhan ci.ry our two seferate shots at different eip.ii,i*, i"l .".rr'*iaor position, cassetres mav be-loaded *i*ir*o-nf-i. i*o raaiog.Jphs ;'i;;;;;Lproduced-one for rhe thick side ana tr,. oir,"r-ro. tt Jininn", siae-rfi;;"t;iii;;;;;;"produced in a single exposure. i,jThe filrns are usuallv of different

!pudsl.9.g.a fine grained film Ioaded wirh a very fineqrained rr.lqr' howevir, rhe same "ii..t *hi L piJ-u;Ji;v plil;; l*i i.,..","i(i.r",than usual, betwssn rwo f i lms of rhe same,o""d. ' - ---- -

8.7 Parallax technique

,r!::y:!!y.r:!iographic techniquer may be.used to determine the depth of defecrs belowrnesunaceof a comDonen r: this may be uiefur to know for reparr purposes. Itisatechnique::i::q!!:",bl.,ro rhick specimens,-e.g. over 50 ,"-, il; ;; rarely used because ulrrasonicteshng can usualry give rhe same inforiradon quictei ana at a lower cost.The technique is used afrer a defect has arreadybeen detected by conventional merhods. Theprocedure involves rhe oracement ofa tead-mirker on trr"iJJ."e ,iae of a specimen,s surfaceclose ro the plan view'rocarion of rhe ;"f"*-i;;;;-p;res are made, each at half rhel#3 tr!?:1:";,and

offset to each other in ora", to flJorc" a aouui"1.a!. "i ir,.l"raThe following criteria are used ro carcurarcr the distance of the dcfecr from the firm:

Gap berween defecr imaees.!1p. betwee n lead marke"r images.f . r .o. /s. t .d.Specimen rh ickness.Dimension of shifr berween source of radiadon.

9 DETERMINATION OF EXPOSURE9.1 GeneralMany.factors govern rhe final qualirys of a radiographic image; all these facrors must beconsidered and conrolred in ord'er ro'meet *irh a ipeiiEcaiiJ,iii.!'i,r*-.!"-s-ry'

J "'uJr

T'he time ro use for an exDos-ure is onry one factor to consider for an exposure, but it is thisfac,torwhich changesmosrofren. cr'n;;;;p;s;;ilriirL u,u"ilycarcurated from speciarslrde rules' usually refened rc as ganma cxposure calculators, these take into consideiarronthe followins:

a.b.

d.

a.b.c.d.e.f.

Film densiq' ro be achieved.Source lype.Acriviry of source.Film speed.Jource ro f i lm distance.Material ryoe.Marerial rhickness.

I Thc parallax tcchniquc is somcdmcs (crcncd to as thc tube shift method ethcn anx-ray rubc is uscrJ.: A formula or a spccial graph ma, bc uscd lo dctcrminc defcct dcpth.J Quality is rcfcring to dcnsiry. conuasr and dcllnirion.

i" l0 ljch 92! 5

RUAIVE & T P O'NEILL

rf 'When using x-ray equipment, the determination of exposure is less straightforward' This is

) because the wavelength -o j"i""iiiv-.r rad-iation may be adiusted, and different machines

I produce differenr quantities *i+iiii"t of *-radiati6n everi though they may _be- o. perated

I bn r-h" ,uln" punel ierdngs. fne f6tto*ing methods are used to determine correct eKposures

I when using x-ray equipment:"

". By refercnce to previous exposure records'b. Bv trial and error -test shots 'c. A-combination of the above' 'o,:d, By using exPosure charts.

.2 Considerations for exPosures

9.2.1 Wavelength of radiation

The wavelength of radiation used will affect the densiry' contrast and definition of a

radiographic image.

X-ray equipment-Thc lower the kV used to penetrate tne 1ne9r^ryi',!!:Igl"-t *"'

G tni "o'nuitt, but enough kV must bc used to keep the exposurc trme reasonaDle'

Gamma isotopes-Different radioactive isotopes produce different wavelengths of

i"i.",^-r.aiiii5" ".g. F"oo'i."a""", ,t,on". wa'nelengrh radiation than Irl92 and is

rherefore more p"n"ouung,"U.i, iraJiognpfr proAuced orithe same specimen using Co60will have lowei connast and definition'

9.2.2 Intensity of radiation and expo3ure time

Theintensityoftheradiat ionreachingtheit lmandexposuretimewil laffectthedensityof the image'.

Radiation intensity and exposure ti4" 9t9 related' Exposure time is proportional to the

i;;;iit .i;;di"tion; this ielationship is known as rhe reciprociry law:

Exposure = dme x intensiry

X-ray equipment-If you had an exposure of say 4 minutes and 3 mA' then 4 x 3 = 12'

ih;id _y;"

would be'using iz -elrnin,. you'could also use 3 minutes and 4 mA to

sive vou rhe same "rnoun, of i*potut" because 3 x 4 = 12' or I minute 12 mA'

T'."ri I r j.'"riiiit 'i"io iita, z-;Z = 12 etc.; all these give vou the same amount ofexposure.

ThehigherthemAsetongontheconEolpanel,. the'greatertheintensityofradiat ion;;;;A;-;d tf,.r.ior" tle aarter ttre imige witt bi, unless the time is reduced to

compensate.

Gamma isotopes-If you had an- exposurc of say 5 mhltes using an .isotope with an

""iir-i-tv "i +iiti"s, the; 5 x 4 = 20, therefore you-would be using 20 Ci-mins'

The hisher the acrivjry of rhe rsotope used, the greater the intensity of radiation produced'

;a if;;i;-,he dar'ker rhe imagl will be, unless rhe rime is reduccd to compensale.

9.2.3 X-ray equipment

The intensity of radiadon (govemed by mA) and quality of radiation (go.rerned by kV)

can6;;ff";ilby,r'iir..ii. circuit oithe equipment being used'. The,kV ang 11,1?be on the same pinel setting, but the radiation intensity and wavelengths can vary trom

one set to another.

-P*d,f

\0h

\.!cF\..g

{gIg

*\

.rrij

q

(

tI\

(

I Remembcr tlrat density affccs conrrast, and conra$ affccs sensitivity.

' Flb ql 24

'. 1 RUANE&TPO'NEILL

Filter types and thicknesses also differ between x-ray tubes. Filters are used to cut out. secondary radiation to provide a more homogencous x-ray beam with lower resultant'

scatter levels. Filters affect the exposure time, e.g. an x-ray tube with a ttrick fitter wiiirequire more exposure than an x-riy tube with a thinner filier.

9.2.4 Type of fitm

The higher the speed of the film, the denser the image compared to thar of a slow filmat the same exposure. Howsygl, the radiograph's defi-nition for a slow film ar the Sorrectexposure will bc berrer rhan rhat for a fast-fitm at the correcr exDosure.

9.2.5 Intensifying screens

Usirg intensifying. screens reduces the exposure required to artain the required densiry,but fluorescent and fluorometallic screens have an adverse affect on the definition of theradiographic image.

9.2.6 F.f.d./s.f.d

The greater the f.f.d./s.f.d. rhe smaller the penumbra, therefore the better the radiographicdefinition. But, x-rays and gamma rays obey rhe inverse square law. Thi inverse squarelaw states:

"At twice the distance from the source, the same radiarion covers four rimes rhe areabur the intensity of radiation is four times less. At four times the distance from rhesource the same radiation covers sixteen times rhe area but the inrensity of rheradiadon is sixteen rimes less, etc.,'.

Therefore, with regard to exposure, rhe greater the f.f.d./s.f.d. the greater the exposureshould be ro at tain a given dinsiry.

The inverse square law can be shown mathematicalry in relation to intensiry:

I I D221 2 D t 7

/ = intensiwD = distanie

The following formula, based on the inverse square law, can be used to derermine newexposures when the f.f.d./s.f.d. changes:

New Exposure -Nev'; Distance2 x old Exposure

OId Distance2

9.2.7 Object being radiographedThe radiation absorption and transmission characteristics ofa matcrial depcnds upon irthickness, densiry ind aromic mass. rnis wirr-lrima;ii;;;;.iliaring ioo,eirequ ired.

9.2.8 processing the filmTh.edensiry, contrast and definition ofa radiograph are affecred by rhe type, remperarure,agitation and time in the developer. The develbpmenr pro..., lnouli'nor be adlustedoutside a. specifications req-uirements in order rd co-pJntute ror incorreir exposures,i,e. ro adjust the density oi a r:rdiograph, rhe exposrjre should be changed;'not rhedeveloping process.

e | 4p .92 ! )

RUaNE&t.pO'trgrr r

93 Exposurc cha1(s

Exposurcchans provide the cxposurc condirions for a given rhickness of marerial using x _raycqulpmcnr. An exposure chan will show rhc cxpoiure ro use rn mA_min for a clrosenspecimen rhickness and kV in order ro arrain rne dinsiry thar rhe chan is based on.Exposurc chans are drawn up from preliminary chans made up from cxposures usingdifferenr kilovolragcs on slep wedges. ,r.Thc vcnical scale on ar exposurc chan is rogarithmic and rhe horizonral scare is a'rh-eti..Each chan must show rlrc variables ro which rhc chan is applicablc ro:

a. Type of x-ray ser.b. Film densirv-c. Film type.

-

d- Intensifyingscreense. Focus to Frlrn distancc.f . Developme nt condl r ions.E. Marerial resrcd.

| 2 ( ' ! , { o , r a r d o ; f , o , - 2 c . . 4 ( , -"J(, ia, r. . it r t ;

l r i

II

I

I

I

t t i

t i, z

) !

I

({

t

0 . {

I

I

OZrFcb92

t. 1t

: ' l -1CIt , : -S5

' ' av' 59 1' ' Q

(:.-t LL I h=?i ls )

26

RUANE&TPO'NEILL

9.4 Guideline exposures using x-raysThe following chan shows,guiderine x-ray exposurcs bn standard walr thickncss A. p.l. pipesusing fine grain film with lead screens.

Technique(BS 2910)

Dia. (mm) Time (min) mA kv

I3 DWDI* 50 t . ) 5 20013 DWSI r00 l . l 5 ) 16513 DWSI 300 2.5 5 220I3 DWSI 450 4.75 5 2307 SWSr 450 1 . 1 5 5 t75

13 DWSI 600 5 2457 SWSI 600 t ; 7 5 )

13 DWSI 900 ) 5 2707 SWSI 900 J ) 195

13 DWSI 1050 t2 3007 SWSI r050 J . ) 5 2t0

* Focus to film disrance = 650 mm.

II

e :0 Fcb 92 27

RUANE&TPO'NEILL

APPENDTX A DETERMINATIoN oF FoCAL sPoT SIZEThe focal spot size of x-ray *.f.^:ll.:_,ts_" Ce over a.peri6d of time. To derermine rhe size ofrne rocal spor, e'9. for penumbra carcuradon-s, rn" rorr'c,*iii procedure may bc adopred.t'

ii:::t:lg l!:"1'tP:.?:iTlelv 4 mmrhick conraining a small hote abour 0.25 mmoramerer, exacdy hatf way berween rhe focal spoi-una ;r"dt";;;;; fi;:. " -"

2. Expose-th" "*oorT:.r"fplld.plt .*c"sriu" otherwise the image wiil be blurrec.fll;imaee

on the firm wilr be rhe size of rhefoca]'spor ptus rwice tie diamereiof the3-

o"$illi"_,ll,lTlj:9_1:t* by measuring the rotar diameter of the imase and rhen

O 20 l;cb 92 1r

'jid!ffiS..,.RUANE&TPO'NETLL @

APPENDTX C CHARACTERISTIC CURVES OF FILMSA characterisdc curve is a cT,ve on a graph.produced .for

a panicular film which shows therelationship between differenr exposurci aiplira -a tt " ..."fring densities.

l",ly#ifiXTilJ.":ill show that the densiry does not always vary in the same proponion

A curve is produced bv aoolviro.u.roi,n"iu, i^"-il#r;l"#JXid:,ffiTtf:T;ffiilT:iX"".fi,Hi,il,i:r,H1?iiiif;S,1,:ithe corresponding exposures. Borh the ";;.1;;"d;;"'i,y.1 "no nor,.onrar axis (exposure)1:t^"]tbrFd in a logari-rhmic scale.(log,oE); thir--",iil'ir',n" mosr pracrrcar merhod for rheffiu,1d.1nt"rpr"tadon of a curve. when ihepoinrs obiaineJ rt. .,nr""a'tog.it.i u.r"iJ".il -Pr uquueo.

If characterisdc curves of various ltrns yep superimposed on onc graph, ir wi, bc seen rharthe faster films lie closer ro the lefr venicai aiil,-b#;r;*f*rer firms attain densiry ar rowerexposures. Therefore.itshourdteappreciatedtn"iiiiiprriiii"roobtain ririitiiri'inr"ir^trom the characterisoc curves or ttlms-Thc* highestTt/rn conrrast of a given film ries on the straight litte portionof irs characterisnccurve, this indicares rhe densiruian!e . *-k;ii-h;;;iui'oJi,i,nun,' .onrasr. Arso, rhe sreeper.he gradie of the srraight line pofrion tl.,e t igfrer ifre

'nirn J8ntrur,.

O 20 Fcb 92 30