Isaac Einav International Atomic Energy Agency, Wagramerstrasse 5, P.O. Box 100, 1400 Vienna, Austria

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1 Radiogaphic Evaluation of Coosion and Deposits: An IAEA Co-odinated Reseach Poject 3 d PAN-AMERICAN CONFERENCE FOR NON DESTRUCTIVE TESTING PANNDT 057 John Zinhelt Canspec Goup Inc., 2190 Spees Road, Oakville, Ontaio L6L 2X8, Canada Jzinhelt@canspec.com Isaac Einav Intenational Atomic Enegy Agency, Wagamestasse 5, P.O. Box 100, 1400 Vienna, Austia I.Einav@iaea.og Silvia Infanzón Uuguayan Society fo NDT (AENDUR), Plaza Independencia 812 p2., Montevideo, Uuguay sinfanzon@ancap.com.uy Abstact: The pinciple of coosion measuement/monitoing by means of tangential film-based adiogaphy is aleady known. Most of this expeience, howeve, is limited to qualitative detemination of intenal defects. The ability to eliably measue emaining wall thickness in pipes has not yet been established. Based on this fact, the Intenational Atomic Enegy Agency oganized a Co-odinated Reseach Poject binging togethe eleven Membe States to study validation of potocols fo coosion and deposits detemination in small diamete pipes by adiogaphy. The geneal scope of the poject coveed adiogaphic measuement of coosion and deposits in staight and bent small diamete pipes made of cabon o stainless steels cooded/eoded on the oute o inne sufaces with o without insulation. Duing the execution of the poject, expeimental wok was caied out by laboatoies in the paticipating counties between 1997 and The poject poduced a daft IAEA Tecdoc and a daft ISO standad coveing this subject. Based on the esults of this poject, a new poject was established to extend the wok to lage diamete pipe, and twelve counties wee invited to paticipate. Fom the Ameicas, the paticipants ae Canada and Uuguay. It is expected to define the limits of detection fo each adiation souce using the tangential method and to exploe the double wall technique beyond this limits. This pape summaizes the esults of the fist poject, and discusses the scope and expected esults fom the cuent activity. Keywods: adiogaphy, coosion, pipelines 1. Intoduction The Intenational Atomic Enegy Agency (IAEA) pomotes the industial applications of adiation technology which include Non-Destuctive Testing (NDT) unde its vaious pogammes. One of the ways fo pomoting this technology is though coodinated eseach pogammes (CRPs) and eseach contacts. These ae undetaken keeping in view the cuent status of the technology and the need fo undetaking some eseach. Such eseach contacts and ageements ae woked out between the Agency and univesities, colleges, eseach centes, laboatoies and othe institutions in Membe States. Pipe is a common featue in industies. It povides the most economical, safe and efficient way of tanspoting chemicals in the fom of liquids and gases fom one point to anothe. Howeve, pipe expeiences degadation with time which if not detected might ceate poblems such as leaks and busts which finally can lead to catastophe. Coosion, eosion, deposits and pipe blockage ae some of the possible causes fo this. Fo yeas, many testing methods eithe destuctive o non-destuctive in natue wee developed and applied on pipe to ensue integity and eliability. Of many paametes, pipe wall thickness is consideed as one of the most impotant to be monitoed and measued with a high degee of accuacy. Up to now, appeciable R & D effots have been made to investigate this aspect. Measuement of wall thickness on long pipelines is accomplished with a numbe of established systems such as ultasonic and eddy cuent intelligent pigs. Howeve, fo plant piping, the existence of many bends and a vaiety of pipe diametes, some having insulation cove, do not allow the use of these systems. A new method, pefeably non-destuctive in natue, is equied to pecisely pefom this measuement whose data will be used as a basis fo detemining whethe o not the pipes need to be eplaced. Theoetically, it is believed that adiogaphic method would be able to pefom this function. It has the potential to be used to pefom inspection without the need of costly emoval of insulation mateial duing opeation of the plant. Futhemoe, it offes an additional advantage of being capable to pefom measuement in high tempeatue envionments. The pinciples of coosion measuement/monitoing by means of tangential film-based adiogaphy ae aleady known. Most of this expeience, howeve, is limited to qualitative detemination of intenal defects. The ability to eliably measue emaining wall thickness in pipes has not yet been established and no standad is available. It was based on these facts that an effot was undetaken by the Agency togethe with some Membe States to og anize a CRP on validation of potocols fo coosion and deposits detemination in small diamete pipes by adiogaphy (CORDEP). Membe States involved in this thee yeas poject wee Algeia, China, Costa Rica, Fance,

2 India, Koea, Malaysia, Si Lanka, Syia, Tunisia and Tukey. The geneal scope of the CRP coveed adiogaphic measuement of coosion and deposits in staight and bent small diamete pipes made of cabon o stainless steels cooded/eoded on the oute o inne sufaces with o without insulation. The esults of vaious paticipating laboatoies wee eviewed and compiled. These ae quite encouaging and demonstate the capability of the adiogaphic technique fo coosion detection and measuement. A Technical Document (TECDOC) and an ISO daft wee pepaed and ae unde evision. Encouaged by the esults of pevious CRP on small diamete pipes, a new CRP fo the lage diamete pipes has been initiated to extend the esults to lage diametes. The paticipating laboatoies this time ae fom Algeia, Canada, Gemany, Hungay, India, Ian, Malaysia, Pakistan, Romania, Syia, Tukey and Uuguay. 2. Scope of CRP on Radiogaphic Evaluation of Coosion and Deposits in Lage Diamete Pipes The scope of this CRP includes the evaluation of adiogaphic techniques (I192, Se75, Co60 souces and x-ays) to evaluate atificial defects and simulated o natual coosion attack on cabon steel and stainless steel piping fom 6 inches in diamete (168 mm) up to 20 inches (508 mm) with and without insulation. The majo objective is to define the limits of detection fo each adiation souce using the tangential method. Intenal and extenal defects will be included in the expeimental pogamme. Film and nonfilm detection will be consideed. The double wall technique will be futhe exploed fo application to the pipe sizes in this ange. Results will be veified by othe methods. A futhe TECDOC is poposed based on the esults of this CRP and the ISO Daft Poposal will be extended to include the lage diametes. 3. Lessons fom pevious CRP in Small Diamete Pipes The Co-odinated Reseach Pogamme (CRP) of the IAEA on Validation of Potocols fo Coosion and Deposit Evaluation in Pipes by Radiogaphy aimed at developing potocols and instuctions fo identification and measuement of the coosion attack and deposits in pipes in industial installations duing opeation (on-line and maintenance). The CRP addessed the needs of end-uses in tems of developing eliable and appopiate NDT measuement potocols which should efe to geneal equiements of intenational standads, (e.g. ISO 5579 RT basic ules, ISO 1160/3 RT cicumfeential weld in pipes, etc.) with full implementation of ecognised quality assuance methodologies. The activities of the CRP wee implemented in the thee goups. Each goup caied out the Round-Robin Tests in ode to compae the measuement esults to detemine the optimum test paametes. The geneal scope of the CRP coveed adiogaphic measuements of coosion and deposits in up to 6 staight pipes and bends made of cabon o stainless steel cooded/eoded on the oute o/and inne suface without insulation o having themal o/and bituminous insulation coveing the oute diamete of pipe, some of them with deposit o sediments inside the pipe woking in powe secto, in petoleum and gas industy, in wate installations. Film based tangential adiogaphy and double wall double image technique was used as the basic method and film density measuement technique used as an altenative o complementay method. The esults of adiogaphic testing wee veified by ultasonic measuements and destuctive testing when appopiate. Results obtained by all the counties fo all pipes in thei espective goups wee discussed in a joint meeting. Evaluation was done consideing the success ate in detection of defects and finding thei natue as well as the minimum emaining wall thickness. Thickness loss caused by eosion/coosion phenomena was measue d with a maximum deviation of 1.5 mm (fo two pieces) and 1 mm maximum fo the othes (25 pieces) The best accuacy achieved fo thickness loss measuement was 0.5 mm. The following conclusions wee dawn fom the CRP s wok: Tangential adiogaphy and density measuement techniques ae complementay methods. Howeve fo insulated pipes only tangential adiogaphy is ecommended, since the density measuement method equies complicated simulations. It is expected that the wall thinning due to unifom coosion is iegula in the pipe s coss section, so the density measuement method is not ecommended, because this method give only the aveage wall thickness. Fo detemination of the depth of pits, the density measuement method is ecommended as limited to the small diamete pipes (6 inches). Tangential adiogaphy is a moe time consuming method fo pit depth measuement, because it is difficult to get the tangential position of pit, thus equiing a lage numbe of shots. In the density measuement method, use of low enegy is advisable to get a high contast. It is impotant to locate the pit (local coosion aea) coectly. It should lie on film side duing exposue to pevent an undeestimation of its depth. In the tangential adiogaphy the maximu m penetation thickness of pipe wall has to be consideed fo the enegy selection of x-ays. To pevent the bun-off in outside extemity of the pipe, a filtation is necessay in ode to cut the low enegy components of x-ay beam. If available I-192 isotope is ecommended instead of x-ay to get a bette definition in tangential technique. Low speed films ae ecommended especially fo density measuement technique. Fo tangential technique, the speed of film is not vey impotant. A lead-intensifying sceen shall be used in close contact with films. A lead plate shall also be used behind the film to potect against backscatteing.

3 The dimensions of pipe wall o pit can be detemined by scanning the adiogaph with scanning micodensitomete. Othe tools, such as optical devices o ule, may also be used to dimension of the image. In the density measuement method the pit depth is detemined fom density-thickness efeence cuve. The accuacy of the technique is also depending on measuement conditions. Using the film density as high as possible is advisable fo bette definition measuement. Detemination of deposit in pipes, which ae filled with fluids (opeational pipes), is esticted because of small density diffeence between deposits and the fluids. 4. Theoetical aspects elated to adiogaphic pipe inspection 4.1. Intoduction to adiogaphy Radiation souces Common adiation souces used fo NDT ae X-ay between 30kV and 450 kv and gamma ay souces (adioactive isotopes such as Iidium-192, Cobalt -60, Thulium-170 o Selenium-75. All ae examples of electomagnetic adiation. These two types of adiation diffe only in thei wavelength and the way they ae poduced. Gamma ays ae emitted duing the disintegation of adio -active atomic nuclei. Unlike x-ays, the enegy of gamma adiation souces cannot be alteed. It depends upon the natue of adioactive souce and is fixed fo a paticula souce. The intensity is also not contollable, since it is impossible to alte the a te of disintegation of a adioactive gamma souces Radiation absoption in mateials When x-ays o Gamma ays pass though the specimen the intensity educes due to attenuation of the ays. The intensity of the ays coming out of the specimen is given by: I = I o e -µt (1) Whee: I = Intensity of the tansmitted adiation I o = Intensity of incident adiation µ = Linea absoption coefficient of the mateial though which adiation passes. It depends on enegy of adiation and atomic numbe of mateial. t = Thickness of specimen in adiation diection The above equation is tue fo naow beam geomety (vey good beam collimation) usually not encounteed in pactical applications. But pactically besides the pimay adiation also scatteed adiation exposes the film. This additionally exposue (additionally film blackening) can be consideed fo example by an additionally build-up facto. This is defined as: I = B I o e -µt (2) Whee B is called the Build-up Facto, consideing the contibution of the scatteed adiation. But this concept implies a constant scatteing backgound like it is valid fo flat plates and weld inspection. This concept is not applicable to the pipe inspection with it vey lage ange of penetated wall thicknesses. The absoption coefficient µ is connected with half value laye (HVL) by a elationship: µ = / HVL (3) Fo pactical puposes, the half value laye and tenth value laye would be geat advantage fo calculations. Both values µ and HVL depend on the mateial and the enegy ange used at the RT inspection Geometical unshapness X-ay tubes and adioactive souces always poduce a cetain isometic unshapness because of the finite dimensions of the focus o souce. The value of geometic shapness (Ug) is given by following equation : Ug d t = (4) SFD - t Whee d is the size of the souce; t is the wall thickness of the object; SFD is the souce to film distance. It is desiable to keep Ug to minimum in ode to detect fine defects.

4 Films and detectos Radiogaphic films ae coated with sensitive emulsion of silve bomide on both sides of the cellulose tiacetate o polyeste base. The size of silve bomide paticles detemines the speed of the film. Fast films save exposue time but give lesse esolution than the slow films. Fo the x-ay enegies highe than about 120 kv, film is used in conjunction with the foils of lead called intensifying sceens. These sceens impoves the x-ay absoption and esult in a highe signal-to-noise-atio at the same exposue time. They also pevent scatteed adiation with low enegy eaching the film, impoving contast. In moden day adiogaphic film is quickly getting eplaced by non-film type of adiat ion detectos. Thee is a wide ange of such detectos fom simplest fluoescent sceen to linea diode aay. All these pemit on-line inspection and hence such method is called Real Time Radiogaphy (RTR). Most of them ae amenable to computeization by digitising the image. Thee is yet anothe compute suppoted detecto called Imaging plate. It is a modified fluoescence sceen, whee the fluoescence is hampeed and must by stimulated by lase stimulation with a ed HeNe -LASER beam. At this time the imaging plate (BaFB:Eu) emits blue light, which intensity is popotional to the exposed adiation dose of the imaging plate. Because of the Lase stimulation this technique does not povide ealtime imaging Optical film density Film density is a means of expessing the degee of dakening poduced on a film. It is expessed as follows : D = log10 (Io/It) (5) Whee D is density of adiogaphic film, Io is the intensity of incident light fom the film viewe, It is the intensity of tansmitted light which eaches the eye of the inspecto Quality of adiogaphs Any adiogaphic image is chaacteised by thee basic popeties i) optical density of the film ii) contast esolution iii) special esolution Optical density is detemined by the film speed, and exposue time fo a given specimen. Contast on a film is govened by the specimen type, adiation used as well as by the film type. Resolution of the image is mainly influenced by the inne film unshapness (detemined by the adiation enegy) and geometical unshapness of the geometical setup aangement. Oveall, the combined effect of all the 3 factos decides whethe the image is capable of evealing intended flaws. Fo veifying its capability, a device called image quality identificato (IQI) o penetamete is used Image quality indicatos (IQI) As a check on the quality of the adiogaph and the techniques adopted, a penetamete, othewise known as image quality indicato, is used duing the exposue. The penetamete is placed suitably on the test mateial and the exposue is taken. A vaiety of penetametes ae suggested by diffeent standad oganisations and ae used in industial adiogaphy; none of which give infomation about the eliability of wall thickness measuementes by adiogaphy Double wall technique (DWT) fo pipe inspection (a) (b) Souce Souce Souce Souce Film Film Film Film Figue 1. Double wall technique (DWT).

5 Double wall single image (DWSI): If thee is no access to the inside of the pipe eithe to keep film o souce, this method can be adopted. This is mostly suitable fo pipes of diamete above 85mm. Souces can be kept on the pipe o away fom the pipe depending on the diamete of the pipe, SFD equied and accessibility. See Fig. (1a) Double Wall double image (DWDI) This technique is adopted fo smalle size pipes of diamete up to 85mm. The souce is kept at an angle with espect to the weld so as to avoid the ovelap of the top and bottom welds. Usually two exposues ae taken by otating the pipe though 90 degees. See Fig. (1b) Tangential Radiogaphy technique (TRT) Although the methods descibed in 4.2 ae commonly used fo RT of pipes, thee is a cetain geometical set-up fo pipe inspection and diect wall thickness measuement (Fig. 2). This method is called tangential exposue method. Hee the pats of adiogaph which lie below the tangential location on the pipe only ae intepeted. The middle pat of the pipe image is ignoed. To get the pope image at tangential location, the enegy of adiation used must be highe than that used fo double wall inspection of the same pipe. This is the effect of the maximal penetated wall thickness Lmax at the point of the inne pipe suface. y w insulation pipe I 192 x film R f Figue 2. Tangential Radiogaphy Technique (TRT) The most impotant application of this method is in absolute measuement of the wall thickness of the pipe. This is because the wall thickness is seen in pofile in tangential adiogaphy, almost like a longitudinal section of the pipe. Cae must howeve be taken to coelate only that pat of the pipe wall which lies at the tangent. Mino otation will bing a diffeent segment in image Tangential RT and Wall thickness assessment If a monochomatic adiation beam is passed though an insulated pipe with deposit, as shown in Fig. (3), the fomula of tansmitted adiation intensity (I) is, as follows: I = I 0 B e -2 (µ c x c + µ s x s + µ d x d + µ m x m ) (6) Whee µc, µs, µd, µm ae the linea absoption coefficients of the insulato, steel, deposit, and tanspoted matte, xc, xs, xd, xm ae the tansmitted thickness of the insulation, steel, deposit and tanspoted matte. Using geomety pinciple showed in Fig. (3) the tansmitted thickness of evey laye can be calculated accoding to a cetain co-odination ():

6 Figue 3. Absoption of adiation Tansmitted tanspoted matte thickness: x m = Tansmitted deposit thickness : x d = Tansmitted pipe wall thickness: xs = Tansmitted insulato thickness xc = 2 2 d - (7) 2 2 i - -x m (8) 2 2 o - -(xd + xm) (9) 2 2 c - -(xs + xd + xm) (10) Whee: c = outside adius of insulato, o = outside adius of pipe, i = inne adius of pipe, d = inne adius of deposit. When using tangential adiogaphic method the minimum tansmitted pipe thickness is zeo, which is the pipe outside tangential point. The maximum tansmitted thickness (Lmax) is the chod which is though the tangential point on pipe inside the diamete (see Fig. (2)). Because the thinnest potion will cause a too dak image (bun-off) and the thickest potion will cause a too bight image, the selection of optima iadiation souces enegy and RT paametes ae vey impotant. Using the geneal fomula (6), we can get the paticula fomula fo diffeent types of piping, such as bae empty pipe (xc = 0, xd = 0, xm = 0), bae empty pipe with deposit (xc = 0, xm = 0), insulated empty pipe (xd = 0, xm = 0), insulated empty pipe with deposit (xm = 0) Using the equation (6), the theoetical intensity co-odinato (I-) cuves can be made, as shown in Fig. (4). The inflection points of the cuves will coespond with the boundaies between diffeent layes. The distances between the inflection points will coespond with the thickness of layes. I O Deposit I O Insulato I O Tanspoted fluid I O I I I I Figue 4. Typical intensity cuves of TRT adiogaphy.

7 It may be noted that the eal tavesed maximum thickness is much moe than pipe-wall thickness while using the tangential adiogaphy technique. Selection of iadiation souce must theefoe be accoding to the maximum of the tansmitted thickness, L max : L max = 2w OD w - 1 (11) Whee w = pipe-wall thickness, OD = outside diamete. Selection of highe enegy adiation ay helps in educing the contast. Highe contast would extend the low density zone coesponding to the wall much inside the diamete of the pipe. That makes the detemination of wall thickness difficult. Lowe contast pictue obtained at highe adiation enegy has bette delineation of the ID pofile. The technique of Tangential Radiogaphy can be used fo assessing the esidual wall thickness in those segments of pocess pipelines whee coosion o eosion ae likely to have occued. It can similaly be used fo assessing the scaling of ID o finding deposit inside the tubes. This CRP addesses the poblem of detemining effectiveness of application of technique detemination in coosion depth detemination in the pipelines Density measuement method and pit depth evaluation When a pit is just located on a side tangential wall, its size and depth can be easily evaluated by the TRT adiogaphy (Fig. (5a) pit 1). In othe cases the DW adiogaphy and density-thickness efeence cuves (Fig. (5c) should be used. The pit distibution, its size, will be obviously shown on the DWDI film. Its depth, howeve, will be evaluated by the following pocedue. When a pit (Fig. (5b) pit 2) is located on the axis aea, the pit depth and emaining wall thickness can be detemined by using measued densities of the pit and sound wall, and the efeence density-thickness cuve of a step wedge is exposed (Fig. (5 b, c)). Fo establishing the density-thickness efeence cuve, the stepped wedge should be made fom the same mateial as the tested pipe and its thickness should cove twice the pipe wall ange. When a pit is located on some angle fom the axis (Fig. (5b) pit á) the eal depth (H) should be calculated using a coection fomula: H = cosα (12) Whee Ä = tansmitted pit wall length, á = pit location angle. (a) (b) (c) IO IO Pit 1 Pit α α H Pit 2 Figue 5. Measuement of cooded depth Magnification coection Accoding to the geometical set-up of the tangential exposue technique (see Fig. (2)) thee is a magnification facto inheent to this set-up. To conside this, a coection on the estimated wall thickness must be done. The following coection can be applied. The tue wall thickness is: w = w' (f - R) f (13) Whee: w is the appaent wall thickness, R is the pipe adius (including insulation) f is the Souce FilmDistance (SFD).

8 4.4. Limits of tangential inspection technique One of the main aims of the CRP is to establish the application limits of tangential inspection technique. As a stating point BAM povides a diagam (see Fig. (6)). It is based on maximum penetable wall thicknesses of pipes (L max ) in depending on the adiation enegy. L max detemined the maximum wall thickness which can be inspected at a given pipe outside diamete D a. If a given combination of oute pipe diamete and wall thickness is exceeding the limiting dashed line fo the chosen enegy, this enegy can not be applied fo successful tangential inspection, because the position of the inne wall cannot be detemined fom the adiogaph. As altenative a highe adiation enegy can be used (e.g. eplace I 192 by Co 60), o the double wall inspection technique must be used. Hee the double wall technique (DWT) can be applied. Figue 6. Suggested application limits fo tangential inspection techniques 5. Geneal Pocedue fo the cuent CRP Each county shall manufactue at least 2 efeence blocks as descibed in this document, coveing the diametes and wall thickness to be tested. Tansmission densitometes shall be calibated using X-ay step tablets cetified by the BAM. Density measuements shall be coected to each a ± 0.1 pecision. Developing systems shall be checked using cetified pe-exposed stips, which ae to be developed at the same time as the films. Refeence blocks shall be tested accoding to the pocedue and fo each adiogaphic aangement descibed in this document. Results will be intechanged between paticipants woking with the same diametes, establishing the limits of each adiation souce and exposue technique. Othe pobes will be tested, with atificially intoduced natual defects, accoding to the established limits Standad efeence objects Type and size of defects to be consideed ae as follows: i. Step block with holes inside and outside (one pipe specimen with machined steps inside and outside) ii. Each step will be chosen to ange fom 0 to 0.7 t in steps of 10% wall thickness ounded up to neaest half mm; mm in length; pecision in wall thickness shall be ± 0.1 mm. iii. Hole diamete will be equal to emaining wall thickness, minimum of 2 mm. iv. Hole depth shall be 10, 20 and 50% of the step thickness spaced at diffeent cicumfeential positions (sepaated by 120 ), holes shall be flat bottom.

9 v. Whee steps ae located at the inside suface of the pipe, mateial will be emoved by ginding o machining to a depth of 15% of maximum wall thickness of the pipe, foming a flat suface. Length coveing all the steps. 30 sepaation fom closest holes. Pecision shall be ± 1%. vi. Whee steps ae located at the outside suface of the pipe, mateial will be emoved by dilling with a mm diamete tool, paallel to the pipes axis to a depth of 15% of maximum wall thickness of the pipe. 30 sepaation fom closest holes. Length coveing all the steps. Pecision shall be ± 1% Pipe Dimensions and kind of tests Twenty fou specimens will be equied distibuted amongst twelve paticipants coveing commonly used outside pipe diametes and suitable wallthickenss anges to each the application limits of tangential adiogaphy technique. On evey pipe size adiogaphic tests will be pefomed in 6 diffeent positions fo the tangential method and in 5 diffeent positions fo the double wall technique, exposing evey atificial discontinuity to the tangential o cente position espectively. Each test will be pefomed with and without emovable glass wool insulation of appoximately 50 mm thickness. Additional defects can be intoduced in sepaate blocks o in the efeence block, povided they do not intefee with the ones descibed befoe. These could be atificially induced to simulate shapes and sizes of natual defects. Samples fo eosion, coosion and pitting shall be selected in the same diamete and thickness anges as above Pocedue Tangential pojection technique (shadow shots) shall be used using I 192 and Co60 adiation souces. The same specimens and efeence blocks may be used fo double wall technique. Beyond the limits of this technique fo Co 60, double wall single view technique will be used. Figue 7 shows the expeimental setup. Position 1 is applicable up to oute diamete max 220 mm (8 inch nominal). Lage pipes should be exposed accoding to position 2. Figue 7. Radiogaphic set-up fo tangential pojection technique Double wall technique should be used in the case, whee tangential technique fails because of too high Lmax. (wall thickness cannot be measued because inne pipe diamete cannot be detected). Expeimental set-up showed in Fig. (1a) is pefeed fo lage pipe diamete depending on the geometical unshapness. Radiation souces can be X-ay (including 2 mm Cu pefilteing), Se 75 o in most cases I 192. Limit enegy fo x- ay inspection should be 20 % highe than ecommended in ISO Many details about the adiogaphic pocedue have been established to allow bette compaison of expeimental esults, egading adiogaphic aangement, adiation souces, SFD, Ug, desied density ange, exposue time

10 calculation, seen/film systems, magnification coection, shielding against scatteed adiation, IQI, film pocesing and film evaluation pocedue. 6. Conclusions The cuent CRP is well undeway with expeiments being caied out in all of the paticipating counties. With this level of coopeation, the majo objective of defining the limits of validity of the technique will be achieved, the esults will be published in a TECDOC, and an ISO document poduced which will make it available to all. 7. Refeences Bukle, W.S., 1989, Application of the tangential adiogaphic technique fo evaluating pipe system eosion/coosion.. Mateial evaluation. Vol. 47, Lee, S., Kim. Y.H., 1999, Detemination of pipe thickness using tangential adiogaphy and film density-thickness coelation., Reppot AIEA. Onel, Y., Ewet, U., Willems. P., 2000, Radiogaphic Wall Thickness Measuements of Pipes by a New Tomogaphic Algoithm, IDN 369, Poceedings of the 15th WCNDT, Roma Wawzinek, T., Zschepel, U., Bellon, C., 1997, Wall Thickness Detemination in Digital Radiogaphy, COFREND Congess on NDT, Nantes 1997, confeence poceedings, vol. 1, pp Willems, P., Vaessen, B., Hueck, W., Ewet, U., 1999, Applicability of compute adiogaphy fo coosion and wall thickness measuements, INSIGHT, vol. 41 No. 10, pp Zschepel, U., Bellon, C., Nimtz, R., 1998, Wall Thickness Estimation fom Digitized Radiogaphs, poceedings of the 7th ECNDT, Copenhagen 1998, pp