PEDS: SOFTWARE TO ASSESS WALL THICKNESS LOSS AND WELD THICKNESS LOSSIN OFFSHORE PIPELINES THROUGH DIGITAL RADIOGRAPHY

E.M. SOUZA1,2*, A.L.S. GERMANO1, D.F. OLIVEIRA2,3, S.C.A. CORREA4, A.X. SILVA5, R.T. LOPES2

1Fundação Centro Universitário Estadual da Zona Oeste/UEZO. edmilsonsouza@uezo.rj.gov.br ­ ativa1@gmail.com2 Programa de Engenharia Nuclear/COPPE Centro de Tecnologia, Cidade universitária, Ilha do Fundão. ricardo@lin.ufrj.br ­emonteiro@nuclear.ufrj.br ­ davi@lin.ufrj.br3 Universidade do Estado do Rio de Janeiro/ UERJ ­ Rua São Francisco Xavier, 524. CEP 20550­013 Maracanã/RJ, Brazil4 Comissão Nacional de Energia Nuclear/CNEN ­ R. Gal. Severiano 90, sala 409, 22294­900, Rio de Janeiro, RJ, Brazil. scorre@cnen.gov.br5 Departamento de Engenharia Nuclear / Escola Politécnica ­ Universidade Federal do Rio de Janeiro. ademir@nuclear.ufrj.br@nuclear.ufrj.br

ABSTRACT:A computer software to assess wall thickness loss and weld thickness loss in offshore pipelines is presented. This software calculates the thicknessloss through a data bank obtained using computational modeling based on Monte Carlo MCNPX code, and digital radiography images obtainedusing image plate (BaFBr) detector. In order to give users more flexibility, the computer software was written in Java, which allows it to run onLinux, Mac OS X and Windows. Tools are provided to image display, select and analyze specific areas of the image (measure average, area ofselection) and generate profile plots. Applications of this software in onshore and offshore inspections are presented. Preliminary results showngood agreement between real and calculated value of thickness loss.Palavras­chave: Software de Computador; Perda de espessura; Radiografia, MCNPX.

1.INTRODUCTIONDegradation processes such as corrosion havea substantial bearing on the security andreliability, mainly in petroleum plants, causingleakages, fires, expensive non­programmedstops and even environmental disasters ofgreat proportions (Cardoso, 2005; IAEA,2005; DD, 1978). In order to guarantee the thestructural integrity of petroleum plants it iscrucial to monitor the amount of wall or weldthickness loss in onshore and offshorepipelines. Computed radiography with imagingplate detectors is one of the most helpfultechniques for the inspection of the most

helpful techniques for the inspection ofonshore and offshore ducts (IAEA, 2005; Veithet al., 2001; HSE, 2005; Patel, 2005; Shinoharaet al., 2002; Davis et al., 2000; Marinho et al.,2005). It has the potential to be used toperform inspection without costly removal ofinsulation material during operation of theplant, and it is also preferred because of lesserexposure time, no chemical processing, lessercost of consumables and advantage of a digitalimage output (IAEA, 2005; Veith et al., 2001;HSE, 2005; Patel, 2005; Shinohara et al., 2002;Davis et al., 2000; Zscherel et al., 2000;Marinho et al., 2005). However, in spite of itsrelevance, the thickness loss is very difficult to

RESUMO:Um software de computador para avaliar a perda de espessura da parede e da solda dos canos das tubulações marítimas é apresentado. Thissoftware calculates the thickness loss through a data bank obtained using computational modeling based on Monte Carlo MCNPX code, and digitalradiography images obtained using image plate (BaFBr) detector. In order to give users more flexibility, the computer software was written in Java,which allows it to run on Linux, Mac OS X and Windows. Tools are provided to image display, select and analyze specific areas of the image(measure average, area of selection) and generate profile plots. Applications of this software in onshore and offshore inspections are presented.Preliminary results shown good agreement between real and calculated value of thickness loss.Palavras­chave: Software de Computador; Perda de espessura; Radiografia, MCNPX.

ISSN: 2317­8957Volume 2, Number 1, Jun. 2014

determine, due to both the large diameter ofmost pipes and the complexity of the multi­variable system involved (IAEA, 2005).Over the years, modeling became moreimportant in modern non­destructive test(NDT) techniques. It is used to optimizetechniques for complex applications and tosupport the preparation of written procedures.Depending on the formulated inspectionproblem or the influencing factors that shouldbe accessed by modeling, an appropriatephysical model can allow the implementationof NDT measurement models that are capableto predict the signals seen in NDT inspectionsand that can be used to quantitatively study theeffects of various parameters on those signals.A methodology for calculation of wall andweld thickness loss using Monte Carlo codeMCNPX and digital radiography wasdeveloped by our group (Correa et. al, 2009).This methodology takes into account theenergy­dependent response of a BaFBrimaging plate detector. It has been used toobtain a data bank in order to calculate thethickness loss. With this in mind, the objectiveof this paper is to present an evolution of acomputer software named PEDS (Souza et. al,2010), to assess weld thickness loss in offshorepipelines, where the data bank previouslymentioned was implemented. Moreover, PEDSalso provides the main tools for imagemanipulation in non­destructive test (NDT)applications.2. MATERIALS AND METHODS.................2.1 THE PEDS SOFTWAREThe PEDS is a program originally developedto estimate weld thickness loss in offshorepipelines through a data bank obtained withcomputational modeling based on Monte Carlocode MCNPX (Correa et. al, 2009). Theprogram correlates the ratio between thepixels’s average intensity in the region of thediscontinuity and the pixels’s average intensity

in the neighborhood of the discontinuity inimages obtained experimentally, with the ratiopreviously simulated in the data bank toestimate de thickness loss. This program, up tothe present moment, allows not only theestimate of weld thickness loss, but also theestimate of wall thickness loss through digitalradiography images obtained using image plate(BaFBr) detector, radiography technique ofdouble wall single image (DWSI), and Iridium192 (192Ir) source. Figure 1 shows the PEDSinterface.

Figure 1. PEDS interface.......................................The PEDS is written in Java language. Thedevelopment environment used is theNetBeans IDE version 6.9. NetBeans is amodular and extensible application frameworkfor the development of Java desktopapplications. It contains several applicationprogramming interfaces (API), thus providingthe functionality that every programmer wouldhave to write themselves, including: windowmanagement, saving state, connecting actionsto menu items, toolbar items and keyboardshortcuts.In order to give users more flexibility, thePEDS also provides the main tools for imagemanipulation in nondestructive test (NDT)applications. This program can read manyimage formats such as TIFF, GIF, JPEG, BMPand DICOM, besides display, edit and analyze8­bit, 16­bit and 32­bit images. Moreover,

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PEDS can calculate area and pixel valuestatistics of user­defined selections, and createdensity histograms and profile plots. It alsosupports standard image processing functionssuch as contrast and brightness manipulations.Additionally, in the PEDS the image can bezoomed up to 32:1 and down to 1:32, and allanalysis and processing functions are availableat any magnification factor. The program alsosupports any number of windows (images)simultaneously, limited only by availablememory. In order to implement the tools forimage manipulation in the PEDS, wasconsidered the class structures of the ImageJ(public domain Java image processingprogram) available through tutorial (Bailer,2006).2.2 THE DATA BANK.................................The data bank implemented in PEDS softwareconsist of an set of equations obtained bysimulations of several radiographic systemswhere the ratio between a value obtained bythe detector aligned with the discontinuity andanother obtained by the detector aligned with aregion in the neighborhood of the discontinuityis correlated with the percentage of wallthickness loss or weld thickness loss in pipes.The calculations were made using the MonteCarlo code MCNPX version 2.5.0. (Pelowitz,2005). The photons were transported takinginto account photoelectric absorption, coherentand incoherent scattering, in order to reproducethe main phenomena involved in radiationinteraction with the matter.................................Offshore and onshore pipes are usually large­diameter steel tubes that are welded to oneanother to form a long pipeline. Due to thetypically large diameters of this kind of pipes,radiographic inspections are only viable if thedouble wall single image (DWSI) technique isused (IAEA, 2005). Considering this, thesimulation procedures in order to obtain thedata bank involved DWSI radiographic systemfor inspection of steel pipes with 8, 10, 12, .

16 and 20­in external diameter........................The iron pipe size­IPS (external diameter) andthe wall thickness were defined according tothe SCH 10­S schedule (ANSI B36.10, 1979).Defect percentages inserted in the pipes werelarger than 20% in order to consider thethickness reductions where repairs of the pipesin terms of maximum allowable operatingpressure are recommended (ASME B31G,1991). The simulation procedures in order toobtain the data bank take in to account thepresence of liquid (water) inside and outsidethe pipes, and pipe without water (air).The DWSI radiography simulations reproducea 0.3cm diameter Iridium 192 (192Ir) sourcecollimated into a cone by applying MCNPX’ssource biasing variance reduction technique(Pelowitz, 2005; LANL, 2003). This techniqueallows a radiation source to be modeled as if itwere collimated, without compromising thefinal result of the simulation (Pelowitz, 2005).The radiation beam was directed through thecenter of the pipe’s cross section. In DWSIradiographic technique, the thickness losscaused is determined by associating it withintensity differences between regions in thecomputed radiographic image after propercalibration. Considering this, point detectors(tally F5), placed at 0.1cm from the simulatedobject, have been used to detect photonsemerging from the test specimen. The numberof histories simulated in all cases assures theestimated statistical error is less than 5%. Thelayout of the radiography system developedfor experimental weld thickness lossevaluation in offshore pipelines, and modeledin this work, and the locations of the pointdetectors (F5) and the 192Ir source can be seenin Figure 2..........................................................

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Figure 2. System designed for radiography of offshorepipes and locations of the point detectors, F5, and of 192Ir

.....source.

In order to take into account the energyresponse of the BaFBr image plate detector,the methodology for digital radiographysimulation developed by our group wasutilized (Souza et al., 2008; Correa et al.,2008). The curve which represents the wallthickness loss in 8­in pipe obtained byMCNPX simulations is shown in Equation 1,where R is the ratio between a value obtainedby the detector aligned with the discontinuityand another obtained by the detector alignedwith a region in the neighborhood of thediscontinuity, and TL is the thickness loss.

2.3VALIDATION OF THE METHODOLOGYThe software PEDS was tested withexperimental digital radiography images. Agamma irradiator with a 36 Ci 192­Ir sourceof approximately 0.3cm diameter was used inthe experiments. Every testing was performedthrough GEIT’s computed radiography systemCR50P. In order to analyze the wall thicknessloss in onshore pipelines, the PEDS was testedwith digital images of 8 and 12­in nominalexternal diameter pipe. In order to analyze theweld thickness loss, a digital image of a 10­inpipe with water inside and outside was utilized.

Table 1 show the specifications of thepipelines used in experimental procedures.

Table 1. Specifications of the pipelines used in experimental...and simulated procedures......................................The thickness loss was correlated with theratio between the pixels’s average intensity inthe region of the discontinuity and the pixels’saverage intensity in the neighborhood of thediscontinuity. Images obtained experimentallyhelped make this correlation. This can be seenin Figure 3.........................................................

...................................

Table 1. Specifications of the pipelines used in experimental...and simulated procedures......................................3. APPLICATION OF THE PEDS..................A script for the PEDS utilization is shown inthe next sections.................................................3.1 READING IMAGE FILE.........................In order to open an image file in the PEDS, themenu command “File/Open” should beselected. Afterwards, the user should select theimage file and click the open button (“Abrir”),as shown in Figures 4 and 5. TIFF, GIF, JPEG,BMP and DICOM formats can be supportedby the PEDS by default. The image file isopened automatically.........................................

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Figure 4. Opening a image file in the PEDS...............................

Figure 5. Selecting an image file to open in the PEDS.

3.2 BRIGHTNESS AND CONTRASTTo improve the visualization of the image, thedisplayed brightness and contrast can beadjusted with “Image/Adjust/Brightness­Contrast”. Figure 6 shows the brightness andcontrast window.................................................

Figure 6. Brightness and contrast window.

In the Figure 6, “Minimum and Maximum”sliders control the lower and upper limits of thedisplay range, and “Brightness and Contrast”sliders increase or decrease the brightness andcontrast, respectively, by moving the display

range. The “Auto” applies an intelligentcontrast stretch to the way in which the imageis displayed. The brightness and contrast areadjusted based on an analysis of the image'shistogram. “Reset” restores the originalbrightness and contrast settings, the “Set”allows to enter the minimum and maximumdisplay range values in a dialog box, and the“Apply” applies the current display rangemapping function to the pixel data.PEDS also allows the user obtain histogramplot, profile plot, and ordinary measurementssuch as average gray value within theselection, area of selection in square pixels,and maximum and minimum pixel valueswithin the selection...........................................3.3 MEASUREMENTSTo access measurement function,“Analyze/Measure” should be selected and arectangular selection must be created. Figure 7shows the measurement window..................,....

Figure 7. Measurement window.

3.4 ASSESSMENT OF THICKNESS LOSSIN PIPELINESIn order to assess the weld thickness loss, thefirst step is to choose the diameter of thepipelines. Afterwards, it is necessary to informthe pixels’s average intensity in the region ofthe discontinuity and the pixels’s averageintensity in the neighborhood of thediscontinuity. Those values can be obtainedusing the measurement function. The last stepis the selection of the calculate button.

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Figure 8 shows the weld thickness loss value.

Figure 8. Weld thickness loss value.

In this specific case, PEDS presents 31.26% ofthickness loss to a 8­in external diameter pipe.4. RESULTSIn Tables 2, 3 and 4, the results obtainedthrough computational modeling are comparedwith the experimental results for differentvalues of thickness loss in 8, 10 and 12­indiameter pipes, whose specifications wereshowed in Table 1. There is good agreementbetween the simulated and the experimentalresults, as shown in Tables 2–4. The maximumpercent difference found is 11.11 for athickness loss equal to 29.25%, in 8­indiameter pipes, and 12.13 for a thickness lossequal to 50.33%, in 12­in diameter pipes . Itshows that the methodology developed toestimate wall and weld thickness loss in pipesand implemented in PEDS software is useful toreproduce the NDA system and predict thedetectability of imaging indicative details suchas a reduction in welding thickness due tocorrosion. The largest percentile differencesobserved between experimental and simulatedresults are due to variations in density,thickness or absorption characteristics of thematerial analyzed due to alterations in itscomposition, that have not been reproduced byMCNPX. It can influence the scatteredradiation distribution in the detector, andconsequently the quantitative measure ofthickness loss.....................................................

Table 2. Wall thickness loss: comparison between the results obtained. through PEDS and the experimental data for several values of...thickness loss in 8­in diameter pipes..............................................

Table 3. Wall thickness loss: comparison between the results obtained.through PEDS and the experimental data for several values of.thickness loss in 12­in diameter pipes....................................................

Table 4. Weld thickness loss: comparison between the results obtained.through PEDS and the experimental data for several values of.thickness loss in 8­in diameter pipes......................................................

5. CONCLUSIONSThe software PEDS has proven useful, beingcapable of successfully reproduce theprocesses of radiation interaction with matter,in good agreement with the experimental data.6. PERSPECTIVESAs mentioned previously, the aim of this workis to present a first evolution about PEDS. Asfuture perspectives, the aim is to increase thedata bank for calculation of thickness lossincluding Selenium and Cobalt gammaradiation source and more radiographyconfigurations.ACKNOWLEDGEMENTSThe authors wish to thank the financial supportof the Coordenação de Aperfeiçoamento dePessoal de Nível Superior (CAPES), ConselhoNacional de Desenvolvimento Científico eTecnológico (CNPq), and Fundação Carlos

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Chagas Filho de Amparo a Pesquisa do Estadodo Rio de Janeiro (FAPERJ), Brazil.REFERENCESANSI B36.10, 1979. Nominal Thickness andWeights of Stainlss Steel Pipes. AmericanNational Standards Institute, Washington DC.ASME B31G, 1991. Manual for Determiningthe Remaining Strength of Corroded Pipelines:A Supplement to B31, Code for PressurePiping. American Society of MechanicalEngineers, New York........................................

BAILER, W. 2006. “Writing ImageJ Plugins: ATutorial”. Upper Austria University of AppliedSciences.CARDOSO, C.O.. 2005. Methodology foranalysis and project of highpressure/temperature pipelines by applicationof finite element method. Thesis of D.Sc.,COPPE/UFRJ, Rio de Janeiro, RJ, Brazil.CORREA, S.C.A. et al. 2008. Dose–imagequality study in digital chest radiography usingMonte Carlo simulation. Appl. Radiat. Isot. 66:1213–1217.CORREA, S.C.A et al. 2009. Assessment ofweld thickness loss in offshore pipelines usingcomputed radiography and computationalmodeling. Appl. Radiat. Isot. 67: 1824–1828.DAVIS, W.A. et al. 2000. An analysis ofindustrial nondestructive testing employingdigital radiography as an alternative to filmradiography. LA­UR­00­2560, Los AlamosNational Laboratory.......................................DD, 1978. USA Maintenance of WaterfrontFacilities, Manual, 1978, Department ofDefense, USA....................................................HSE, 2005. Recommended practice for therapid inspection of small bore connectors using

Research Report 294, Health and SafetyExecutive.IAEA, 2005. Development of protocols forcorrosion and deposits evaluation in pipes byradiography—IAEA­TECDOC­1445.International Atomic Energy Agency, Wien.LANL, 2003. X­5 Monte Carlo team. MCNP:a general Monte Carlo n­particle transportcode. LA­CP­03­0245, Los AlamosLaboratory.MARINHO, C.A. et al. 2005. Gamagrafiacomo Técnica de Inspeção em DutosSubmarinos. In: Proceedings of EighthCOTEQ, Salvador, Brazil, pp. 1–15..................PATEL, R.J. 2005. Digital applications ofradiography. In: Proceedings of the ThirdMENDT, Bahrain, Manama............................PELOWITZ, D.B. 2005. MCNPXTM User’sManual. Version 2.5.0. LA­CP­05­0369, LosAlamos National Laboratory report...................SHINOHARA, A.H., ACIOLI, E., KHOURY,H.J. 2002. Avaliação da Técnica deRadiografia Digital em Gamagrafia. In:Proceedings of the Review of SixthCOTEQ—Conferência Sobre Tecnologia deEquipamentos, Brasil.........................................SOUZA, E.M., et al. 2010. Computer Softwareto Assess Weld Thickness Loss in OffshorePipelines: PEDS. In: Proceedings of thirteenthENCIT ­ 13th Brazilian Congress Of ThermalSciences and Engineering, Brasil.....................SOUZA, E.M., et al. 2008. Methodology fordigital radiography simulation using the MonteCarlo code MCNPX for industrialapplications. Appl. Radiat. Isot.: 66 ­ 587–592.VEITH, E. et al. 2001. Inspection of offshoreflexible risers with electromagnetic andradiographic techniques. Insight 43: 404–408.

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ZSCHEREL, U., ONEL, Y., EWERT, U. 2000.New concepts for corrosion inspection ofpipelines by digital industrial radiography(DIR). In: Proceedings of 15th WCNDT,Roma.

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