A. Bastola et al. / Procedia Structural Integrity 2 (2016)

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1 Aville online t ScienceDirect Procedi Structurl Integrity 2 (2016) st Europen Conference on Frcture, ECF21, June 2016, Ctni, Itly Full- nd smll-scle tests on strin cpcity of X80 semless pipes A. BASTOLA *, J. WANG, H. SHITAMOTO, A. MIRZAEE-SISAN, M. HAMADA c nd N. HISAMUNE c DNV GL, Plce House, 3 Cthedrl Street, London, SE1 9DE, United Kingdom Nippon Steel & Sumitomo Metl Corportion, 1-8 Fuso-Cho, Amgski, Hyogo, Jpn c Nippon Steel & Sumitomo Metl Corportion, 1850 Minto, Wkym City, Wkym, Jpn Astrct Appliction of high-strength steels such s X80 grde my help reduce cost in offshore pipeline projects through wll thickness optimistion nd ssocited instlltion costs. To ensure reliility of such ppliction during the pipeline instlltion nd opertion stges, further understnding on the strin cpcity of girth welds of X80 grde pipes is required. This pper presents detils of reserch project contining smll-scle nd full-scle experiments on X80 line pipe specimen contining girth welds. Initil defects re introduced on the Het Affected Zone (HAZ) nd Weld Metl (WM) of the girth welds prior to the test in order to understnd their frcture ehviour. The full-scle experimentl progrm includes four-point ending tests with nd without internl pressure pplied, nd reeling tests. Tensile properties of se metl, WM nd HAZ re mesured. Frcture toughness tests of WM nd HAZ re lso crried out. No through-thickness crck growth hs een oserved in the reeling tests nd ending tests without internl pressure. However, some ending tests with internl pressure hve seen crck growing through the thickness of the girth weld. Results from this study hve shed light on the extent of crck growth in the girth welds of X80 pipes s influenced y their initil size, loction, nd internl pressuriztion. Copyright 2016 The Authors. Pulished y Elsevier B.V. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of the Scientific Committee of ECF21. Keywords: X80; line pipes; frcture mechnics, full-scle test; girth weld 1. Introduction Deep wter pipelines must withstnd extremely high externl pressures t high wter depth. Pipe mterils with enhnced properties such s etter toughness, elongtion nd strin cpcity cn e more ttrctive in deep wter. * Corresponding uthor. Tel.: E-mil ddress: jit.stol@dnvgl.com Copyright 2016 The Authors. Pulished y Elsevier B.V. This is n open ccess rticle under the CC BY-NC-ND license ( Peer review under responsiility of the Scientific Committee of ECF /j.prostr

2 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) High strength steels such s X80 could e good cndidte for deep wter pplictions. However, strin cpcity of the high strength steel pipes contining flws need to e etter understood when considering strin sed design. Moreover, its frcture ehviour during reeling instlltion process where the X80 pipe will e sujected to high plstic deformtion is not yet fully investigted or understood. Current frcture mechnics procedure such s BS7910 (2013) provides generl guidelines on girth weld defect cceptnce criteri for longitudinl strins rnging from elstic to plstic. Also, common offshore pipeline design stndrds such s DNV-OS-F101 (2013) provides some useful ut limited guidnce on the girth weld defect cceptnce criteri. However, these procedures do not provide explicit nd detiled solution for strin limit (cpcity) of pipelines contining flws. Nomenclture API BM CMOD CTOD DIC ECA HAZ NSSMC SENB SENT SMYS WCL WM WPS ε ve Δ Americn Petroleum Institute Bse Metl Crck Mouth Opening Displcement Crck Tip Opening Displcement Digitl Imge Correltion Engineering Criticl Assessment Het Affected Zone Nippon Steel nd Sumitomo Metl Corportion Single Edge Notch Bend Single Edge Notch Tension Specified Minimum Yield Strength Weld Centre Line Weld Metl Welding Procedure Specifiction Averge Nominl Strin Crck extension Vrious studies hve een crried out on fctors tht cn ffect the tensile strin cpcity of girth welded highstrength steel pipes. Hn et l (2012) studied the effect of microstructure on strin hrdening for X80 steels. Similrly, Igi et l (2011) showed effect of internl pressure on tensile strin cpcity, Fgerholt et l. (2012) crried out frcture nlysis of SENT specimens, nd Yi et l (2012) performed fcture nlysis of known flws. These studies hve highlighted the multiple fctors tht cn influence the strin cpcity of girth welded high strength pipes. Presence of geometricl imperfections (mislignment, Hi-Lo, etc.), welding relted defects (lck of fusion, slg inclusion, etc.) nd residul stress mke the girth welds the wekest link in the high strength steels linepipes. Strength mismtch effect (strength under mtching) nd HAZ softening re oserved on high strength steel pipes. Motohshi et l. (2007) tested X80 steel curved wide pltes nd mesured the strin loclised close to the surfce nd over the specimen s guge length. Yng et l. (2015) lso tested welded joint of X80 grde steel nd oserved the HAZ ws the frcture risk zone of the X80 steel weldment due to the presence of hrd-rittle mrtensiteustenite (M-A) constituents. The study suggests the HAZ properties to hve n effect on the tensile strin cpcity of X80 pipes. Tensile strin cpcity of pipe is often governed y the tensile strin (elstic nd plstic) limit of the pipe s girth nd the presence of defects in the girth weld is detrimentl to the tensile strin cpcity. In cse of girth welded pipes with flws, tensile strin cpcity shll e clculted using frcture mechnics sed pproches clled ECA. ECA procedures were developed for stress-sed situtions ut currently eing under development for the strin-sed cses. Pipelines re sujected to ixil stress-strin stte during opertion nd DNV-OS-F101 provides guidnces on ECA procedures for unixil loding conditions s well s ixil loding conditions.

3 1896 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) No distinction is mde etween the effects of mislignment on strin cpcity of high strength nd conventionl pipes in BS7910 (2013). Under qusi-sttic loding condition (for e.g. ending during opertion), mislignment my e treted s source of stress intensifiction which cn reduce girth weld s defect cceptnce criteri, prticulrly for surfce reking defects. Swnkie et l. (2012) conducted tests on curved wide pltes mde of X100 grde steel, nd showed the rtio etween ctul filure stress nd tht predicted y BS7910 rnges typiclly from 1.15 to 6.5. This illustrtes the existing conservtism in BS7910 pproch. For high strength steels, Uniform Elongtion Limit (UEL) is low, i.e., in the order of few percent for X80 nd X100, menwhile negligile for X120 steel grde. Low UEL is detrimentl to the strin cpcity of high strength steels. Kiey et l. (2009) looked t correltion etween strin cpcity nd the comined effect of low UEL nd flw depth for X80 pipe specimens. One interesting conclusion drwn ws tht reducing UEL from 8% to 4% led to corresponding reduction of pproximtely 0.5% in strin cpcity for constnt flw depth. It ws lso shown tht therml geing s result of therml coting could chnge mechnicl properties of X80 linepipes. In this pper, the ppliction of high strength X80 steel grde pipes in strin-sed (displcement-controlled) sitution is studied. This study emphsised on the strin cpcity of the girth welds, nd to elorte their effect, welds contining flws hve een introduced deliertely into the girth welds. This extensive reserch progrmme fetures smll-scle specimen tests, full-scle ending tests nd full-scle reeling tests. A lrge numer of ccompnying detiled FEA hve lso een crried out nd will e pulished in due course. Although the terms flws, defects, notches nd crcks hve somewht different mening, they re used interchngely nd indicte n Electronic Dischrge Mchining (EDM) notch in the context of testing in this pper. 2. Experimentl Procedures nd Mesurement In this reserch, totl of 11 API-5L X80 semless linepipes (nominl outer dimeter, OD, of mm nd nominl wll thickness of 14.3 mm) hve een mnufctured nd welded s per the pproved WPS y NSSMC. Girth welded joints re produced y Pulsed Gs Metl Arc Welding (PGMAW), further detils of the weld nd its typicl mcrostructure is given in Tle 1. Tle 1. Welding prmeters Welding detils AWS Clssifiction Welding Position Equipment Prehet Groove design Bcking Mcrostructure Prmeters A5.28 ER80S-G 5G Root: Power Wve 455M/STT (LINCOLN) Others: DP-350 (DAIHEN) Not Applied J Groove Not Applied (Root pth welding) Specimens from two 3m-long pipes with two girth welds re used to crry out smll-scle tensile, SENB nd SENT tests. Another seven pipes re used for the full-scle ending tests, nd the remining two pipes re used for full-scle reeling tests. The pipes used for the full-scle tests re ll 11m long. Accompnying sets of sensitivity studies vi 3D FEA re then crried out to determine the required initil flw sizes in full-scle tests. Flws re introduced on the WM nd HAZ of the pipes in preprtion for the full-scle tests through the EDM technique. Fullscle ending (with nd without internl pressure) nd reeling tests re then conducted to exmine the strin

4 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) cpcity of X80 pipes with girth welds nd known initil flws sizes nd loctions under relistic strin-sed conditions Smll scle tests Both pipes dedicted for smll-scle tests consist of three pieces of 1m-length pipe segments welded together to totl length of 3m ech. The welded pipes for mteril testing hve een selected y the mnufcturer, NSSMC, to e fully representtive of typicl production. The testing covered in this procedure were tensile, SENB nd SENT. Ten full stress-strin curves hve een produced, five for BM nd the other five for WM in ccordnce with DNV- OS-F101 nd EN ISO (2009). Round r test specimens hve een extrcted in the longitudinl direction of the pipe for the BM nd in the circumferentil direction for the WM. The guge length is four times the dimeter of the specimen. Fourteen deeply notched SENB specimens re tested to otin the R-curves in ccordnce with EN ISO (2010). SENB specimens hve high constrint condition t the crck tip nd will provide conservtive R- curves (DNV-RP-F108 (2006)). Six specimens were notched t the WM nd eight t HAZ. Both J-R (Crck driving force Resistnce) curve nd CTOD-R (Crck Tip Opening Displcement Resistnce) curve were determined using the multiple-specimen method (minimum six specimens for ech crck loction). Likewise, fourteen SENT specimens hve een tested; six notched t WM nd eight notched t HAZ. The testing hs een conducted ccording to DNV-RP-F108. J-R curves for WM nd HAZ re determined using the multiple-specimen method. The loding mode nd crck tip constrint in the SENT specimen re close to those for flw in pipeline s girth weld under ending nd xil loding conditions. Additionlly, DIC technique hs een used to chrcterise the locl stress-strin ehvior in the BM, WM nd HAZ region s well s produce representtive full stress-strin curve for HAZ. DIC specimens re cut from the welded pipes using the EDM technique, providing rough smple surfce which produces photogrphic imges with rndom contrsting fetures (speckles) tht DIC softwre cn trck to determine locl displcements. Ech DIC test hs een verified using strin guges, nd clip extensometer s dditionl verifiction for one test Full scle tests Two types of full-scle testing hve een performed: ending tests nd reeling tests. The ending tests re crried out with nd without internl pressure to simulte certin opertionl conditions of these pipelines; menwhile, the reeling tests were crried out to simulte instlltion conditions under high plstic deformtion. The pipes for fullscle ending tests re 11m long nd ech contining one girth weld in the middle. The pipes for reeling re lso 11m long ut hve two girth welds spced 1m prt t the centrl section. The pipes hve een fricted nd welded in NSSMC s mill in Jpn nd shipped to DNV GL s lortory in Norwy for testing. Seven out of eleven X80 pipes hve een fricted for 4-point full-scle ending test. Among those, four pipes hve een tested for ending without ny internl pressure. A smll internl pressure of 10rs is pplied on these four pipes to detect the through thickness crck growth esily. Menwhile, n internl pressure of 479 rs (70% Specified Minimum Yield Strength (SMYS) of hoop stress) is pplied on the remining three full-scle ending tests. 10mm thick end cps with control vlves re used on oth sides of the pipe to mintin the desired internl pressure. Pre-defined EDM notches re introduced to simulte the tip of the crck in WM nd HAZ. The pipes re supported in the ends with two lrge steel rollers nd the lod is pplied on the pipe through two rigid strips ttched to fixed hydrulic cylinders. The hydrulic cylinders re mounted with 500kN lod cells. The tests re then crried out in displcement-controlled mode. A schemtic of the 4-point end test-setup nd n imge of ctul test for 4- point end test re given in Fig. 1. Two pipes hve een fricted for the full-scle reeling tests. Similrly, smll internl pressure of 10rs is lso pplied on these two pipes detect the through-thickness crck growth. A former with two curved sides is used to simulte the reeling nd strightening processes. The rdius of curvture of the former is 5300mm, which cn induce up to 2.5% nominl strin on the pipe. Unlike 4-point ending test, hydrulic cylinders re connected using 100mm-

5 1898 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) dimeter rods to the former nd then drwing the former ginst the pipe until the pipe is fully ent ginst the former. Two reeling cycles re performed nd fter ech reeling cycle, the pipe nd the former re flipped in order for the strightening process. The cut-outs on the strightener provide room for mounting the clip guges to mesure CMOD. A schemtic of the reeling test setup nd representtive photo of reeling tests re shown in Fig. 2. Fig. 1. () Schemtic digrm of the 4-point ending test set-up for 11m long linepipe; () 4-point end test setup Fig. 2. () Schemtic digrm of the reeling test set-up for 11m long linepipe; () reeling test setup The semless pipes re expected to show wll thickness vrition in the circumferentil nd xil directions. Ultrsonic mesurement technique is used to mesure thicknesses t distnces of 0.5, 1.0, 1.5, 2.0 nd 3.0 times OD on oth sides of the weld t 12, 3, 6 nd 9 o clock positions (hence ltogether 20 mesurements). The wll thickness vlues mesured rnge from 13.5mm to 14.9mm for ll pipes considered. Also, in order to hve ccurte mesurements of the weld geometry including weld cp nd weld toe, 3 pipes considered for pressurised 4-point ending tests re scnned using 3D scnning technique. The mislignments mesured re ll less thn 0.2mm. For 4-point ending tests, ech pipe is ttched with strin guges (5mm, unixil) t 0.5 OD, 1 OD nd 2 OD from the WCL nd on the WCL t oth 6 o clock nd 12 o clock positions (hence 16 strin guges mounted on ech pipe). Likewise, for reeling tests, ech pipe is ttched with strin guges (5mm, unixil) t 1 OD from the WCL, on the WCL nd t the middle of the pipe length, t oth 6 o clock nd 12 o clock positions (hence 18 strin guges mounted on ech pipe). Clip guges re mounted t the centre of the crck to mesure CMOD nd silicon replic (Microset 101RF synthetic ruer) is used to mesure the initil flw depth nd CTOD y injecting the silicon compound into the flw during the test nd mesuring the solidified compound in stereo light microscope. The silicon replic is lso injected periodiclly during the tests to mesure CMOD, CTOD nd crck growth for n pplied strin, n exmple of which is shown in Fig. 3.

6 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) Experimentl results nd discussion 3.1. Smll scle results Fig. 3. An exmple of silicon replic used to mesure CMOD, CTOD nd Δ Comprison of ten tensile tests etween BM nd WM re shown in Fig. 4 (). Yield strength of the WM overmtches tht of BM y pproximtely 20%. Uniform curves hve een produced nd no chnge in tensile properties due to circumferentil position hs een oserved. Through DIC technique, locl stress-strin curves from vrious regions of the inner dimeter specimen re generted nd shown in Fig. 4 (). The HAZ loctions mentioned here re t 3.2mm from the WCL to either side of the weld i.e. loctions 1 nd 2 in Fig. 4 (). The HAZ tensile tests shows tht it is softer y out 7.5% compred with BM t 1% strin. The prent mteril undergoes very little yielding with much of the strin concentrted t nd ner the weld line nd HAZ. A hrdness mp of the weld cross-section is shown in Fig. 5. The hrdness increses from the outer dimeter to the inner dimeter in BM. The WM hs the highest hrdness, followed y drop in the hrdness in the HAZ region, which is roughly t 5mm from the WCL for mid-thickness. In ddition to tht, high hrdness in the fusion zone is oserved. Locl strin mesured from DIC shows the prent mteril undergoes very little yielding with much of the strin concentrted t nd ner the weld line nd HAZ for inner dimeter region. The strin is concentrted in regions close to the weld, with prticulrly high concentrtion in the HAZ regions on the either side of the weld. For oth the mid-thickness nd inner dimeter specimens the yield strength of the HAZ regions is significntly lower thn tht of the prent mteril. All the frcture toughness tests were performed t room temperture. Lower ound fit of SENB HAZ nd WM CTOD-R curves re shown in Fig. 6 (). The frcture toughness (CTOD) of HAZ is more thn doule tht of the WM for unit stle crck extension. Fig. 6 () shows the lower ound fit of SENT HAZ nd WM CTOD-R curves. It shows the frcture toughness (CTOD) of HAZ is more thn 1.5 times tht of the WM for unit stle crck extension from SENT specimens.

7 1900 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) Fig. 4. () BM nd WM tensile tests results; () DIC test results Fig. 5. Hrdness mp cross the weld cross section Fig. 6. () CTOD-R curve from SENB tests; () CTOD-R curve from SENT tests 3.2. Full scle results Bending results Four pipes re suject to 4-point ending test without internl pressure. Three of them feture initil flw sizes of 3 50mm, 4 50mm nd 5 50mm in the HAZ region respectively, nd the remining pipe fetures n 3 50mm initil flw on the WCL. The pipes re loded until the full stroke of the hydrulic cylinders is reched; this produces significnt tering of these flws. No through-thickness crck growth hs een oserved in these tested pipe since no pressure drop (-10 rs) hs een oserved. Before ech mesurement the pipe is unloded up to 10% of the

8 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) mximum lod so the technicin cn sfely conduct mesurements. The silicon smples from the non-pressurized 4- point ending tests show no significnt tering occurred initilly nd the crck extending y lunting. After CMOD reches pproximtely 1mm, significnt tering occurs with shrp crck tip. Likewise, three pipes with defects on WCL nd HAZ hve een tested for 4-point ending with internl pressure. One pipe hs defined initil flw size of 3 50mm on the WCL nd the other two hve flws of 3 50mm nd 4 50mm on the HAZ respectively. All three pipes re loded until filure. A through thickness crck hs een oserved in the pipe with WCL 3 50mm initil flw when loded to filure. Significnt drop in the pressure nd visile wter jet round the flw region indictes through-thickness crck hs occurred. The pipes with HAZ flws fil y unstle crck growth nd rupture of the pipe. In oth tests with HAZ flw, the crck kink into the se mteril nd propgted round the circumference of the pipe. All three pipes undergoing 4-point ending with internl pressure filed t strin levels close to 1.3%. A summry of the ll the ending tests in terms of CTOD ginst the verge strin t 12 o clock position is presented in Fig. 7. The rte of increment of CTOD ginst strin is higher for the pressurised pipe regrdless of the loction or size of the flw nd could not rech to 2% nominl strin efore through-thickness crck occurred. Fig. 7. Averge strin vs. CTOD digrm for 4-point ending test of the pipes with nd without internl pressure Tle 2. Flw geometry mesurements from 4-point ending test HAZ 3 50mm flw without internl pressure HAZ 3 50mm flw with internl pressure ε ve CMOD (mm) CTOD (mm) Δ (mm) ε ve CMOD (mm) CTOD (mm) Δ (mm) Comprison of CMOD vs. strin on either side of the weld shows non-uniform strin distriution. It cn e due to locl non-uniformity of the mteril nd vrition in pipe thicknesses. The CTOD results presented in this pper re ginst the verged strin (ε ve ) t 12 o clock position. CMOD, CTOD nd Δ re ll mesured from the crck growth replic. Comprison of these mesurements for ending tests with nd without internl pressure is given in Tle 2.

9 1902 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) Reeling results The pipes with WCL defects of 3 30mm nd 3 40mm nd HAZ defects of 3 30mm nd 3 40mm flw sizes hve een tested in the reeling test set-up. No through thickness crck ws oserved in the tested pipe. The through thickness crck would hve een identified y pressure drop of 10 rs during the test. Likewise, silicon replic mesurements re lso performed for ech test. Similr to ending test, efore ech mesurement, the pipe is unloded up to 10% of the mximum lod for sfety resons. The verge strin redings (ε ve ) t 12 o clock position re presented long with CMOD, CTOD nd crck growth from replic s shown in Tle 3. The strin is verged from two remote strins, ech t 1 OD distnce from the WCL towrds the ends of the pipe. Only results from two cycles of reeling tests re shown. No results from the strightening of the pipe re shown s the crck is closing during strightening nd no loding t the crck tip is expected. A summry of ll the reeling tests in terms of CTOD ginst the verged strin t 12 o clock position is presented in Fig. 8. CTODs for 3 30mm HAZ flws incresed fster with nominl strin compred with 3 40mm HAZ flws. For WCL flws, on the other hnd, no cler distinction etween 3 30mm nd 3 40mm hs een oserved. Nonetheless, the CTODs re higher for the second reeling cycle thn the first reeling cycle. Tle 3 lso revels tht increment of CTOD s function of crck growth is pproximtely liner for 3 30mm nd 3 40mm HAZ flws. Fig. 8. Crck growth vs. CTOD digrm for 2 cycles of reeling test with HAZ nd WCL flws Tle 3 Flw geometry mesurements from reeling tests HAZ 3 30 mm HAZ 3 40 mm ε ve CMOD (mm) CTOD (mm) Δ (mm) ε ve CMOD (mm) CTOD (mm) Δ (mm) Cycle 1 Cycle Cycle 2 Cycle

10 A. Bstol et l. / Procedi Structurl Integrity 2 (2016) Conclusions Smll-scle nd full-scle experiments on X80 line pipe specimen contining girth welds hve een crried out to determine the strin cpcity X80 pipes with girth welds. The oservtions re s follows: - Smll-scle tests hve reveled vrition of through-thickness tensile nd hrdness properties in the X80 pipes. Results of the tensile tests indicte tht the yield stress overmtch of pproximtely 20% for the weld metl, nd tht the HAZ region is out 7.5% softer compred with BM t 1% pplied strin. Both SENB nd SENT test results show tht the frcture toughness from the WM is lower thn tht from the HAZ. Hrdness mesurements on the weld cross-section show tht hrdness is consistently high in the fusion zone, it decreses on either side of the fusion zone in the HAZ regions. The hrdness of the prent mteril vries significntly with position (distnce from the weld root). High hrdness in the prent mteril t the inner dimeter of the pipe is lso oserved which decreses towrds the outer dimeter. - The full-scle reeling tests hve shown tht the welded X80 pipes cn sustin nominl strin level of up to 2.5% without ny instility for the rnge of defect sizes considered. - The full-scle ending tests hve shown tht, for similr levels of pplied strin, the CMOD of the HAZ flw is generlly higher thn tht of the WCL flw of the sme initil size. In ddition, tering of HAZ flws cn e much higher thn tht of WCL flws. During pressurised full-scle ending tests, through thickness crck nd unstle crck growth re oserved for WCL flw nd HAZ flw respectively, leding to the conclusion tht HAZ softening my limit the cceptle criticl size in n ECA for X80 pipes. Acknowledgements The uthors grtefully cknowledge the significnt contriution to this work from the Open University, UK nd from DNV GL Høvik Mterils Lortory, Norwy. The uthors would lso like to thnk Erling Østy for reviewing nd providing feedck on this pper. References BS7910, Guide to methods for ssessing the cceptility of flws in metllic structures. British stndrd institution DNV-OS-F101, Offshore Stndrd Sumrine Pipeline Systems. DNV GL DNV-RP-F108, Recommended Prctice - Frcture Control For Pipeline Instlltion Methods Introducing Cyclic Plstic Strin. DNV GL EN ISO 15653, Metllic mterils - Method of test for the determintion of qusisttic frcture toughness of welds. Europen Committee for Stndrdistion Fgerholt E, Østy E, Børvik T, Hopperstd OS, Investigtion of frcture in smll-scle SENT tests of welded X80 pipeline steel using Digitl Imge Correltion with node splitting. Engineering Frcture Mechnics 96, Hn SY, Sohn SS, Shin SY, Be JH, Hyoung SK, Lee S, Effect of microstructure nd yield rtio on strin hrdening nd Buschinger effect in two API X80 linepipe steels. Mterils Science nd Engineering 551, Igi S, Skimoto T, Endo S, Effect of Internl Pressure on Tensile Strin Cpcity of X80 Pipeline. Procedi Engineering 10, ISO , Metllic mterils-tensile testing, Prt 1: Method of test t room temperture. Europen Committee for Stndrdistion Kiey S, Iss J A, Wng X, Minnr K, A simplified, prmetric eqution for prediction of tensile strin cpcity of welded pipelines. Pipeline Technology Conference, Ostend, Belgium. Motohshi H, Hgiwr N, Effect of strength mtching on ductile frcture ehviour of X80 linepipe girth welds sujected to tensile loding. Mterils Science Forum, vol , nd Advnced Mterils Reserch vol Swnkie T, Chuhn V, Wood I, Espiner R, Kie M, Quong S, Evlution of girth weld defect cceptnce criteri for grde X100 pipelines. Proceedings of IPC 2012, Interntionl Pipeline Conference, Clgry, Alert, Cnd. Yng Y, Shi L, Xu Z, Lu H, Chen X, Wng, Frcture toughness of the mterils in welded joint of X80 pipeline steel. Engineering Frcture Mechnics 148, Yi D, Xio ZM, Idplpti S, Kumr SB, Frcture nlysis of girth welded pipelines with 3D emedded crcks sujected to ixil loding conditions. Engineering Frcture Mechnics 96,