study on the limit load of large diameter natural gas
TRANSCRIPT
ScientificJournalofTechnologyVolume1Issue02,2019
ISSN:2688‐8645
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StudyontheLimitLoadofLargeDiameterNaturalGasPipelinewithInternalandExternalDefects
FeihongQina,LeiYangb,KaidieYangc,YiLidandYuchuanGuoe
Schoolofpetroleumengineering,SouthwestPetroleumUniversity,Chengdu610500,[email protected],[email protected],[email protected]
[email protected],[email protected]
AbstractInthispaper,theD1016×18.4X80pipelineinarivercrossingsectionofMyanmarChinanatural gas pipeline project is taken as the research object, and the plastic failurecriterion and the double elastic slope criterion are selected as the determinationmethodsof theultimate internalpressure load.Basedon theABAQUS finiteelementanalysis,theeffectsofthedepth,lengthandwidthofinternalandexternaldefectsontheultimateloadofthepipelinearestudiedrespectively.
Keywords
Large Diameter Pipeline; Ultimate Load; X80 Pipeline Steel; Internal And ExternalDefects;Interference.
1. Introduction
Oil and natural gas promote the development of the world economy, which is of greatsignificance to the national economy and national development. At present, the pace ofdevelopmentofChina'soilandnaturalgasindustryisspeedingup,andtheconstructionofoilandgaspipelineshasenteredahigh‐speeddevelopmentperiod.Therearemanyreasonsforpipeline corrosion, moreover the mechanism is complex and the location of corrosion israndom.Theappearanceofcorrosiondefectswillaffectthefailureformandultimatepressureofpipeline.Thelong‐distanceoilandgaspipelinepassesthroughawideareawheretheterrainis complex. Furthermore, there are different soil properties, diverse pipeline structure andvarioustransmissionmediumproperties,thusitiseasytocausealargenumberofinternalandexternaldefectsofthelong‐distancepipeline.Thepipelinewithinnerandouterwalldefectsdoes not necessarily lose the bearing capacity. Repair and replace the pipeline when thepipeline does not completely lose the bearing capacity,which will force to stop pipelinetransmission,causingunnecessaryeconomiclossestoacertainextent.Basedonthefiniteelementmethod,X.Lietal.[1](2016)proposedanevaluationmethodforthe interference between adjacent corrosion, which has better accuracy and applicability,especiallyfortheaxiallongcorrosiondefects.S.s.al‐owaisietal.[2](2016)usedfiniteelementsoftwaretoanalyzeX60withadjacentdefectsofdifferentshapes.Itwasfoundthattheadjacentdefectsoftwoshapes(ellipseandrectangle)willinteractwhentheaxialdistanceisnotmorethan3timesofthewallthicknessorthecircumferentialdistanceisnotmorethan0.5timesofthewallthickness.InGB/T19624safetyassessmentofpressurevesselswithdefectsinservice(2004) [3], considering themutual influence ofmultiple cracks, a crackmergingmethod isproposedaimingatmultipleadjacentcracks,inwhichtheinternalandexternalcrackdefectsare treated as penetrating crack defects, but this method does not propose the treatmentmethodofinternalandexternalvolumecrackdefects.Tosumup,therearefewresearchresultsonthelimitloadofdoubledefectpipelineatpresent,except for the research of crack defects on the inner and outer walls of the pipeline.
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Furthermoretherearefewresearchonthelimitloadofthepipelinewithinternalandexternalvolumedefects.Atpresent,theresearchonthelimitloadofthepipelinewithdoubledefectsismainlyaimedatthesamesurfacedefects,whereasthereisnowaytoavoidtheexistenceandinteraction of internal and external wall defects in actual working condition. Adopting thecurrentpipelinesafetyevaluationsystemtodeterminethepipelinewithinternalandexternaldefects will result in relatively conservative judgment results, thus increasing the pipelineoperationrisk.Therefore,itisnecessarytofurtherstudytheultimateloadofpipelineundertheinterferenceofinternalandexternaldoubledefects.
2. LiteratureReferences
Theprocessofpipelinematerialfailureisrelativelycomplex.Throughthecomparativeanalysisoftheexistingtheoryandmethodofpipelineultimateloadandpipelinefailurecriterion,thispaper finally selects the plastic failure criterion to analyze the ultimate bearing capacity ofpipeline,andchoosesthedoubleelasticslopemethodasthedeterminationcriterionofpipelineultimateload.
2.1. PlasticFailureCriterionInordertoobtaintheultimateloadwithengineeringpracticalsignificance,theplasticfailurecriterion is used to analyze the ultimate bearing capacity. The plastic failure criterion isexpressedasfollows:
00
2ln
3L f
i
RP
R (2‐1)
Inwhich
0LP ——Plasticlimitinternalpressureofflawlesspipelineunderinternalpressure,MPa;
0R ——Outerradiusofpipe,mm;
iR ——Innerradiusofpipe,mm.
The X80 steel studied in this paper belongs to high‐strength steel grade, which has greattoughness.Inordertoexertthebearingcapacityofthematerialandobtainthelimitloadwithengineeringpracticalsignificance,thelocalandcontrollableplasticdeformationofthepipelineisallowed.Inconclusion,thefailurestateofthepipelinewithinternalandexternaldefectsisanalyzedbyusingtheplasticfailurecriterioninthispaper.
2.2. LimitLoadDeterminationCriteriaAccordingtothedifferentcriteriaofsignificantplasticflowwhenthesteelreachestheplasticlimit,therearemanycriteriatodeterminetheultimateloadinengineering.Inthispaper,thedoubleelasticslopecriterionisusedasthecriteriatodeterminetheultimateload,asshowninFigure1,makeaninternalpressure‐straincurve,andmakeastraightlinethroughtheorigin,sothatitsslopeistwicetheslopeoftheelasticsectionoftheloaddeformationcurve.Theloadvalue corresponding to the intersectionof the straight lineand the internalpressure‐straincurveisthelimitload.
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tanψ=2tanθ
Limit load line
Ultimate load point
Ultimate test load
Regression line
Maximum principal strain or displacement
ψ
θ
Loa
d
Figure1:schematicdiagramofdoubleelasticslopecriterion
ThedoubleelasticslopecriterionisamoderncriterionadoptedbyASMEBoilerandpressurevesselcode.IthasarelativelygoodapplicabilityandhighaccuracytothemainstreamsteelinChina.Therefore,thedoubleelasticslopecriterionisadoptedasthedeterminationcriterionofultimateloadinthispaper.
3. FiniteElementAnalysisofLimitLoadofInternalandExternalDefects
3.1. ModelEstablishmentandParameterSettingInthispaper,theparametersofarivercrossingsectionofMyanmarChinanaturalgaspipelineare used for modeling and finite element analysis. In engineering practice, the pipeline isaffectedbymanyfactors.Inordertoaccuratelyanalyzethepipeline,thefull‐sizeD1016×18.4steelpipemodelisusedinthispaper.According toSaintVenant's theorem[4], the lengthof thepipeaffectedby theendeffect iscalculatedasfollows:
10162.5 2.5 18.4 241.7
2L Rt mm (1)
Itshowsthatthelengthof241.7mmawayfromthetwoendswillbeaffectedbytheconstraintsofthetwoends.Thus,inordertofullyavoidtheinfluenceoftheendeffectofthepipesection,bettermodelingandanalysis,thelengthofthefiniteelementmodelinthispaperissetas4m,andthedefectsarelocatedinthemiddleofthemodel.ModelparametersareshowninTable1.
Table1:finiteelementmodelparametersofpipesection
Steels
Yieldstrength(M
Pa)
Ultimatetensile
strength(MPa)
Youngmodulus(G
Pa)
Poisson'sratio
Length(m)
Externaldiameter(m
m)
Wallthickness(m
m)
API5L
SPECX80
555 625 210 0.3 4 1016 18.4
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Themodelofpipesectionisformedbydrawing,thetypeofdefectissetasrectangularvolumedefect, and the corrosion rectangular pit is formed by rotating cutting. Besides, themodeladopts C3D8R eight nodes linear hexahedron reduction integral element. In addition, thestructuredgriddivisiontechnologyisusedtofinallyformthegrid.ThegriddivisionresultsareshowninFigure1.
Figure2:schematicdiagramofgriddivision
3.2. AnalysisoftheInfluenceofInternalandExternalDefectParametersontheUltimateLoad
3.2.1. AnalysisoftheInfluenceoftheDepthofInternalandExternalDefectsontheUltimateLoadofPipeline
Inthissection,theinfluenceofdifferentdefectdepthontheultimateloadwillbeanalyzed.Inordertofacilitatetheanalysisandsummaryofthelaw,thedefectdepthwillbedimensionlesstreated,anda/t=0.1willbeusedasthedefectfoundationdepthofthestudy.Whenstudyingtheinfluenceofthedepthofinternalandexternaldefectsontheultimateloadofpipeline,setthelengthofinternalandexternaldefects /b Rt =1,widthc=20mm,andthedepthaofinternalandexternaldefectsarea/t=0.1,0.15,0.2,0.25and0.3respectively.Thereare25typesofdefectsintotal.AsshowninFigure2,basedonfivekindsofpipeaxialspacingofL=50mm,150mm,250mm,350mmand450mm,125modelswithexternaldefectsa1/tandinternaldefectsa2/tof0.1,0.15,0.2,0.25and0.3,wererespectivelyestablished.
(a)a1/t=0.1(b)a1/t=0.15(c)a1/t=0.2(d)a1/t=0.25(e)a1/t=0.3
Figure3:schematicdiagramofexternaldefectmodelbasedondepthchange
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Theabove125kindsofpipelinemodelsareimportedintoABAQUSforfiniteelementanalysis,andthecorrespondinginternalpressure‐straincurveisobtained.Further,thelimitloadcanbeobtainedbyintroducingitintoOriginsoftwarewiththeuseofthedoubleelasticslopemethod.
L=50mm
Figure4:3Drainbowmapofinnerdefectdepthouterdefectdepthultimateload
0.10 0.15 0.20 0.25 0.300.10
0.15
0.20
0.25
0.30
Dep
th o
f ex
tern
al d
efect
Depth of internal defect
13.18
14.30
15.42
16.54
17.66
18.78
19.90
21.02
22.14
L=50mm
Figure5:contoursectionofinternaldefectdepthexternaldefectdepthultimateload
ItcanbeseenfromFigure3andFigure4thatwhenL=50mm,withtheincreaseofthedepthofinternalandexternaldefects,thelimitloadvalueofpipelinedecreasesfrom22.13MPato13.19MPa,withatotaldecreaseof8.94MPaandthedecreaseof40.40%.Theaboveanalysisshowsthatwhentheaxialdistancebetweentheinnerandouterdefectsissmall,theinterferenceeffectofthedoubledefectsisnoticeablystrengthened,whichleadstothedeclineoftheultimateloadofthepipeline.ItcanbeseenfromFigure4thattheultimateloadofpipelinedecreasesrapidlywiththeincreaseofdefectdepth,andtherateofchangeisincreasing,whichfullyshowsthattheinfluenceofdefectdepthontheultimateloadofpipelineissignificant.
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3.2.2. AnalysisoftheInfluenceoftheLengthofInternalandExternalDefectsontheUltimateLoadofPipeline
Inthissection,theinfluenceofdifferentdefectlengthsontheultimateloadwillbeanalyzed.Inordertofacilitatetheanalysisandsummaryofthelaw,thedefectlengthwillbedimensionlesstreatedand /b Rt =0.5willbeusedasthebasicdefectlengthofthestudy.Whenstudyingtheinfluenceofthelengthofinternalandexternaldefectsontheultimateloadofthepipeline,setthedepthofinternalandexternaldefectsa/t=0.25,a=4.6mm,widthc=20mm,andthelengthbofinternalandexternaldefectsare0.5 Rt , Rt ,1.5 Rt ,2 Rt ,2.5 Rt ,respectively.Thereare25typesofdefectsintotal.AsshowninFigure5,basedonfivekindsofpipeaxialspacingofL=50mm,150mm,250mm,350mmand450mm, the lengthofexternaldefectb1andinternaldefectb2 as0.5 Rt , Rt ,1.5 Rt ,2 Rt , 2.5 Rt are respectivelyestablished,andthereare125pipemodelsintotal.
(a)b1=0.5 Rt (b)b1= Rt (c)b1=1.5 Rt (d)b1=2 Rt (e)b1=2.5 Rt
Figure6:schematicdiagramofexternaldefectmodelbasedonlengthchange
Theabove125kindsofpipelinemodelsareimportedintoABAQUSforfiniteelementanalysis,andthecorrespondinginternalpressure‐straincurveisobtained.Further,thelimitloadcanbeobtainedbyintroducingitintoOriginsoftwarewiththeuseofthedoubleelasticslopemethod.
L=50mm
Figure7:3Drainbowmapofinnerdefectdepthouterdefectdepthultimateload
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L=50mm
Figure8:contoursectionofinternaldefectdepthexternaldefectdepthultimateload
ItcanbeseenfromFigure6thatwhenL=50mm,withtheincreaseofthelengthofinternalandexternaldefects,theultimateloadvalueofthepipelinedecreasesfrom19.41MPato14.83MPa,withatotalof4.58MPaandthedecreaseof23.60%.Thus,theultimateloadofpipelinewilldecreasewiththe increaseofdefect length,butthechangeratewillbesmallerandsmaller.Besides,asshowninFigure7,thecontourdistributionbecomessparserwiththeincreaseofthelength,indicatingthatwhenthedefectlengthislonger,itsinfluenceontheultimateloadofthepipelinedecreasesgradually.3.2.3. AnalysisoftheInfluenceoftheWidthofInternalandExternalDefectsonthe
UltimateLoadofPipelineThissectionwillanalyzetheinfluenceofdifferentdefectwidthontheultimateload.Inordertofacilitatetheanalysisandsummaryofthelaw,widthc=20mmisusedasthewidthofdefectfoundation.Whenstudyingtheinfluenceofthewidthofinternalandexternaldefectsontheultimateloadofthepipeline,setthedepthofinternalandexternaldefectsa/t=0.1,a=1.84mm,lengthb/ Rt=1,b=96.68mm,andthewidthcofinternalandexternaldefectsarerespectively20mm,50mm,100mmand200mm.Thereare16typesofdefectsintotal.AsshowninFigure8,themodelswiththewidthofexternaldefectc1andinternaldefectc2of20mm,50mm,100mmand200mmarerespectivelyestablishedbyusingtheaxialspacingofL=50mmand150mm.Thereare32pipelinemodelsintotal.
(a)c1=20mm(b)c1=50mm(c)c1=100mm(d)c1=200mm
Figure9:schematicdiagramofexternaldefectmodelbasedonwidthchange
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Theabove32kindsofpipelinemodelsareimportedintoABAQUSforfiniteelementanalysis,andthecorrespondinginternalpressure‐straincurveisobtained.Further,thelimitloadcanbeobtainedbyintroducingitintoOriginsoftwarewiththeuseofthedoubleelasticslopemethod.ItcanbeseenfromFigure9thatwhenL=50mm,withtheincreaseofthewidthofinternalandexternaldefects,thelimitloadvalueofpipelinedecreasesfrom22.13MPato21.48MPa,withonlyatotaldecreaseof0.65MPaandadecreaseof2.94%.Inaddition,withtheincreaseofthewidthofinternalandexternaldefects,thelimitloadofthepipelinedecreasesslightly,whiletheoverallchangeisnotsignificant.Furthermore,itcanbeseenfromFigure10thatmostareasoftheultimateloadareinastateofvery low rate of change, indicating that the influence of thewidth of internal and externaldefectsontheultimateloadofthepipelineisinsignificant,whichcanbeignoredinengineering.
L=50mm
Figure10:3Drainbowmapofinnerdefectdepthouterdefectdepthultimateload
L=50mm
Figure11:contoursectionofinternaldefectwidthexternaldefectwidthultimateload
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4. Conclusion
In this paper, theD1016×18.4X80pipeline of a river crossing section ofMyanmarChinanatural gas pipeline project is used as the modeling basis, meanwhile the ABAQUS finiteelementsimulationisusedtoresearchontheinfluenceofinternalandexternaldefectsontheultimateloadofthepipelineundertheinterference.Besides,theinfluenceofthedepth,lengthand width of internal and external double defects on the ultimate load of the pipeline isanalyzedanddiscussedrespectively.Theconclusionisasfollows:Theultimateloadofpipelinedecreasessignificantlywiththeincreaseofthedepthofinternalandexternaldefects,andtherateofchangeisincreasing.Thus,thedepthofdefectsisthemainfactoraffectingtheultimateloadofpipeline.While,theultimateloadofpipelinedecreaseswiththe increaseof the lengthof internal and external defects, but the rate of change is gettingsmallerandsmaller,whichindicatesthatthelengthofdefectshasanimpactontheultimateloadofpipelinetosomeextent.Furthermore,whenthelengthofdefectsislongerthan2.5 Rt ,theinfluenceoflengthonthepipelinecanbeignored.Moreover,comparedwiththedepth,thedefectlengthisthesecondaryinfluencefactoroftheultimateloadofthepipeline;atlast,theultimateloadofthepipelineisalmostconstantwiththeincreaseofthewidthoftheinternalandexternaldefects,indicatingthatitsinfluencecanbeignored.
Acknowledgements
SupportedbytheOpenExperimentFundofSouthwestPetroleumUniversity.
References
[1] LiX,BaiY,SuC,etal.Effectofinteractionbetweencorrosiondefectsonfailurepressureofthinwallsteelpipeline[J].InternationalJournalofPressureVessels&Piping,2016,138:8-18.
[2] Al‐OwaisiSS,BeckerAA,SunW.Analysisofshapeandlocationeffectsofcloselyspacedmetallossdefectsinpressurisedpipes[J].EngineeringFailureAnalysis,2016,68:172-186.
[3] GeneralAdministrationofqualitysupervision,inspectionandQuarantineofthepeople'sRepublicofChina.Safetyassessmentofpressurevesselswithdefectsinuse(GB/T19624‐2004)[S].Beijing:ChinaStandardsPress,2005.
[4] QiuChangsheng.StudyonextremepressureofUHPreactiontube[D].SouthChinaUniversityoftechnology,2013.