P91钢管的焊接和残余应力以及焊后热处理的数值模拟

://sdj.sagepub.com/content/43/5/275Theonlineversionofthisarticlecanbefoundat: DOI:10.1243/03093247JSA372200843:275TheJournalofStrainAnalysisforEngineeringDesignAHYaghi,THHyde,AABeckerandWSunphasetransformationandpost-weldheattreatmentFiniteelementsimulationofweldingandresidualstressesinaP91steelpipeincorporatingsolid-state  Publishedby:  InstitutionofMechanicalEngineerscanbefoundat:TheJournalofStrainAnalysisforEngineeringDesignAdditionalservicesandinformationfor     : : : : : WhatisThis? -May1,2008VersionofRecordatXi’anJiaotongUniversityonNovember8,2011sdj.sagepub.comDownloadedfromFiniteelementsimulationofweldingandresidualstressesinaP91steelpipeincorporatingsolid-statephasetransformationandpost-weldheattreatmentAHYaghi*,THHyde,AABecker,andWSunDepartmentofMechanicalEngineering,UniversityofNottingham,Nottingham,UKThemanuscriptwasreceivedon12November2007andwasacceptedafterrevisionforpublicationon19February2008.DOI:10.1243/03093247JSA372Abstract:Thefiniteelement(FE)methodhasbeenappliedtosimulateresidualaxialandhoopstressesgeneratedintheweldregionandheat-affectedzoneofanaxisymmetric50-beadcircumferentiallybutt-weldedP91steelpipe,withanouterdiameterof145mmandwallthicknessof50mm.TheFEsimulationconsistsofathermalanalysisandasequentiallycoupledstructuralanalysis.Solid-statephasetransformation(SSPT),whichischaracteristicofP91steelduringweldingthermalcycles,hasbeenmodelledintheFEanalysisbyallowingforvolumetricchangesinsteelandassociatedchangesinyieldstressduetoausteniticandmartensitictransformations.Phasetransformationplasticityhasalsobeentakenintoaccount.Theeffectsofpost-weldheattreatment(PWHT)havebeeninvestigated,includingthoseofheattreatmentholdingtime.Residualaxialandhoopstresseshavebeendepictedthroughthepipewallthicknessaswellasalongtheoutersurfaceofthepipe.TheresultsindicatetheimportanceofincludingSSPTinthesimulationofresidualstressesduringtheweldingofP91steelaswellasthesignificanceofPWHTonstressrelaxation.Keywords:P91steelpipe,finiteelementweldsimulation,residualstress,phasetransforma-tion,post-weldheattreatment1INTRODUCTIONTheefficientoperationandsafetyofpowergenera-tionplantshavebeentheconcernofthesciencecommunityfordecades.Inparticular,theintegrityconsiderationsforsteelpipelinesinpowerplantsdeliveringsteamatahightemperatureandpressurehaveplayedacriticalroleintheoverallsafetyassessmentofpowerplantcomponents.Sincethe1970sand1980s,followingsignificantadvancementinthemetallurgicalpropertiesofthesteelgradechosenintheconstructionofpowerplantpipelines,suchasenhancedcreepstrength,modified9percentCr(P91)steelhasbeenusedforthatpurpose,withtheaddedcomplicationofhavingtoweldmanypipejointstogether.Theprocessofweldinginvolvesalargenumberofthermalcyclesresponsibleforalterationsinthesteelmicrostructureaswellasinitsmechanicalandphysicalproperties.Weldedsteeljointsaresometimesconsideredtheweakestpartinapipelineowingtothepossiblereducedcreepstrengthoftheweldmetalandthesurroundingheat-affectedzone(HAZ).Powerplantsteelpipesareusuallyjoinedtogetherbyfusionwelding,whichisaprocessinvolvingthemeltingofwhatsolidifiesintoweldbeadsbyapplyingthermalfluxes,causingtheweldmaterialtoreachthematerial’smeltingpointorevenhighertemperatures.Insomeotherengi-neeringcomponents,ajointcanbeformedwithfrictionwelding[1],whichisamorerecentapplica-tion,involvingfrictionunderpressureofthetwometalsurfacestobejoined,therebyallowingtheproducedfrictionweldtoformatsubstantiallylowertemperaturesthanthematerial’smeltingpoint.Thispaperisonlyconcernedwiththefusionweldingprocess.P91steelshavedesirablecreep-resistantproper-ties.Theefficiencyofpowerplantshasbeen*Correspondingauthor:DepartmentofMechanicalEngineering,UniversityofNottingham,UniversityPark,Nottingham,NG72RD,UK.email:[e-mail].43atXi’anJiaotongUniversityonNovember8,2011sdj.sagepub.comDownloadedfromimprovedsignificantlybybeingabletoraisethetemperatureofsteamto593uCinP91pipesinservice[2].CreepdamageanalysesandfailurepredictionshavebeencarriedoutforrepresentativeweldedcomponentsofP91steel[3],includingrepairwelds[4],toreachabetterunderstandingofhowcreepcanleadtothefailureofpipes.Thefiniteelement(FE)simulationofcreephasbeenoneofthemosteffectivetechniquesintheintegrityassessmentofweldedcomponentsandpipes.Althoughcreephasbeenextensivelyinvestigatedforweldedpipejoints,theusualassumptionhasbeentohavenoresidualstressesattheinceptionoftheanalyses.Theprocessofweldingisresponsibleforsubstantialresidualstresses,whichcanbeashighasthematerialyieldstressinplaces,ifnopost-weldheattreatment(PWHT)isapplied.EvenafterPWHT,someresidualstresseswillpersist,albeitwithreducedmagnitude.TheFEsimulationofthe