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ReportNO：M-2014SZRE110Z-Classification：DrumRepairingServiceof#2BoilerinLaibinBPowerPlantTechnicalSuzhouNuclearPowerResearchInstituteReportNO：M-2014SZRE110Z-Classification：DrumRepairingServiceof#2BoilerinLaibinBPowerPlantTechnicalproject ZHAOtechnical CHENproject SuzhouNuclearPowerResearchZHAOJiancang WANGGangang CHENZhongbin Jia LIANGZhenxin DONGPeixin LIUXiaoHU MA SONGLaibinBPowerSUZHULULIUZHONGMODraftedDraftedJiaCHENWANGZHAOSuzhouNuclearPowerResearchInstituteProject Theposition,typicalappearanceandfeaturesof TechnicalPlansofDrumCracksWelding OverallTechnicalProcessofthe PlanofCracks ResidualStress Measuresavoidingdrum Displacementmonitoryoftherepairzoneduringheat TechnicalPlansonWelding TestAfter Qualityinspectionafter ysisonCrack ysisonCrackMorphologyand ysisonMaterial ResidualStressTestbefore OperatingConditionsandDrumStructure OverallysisonCrackCausesand PreparationofDrumCrack CrackDefect Repairplanoncrack ysisontheFeasibilityofWelding FeasibilityofWelding DifficultiesfacedinWelding MainTechnicalMeasuresonCrack Weldingrepairprocedureon Theprocessoftheweldjointdefect Removedefectsandprepareweld Drytheweldingelectrodes PreheatingandInter-pass Weldingprocedureandtheprocess Heat Quality MainItemstobe Inspection Visual MicrostructureandHardness Stress DrumOvalityMonitoringandMeasuringDuring Monitoringandmeasuringofdrumdeflectionanddisplacementduring TemperatureMeasuringandMonitoringDuringDrumHangers QualityControlwas RepairQualityis SafetyGradingAfter The#2BoilerinPowerPlantB,LaibinGuangxi,ModelHG-1069/18.2-YM1,madebyHarbinBoilerCompany,isa360MWcoalfiredboilerofcontrolledcycle,subcriticalpressure,singlereheat,fourcornersburner,tangentiallyfired,single-chambersingledrum.Its umcontinuousevaporationis1069t/h;thesuperheateroutletpressure/temperatureis20.62Mpa/543°C;andthereheateroutletpressure/temperatureis4.695Mpa/541°C.The#2Boilerwasputintooperationon11thOctober,1999,andconnectedintothegridinFebruary,2000.Thedrumconsistsoftwocylindersectionsandtwoheads,bothofthemaremadefromSA299.Thedrumismadeunderthespecificationsofunevenwallthickness,thus,theupperinternalradiusis872.3mm,wallthicknessis200mm;thelowerinternalradiusis889mm,wallthicknessis166.7mm.Therearealtogether4largeΦ526×120mm erscameoutfromthedrum,socketmaterialis20MnMo,tubematerialisSA106B,tubedimensionisΦ368×42mm,thesocketsareinner-flat.Thereare3economizerfeedwatertubesgoingintothedrum,thematerialofthejoinis20MnMo,thedimensionisΦ414.3×91.25mm.Thematerialofthesafetyvalvesocketis20MnMo,thedimensionisΦ168.3×47.6mm.Annealingheattreatmentwasperformedafterdrumweldingcompleted.Hydrostatictestshowsittobequalified.Thedrumworkingtemperatureis369°C,workingpressureis19.6MPaand umworkingpressureis20.62Mpa.TheconfigurationofthedrumisshowninFigure1-Fig.1- DrumofUnitDefectsTheinspectionandrepairprojectoftheBoiler#2startedinApril2014.TheinspectionoftheboilermetalwasunderthesupervisionofGuangxiSpecialEquipmentInspectionInstitute.InspectiononBoiler#2showedthat,therewerecracksinvariousdegreeoncylinder,centralized economizerfeedwatertubeandthesocketofsafetyvalve.CommissionedbytheownerofGuangxiLaibinPowerPlantB,SuzhouNuclearPowerResearchInstitution(a.k.a.SNPI)wasinchargetoconfirmdefectinspection,assessdrumsafetygradeandrepairdefects.DNTofvariouspositionsondrumandsocketshadbeencarriedoutfrom22ndto30thApril2014.TestedlocationsandthesummaryofinspectionresultsareillustratedinTable1-1.UTandMTdiscovered52meterscracksintotalon60%longitudinalweldseamand1/3horizontalweldseamondrumcylinder.Crackshavebeenfoundon3weldjointsonbothinsideandoutsideoffilletweldonsocketofcentralizeder,inDNTandMT.Crackson55weldjointsonfilletweldonsocketsof -waterdistributionpipe, returnpipe,havebeendiscoveredbyMT.Crackshavebeenfoundon3filletweldseams(bothinsideandoutside)onthesocketoffeedwatertube,inDNTandMT.Crackson6filletweldseamsintotal(bothinsideandoutside)onthesocketofthesafetyvalveofthedrum,havebeendiscoveredbyMT.Crackson7filletweldsonsocketsofdischargefittingshavebeendiscoveredinCrackson15filletweldsintotalhavebeenfoundonthesocketjoint(testjointsandlocalwaterlevelindicatortubeareincluded)onbothsidesofthedrumheads,inMT.Cracksanddefectsdiscoveredin19locationshavebeenconfirmedduringtheexam,asillustratedintable1-1 Namesoftheoftheofthe ofthe\\\Jointofthesafetyvalveinthebacksideoftheright\\Jointofthesafetyvalveinthefrontsideoftheright\\\Jointofthedrainpipeinthebacksideoftherightdrum\Testjointinthefrontsideoftherightdrum\\Jointofthelocalwaterlevelindicatortubeinthebacksidetherightdrum\\Jointofthelocalwaterlevelindicatortubeinthefrontoftherightdrum\\\Jointofthelocalwaterlevelindicatortubeinthebacksidetheleftdrum\\\Jointofthelocalwaterlevelindicatortubeinthepartoftheleftdrum\\Jointofthesafetyvalveoutofthebacksideoftheright\\\Jointofthesafetyvalveoutofthefrontsideofthedrum\\\longitudinalweldseamonthebacksideofthe\\\circumferentialweldseamonthedrumattheleft\\\ thirdrowonthefrontsideofthe fourthrowonthefrontsideofthe8PressuremeasuringtubeinthecenterofTheposition,typicalappearanceandfeaturesofCracksontheeconomizerfeedwatertube(inside)ontherightsideoftheInsidethedrum,a250mmintermittentcrackatposition0’to3’;a190mmintermittentcrackatposition3’to5’;a150mmintermittentcrackatposition6’to8’anda70mmintermittentcrackatposition9’havebeenfoundonthefilletweldontheeconomizerfeedwatertubeontherightsideofthedrum.Asshowninfigure1-2. Figure1- CracksontheeconomizerfeedwaterCracksonthesecondeconomizerfeedwatertube(inside)ontherightsideoftheInsidethedrum,a270mmintermittentcrackatposition0’to3’;a100mmintermittentcrackatposition7’7.5’;a185mmintermittentcrackatposition7.5’to9’anda150mmintermittentcrackatposition9’to10.5’havebeenfoundonthefilletweldonthesecondeconomizerfeedwatertubeontherightsideofthedrum.Asshowninfigure1-3. a)Location b)FeatureofthecracksFigure1-3CracksonthesecondeconomizerfeedwatertubeCracksonthethirdeconomizerfeedwatertube(inside)ontherightsideoftheInsidethedrum,a300mmintermittentcrackatposition1’to3’;a300mmintermittentcrackatposition3’to5’;a300mmintermittentcrackatposition7’to9’anda200mmcrackatposition10’neartheweldtoeonthebasemetal,havebeenfoundonthefilletweldonthethirdeconomizerfeedwatertubeontherightsideofthedrum.Asshowninfigure1-4. b)FeatureofthecracksFigure1-4CracksonthethirdeconomizerfeedwatertubeCracksonthefourth er(outside)ontherightsideoftheOutsidethedrum,nearthefilletweldtoeonthebasemetal,a50mmintermittentcrackatposition0’to3’;a15mmintermittentcrackatposition3’to6’;havebeenfoundonthefourthcentralized erontherightsideofthedrum.Asshowninfigure1-5. b)FeatureofthecracksFigure1-5Cracksonthefourthcentralized CracksonthejointofthesafetyvalveinthebacksideoftherightdrumAnapproximay20mmcrackatposition7.5’neartheweldtoeofthebasemetalhasbeenfoundonthejointofthesafetyvalveinthebacksideoftherightdrumhead.Itturnedouttobeaweldpatchareainthemetallographictestfollowedup.Itshardnessexceeded300HBasshowninfigure1-6. Cracksonthejointofthesafetyvalve(backsideoftheCracksonthejointofthesafetyvalveinthefrontsideoftherightdrumInsidethedrumhead,therearetwocracksof3to5mmlongatposition6’to8’onthejointofthesafetyvalveinthefrontsideoftherightdrumhead.Asshowninfigure1-7. Cracksonthejointofthesafetyvalve(frontsideoftheCracksonthejointofthedrainpipeinthebacksideoftherightdrumInsidethedrumhead,therearemanyintermittentcracksatposition4’to12’near¾circleoftheweldtoe,onthejointofthedrainpipeinthebacksideoftherightdrumhead.Asshowninfigure1-8. Cracksonthejointofthedrainpipe(backsideoftheCracksonthejointofthelocalwaterlevelindicatortubeinthebacksideoftherightdrumheadInsidethedrumhead,therearetwointermittentcracksof10mmlongatposition5’to7’ofweldtoeareaonthejointofthelocalwaterlevelindicatortubeinthebacksideoftherightdrumhead.Asshowninfigure1-9. Cracksonthejointofthelocalwaterlevelindicatortube(backsideoftheCracksontheJointofthelocalwaterlevelindicatortubeinthefrontsideoftherightdrumndicatortubeinthefrontsideoftherightdrumheadasshowninfigure1-Insidethedrumheadndicatortubeinthefrontsideoftherightdrumheadasshowninfigure1-ofofthelocalwaterlevel Cracksonthejointofthelocalwaterlevelindicatortube(frontsideoftheCracksonthetestjointinthefrontsideoftherightdrumInsidethedrumhead,there’sanintermittentcrackatposition6’to12’ofweldtoeareaonthetestjointthefrontsideoftherightdrumhead,asshowninfigure1- CracksonthetestjointinthedrumCracksontheJointofthesafetyvalveoutofthefrontsideoftherightdrumOutsidethedrumhead,there’sa20mmlongcrackatposition6’to9’ofweldtoeareaonthejointofsafetyvalvesocketoutsideofthefrontsideoftherightdrumhead.Thissurfacedefecthasbeenremovedafterbeenpolishedduringthemetallographictest.Refertofigure1-12. FeatureoftheFig.1- RemoveddefectonthejointofthesafetyCracksonthejointofthesafetyvalveoutofthebacksideoftherightdrumOutsidethedrumhead,there’sa20mmlongcrackatposition3’to6’ofweldtoeareaonthejointofvalvesocketoutofthebacksideoftherightdrumhead.Refertofigure1- FeatureoftheFig.1- CracksonthejointofthesafetyCracksontheJointofthelocalwaterlevelindicatortubeinthemiddlepartoftheleftdrumheadInsidethedrumhead,there’sanintermittentcrackatposition10’to12’oftheweldtoeareaonthelocalwaterlevelindicatortubeinthemiddlepartoftheleftdrumhead,asshowninfigure1-14. FeatureoftheFig.1-14CracksontheJointofthelocalwaterlevelindicatorCracksontheJointofthelocalwaterlevelindicatortubeinthebacksideoftheleftdrumheadInsidethedrumhead,there’san13mmlongintermittentcrackatposition0’andmanyintermittentcracksatposition3’to7’oftheweldtoeareaonthelocalwaterlevelindicatortubeinthebacksideoftheleftdrumhead,asshowninfigure1-15. FeatureoftheFig.1- CracksontheJointofthelocalwaterlevelindicatorCracksonthelongitudinalweldseamonthebacksideoftheThere’sa40mmlongcracklocatedonthelongitudinalweldseamonthebacksideofthedrum,atthecircumferentialsurfacepositionofthethirdeconomizerfeedwatertube(inside)ontherightsideofthedrum.Moreover,therewasapatchontheoriginalweldbeadatthisposition.AsshowninFig.1- Fig.1- CracksonthelongitudinalweldseamonthebacksideoftheCracksonthecircumferentialweldseamondrumattheleftAttheleftdrumhead,thereisa40mmlongintermittentcrackatthepositionof3’to6’ofthetoeareaonthecircumferentialweldseamonthedrum,asshowninfigure1- Fig.1- CracksonthecircumferentialweldseamontheThreecracksonthefilletweldonthesocketatthetopoftheTherewasacrackatthepositionoffilletweldtoesoneachfollowingparts:pressuremeasuringtubeinthecenterofdrum;the16th(countedfromleft) -wateroutletpipeinthefourthrowonthefrontsideofthedrumandthe17th(countedfromleft) distributionpipeinthethirdrowonthefrontsideofthedrum;Asshowninfigure1-18.Featuresofthecrack FeaturesofthecrackFig.1-18 cracksonthefilletweldonthesocketatthetopofthedrumTechnicalPlansofDrumCracksWeldingOverallTechnicalProcessofthe OverallTechnicalProcessofthePlanofCracksSize ysison ysisofthecracknatureandtheessentialConclusionofysisofthedrumcracknatureandessentialFilletweldoftheeconomizerfeedwatertubeonthedrum'srightside:Basemetal,weldseam,HAZshouldbetested,includingthemiddleand softhecrack.Filletweldofthesecondeconomizerfeedwatertubeonthedrum'srightside:Basemetal,weldseam,HAZshouldbetested,includingthemiddleand softhecrack.Forshortcracks,wholelengthofthecrackshouldbetested.Crackareaonthelowerpartofthedrumcylinder:ThemiddleandsofthecrackshouldbeFilletweld:Basemetal,weldseam,HAZshouldbetested,includingthemiddleandsoftheFilletweldonthecentralized eronthedrum'srightside:Basemetal,weldseam,HAZshouldbetested,includingthemiddleandsofthecrack.ResidualStressFilletweldoftheeconomizerfeedwatertubeonthedrum'srightoneonthecrackornearthecrackoffilletweld;oneonthedrumOneonthefilletweldswherethereisnoFilletweldofthesecondeconomizerfeedwatertubeonthedrum'srightOnetestpointonthecrackornearthecrackoffilletweld;OnetestpointonthedrumOnetestpointonthefilletweldwherethereisnoFilletweldofthethirdeconomizerfeedwatertubeonthedrum'srightTestposition:onetestpointonthefilletweld,oneontheThecrackareaonthelowerpartofdrumOnetestpointonthecrackornearthecrackoffilletOnetestpointfarawayfromtheFilletweldofsafetyOnweldswithcrack:Onetestpointonthecrackornearthecrackoffilletweld;Onetestpointonthefilletweldbutfarawayfromthecrack;Onetestpointonthebasemetalofthecylinder.Onfilletweldofsafetyvalveatdrumexpansionside:Onetestpointonthefilletweld;Onetestpointonthebasemetalofthecylinder.MeasuresavoidingdrumForceonthedrumForceonthe CalculatethedeflectionofCalculatetheadditionalstrengthoftheDisplacementmonitoryoftherepairzoneduringheat表表11表表表21表 表 Figure2- DisplacementmonitoryoftherepairzoneduringheatTechnicalPlansonWeldingTheouterwallisheatedbyheatingplate(around800kWintotal),duringpreheatingbeforeweldingrepair;bothinnerwallandouterwallshallbeheatedduringPWHT.TheprocessgraphandparameterareillustratedhereinFigure2-3.Heatingplatesforouterwall,heatingframesforinnerwallandheatingropeforthesocket.Thearrangementofheaterspleasereferstorelatedcontent.Fig2- TheprocessgraphandparameterofdrumcracksweldingThedrumouterwallisheatedbyheatingplate;heatingwidthis1000mmfromeachsideoftheto-be-repairedtubecenter(around600kWintotal).Thedruminnerwallisheatedbyheatingrope;theheatingwidthis3to5timesofthewallthickness.Cleanupeachinter-passduringrepair,whennecessary,hammeronitinordertorelieveTable2- weldingprocessandDiameterJ507RH120toJ507RH160toThearrangementofinnerheatingframes(1000x900x40mm)isshownintheFigure2-4,eachheatingframeis10KW,60to80piecesintotal,makingupto600to800KW.4setofDWK-360computertemperaturecontroldevicesareequipped.Figure2- ThearrangementofinnerheatingTestAfterNDTtestwereperformedin24hoursafterheatTheacceptancecriteriaofvisualexaminationonweldThereshouldbenoundercut,cracks,porosity,slagorotherdefectsonweldMTandUTTheacceptancecriteriaareaccordingtoJB/T4730,qualitygradeNomicrocracksorabnormalstructuresshouldbefoundin Thehardnessoftheweldrepairshouldnotbe+100HBmorethanthebasemetal,moreover,shouldnotexceed270HB.QualityinspectionafterTable2- AcceptanceCriteriaofweldWeldGroovefilletWeldseam(WidenedthantheCornerfillet+(2toGroovefilletwelddimensionCornerfilletwelddimensionTable2- AcceptanceCriterirmittedrangeofdefectontheweld NotDepth≤0.5mm;socketweldseam≤10%oftheweldseamtotallength,andalso≤40mm;longitudinalandcircumferentialweldseam≤10%oftheweldseamtotallength Requirementfordeflection,roundnessandresidual123ResidualResidualstressinrepairedareashouldnotexceed100MPa,Individualpointsshouldnotexceed140MPaysisonCrackysisonCrackMorphologyandTakeTakeasamplefromthefilletweldofthedrum'srightsidesecondeconomizerfeedwatertube.AsshowninFig.3-1,thesampleisatriangularprism;partofthelineardisplayareaisretainedinthesample.Interceptthreesequentialsamplesfromtheareawherethelinearshowsmorecontinuous,numberthemassample1,sample2andsample3,withlengthof10mm,5mmand3mm.Observedtheappearanceandthestructuresofthem,crackswereallfoundneartheoutersurface.LocationsofcracksareshowedinFig.3-2.Cutoffa3mmhighpiecealongthedirectionofcrackpropagationofsample3forcrosssectionalobservationofthecrack.Fig.3-1Featureofthe Fig.3-2CracklocationonthecrosssectionoftheObservetheappearancesandstructuresofsampleNumber1and2.Itcanbeseenthatcracksfrombothsampleslocatedonweldseams,nearthefusionline.ThecracklengthofsampleIis726μm,andthecracklengthofsample2is1004μm.Bothofthecracksarewidelyopen,yetonsample1,itismoreflatandstraight.Thereisanellipsecanbeseeninthecrackofsample2,whichcouldbearesultofencounterwithporedefectduringthedevelopmentofthecrack.CracklocationonSample b)CracklocationonSamplec)CrackLengthonSample1 d)CrackLengthonSample2Fig.3-3 MetallographicexaminationoftheMacrostructureofthecrackMetallographicexaminationsofthemicrostructureareshowninFigure3-4toFigure3-6.Itcanbeseenthatatransgranularcrackinghadoccurred.Fromtheobviousoxideonthecracktip,wecan lthatthecrackwasformedwhendrumoperatedinhightemperature.However,asthesamplecouldhavebeendamagedbeforetheinterceptiononsite,metallographicysisfromacross-sectionofthesamplecannotdeterminetheinitiallocationofthecrackanditsproperties. Cracktiponsample CracktiponsampleFig.3-6CrackinitiallocationareaonSampleObservethesurfaceofthecrackAfterbeenimmersedinliquidnitrogenandcleanedbyultrasonic,crackofsample3wasopenforobservationandexamination.TheappearanceandthestructureofthecrackfractureareshowninFigure3-7.Fig3- thecrackObservethecrackfracturethroughSEM(scanningelectronmicroscopy)andyzebymicro-spectroscopy,itcanbeseenthatthecrackfractureismostlycoveredbyoxides.Whichindicatedthatthecrackswereformedinhigh-temperatureoperationduringalongertime,refertoFig.3-8,therearedimpleandtornedgesnearpartialfracturesofthecracktip.AsitisshowninFig.3-9,combinedwiththetransgranularfractureofthecrack,itcanbediagnosedasductilefracture.Thematerialhasacertaintoughnessreserves.ThemorphologyofsecondarycracksnearthecracktipisshowninFigure3-10.ThefracturesurfacenearthecracksurfaceisshowninFigure3-11.Duetothepolishdestructionduringsamplingonsite,theoriginalmorphologyofthecrackcan'tbeeasilyobserved.theoxidesontheOxidesspectroscopyFig.3- thefeaturesoftheoxidesonthe a)Dimplesonthefracture b)Tornedgesonthefracture Featuresofpartialfracturesonthecrackinitiation Secondarycracksnearthecrack featureofthecracknearThemacrostructureobservationandMicro-spectroscopyysisonthecross-sectionandfractureofthesamplecracksshowedthatthecrackscanbedeterminedastransgranularcrack,locatednearthefusionlineofweldseams.Thereisanellipseinthemiddleofcrack.Andthecrackfractureismostlycoveredbyoxides.Onsomepartofthefracture,dimpleandtornedgescanbeobserved.Featuresofsecondarycrackswerefoundnearthecracktip..Duetothepolishdestructionduringsamplingonsite,theinitialmorphologyofthecrackcan'tbeeasilyobserved.However,theresultsofthetestindicatedthecrackstobeductilecrack;thematerialhasacertaintoughnessreserves.Cracksmaybeformedinhigh-temperatureenvironment,whenencounteredwithsomeporedefect,anellipseformedduringthedevelopmentofthecrack.Sothatithasanobviouscharacteristicoffatiguecrack.ysisonMaterialChemicalCompositionTable3-1presentedtheresultofchemicalcompositiontestsonthebasemetalandweldseamsbyspectroscopy.ThematerialisinaccordancewithASMEstandardsforSA-299carbonsilicon-manganesesteelrequirements.ComparedwiththeE7015electrodeinmetaltest,theMocontentintheweldseamswasabithigh;however,therestofthecompositionmettherequirements.Moimprovedthehardenabilityofsteelsignificantly,andplayedaroleofsecondaryhardenduringtempering.Soinmulti-passwelding,duetotheweldthermalcycling,itcouldeasilyembrittletheweldseams,andsharplydeclineitslow-temperatureimpacttoughness.Table3-1ResultsoftheChemicalCompositionTest(Wt.CPSVoBasemASMESWeldsMetallographicUsing4%nitratealcoholasetchantforsample1inmetallographictest,asshowninfigure3-12tillFig.3-15.Thebasemetalofthesampleismainlyferriteandpearlitestructureevenlydistributed;thefine-grainedHAZismainlyferriteandpearlite,whilethecoarsegrainismainlybainitestructure;weldseammetalismainlyferriteandbainite,thelatteronehasaveryclearstructure.Themetallographicexaminationindicatedthattherewasnoabnormalstructureinthesamplebasemetal,heataffectedzoneandweldseams. StructureoftheBase Structureofthefine-grained Structureofthecoarse spectroscopyofinclusionMicro-hardnessTestmicrohardnessoftheweldseams,HAZandthebasemetalofsample2.Selecta10mmlongstraightlinefromthebasemetaltotheweldseam,measuring20pointsspacing0.5mm.HardnesstestdataandcurvesareshowninTable3-2andFigure3-16.Thecurveindicatedaslowgrowingtrendofthehardnessfromthebasemetaltotheweldseam.AccordingtoGB/T1172-1999<BlackMetalHardnessandStrengthConversionValue>,theconvertedhardnessofthebasemetal,theweldseamandHAZmetthestandardrequirementsofDL/T752-2001<DissimilarSteelWeldingPowerPlantTechnicalTable3-2ResultsofMicro-hardnessBaseFine-grainedCoarsegrain Micro-hardnessChemicalcompositionexamination,Metallographicexaminationandhardnessmeasurementsonthebasemetal,fine-grainedzone,coarsegrainzoneandtheweldseamofthesampleshows,thecompositionandhardnessofthebasemetalandHAZbothmeettherequirementsofstandardspecification;noabnormalstructurewasfound.However,theMocontentwashigher,whichcanleadtoembrittlementoftheweldseamsandadverselyaffecttheweldcracking.ResidualStressTestbeforeResidualstresstestwasconductedbeforetherepairofthedrumcylinderandthetypicallocationLocationofmeasuring1feedwatertubeofright2Non-crackareaonofright3Non-crackareathefeedwatersocketsfilletweldsarea.Table3-3isthesummaryoftestTable3-3ReportonresidualstresstestbeforetherepairofcracksondrumcylinderandsocketFeedwatertubesocketsofthe ,secondandthirdeconomizersontherightsideinthedrumanddrumcylinder;ThejointofthelocalwaterlevelindicatortubeinbothbacksideandfrontsideofleftdrumMeasuringRefertothefigureofthemeasuringpointlistedMeasuringSRSS3-1StaticstrainMeasuringHoledrillingFigureofthemeasuring 9 炉6 4 12'1 炉ofright4feedwatertubeofright25Drumbase6feedwatertubeofright79Non-crackareaonofright8Crackingareaonsocketofdrum9Non-crackareaAfterlongtermrunning,thestresslevelofthedrumisnotveryhigh.Amongallmeasuringpoints,thehigheststressvalueis261.2MPa,locatednearoratthecrackingspotontheweldtoeofthejointofthelocalwaterlevelindicatortubeinthedrumhead.TheumprincipalstresslevelwithinthecylinderisataboutOperatingConditionsandDrumStructureOperatingThe#2BoilerinPowerPlantB,LaibinGuangxi,ModelHG-1069/18.2-YM1,madebyHarbinBoilerCompany,isa360MWcoalfiredboilerofcontrolledcycle,subcriticalpressure,singlereheat,fourcornersburner,tangentiallyfired,single-chambersingledrum.Itsumcontinuousevaporationis1069t/h;thesuperheateroutletpressure/temperatureis20.62Mpa/543°C;andthereheateroutletpressure/temperatureis4.695Mpa/541°C.The#2Boilerwasputintooperationon11thOctober,1999,andconnectedintothegridinFebruary,2000.StructureThedrumis15866mmlongintotal.Thecylinderismadeunderspecificationsofunevenwallthickness,inwhich,theupperdruminternalradiusis872.3mm,wallthicknessis200mm;thelowerdruminternalradiusis889mm,wallthicknessis166.7mm.Therearealtogether4large erswithadimensionofΦ526×120mmcameoutfromthedrum,thematerialofthesocketsis20MnMo,thematerialofthetubesisSA106B,tubedimensionisΦ368×42mm,thesockettypeisinner-flat.Thereare3economizerfeedwatertubes(Φ414.3×91.25mm)gointothedrum.ThedimensionofthesafetyvalvesocketisΦ168.3×47.6mm.Onthesideofthedrumcylinder,thereare57passoffilletweldonsocketsofΦ159×29mm distributionpipes, by-passpipe,and returnpipe.Thecharacteristicofdrumstructureislargedimensions,thickcylinderwall,largepipefittingsandagreatnumberoflongitudinalweldedjointsonthecylinder.Thefilletweldscausedthemutantofitsstructure,stresswashighlyconcentrated,andtheweldingresidualstressesfrommanufacturingprocesswerehigh.Theresidualstresstestresultsbeforethedrumrepairshowedthatthehigheststressvalueis217.5MPa,locatedonthebasemetalofthedrumcylinderwhichismorethanprescribed140MPaaccordingtoDL/T734-2000<powerplantboilerdrumrepairweldingtechnologyguidelines>.TheStressconcentrationatthefilletweldsandhighresidualstressprovidedthenecessaryconditionsfortheinitiationandexpansionofthecracks.OverallysisonCrackCausesandVisiblecharacteristicsofthedrumAllthefilletweldcracksappearedoncylinderbasemetal,nearthefusionlinesoftheweldseams.Nonewasfoundatthetubesideofthesocket.Allthefilletweldcracksappearednearthetoeofweldjoint,whereon,thestressconcentratedthemost.Allthefilletweldcracksappearedattheplacewheretheweldseamswerebadlyformed,wheretherewasdifferentlevelofundercutortheinadequateheight.Thoseweldseamsformingdefectscausedtheconcentrationofstress.Therewasonecrackfoundonbasemetaloftheinnersideofthelowerpartofthedrumcylinder,onboiler#2.Insummary,mostofthecrackslocatedonthetoeofthefilletweld,wh