ML18031A105

From kanterella
Revision as of 09:17, 20 April 2018 by StriderTol (talk | contribs) (Created page by program invented by StriderTol)
Jump to navigation Jump to search
Final Deficiency Rept on spot-welded Struts
ML18031A105
Person / Time
Site: Susquehanna  Talen Energy icon.png
Issue date: 12/29/1978
From:
PENNSYLVANIA POWER & LIGHT CO.
To:
Shared Package
ML18031A103 List:
References
P23-9, NUDOCS 7903010285
Download: ML18031A105 (22)


Text

Revision1JN4'~'-'0'8012FINALREPORTONSPOT-WELDEDSTRUTSFORSUSQUEHANNASTEAMELECTRICSTATIONUNITS1AND2Preparedby:Checkedby:Approvedby:BECHTELPOWERCORPORATIONSanFrancisco,CaliforniaSeptember29,1978December29,197U(Revision1)(P23-9)o80102$

0le' Revision1~JN4>"-">OJSG'32TABLEOFCONTENTSSectionTitle~Pae1.02.0PurposeSpot-weldedStruts3~0Background4'DeficiencyanditsSafetyImplications5'ImmediateAction6.0TestProgram7'TechnicalEvaluationofDeficiency8.0CorrectiveAction109.0RepairMethods10'Conclusion14ATTACHMENTS(P23-9)TestReportby'PittsburghTestingLaboratory'estResultsSpecifications*TheAttachmentswerepreviouslytransmittedviaPLA-295datedOctober9,1978andarenotforwardedwiththisreport.

Revision11'PURPOSEThepurposeofthisreportistoprovidefinaldataand.informationasrequiredby10CFR50.55(e)(3)subsequenttothenotificationofareportabledeficiency.Thesubjectdeficiencyisassociatedwithspot/resistanceweldinginstrutmaterial.2.0SPOT-WELDEDSTRUTS2.1StrutsBasicstrutsectionsarelightgage(thicknessvaryingfrom0.105to0.109inch)channelsmanufacturedbycoldformingmildsteelstrip.Thesechannelsec-Vtionsareconnectedtoeachotherinvariousconfigura-tionssuchasback-to-back,back-to-side,orside-to-sidebyusingaweldingprocesscommerciallyknownasspot-weldingorresistancewelding.Thechannelsectionsandbuilt-upsectionsusedonSusquehannaprojectareeithermill-galvanizedorhot-dipgalvanizedafterspot-weldingandaresuppliedbyUnistrutCorporation,Wayne,Michigan;PowerStrut,DivisionofVanHuffelTubeCorporation,Warren,Ohio;andB-LineSystemsIncorporated,Highland,Illinois.Thesewereprocuredasstandardoff-the-shelf,itemswithnoformalQualityAssurance.VariousconfigurationsusedonSusquehannaaregiveninFigureI.Strutmembersareusedinfieldfabricatedsupportsforelectricalraceways,HVACductsandinstrumentation

>e4r-'69BQj2..lines.Thegoverningdocumentsaredrawing8856-E-53forelectricalraceways,Specification8856-M-323-CforHVACductsandDrawing8856-JG-16forinstrumenta-tion.Thesupportsaredesignedinaccordancewith'Specifi-cationfortheDesignofCold-formedSteelStructuralMembers'1968Edition),publishedbyAmericanIronandSteelInstitute.Thespot/resistanceweldingprocessconsistsofpassinghighcurrentthroughthethicknessesofadjoiningplatesresultinginmetal-to-metalfusion.Thequalityofaspotweldisdependentonmanyvariablessuchaspres-sureontheelectrodetips,finishofthematerial,presenceofimpuritiesonthematerial,build-upofzincandothercontaminentsontheweldingelectrodes,contactbetweenjoiningsurfaces,voltageandamperage.Therefore,unlesstheseparametersarecloselymoni-toredandcontrolled,theresultmaybeinadequatefusion.3.0BACKGROUNDSincetheuseofstrutmaterialbeganontheSusquehannaPro-ject,therewerethreeisolatedinstanceswhentheadjoiningFchannelsseparatedduringhandlingorassembling.Thesememberlengthswererejected.(P23-9) evision1.)(z-r=.E8612However,inrecentmonthstherehavebeensignificantin-stancesonothernuclearprojectswhereinadequatefusionwasobservedattheweld.spots.Asaresultofth's',onMarch25and26,1978,BechtelfieldengineeringpersonnelperformedaninspectiononUnistrutmemberP-1004A,Power-strutmemberPS-3022andB-LinememberB22-X.ThetestedmemberswerepartofinstalledelectricalracewayandHVACductsupports..Themethodofinspectionconsistedof'sounding'hememberswithaballpeenhammertodetectseparatedspotweldsandverificationoftheseparationbyinsertionofacardbetweenthemembersatthespotwelds.Theinspectionindicatedahighincidenceofspot-weldswithinadequateornofusion.Therefore,ProjectQualityAssurance(QA)issuedManagementCorrectiveActionReport(MCAR)1-23onMarch28,1978.4.0DEFICIENCYANDITSSAFETYIMPLICATIONSBasedupontheresul'tsoftheinspectionasdescribedinSection3.0,itwasdeterminedthat:a.Thedeficiencyisrelatedtospot-weldingtechniqueand/orprocedure.b.Thequalityofthespot-weldingisindeterminate,withoutfurtherinvestigation.Variouscombinationsandconfigurationsofchannelstrutshavebeenusedinthesupportsystems.Individualmembers(P23-9) vision10.8012havebeendesignedascompositesectionsforwhichthecon-nection(spot-weldingusedinthisinstance)betweenadjoin-ingchannelsisreliedupontocarrythepostulatedloadswithinestablisheddesignmargins.Thus,inadequatefusionatthespot-weldingmayresultininadequatestrength,andmayadverselyaffectthesafeoperationoftheplantunderdesignloadingconditions.5.0IMMEDIATEACTIONA'Hold'asimposedonfurtherinstallationofmemberP-1004Aoritsequivalentunlessthememberwasstitch-weldedtodevelopequivalentdesignstrengthofthespot-welding.6.0TESTPROGRAM6.1General.Althoughitwasdeterminedthatadeficiencyexistedinsomespot-weldedmembers,theextentofthede-ficiencywasunknown.Sothefirststepwastoes-tablishthescopeoftheproblem.Sincethereisnopracticalnondestructivemethodforexaminingthesound-Inessofspotweldsintheerectedmaterial,itwasde-cidedtoinitiateadestructivetestprogram.6.2BasisofTestProramTheunderlyingapproachisdescribedbelow.(P23-9)

Resion1Jw4'r-I,:-"Q.Q'lRa.Obtainrepresentativesamples,selectedatrandom,fromthe'nstalledandstockmaterialforallshapesandmanufacturers.b.Performdestructivesheartestonthesamplestoobtainfailureloads.c.Analyzethetestresultsstatisticallyforeachshapeandmanufacturertocomputecorrespondingexpectedstrengthperspot-weldatacertainconfidencelevel.6.3~samlesSampleswereobtainedbyBechtelfieldengineeringpersonnelandsenttoarecognizedtestinglaboratory.Samplesweretypically6"longcontainingtwospot-welds.Forthestockmaterial,twosampleswereobtainedfromeach20'-0"lengthandonlyonesamplefromanygiveninstalledmemberselectedatrandom.Forthcinstalledmaterial,generallyonesamplewasobtainedforevery100feetoftheinstalledquantity.6.4~TestisTestingwasdonebyPittsburghTestingLaboratory(PTL)inPittsburgh,Pennsylvania.TestmethodandproceduresarefullydescribedinPTL'sreport.(SeeAttachmentA).(P,23-9)

Revision16.5StatisticalAnalsis>e4-isgasp:g.pBaseduponthetestresults,histogramswereplottedforeachshapeandmanufacturer.Meanandstandarddeviationwerecomputedforeachcase.Thetestresultsgenerallyfollowthenormaldistribution.Theexpectedfailureloadperspotweldwasdeterminedbyusingthemeanofthefailureloadbaseduponthetestresultsandsubtractingoneandahalftimesthestandarddeviation.Thisapproachprovidesmorethan90%confidencelevelfortheexpectedfailureload.Baseduponabovecriteria,theexpectedfailureloadswerecomputedandaregiveninTableI.7.0TECHNICALEVALUATIONOFDEFICIENCY7.1GeneralThetechnicalevaluationinthissectionislimitedtoallstrutmembersinstalledand/oratthejobsitewhicharenotfabricated.7.2DesinCriteriaandTheoreticalConsiderationsAISIspecificationspecifiesallowableshearstrengthperspot-weldtobeequalto1.65kipswithafactorofsafetyof2.5for0.109inchthickness.Thisal-lowableshearisbasedupon"RecommendedPractices(923-9)

Revision1Jgg-(cg,gg.Q'j'fforResistanceWelding,"AWSC1.1,byAmericanWeldingSociety.Basedonthiscriteria,thefailureloadforaspotshouldbeover4,000pounds.However,inlightoftheproblemassociatedwithspot-welding,itisnecessarytoassessbasesofcoderequirementsandevaluatestructuraladequacyoftheinstalledmaterialwithoutcompromisingthebasicdesignphilosophy.Theconnectionprovidedbyspotweldsbetweenadjoin-ingchannelsectionsisreliedupontomaintaintheintegrityofthebuilt-upsections.Thecalculatedshearinaspotweldinamemberdependsuponmanyvariablessuchasloading,sectionalproperties,endconditionsandifthememberisusedasabeam,brace,columnortie.Theallowableshearof1.65kips/spotspecifiedbythecodeistheupperlimitfordesigningpurpose.However,fromtheevaluationpointofview,itismorerealistictoconsideractualmaximumdesignshearcal-culatedindividuallyasrequiredforeachshape.Sec-ondly,forthestrutmaterial(Fy=33k.s.i.)theallowablebendingstress(Fg)percodeis20k.s.i.for0.105inchthickness.Therefore,thefactorofsafetyforthebendingstressisconsideredtobe1.65whileforthespot-welds,itis2.5,whichisratherhigh.Reasonforthiscouldbeattributedtomanyvariable,w7(P23-9)

Revision1Ju4ra098012affectingtheweldstrength.Forthematerialinques-tiononSusquehanna,anextensivetestprogramhasbeencarriedoutandexpectedfailureloadsforeachshapearewelldefined.Therefore,itisreasonabletoas-sumethatafactorofsafetyof2.0forspot-welds,whichisstillhigherthanthefactoryofsafetyforbendingofthestrutmaterialwouldstillbeadequateandconsistentwiththebasicdesignphilosophy.73Thedesignofframingmembersinthesupportsystemisbaseduponallowableshearof1650lbs.perspotweld.Therefore,tomaintainaminimumsafetyfactorequalto2.0,theexpectedfailureloadmustbe3300lbs.orgreater.7.3.1Thestrutsectionswiththeexpectedfailureloadequaltoorgreaterthan3300lbs/spotweld,areconsideredtobestructurallyadequate.7.3.2However,fortheothersections,furtherevaluationisnecessary.Designloadsonthesupportsystemsaregovernedbymanyconsiderationssuchastypeofsupport,structure,elevation,etc.Forindividualmem-bersinasupport,designshearforcesaddition-allydependuponifthemembersareloadedflex-urallyoraxially.Etisnotedthatforflexuralmembers,shearforcesaregenerallyhigh.

Revision1JhNg<cg>GOjpFortheearlierinvestigation,a5'-0"longmember'sup-portinguniformlydistributedloadwasconsideredtobearepresentativecaseforvariousloadingconditions,andmembershapes,andcomparisonwasmadebetweencom-puteddesignshearsandexpectedfailureloads.However,inthefinalanalysis,actualdesignshearswerecomputedinindividualmembersforallsupport~typesinvariousbuildingsandatdifferenteleva-tions.Theseshearvaluesvaryconsiderably;therefore,theexistingmembers,whichmaybeadequateatacertainlocation,mayneedstrengtheningelsewheredependingontheaforementionedvariables.'nanycase,afac-torofsafetyof2.0hasbeenmaintained.7.4~SummarBaseduponafactorofsafety,of2.0,allshapesaregroupedinthreecategories.CateorIUnistrut:P-5501,P-1001C,P-3301,P-1001AP-1001C3Powerstrut:PS-151,PS-202Theseshapesarestructurallyadequateandneednorepair.

CateorIIUnistrut:P-1001,P-5001Powerstrut:PS-201,PS-101,PS-204PS-3080B-Line:.B-12AThesesectionsareconsidereddeficientatcertainlocationsandneedtoberepairedasrequired.CateorIIIUnistrut:P-1004APowerstrut:PS-3022B-LineB-22X,B-11AAllmembersofaboveshapesaretoberepaired/strengthenedtoprovideshearconnectioncapacityequaltotwicethedesignstrengthrequired.8.0CORRECTIVEACTION8.1GeneralCorrectiveactionsaregroupedinseveralcategories.Eachcategoryandcorrespondingactionisdescribedbelow.8.2InstalledandStockMaterial8.2.1PowerstrutPS-3022,IUnistrutP-1004AB-LineB-22X.BasedupontheinspectionbyBechtelfieldengineeringpersonnel,allmaterialofthis-10-(P23-9) evisionlconfigurationwasdeemedtobedeficient,andwillbecompletelyrepairedwithouttakinganycreditfortheexistingspotwelds.8.2.2B-LineB-11A.Installedandstockquantityforthisshapewassmall;therefore,.nosampleswereobtained.Intheabsenceofanytestdataontheexistingspotwelds,thissectionwillberepairedtodeveloprequireddesigncapacitytomeetthedesigncriteria.8.2.3Powerstrut:PS-151,PS-202Unistrut:P-5501,P1001G,P-3301,P-1001A,IP-1001C3BaseduponthetechnicalevaluationinSection7.0,existingspot-weldingisadequateandwillperformsatisfactorilyunderdesignloads.Therefore,nofurtheractionisdeemedneces-sary.8.2.4Powerstrut;PS-201,PS-101,PS-204,PS-3080Unistrut:P-1001,P-5001IB-Line:B12A-11-(P23-1/1)

Revision1igu7.0912Thesemembersdonotmeetthedesigncriteria,therefore,adetailedre-analysisandredesignhasbeenperformedtocomputerequiredadditionalstrengthanddesigndrawingshavebeenpreparedtoshowthenecessaryrepairdetails.There-quiredrepairwillbeperformedontheinstalledandstockmaterial.Oncompletionoftherepair,thestrutmaterialwillsatisfythedesigncri-teria.8.3StrutMaterialtobeReceivedintheFutureUntilnow,thestrutmaterialwasprocuredasastan-dard'offtheshelf'tem.However,inlightoftheproblemexperiencedwiththespot-welding,anewspeci-.fication8856-C-92(seeAttachmentC)wasdevelopedforprocurementof,allspot-weldedstrutsinthefuture.TheresultsofthetestingbyPTLpositivelyindicatethatthespot-weldsonaplainmaterialhavemuchhigherstrengththanspot-weldsonmill-galvanizedmaterial.Therefore,thespecificationstipulatesthatstrutmaterialtobecoatedafterspotwelding.Inadditiontothis,toprovideareasonableassuranceofattainingthedesignstrength,thesupplierisre-quiredtointroduceadestructivetestingprogramontheproductionsamplesandnomaterialwillbeshippedtoSusquehannajobsiteunlessitmeetstheacceptance.criteria.Thisactionshouldpreventtherecurrenceofthisprobleminthefuture.(P23-1/2)

Revision19.0REPAIRMETHODSN4'Kid+Q3,+r,'.1GeneralConstructionhasbeenprovidedtheoptiontoselectanyoneofthefollowingmethodsonacase-by-casebasis.9.ThismethodistoreplacethedeficientmaterialwithnewmaterialtobeprocuredperSpecification8856-C-92(seeAttachmentC).9.3MechanicalFastenersSecondmethodistoprovide1/4"dia.self-drillingandself-tappingmetalscrewstoobtainrequiredshearstrength.These,screwswillbeprocuredperSpecification8856-C-91(seeAttachmentC).Inordertoassurestrengthrequirementsforthescrews,itisrequiredtoperformadestructivesheartestonsamplesandeachlotmustmeettheacceptancecriteria.Inadditiontoself-drillingandself-tappingscrews,othermechanicalfastenersarebeingconsideredsuchaspop-rivetsorclamps.Ifthesearedeterminedtobetechnicallyacceptable,theywillbeusedasalternatetothescrews.-13-(P23-1/3)'

ision19.II~VeldknThirdapproachistoprovideintermittent.stitchweldingatthejointbetweenchannelsand/orchan-nelandsideplate.

10.0CONCLUSION

Oncompletionoftherequiredrepair/replacementoftheexistingspot-weldedstrutsdeterminedtobedeficient,theexistingsupportsystemswillbestructurallyade-quatetosatisfythedesignrequirements.Secondly,pro-curementofnewspot-weldedstrutmaterialpernewspec-ification(seeAttachmentC),willprovideadequateas-suranceofpreventingtherecurrenceofthisprobleminthefuture..-14-(F23-1/4)

Hevislon1TABLE1EXPECTEDFAILURELOADS~FE82'80C99480StandardExpectedFailureLoadMeanDeviation=A-1.5BMeuufacturerMember(1bs)(1bs)(lbs)RemarksUnistrut(A)(B)P-10014140-1213P-550154991229P-50014357-,1072P-1001C53861033P-3301'4651025P-1001A4192554P-1001C3,5186629232136563837392833614243Cat.IICat.ICat.IICat.ICat.ICat.ICat.I(Backtoback)P-1001C351264584439Cat.IPowerstrut(Backtoside)PS-2014418,1194PS-1515533892PS-1013855782PS-20441502233PS-308041261252262741952682801Cat.IICat.ICat.IICat.IIICat.II(Backtoback).PS-30804666(Backtoside)PS-2025783B12A356515111317240039501590Cat.IICat,ICateIINote'.1.Abovenumbersinthetablearebasedupononespotveld.2.ForexplanationofRemarks"column,refertosection7.4.3.ForshapesinFigure1andnotintableabove(i.e.thoseinCategoryIII),refertosection7.4.(P23-10)

FIGURE1STRUTSHAPESANDIDENTIFICATIONRevision1~Shae0UnistrutP-5001PowerstrutPS-101B-LineB-11A~ShaeRUnistrutP-5501PowerstrutPS-151B-LineB-12A~ShaeKUnistrutP-1001PowerstrutPS-201.~ShaeNUnistrutP-1004APowerstrutPS-3022B-Line,B-22X3~haeNUnistrutP-1001C3PowerstrutPS-3080~ShaeLUnistrutP-1001CPowerstrutPG-204~Shae0UnistrutP-1001APowerstrutPS-202ShauePUuiattutP-3301