why do pvc & cpvc pipes occasionally fail?

Download Why Do PVC & CPVC Pipes Occasionally Fail?

Post on 11-Dec-2016

223 views

Category:

Documents

2 download

Embed Size (px)

TRANSCRIPT

  • WhyDoPVC&CPVCPipesOccasionallyFail?ByDr.DuanePriddy,PlasticFailureLabs,Midland,MI

    PrefacePVCandCPVCpipesandfittingsareexcellentproductsandhavebeenusedsuccessfullyfordecades.ThereisalowfailurerateandtheuseofPVC/CPVCmaterialsoffersignificantadvantagesovermetalpipingmaterialsincludingeaseofinstallationandverylowfailurerates.IamnotawareofanyhealthcautionsregardingtheusageofPVC/CPVCpipesandfittingsotherthantheneedtoinstallthemproperlywithoutusingincompatiblematerialsduringtheinstallation.However,aswithallplumbingproductsincludingmetalpiping,occasionallyapipeorfittingmayfail.Whenafailuredoesoccur,ourexperienceindicatesthatmostoftenthefailurecanbelinkedtoimproperinstallationpractices.TheintentofthisarticleistoprovideassistanceregardinginstallationerrorstoavoidandtherebyreducetheoccurrenceofafailureinPVCandCPVCplumbing.Again,letmeemphasizethatbyteachingaboutthemaincausesofoccasionalfailureofPVCandCPVCpipesandfittings,Iaminnowaysuggestingthattheseplumbingproductsarelessreliableormorepronetofailurethananyotherplumbingmaterial.Further,IamoutragedbythemisuseofmyteachingsbysometoattackPVCandCPVCplumbingproductsasbeinginherentlyunsafe.IfIweretobuildahomeformyownfamily,Iwoulduseasmuchplasticplumbinginmyhomeaspossibletokeepthecoststoaminimumwhileprovidingmyfamilywithasafelivingenvironment.MostoftheMainCausesofCPVC/PVCPipeFailureListedBelowareDiscussedinthisArticle

    I. ImproperSystemEngineering/InstallationA. InadequateprovisionforlinearthermalexpansionB. ExcessuseofCementC. InsufficientamountofCementD. WrongClampsusedorClampstootightE. IncompatiblefirecaulkusedF. Contactofoutsideofpipewithincompatiblematerial(e.g.,solderflux)

    II. ImproperOperationA. ExposuretofreezingtemperatureswithoutfreezeprotectionB. OverpressurizationC. PulsatingwaterpressureD. Useofincompatiblematerialsaroundpipes

    III. Contamination

    A. Internal1. Useofcontaminatedantifreeze2. Contaminantsfrommetalwatersupplypiping;e.g.,antimicrobial(MICinhibitor)linings,

    corrosioninhibitors,phthalateplasticizersfrompumpseals/gaskets,refrigerationsystemlubricants

    B. External1. IncompatibleFireCaulk2. Useofincompatible(blackProset)grommetstosealpipeagainstholeinconcrete

  • Page2of16

    3. Contactwithincompatibleplasticcoatedwires4. Exposuretohotsolderflux5. Exposuretohotpolyurethanefoaminsulation

    IV. Manufacturingdefects

    A. DirtyextrusiondieB. IncompleteresinconsolidationC. Highstressesinpipewallduetorapidcooling

    V. ResinDefects

    A. Occlusions,charparticles,voidsB. Filler/pigmentnotwelldistributed

    IV.AbusebyDistributor

    A. StoreinsunB. Damageduringtransport

    IntroductionPVCandCPVCpipesareoneofthemostextensivelyusedplasticpipingmaterials.Themainreasonforthegreatsuccessofthesepipesistheirlowcost,extremelylowfailurerate,andrelativeeaseofinstallation.However,aswithallpipingmaterials,thereareoccasionalfailures.OccasionalfailuresmaybecausedbyanumberoffactorshoweverimproperinstallationisgenerallythemostcommoncausewhenPVCandCPVCpipesfail.PlasticFailureLabsisanindependentforensiclaboratory.Wehavebeenconductingforensicfailureanalysesofplasticpartsforseveralyears.WehavecarriedouthundredsofforensicfailureanalysisinvestigationsofCPVCandPVCpipesandfittingsattherequestofinsurancecompanies,installers,pipemanufacturers,generalcontractors,condominiumassociations,andprivateowners.Wehavefoundthattheoverwhelming/mostcommoncauseoffailureisimproperinstallationpractices.Sometimesinstallationerrorsresultincontamination,althoughthesetwoissuesarenotalwaysrelated.Thecombinationofpipesunderstressplustheexposuretoincompatiblematerials,canleadtoenvironmentalstresscrackingfailureorESC.ThisisespeciallythecasewithCPVCsprinklersystempipingifnotadequatelyflushedasrecommendedinNFPA13toremovedebrisandtracechemicals.IfCPVCfiresprinklersystemsarenotflushed,tracechemicalsremaintrappedinsideforperiodsoftimeandmaybecomeabsorbedintotheCPVC.CPVCisaveryductilematerial.However,thecombinationofprolongedhighstressandabsorptionofcertainhydrocarboncontaminantsmaycauseittoweakenanddevelopstresscracks(Figure1).ThemostcommoncausesofoccasionalfailureofPVCandCPVCpipesandfittingsarelistedinTable1.Alsoincludedinthetablearecommontechniquesthatareusedtodetectthelistedcauses.Therearemanytoolsavailabletotheforensicscientistbutthemostcommonlyusedtoolsareopticalmicroscopy,scanningelectronmicroscopy(SEM),Fouriertransforminfraredspectroscopy(FTIR),andgaschromatographymassspectroscopy(GCMS).

  • Page3of16

    Figure1.FormationofastresscrackontheinsideofaCPVCfiresprinklerpipeatapointwhereatightfittingclampwasused. Table1.Sixmaincausesofoccasionalpipefailureandtestingmethodsgenerallyusedfordiagnoses:

    TypeofFailure RootCauseofFailure TestsImproperinstallation excessivecement sectioning&inspection insufficientcement sectioning&inspection wrongclampused siteinspection clampstoofarapart siteinspection clampstootight outofround/clampmarks noallowanceforthermalexpansion siteinspection pipesnotproperlyaligned siteinspection shortinsertion sectioning&inspection Pipeendnotdeburred sectioning&inspection Pipeendnotchamfered sectioning&inspection nonsquarepipecuts sectioning&inspection wrongantifreezeused* FTIR Contamination Incompatiblethreadsealants FTIR/GCMSChemicalCompatibility Incompatiblethreadcuttingoils FTIR Phthalatesfromgaskets/seals GCMS IncompatibleMICinhibitor FTIR/ESIMS/GCMS Incompatibleantifreeze* GCMS/FTIR Productdefects pipedimensionswrong resinnotfullyconsolidated SEM weakextrusionknitlines dirtydiecreatingextrusionlines blacklight voidsorparticulates OM/SEM/EDS residualstressduetorapidcooling OM

  • Page4of16

    Resindefects resinMWtoolow MI fillercontentwrong TGA additives/pigmentsdispersion SEM/EDS chlorinecontentwrong** EA Improperoperation waterhammer OM/SEM overpressurization OM/SEM areacontamination GCMS/IR freezing OM Abusebydistributor storeinsun IR damageduringhandling/transport OM *uniquetofiresprinklerpipes **uniquetoCPVC

    Key: OM=optical microscopy; IR=infrared microscopy; GC-MS=gas chromatography-mass spectroscopy; SEM/EDS=scanning electron microscopy/electron dispersive spectroscopy; EA=elemental analysis; DSC=differential scanning calorimetry; TGA=thermal gravimetric analysis ImproperInstallationExcessivecementuse:Aninstallationproblemthatweoccasionallyseeistheuseofexcessivecement.ThesolventsinthecementthemselvesarereadilyabsorbedintoCPVCandPVC;i.e.,theyreadilyareabsorbedintothewallofthepipeandinsidefittingsocketresultinginsolvation/softeningofthematerial.Figure2showsashortpieceofpipewithafittingoneachendhavingexcesscementpuddledinsidetheshortpieceofpipe.Thesolventsinthecementabsorbedintothepipewallresultinginsofteningofthepipewalltothepointthatthepipewallbecameswollen/softenedandnolongerhadsufficientstrengthtoholdwaterpressureresultinginblowout.

    Figure2.Puddlingofexcesscementinsideoffittingranintoadjacentpiperesultinginsofteningandblowoutofthepipewall.

  • Page5of16

    However,absorptionofthesolventsinthecementintothetoplayerofplasticinthepipeandfittingsocketisnecessarytoachievegoodbonding.Theorganicsolventsincementsoftenthesurfaceofthepipeandfittingsocketallowingthepolymermoleculestointertwinetoformapermanentbond.Theorganicsolventsinthecementarevolatileandquicklyevaporatesothattheyareonlyaroundlongenoughtodotheirintendedjobbutnotlongenoughtocausethepipetoweaken.Theproblemisthatoccasionallyinstallersutilizetoomuchcementresultingindribblesrunningdowntheinsideofverticalrunsofpipe.Wehaveobservedenvironmentalstresscracks(ESC)bothunderneath(Figure3)andadjacent(Figure4)tocementdribbles.ItisnotknownforcertainexactlywhyESCfailuresofpipesoccasionallyoccurunderneathoradjacenttocementdribbles.Onetheoryisthatthecementisporousandabsorbstracehydrocarboncontaminantspresentinthewaterandfacilitatestheirabsorptionintothewallofthepipe.AnothertheoryoftheESCcrackingofCPVCimmediatelyadjacenttoacementdribbleisthatthedrying/shrinkageofthecementcreatesadjacentstressesontheinsidesurfaceofthewallofthepipe.

    Figure3.ESCoftheinsidesurfaceofthewallofthepipeunderneathacementdribble

    Figure4.CementdribbleoninsideofCPVCpipewithESCcracksfoundaroundtheperipheryofthedribble.

  • Page6of16

    Whenexcessivecementisusedontheoutsideofpipeitisnotasmuchofaproblemasontheinside.Thisisbecause,ontheoutside,thevolatileorganicsolventsquicklyevaporate.However,ontheinsideofthepipe,theorganicsolventsaretrappedallowingmoreexposuretimeoftheinsidewallofthepipetothesolvent.Byapplyingtheexcesscementtotheendofthepipe,butnotthefitting,whenthepipeisinsertedintothefitting,theexcesscementispusheddowntheoutsideofthepipeforcingtheexcesstotheoutsideofthepipe.Ifexcesscementisappliedtotheinsideofthefitting,theexcessendsupremainingtrappedinsidethefittingandeitherpuddlesinsidethefittingorelserunsdowntheinsideofthepipe(Figure4).ItisgenerallyquiteeasytospotwhetherafittingwasassembledusingasufficientamountofcementbysimpleexaminationofthecementresidueinthecrevicebetweenthefittingandthepipeasshowninFigure5.

    Figure5.Photosshowingtheexternalappearanceofabad(left)andagood(right)joints.Insufficientcementuse:Sufficientcementmustbeappliedtoendupwithcompletecoverageoftheendofthepipeandtheinsideofthefittingsothatacontinuousbondisformedbetweenthepipeandfittingsurfaces.Ifinsufficientcementisused,voidsmayforminthebondbetweenthepipeandfitting.Thepresenceofthevoidsresultsinaweakenedassemblywhichmayresultinwaterleakingfromthejoint.Note:Wehavedevelopedatechniquetonondestructivelyexaminefittingstodetermineifvoidsexistbetweenthepipeandfittingorifcompletebondinghastakenplace.Ifdesired,oneofourforensicengineerscantraveltoasiteandanalyzesuspectfittingassembliestodetermineifvoidsarepresentinthebondedjoints.CharlottePipe&FoundrysPVC/CPVCinstallationmanual*recommendsthefollowingprocedureforcementapplication:

    Applyaheavy,evencoatofcementtotheoutsidepipeend.Applyamediumcoattothefittingsocket.Applyasecondcementapplicationonthepipeend.Itisimportanttoinsuresufficientpenetra

Recommended

View more >