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FailureModesandEffectsAnalysisAFailureModesandEffectsAnalysis(FMEA)tabulatesfailuremodesofequipmentandtheireffectsonasystemorplant.Thefailuremodedescribeshowequipmentfails(open,closed,on,off,leaks,etc.).Theeffectofthefailuremodeisdeterminedbythesystem’sresponsetotheequipmentfailure.AnFMEAidentifiessinglefailuremodesthateitherdirectlyresultinorcontributesignificantlytoanaccident.HumanoperatorerrorareusuallynotexamineddirectlyinanFMEA;however,theeffectsofamisoperationasaresultofhumanerrorareusuallyindicatedbyanequipmentfailuremode.AnFMEAisnotefficientforidentifyinganexhaustivelistofcombinationsofequipmentfailuresthatleadtoaccidents.openclosedsticksruptureleaksthruFC

PurposeThepurposeofanFMEAistoidentifysingleequipmentandsystemfailuremodesandeachfailuremode’spotentialeffect(s)onthesystemorplant.Thisanalysistypicallygeneratesrecommendationsforincreasingequipmentreliability,thusimprovingprocesssafety.

TypesofResultsAnFMEAgeneratesaqualitative,systematicreferencelistofequipment,failuremodes,andeffects.Aworst-caseestimateofconsequencesresultingfromsinglefailureisincluded.TheFMEAmaybeeasilyupdatedfordesignchangesorsystem/plantmodifications.FMEAresultsareusuallydocumentedinacolumn-formattable.Hazardanalystsusuallyincludesuggestionsforimprovingsafetyinappropriateitemsinthetable.FailureandFailureModeFailure:Theterminationofanitem’sabilitytoperformarequiredfunction.FailureMode:Theeffectsbywhichafailureisobservedonthefaileditem.Alltechnicalitemsaredesignedtofulfilloneormorefunctions.Afailuremodeisthusdefinedasnon-fulfillmentofoneofthesefunctions.ClassificationofFailuresSuddenversusgradualfailuresHiddenversusevidentfailuresAccordingtoeffects(critical,degradedorincipient)Accordingtoseverity(catastrophic,critical,marginalornegligible)Primaryfailure,secondaryfailureandcommandfaultClassificationofFailureModesDemandedchangeofstateisnotachieved.Changeofconditionsorstates.FailtoopenoncommandFailtocloseoncommandLeakagethroughthevalveinclosedpositionLeakagetotheenvironmentExamplesofEquipmentFailureModesUsedinanFMEA

EquipmentDescriptionExampleFailureModesPump,normallyoperating•Failson(failstostopwhenrequired)

•Transfersoff(stopswhenrequiredtorun)•Sealleak/rupture•Pumpcasingleak/ruptureHeatexchanger,highpressureon

•Leak/rupture,tubesidetoshellsidetubeside

•Leak/rupture,shellsidetoexternal

environment

•Tubeside,plugged

•Shellside,plugged

•Fouling

ResourceRequirementsUsingtheFMEAapproachrequiresthefollowingdataandinformationsources:(1)asystemorplantequipmentlistorP&ID,(2)knowledgeofequipmentfunctionandfailuremodes,and(3)knowledgeofsystemorplantfunctionandresponsestoequipmentfailures.FMEAscanbeperformedbysingleanalysts,buttheseanalysesshouldbereviewedbyotherstohelpensurecompleteness.Staffrequirementswillvarywiththesizeandcomplexityofequipmentfunctionsandfailuremodesandhowthefailuresmightaffectotherportionsofthesystemorplant.ThetimeandcostofanFMEAisproportionaltothesizeoftheprocessandnumberofcomponentsanalyzed.Ontheaverage,anhourissufficientforanalyzingtwotofourequipmentitems.AswithanyHEstudyofsystemswithsimilarequipmentperformingsimilarfunctions,thetimerequirementsarereducedsignificantlyduetotherepetitivenatureoftheevaluations.Table4.8listsestimatesofthetimeneededtoperformanHEstudyusingtheFMEAtechnique.TimeEstimatesforUsingtheFMEATechniqueAnalysisProcedure(1)definingthestudyproblem,(2)performingthereview,and(3)documentingtheresults.STEP1:Definingthestudyproblem.ThisstepidentifiesthespecificitemstobeincludedintheFMEAandtheconditionsunderwhichtheyareanalyzed.Definingtheprobleminvolves(1)establishinganappropriatelevelofresolutionforthestudyand(2)definingtheboundaryconditionsfortheanalysis.AdetailedproblemdefinitionisanecessaryingredienttoperformingathoroughandefficientFMEA.(2)Definingtheanalysisboundaryconditionsincludes:Identifyingtheplantand/orsystemsthatarethesubjectoftheanalysis.EstablishingthephysicalsystemboundariesfortheFMEA.Thisincludestheinterfaceswithotherprocessesandutility/supportsystems.OnewaytoindicatethephysicalsystemboundariesistomarkthemonasystemdrawingthatencompassesallequipmentwithinthescopeoftheFMEA.Theseboundaryconditionsshouldalsostatetheoperatingconditionsattheinterfaces.Establishingthesystemanalyticalboundaries,including:(1)thefailuremodes,operatingconsequences,causes,orexistingsafeguardsthatwillnotbeconsideredand(2)theinitialoperatingconditionorpositionofequipment.Asanexampleofeffectsbeyondthescopeofthestudy,ananalystmaychoosenottoconsiderairplanecrashes,earthquakes,ortornadoesascausesoffailuremodes.Anexampleofaninitialconditionisspecifyingwhetheravalveisnormallyopenorclosed.Collectingup-to-datereferenceinformationthatidentifiestheequipmentanditsfunctionalrelationshiptotheplant/system.Thisinformationisneededforallequipmentincludedwithinthesystemboundaryandappropriateinterfaceswiththerestoftheplant.Table6.19TypicalFormatforanFMEAWorksheetFMEA-PC(Primatech,Inc,Columbus,Ohio)

HAZOOPtimizer(A.D.Little,Cambridge,Massachusetts)SAFEPLAN(DuPont,WestlakeVillage,California)StandardwordprocessingandspreadsheetsoftwareprogramscanalsohelpanalystsdocumenttheresultsofFMEAstudies.AnFMEAstudyisperformedtoaddresssafetyhazardstoplantpersonnelinaDAPprocess.TheDAPprocessschematicispresentedinFigure6.7.Eachcomponentofthereactionsy