technical information letter

FLENDER-GRAFFENSTADENAFTERSALESSERVICE19JANUARY2012ComplianceCategory–CTimingCode-3

TECHNICALINFORMATIONLETTER

DANGERSOFBEARINGREFURBISHMENTAPPLICATIONThisTILappliestoallLoadandCompressorGearboxesPURPOSEThisTIListoprovidecustomerswithinformationregardingthedangersofusingrefurbishedbearingsinloadgearboxorcompressorgearboxapplications.COMPLIANCECATEGORYO - Optional Identifies changes thatmay be beneficial to some, but not

necessarily all, operators. Accomplishment is at customer’sdiscretion

M - Maintenance Identifies maintenance guidelines or best practices forreliableequipmentoperation

C - ComplianceRequired Identifiestheneedforactiontocorrectaconditionthat,ifleftuncorrected,may result in reducedequipment reliabilityorefficiency. Compliance may be required within a specificoperatingtime.

A - Alert Failure to comply with the TIL could result in equipmentdamageor facilitydamage.Compliance ismandatedwith aspecificoperatingtime.

S - Safety FailuretocomplywiththisTILcouldresultinpersonalinjury.Complianceismandatedwithinaspecificoperatingtime.

TIMINGCODE

1 PriortoUnitStartup/PriortoContinuedOperation(forcedoutagecondition)2 AtFirstOpportunity(nextshutdown)3 PriortoOperationofAffectedSystem4 AtFirstExposureofComponent5 AtScheduledComponentPartRepairorReplacement6 NextscheduledOutage7 Optional

TechnicalInformationLetter

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BACKGROUNDDISCUSSIONFollowingalubricationissueand/orahighvibrationlevel,slidebearingscanbedamaged.Thewhitemetal(Babbitt)beingtheareasufferingfromthedamages.Bearingswillalsowearduetonormaloperation,andneedtobereplacedattherecommendedserviceintervalsasnotedintheusermanualofyourgearbox(ifyoudonothavethismanualpleasecontactFGoryourlocalservicerepresentative)Assumingbearingshavetobereplaced,eitherduetowearafteralongperiodofoperation,orduetoexceptionaldamagesduetopooroilqualityorvibrationissues,therearetwopossibilitiestoputthegearboxbacktooperation:• Toreplacethedamagedbearingbyanew

one• Torepairthebearing(sametechnologyas

theoneusedfortheturbine/generatorbearing)

TECHNICALDISCUSSION–BEARINGDESIGNDuetothehighloadsandhighvelocitiesrequirements,Flender-Graffenstadengearboxesarefittedonlywithhydrodynamicsleevebearings.Thetorquecomingfromthedriving

machineistransmittedviathegearboxtothedrivenmachine.Thisresultsintangential,radialandaxialforcesinthegearteeth,knownasreactionforces.Axialforcesaresupportedeitherbyaxialthrustbearingsorbythetoothingitselffordoublehelicalgearsconfigurations.Tangentialandradialforcesaresupportedbythegearboxradialbearings.These

loadsaremuchhigherthanonlyshaftweightsandtheycanhavevariableamplitudesdependingontheoperatingconditions.Forthisreason,gearboxbearingloadscannotbecomparedtootherrotatingequipmentbearingloadsliketurbinesorgenerators.Someoftheseotherrotatingmachinerybearingsdonotevenreachthehalfoftheallowableloadlimitusedforgearboxes.

RECOMMENDATION

BasedonourexperienceweDONOTRECOMMENDtorepairtheusedordamagedbearings.


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TECHNICAL DISCUSSION – FAILURE MODES OFREFURBISHMENTThe reasons for this are both technical andpractical.

Figure1:Slidingofwhitemetal

Figure2:Damagetowhitemetal

Figure3:FailedrefurbishedBearing

When refurbishingabearing you canonlydo sowhentheinnerpartofthebearingisdamagedandthe outer diameter being in the requiredtolerances(intherangeof0,05mm)Thedifferentstepsfortherepairarethefollowing:

• Removalofthewhitemetalbymachining• Preparationofthesurface(innerdiameter)–

Babbitting.• MachiningoftheinnerdiameterDuringtheaboveoutlinedoperationsthebearingis machined, heated up, cooled down andmachinedagainwhichhas theconsequenceofabuildupinternalstressinthesteelofthebearingsurface.The metal body of the bearing goes throughdeformation and gets twisted i.e. the outerdiameterisstillwithinthedimensionaltolerances,butitwillfailitsgeometricaltolerances.ThebearinggeometrydefinedbyFlender-Graffenstadenensuresappropriateoilfilmthicknessaswellasproperstiffnessanddampingcharacteristicsrequiredandcalculatedforthegooddynamicalbehaviorofthegeartrain.Thelastmachiningoperationdoesn’tallowthebearingtoremainwithinthetolerancesfortheconcentricityANDtheparallelism.Atthetimeofputtingarefurbishedbearing intoplace inside the casing, theouterdiameter goesback to its previous position, leading to adeformationoftheinnerdiameter.Asaconsequence,thecontactpatternoftheshaftinsidethebearingispartialandwouldleadtoasignificantdisturbanceofthedynamicbehaviorofthebearinggenerating:• Riskofdamageatthestartup• Riskofdamageofthebearingareaofthe

shaft• Riskofunsatisfactorytoothcontactpattern

withpossiblecompletebreakdownofthegearbox.


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CONSEQUENCESThepracticalconsequenceofrefurbishingbearingsisnotjustthereplacementofthebearing–thisisabestcasescenario.Thefinaldamagescanrangefromdamagestotheshaftjournals,aswellasthetoothingofthegearsnecessitatingreplacementoftheentiregearset.

Figure4:Damagetothejournalareaafterfailureofrefurbishedbearings

Figure5:DamagetotheteethafterrefurbishedbearingfailureFromaninitialtimeand/ormoneysaving,financialimpactmightbedisastrousconsideringthecostfornewsparessupply,andabovethattheextendeddowntimeduetotheirlongleadtime.Worstcasemightbeacatastrophicfailurethatleadstothetotaldestructionoftheinstallation,injuredpersonnelorevendeathofpersonnel.

BelowexamplesarefromasiteinSaudiArabiawhichrequiredourinterventionandRCA.

Figure6:Gearboxexplosionduetofailureofbearingatload

Figure7:Totaldestructionofthegearbox

Figure8:HighDamagetosurroundingequipment


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PLANNINGINFORMATIONCompliance• ComplianceCategory:C• TimingCode:3ManpowerSkillsN/APartsN/ASpecialToolingN/AReferenceDocuments• GearboxUserManual• FGM003GearboxMaintenanceSchedulePreviousModificationsN/AScopeofWorkN/AContactyourlocalFGServiceRepresentativeforassistanceoradditionalinformationNOTE:IfyouwouldliketoreceivefutureTILsbyemail,contactyourlocalFGServiceRepresentativeforassistance


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TILCOMPLIANCERECORDCompliancewiththisTILmustbeenteredinlocalrecords.FGrequeststhatthecustomernotifyFGuponcomplianceoftisTILCompletethefollowingTILComplianceRecordandemailitto:TILComplianceflencomm@flender-graff.comTILCOMPLIANCERECORDForinternalrecordsonly#SiteName: CustomerName:CustomerContactInformation FGContactInformationContactName: ContactName:Address: Address: Email: Email:Phone: Phone:Fax: Fax:INSTALLEDEQUIPMENT TILCompletedDate 100%TILCompleted Description:UniteNumbers PartDescription PartNumber DrawingNumber Comments


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USERSATISFACTIONSURVERYFGvaluesyouropinionsandcomments.FGrequeststhatyoucompletetheUserSatisfactionSurveybelowtohelpusbetterserveyouwithaccurateandtimelyinformationonyourequipment.CompletethefollowingSatisfactionSurveyandemailitto:[email protected]

USERSATISFACTIONSURVERY

SerialNumber Date

1.HowmanydaysafterTILissuesdidyoureceivethisTIL?

1–5days 6–10days 10+days

Ratethefollowingbasedonascaleof1to5,where1isExcellentand5isPoor

2.Pleaseratehowwellthisdocumentinformedyouofthetechnicalissue

1 2 3 4 5

3.PleaseratetheoveralleffectivenessofthisTIL

1 2 3 4 5

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