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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.
TechnicalInformationLetter
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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.
TechnicalInformationLetter
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CONSEQUENCESThepracticalconsequenceofrefurbishingbearingsisnotjustthereplacementofthebearing–thisisabestcasescenario.Thefinaldamagescanrangefromdamagestotheshaftjournals,aswellasthetoothingofthegearsnecessitatingreplacementoftheentiregearset.
Figure4:Damagetothejournalareaafterfailureofrefurbishedbearings
Figure5:DamagetotheteethafterrefurbishedbearingfailureFromaninitialtimeand/ormoneysaving,financialimpactmightbedisastrousconsideringthecostfornewsparessupply,andabovethattheextendeddowntimeduetotheirlongleadtime.Worstcasemightbeacatastrophicfailurethatleadstothetotaldestructionoftheinstallation,injuredpersonnelorevendeathofpersonnel.
BelowexamplesarefromasiteinSaudiArabiawhichrequiredourinterventionandRCA.
Figure6:Gearboxexplosionduetofailureofbearingatload
Figure7:Totaldestructionofthegearbox
Figure8:HighDamagetosurroundingequipment
TechnicalInformationLetter
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PLANNINGINFORMATIONCompliance• ComplianceCategory:C• TimingCode:3ManpowerSkillsN/APartsN/ASpecialToolingN/AReferenceDocuments• GearboxUserManual• FGM003GearboxMaintenanceSchedulePreviousModificationsN/AScopeofWorkN/AContactyourlocalFGServiceRepresentativeforassistanceoradditionalinformationNOTE:IfyouwouldliketoreceivefutureTILsbyemail,contactyourlocalFGServiceRepresentativeforassistance
TechnicalInformationLetter
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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
TechnicalInformationLetter
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USERSATISFACTIONSURVERYFGvaluesyouropinionsandcomments.FGrequeststhatyoucompletetheUserSatisfactionSurveybelowtohelpusbetterserveyouwithaccurateandtimelyinformationonyourequipment.CompletethefollowingSatisfactionSurveyandemailitto:TILSurveyflencomm@flender-graff.com
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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