Babbitted Bearing Babbitted Bearing Inspection IntervalsInspection Intervals
John K. WhalenJohn K. WhalenTCETCE
Why this presentation?Why this presentation?
Our customers are currently looking for 6Our customers are currently looking for 6--7+ years between outages7+ years between outagesThey want to know if the bearings are They want to know if the bearings are good that longgood that long
OutlineOutline
Purpose of this discussionPurpose of this discussionBabbitted bearing failure mechanismsBabbitted bearing failure mechanismsCondition MonitoringCondition MonitoringMaximizing bearing robustnessMaximizing bearing robustnessCase studyCase studyConclusionsConclusions
Purpose of this discussionPurpose of this discussion
Users pushing time between outagesUsers pushing time between outagesBearing life a major factor Bearing life a major factor
Especially with Especially with ““cleanclean”” serviceserviceWhat is a reasonable time between What is a reasonable time between bearing inspections? bearing inspections? How can this time be maximized? How can this time be maximized? What can condition monitoring tell us What can condition monitoring tell us about bearing condition? about bearing condition?
Time between outagesTime between outages
There is continuing pressure to:There is continuing pressure to:Keep units runningKeep units runningRunning efficientlyRunning efficientlyRunning safelyRunning safelyNO unplanned outagesNO unplanned outagesMinimize length of outagesMinimize length of outages
Planned and unplannedPlanned and unplanned
Bearing LifeBearing Life
The components in a machine designed to The components in a machine designed to fail first are the bearingsfail first are the bearings““Sacrificial elementsSacrificial elements””Goal is to predict impending failure:Goal is to predict impending failure:
Wait until next scheduled outage?Wait until next scheduled outage?Controlled shutdown?Controlled shutdown?WRECKWRECK
Bearing LifeBearing Life
In a perfect world fluid film bearing life is In a perfect world fluid film bearing life is infiniteinfinite
None of you live in a perfect worldNone of you live in a perfect world
Babbitt Bearing Failure Babbitt Bearing Failure MechanismsMechanisms
Babbitt fatigue damage. Babbitt fatigue damage. Babbitt wiping due to rotor to babbitt Babbitt wiping due to rotor to babbitt contactcontactBabbitt flow due to high temperatureBabbitt flow due to high temperatureForeign particle damage Foreign particle damage Varnish build upVarnish build upElectrostatic discharge damageElectrostatic discharge damage
Babbitt Bearing Failure Babbitt Bearing Failure MechanismsMechanisms
Electromagnetic discharge damageElectromagnetic discharge damageOil Oil ““burnburn”” due to high temperaturedue to high temperatureLoss of bond between babbitt and base Loss of bond between babbitt and base metal.metal.Chemical attack Chemical attack Pivot wear in tilting pad bearings.Pivot wear in tilting pad bearings.
Babbitt Bearing Failure Babbitt Bearing Failure MechanismsMechanisms
Damage caused by unloaded pad flutter Damage caused by unloaded pad flutter (usually only found in large tilting pad (usually only found in large tilting pad bearings bearings –– over 18over 18”” thrust over 13thrust over 13””journal)journal)Cavitation damage to babbittCavitation damage to babbitt
Condition MonitoringCondition Monitoring
In order to properly assess bearing health In order to properly assess bearing health the following is recommended:the following is recommended:
Proximity probes (radial and axial)Proximity probes (radial and axial)Monitoring radial vibration AND rotor positionMonitoring radial vibration AND rotor positionMonitoring axial position AND axial vibrationMonitoring axial position AND axial vibration
Oil analysisOil analysisBearing temperatureBearing temperatureGrounding brush dischargeGrounding brush discharge
Examples of Bearing FailuresExamples of Bearing Failures
Following are examples of failed bearingsFollowing are examples of failed bearings
Low speed wiping/at speed Low speed wiping/at speed fatigue due to misalignmentfatigue due to misalignment
Low speed wiping/at speed Low speed wiping/at speed fatigue due to misalignmentfatigue due to misalignment
Note the Note the ““polishingpolishing”” in in the bottom of the bearing the bottom of the bearing (aligned at low speed)(aligned at low speed)Note the babbitt damage Note the babbitt damage on one end axially at on one end axially at running position (attitude running position (attitude angle)angle)Solved by upgrading to Solved by upgrading to Tilting Pad Journal Tilting Pad Journal bearing with Ball & bearing with Ball & Socket pivots.Socket pivots.
Babbitt FatigueBabbitt Fatigue
Babbitt FatigueBabbitt Fatigue
Fatigue Strength - Effect of Babbitt Thickness
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30
Babbitt Thickness (mils)
Fat
igue
Lif
e (h
ours
)
2000 psi mean load
Fatigue Strength - Effect of Babbitt Temperature
0
50
100
150
200
250
300
350
400
150 200 250 300 350
Babbitt Temperature (deg F)
Fat
igue
Lif
e (h
ours
)
2000 psi mean load
Electrostatic DischargeElectrostatic Discharge
Electrostatic vs. ElectromagneticElectrostatic vs. ElectromagneticBabbitted Bearing Failure AnalysisBabbitted Bearing Failure Analysis
Electrostatic VoltageElectrostatic VoltageStatic Charge Build UpStatic Charge Build Up““FrostedFrosted”” AppearanceAppearanceDischarges through point of minimum oil film thicknessDischarges through point of minimum oil film thickness
Electromagnetic CurrentsElectromagnetic CurrentsResidual magnetism Residual magnetism ““generatesgenerates”” chargechargeCaused by Caused by
RubsRubsImproper welding groundImproper welding groundMag particle inspectionMag particle inspection
Also occurs in improperly insulated electrical machinesAlso occurs in improperly insulated electrical machinesMore severe than electrostaticMore severe than electrostatic““WeldingWelding”” of components possibleof components possible
Electrostatic DischargeElectrostatic Discharge
Electrostatic DischargeElectrostatic Discharge
Pivot WearPivot Wear
Pivot WearPivot Wear
Solved by upgrading Solved by upgrading to low stress Ball & to low stress Ball & Socket pivot Socket pivot Ball & Socket pivot Ball & Socket pivot also allows full axial also allows full axial alignment capability.alignment capability.Used successfully for Used successfully for over 35 yearsover 35 years
Overloaded Thrust BearingOverloaded Thrust Bearing
Overloaded Thrust BearingOverloaded Thrust Bearing
Hot Thrust BearingHot Thrust BearingOil Coking Oil Coking
Varnish Varnish
Varnish Varnish
Varnish Varnish
Varnish Varnish
Too late to tellToo late to tell……
Condition MonitoringCondition Monitoring
Of course there is a lot more to condition Of course there is a lot more to condition monitoring including:monitoring including:
Infrared Thermography Infrared Thermography Ultrasonics Ultrasonics Motor Current Analysis Motor Current Analysis Machine performance monitoringMachine performance monitoring
Robust bearing designRobust bearing design
Tilting pad journal bearings:Tilting pad journal bearings:Thin babbitt to increase fatigue strengthThin babbitt to increase fatigue strengthBall & Socket pivots to:Ball & Socket pivots to:
Substantially reduce pivot stressSubstantially reduce pivot stressEliminate common misalignment issuesEliminate common misalignment issues
Optimized with Rotordynamic analysis to reduce Optimized with Rotordynamic analysis to reduce vibration:vibration:
Less sensitive to synchronous excitation (unbalance)Less sensitive to synchronous excitation (unbalance)Increase log dec Increase log dec
Robust bearing designRobust bearing design
Tilting Pad Thrust BearingsTilting Pad Thrust BearingsCopper alloy/offset pivots to increase load Copper alloy/offset pivots to increase load capacitycapacityHardened pivots/links/retainer interface to Hardened pivots/links/retainer interface to minimize wear. minimize wear. Ball & Socket pivots to minimize pivot stress Ball & Socket pivots to minimize pivot stress and allow full articulationand allow full articulation
Case HistoryCase History-- Nova chemicalsNova chemicals
Just completing outage of unit #2Just completing outage of unit #2Checked 17 B&S Journal bearingsChecked 17 B&S Journal bearingsEthylene PlantEthylene Plant
PGC: Three body + steam turbine driverPGC: Three body + steam turbine driverPropylene + GT (1 bearing) + Helper turbinePropylene + GT (1 bearing) + Helper turbineEthylene + Steam turbine driverEthylene + Steam turbine driver
Checked ClearancesChecked Clearances
Of the 17 B&S TPJOf the 17 B&S TPJ’’s the worst clearance s the worst clearance increase was 0.6 milsincrease was 0.6 milsAll other were less than 0.5 milsAll other were less than 0.5 milsCleaned up and reinstalled all TPJ Cleaned up and reinstalled all TPJ bearingsbearings
They also upgraded to TorlonThey also upgraded to Torlon
Unit #2 Unit #2 –– all compressors upgraded all compressors upgraded Unit #1 Unit #1 –– all but the propylene all but the propylene –– will will upgrade at next outageupgrade at next outageFollowing photos are after 9 years of Following photos are after 9 years of running (4+5)running (4+5)
NovaNova
Previous outage was after 4 yearsPrevious outage was after 4 yearsThis outage was 5This outage was 5Next outage is planned for 6Next outage is planned for 6Outages of course have been and will be Outages of course have been and will be driven by factors other than bearings and driven by factors other than bearings and sealsseals
Questions? Comments?Questions? Comments?