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?