Condition Based MaintenanceAn OverviewPDC Engineering

What is CBM?A maintenance strategy that is based on maintenance being carried out as and when the equipment requires it.Other strategies are:Run to failure.Hours or calendar based.

How do we know when to do maintenance using CBM?By taking measurements which will infer the condition of the machineMeasurement types include:Vibration analysisInfrared thermographyPassive ultrasoundTribologyProcess temperature, pressure etc

We want to monitor the condition of our machineryHow do we start?We carry out a POTENTIAL FAILURE ANALYSIS

PFA for an electric motorWe first decide what the possible failures could be For example, spalled bearings will lead to a bearing failureWe then identify how that failure mechanism will show itself as something we can measureThis example will require a measurement based on a vibration technologyThe applicable parameters for detecting spalled bearings are velocity spectrum and time waveform in GsUsing our experience, we now decide on the specifics when carrying out the analysisThe detection of spalled bearings should be carried out continually (On-Line)In the last column we specify some of the finer details to ensure good, practical failure detection

Base CauseFailure TypeExternalManifestationTechnologyParameterIntervalDetail Dry/MarkedbearingsBearing FailureSpalledbearingsBearing FailureMisalignmentBearing Failure/Shaft FailureLoosenessBearing Failure/Shaft Failure/Structural FailureWindingdefectsMotor burnoutRotordefectsBearing failureMotor burnout100 HP AC Motor PFA Tree

Base CauseFailure TypeExternalManifestationTechnologyParameterIntervalDetail Dry/MarkedbearingsBearing FailureHigh frequency resonance@ bearing defectfrequency intervalsSpalledbearingsBearing FailureHarmonics of bearingdefect frequenciesMisalignmentBearing Failure/Shaft FailureHigh axial vibrationLoosenessBearing Failure/Shaft Failure/Structural FailureRun speed harmonics& subharmonicsWindingdefectsMotor burnoutStator temp. rise/Uneven temp. distributionEarth current leakageRotordefectsBearing failureLine frequency +sidebandsVibration @ rotor barpass frequencyMotor burnout100 HP AC Motor PFA Tree

Base CauseFailure TypeExternalManifestationTechnologyParameterIntervalDetail Dry/MarkedbearingsBearing FailureHigh frequency resonance@ bearing defectfrequency intervalsVibrationEnveloping(HFD/B)(Shock Pulse)(Ultra Sound)Time WaveformSpalledbearingsBearing FailureHarmonics of bearingdefect frequenciesVibrationVelocityTime WaveformMisalignmentBearing Failure/Shaft FailureHigh axial vibrationVibrationVelocityLoosenessBearing Failure/Shaft Failure/Structural FailureRun speed harmonics& subharmonicsVibrationVelocityWindingdefectsMotor burnoutStator temp. rise/Uneven temp. distributionThermographyThermal image(spot temp)MeggerEarth current leakageInsulation testRotordefectsBearing failureLine frequency +sidebandsMotor loadcurrent analysisMotor currentfrequencyVelocityVibration @ rotor barpass frequencyVibrationMotor burnout100 HP AC Motor PFA Tree

Base CauseFailure TypeExternalManifestationTechnologyParameterIntervalDetail Dry/MarkedbearingsBearing FailureHigh frequency resonance@ bearing defectfrequency intervalsVibrationEnveloping(HFD/B)(Shock Pulse)(Ultra Sound)Time Waveform1 month1 monthSpalledbearingsBearing FailureHarmonics of bearingdefect frequenciesVibrationVelocityTime Waveform1 month1 monthMisalignmentBearing Failure/Shaft FailureHigh axial vibrationVibrationVelocity3 monthLoosenessBearing Failure/Shaft Failure/Structural FailureRun speed harmonics& subharmonicsVibrationVelocity1 monthWindingdefectsMotor burnoutStator temp. rise/Uneven temp. distributionThermographyThermal image(spot temp)Megger6 month6 monthEarth current leakageInsulation testRotordefectsBearing failureLine frequency +sidebandsMotor loadcurrent analysisMotor currentfrequencyVelocity6 month3 monthVibration @ rotor barpass frequencyVibrationMotor burnout100 HP AC Motor PFA Tree

How do I start?First define your PFAsDecide on applicable technologiesDecide on measurement intervalsDecide on measurement strategyMaintain copies of PFAs for ISO 9002 audit compliance

Applicable TechnologiesVibration AnalysisInfrared ThermographyPassive UltrasoundTribology

Vibration AnalysisOn Line or Off Line?How long is the failure mechanism?Will the machine always run at measurement time?Does the machine run under consistent conditions? Is access safe?Is access convenient?Rule of thumbUse on-line for process critical or high capital cost equipmentUse off line for spared or non-critical equipment

The Failure MechanismExample:A bearing on a large slow moving fan may last for a year after the onset of lubrication failure.A bearing on a pump may only last 2 days depending on load, speed, alignment, initial lubrication etc.Remember:Vibration will only detect defects that exhibit a measurable difference prior to failure.Vibration WILL NOT detect fatigue or stress failures in advance as there is no external change to influence the vibration parameters.

Run ConditionsModern on-line systems can store data in separate locations for different running conditions (load, speed etc).On-line systems should not store data when the equipment is not running.Remember the value of a vibration analysis system is in the DATA NOT the equipment. On-line gives full value continually.

Vibration examplesMill gearboxesLauter Tun drivesGeneral examples

Mill Crankshaft GearboxesMill #2 Drive GearboxesTop/Middle/Bottom8th of July 1999 at 8:16 am

Lauter Tun GearboxesLauter Tun 1 (red)Lauter Tun 2 (blue)Output Shaft31st January 2002

General ExamplesImbalanceLoosenessBad Bearings

Infrared ThermographyNon contactNon intrusiveRadiometric capabilityImages stored for history

Infrared Thermography Electrical ExampleBoiler Primary 46B/7520th October 2000

Infrared Thermography Mechanical ExampleBrine Fixed Speed Pump 53C/00720th October 2000

Passive UltrasoundTrouble shootingBearingsAir leaksHydraulic valvesSteam traps

Passive UltrasoundUltrasound recording of a good bearingUltrasound recording of a bad bearing

TribologyVery early warning of defectsMost useful in hydraulic systemsISO cleanliness or SOAPSpectrographic Oil Analysis Progamme

Oil Analysis SOAP Trend

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450A

Alarms9/15/9411/5/9412/1/941/26/954/14/955/16/957/7/958/17/9510/6/9511/16/9512/26/951/19/96

Iron13.0538792973111271010881169124

Copper8.833227979488556568517018647

Viscosity266268.4272.5273.2273.5274275275.3272.6274.7281.2275.8

Oxidation100010111020

Silicon100010000000

Lead00000001017204

Oil RatingSatSatSatSatSatSatSatSatSatSat

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450B

Alarms11/5/9412/1/941/26/953/3/954/14/955/16/957/7/958/17/9510/6/9511/16/951/19/96

Iron34.1651513899202120303028262623241

Copper14.1162646126101110121312131313120

Viscosity262.9256.6258.2257.6255.3253.9254.5256.4255256.1281.2

Oxidation01111122210

Silicon11112222210

Lead04211011110

Oil RatingSatSatSatSatSatSatSatSatSatSatSat

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450 B Oil Analysis

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FerrographyMicroscopic analysis of oil samples

ISO Cleanliness CodesParticle count testing provides a determination of the number of particulates in a specific size range using the International Standards Organization (ISO) Cleanliness Code, ISO 4406. An ISO Code is created by selecting three ISO range numbers that correspond to the number of particles in a milliliter of fluid greater than 2, 5, and 15 microns, respectively.

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CLEANLINESS LEVEL CORRELATION TABLE

21/18450012-

20/182400--

20/17230011-Normal Operating Cleanliness Levels (unfiltered oil)

20/161400--

19/16120010-

18/1558096

17/1428085Approximate New Oil

16/1314074

15/127063

14/1240--

14/113552

13/101441

12/09930

11/0852-

10/083--

10/072.31-

10/061.4--

09/061.20-

08/050.60-

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In-House or Outsource?This must be your decision based on:CostAvailable manpowerTraining commitmentOwnership strategy

Define A ProjectWhichever method you choose, treat the installation of CBM as a maintenance projectDefine targets, milestones and resourcesMeasure your progress and report regularly

The Project Timeline

End PointsBe consistentHave a clearly defined reporting strategyReport your cost savings regularlyIF IT ISNT SAVING YOU MONEY ITS NOT WORTH DOING

The first step is to identify the root causes of potential failure of the machine and how that failure would materialize.Once we have decided on the potential failure, we must decide how the developing failure would show itself at the various stages of the failure mechanism.Now we decide on what is the appropriate technology to detect the developing failure at its various stages. We must also decide what is the most applicable parameter of that technology.For example, a velocity parameter of a vibration technology.Depending on the potential rate of deterioration of the developing defect, we have to decide how often we must take readings so that the failure mechanism does not have time to reach complete failure without detection by predictive maintenance.Finally we fine tune the reading by including details.