Reliability Centred Maintenance and Condition Monitoring

Strategies for Gas Turbines in Industrial Applications

Bob Wellington

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Agenda Reliability Centred Maintenance

What is RCM? Program Development Equipment Hierarchy Failure Modes and Effects Analysis Risk Assessment/Action Planning RCMII Decision Tree P-F Intervals, Hidden Failures and Failure Finding Tasks Tools for Program Development and Sustainment

Condition Monitoring Strategies Defining your Condition Monitoring Standard Cost/Benefit Considerations

Spares Strategies

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Evolution of Maintenance Strategies in Industry

Run to Failure Scheduled Preventative Maintenance/Overhauls

Reliability Centred Maintenance

Pre-WWII 1950s - 1970s 1970s -

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1960 FAA /Airline Industry Reliability Program Study Results

(Kennedy, 2006)

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What is RCM (II)? “A process used to determine what must be done to ensure that any physical asset continues to do what its users want it to do in its present operating context.”(Moubray, 1997)

Maintenance efficiency through risk assessment and functional prioritization of maintenance activities.

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Program Development/Sustainment

Development Sustainment

Develop Equipment Hierarchy

Define Component Functions and

Functional Failures

Define Failure Modes

Evaluate Risk (Likelihood x Consequence)

Establish Action to Manage Risk

Document and Implement

Measure Reliability and Review

Program Effectiveness

Change in Reliability Needs

New Failure Experience/Service Bulletin/Upgrade

Do

Check Act

Plan

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Equipment Hierarchy for a Gas Turbine

Equipment should be broken down into components at a functional level eg. Plant A

Gas Turbine – Lube Oil System

• Main Pump • PRV • On Engine Oil Supply Tubing • Scheduling Valve • Oil

– Air Compressor • BOV • Front Bearing Seal • Rotor

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FMEA Each element identified should have it’s specific functions described and

defined as a hidden function. (eg. On-Engine Oil Supply Tubing System: Deliver Oil from Manifold to

Bearing Cavity) Functional failures must be described for each element. For elements with

multiple functions, each function must have an associated failure. (eg. Failure to contain oil in tubing supplying turbine section bearing) The failure mode for each functional failure must be identified. (eg. Fatigue failure of tubing seal into bearing) Identify failure probability, effects and consequences

(eg. Once in 15000 hours. Oil misting into exhaust path results in fire leading to bearing support distortion and rotor contacting stators. 3 months downtime, $500K in repair costs, Minimal EHS risk with appropriate shut downs in place)

NOTE: A review of failure experiences, OEM standard inspections as well as available instrumentation for most recent model of equipment should be undertaken as part of the complete FMEA.

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Risk Assessment

Determine whether a default action is required for each failure mode (EHS Risks) If not: 1. Establish Likelihood for each failure mode (Once in 15,000

operating hours) 2. Establish Consequence or Effect of each failure mode ($200,000 to

repair and $500,000 in lost revenue) 3. Establish Risk (Probability x Consequence) for each failure mode

Note: For hidden failures, probability = p (protective function failure) x p (protected function failure)

4. Determine appropriate mitigation to manage overall risk profile

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Hidden Failures

A hidden failure is a failure which will not become evident until such time that it leads to multiple failures (protective functions).

eg. Overheat detector in rear bearing vent fails such that the last read measurement is frozen as the control panel input. No consequence until tubing failure occurs and OH detector fails to shut unit down in time to prevent secondary damage.

12 (Moubray, 1997)

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Mitigation for Operational Risks • Design out • Scheduled Failure Finding Tasks for Hidden

Failures Scheduled inspections, calibration, etc. (proactive/detective)

• Scheduled Maintenance/Overhaul/Discard (preventative)

• Condition monitoring improvements (predictive)

• Do nothing (reactive)

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P-F Curve for On-Condition Inspection/Restoration/Discard Tasks

(Wiseman, date unknown)

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Tools for Program Development/Sustainment

• RCM/FMEA Focus Group • RCM Decision Tree • RCM Worksheets • Corporate Risk Matrix/Models • Documentation/Manuals

Working documents w/ scheduled review intervals and staff for upkeep

• CMMS • Reliability/Production KPIs

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Records • Procedure for inspection/maintenance task

(O&M manuals) • Rationale for inspection/maintenance task

(FMEA) • Success in completion of

inspection/maintenance tasks (CMMS) • Asset Maintenance and Upgrade History

(CMMS) • Success of inspections maintenance tasks –

Reliability/Availability KPIs

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Condition Monitoring Strategies FMEA should define the standard for conditions

monitoring • Required Instrumentation • Necessary Failure Finding Tasks and Frequency • Alarm set points and additional response triggers • Trending review frequency • Specific Scheduled Tests – what/when/how? • Requirements for EHM system

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Important Considerations • Cost/Benefit • Define which failures are tolerable • Consider P-F intervals in setting review

frequency for trending or schedule for failure finding tasks

• Consistency of operation • Instrumentation/PLC Failures

• More isn’t always better • Failures often come without warning

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Spares Strategies • Maintenance spares vs. reliability spares • Understand failure probabilities and

inspections/mitigations already in place (FMEA)

• Lead times • Sharing inventory w/ repair shops or other

operators • LTSA requirements

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References Moubray, J (1997). Reliability-Centred Maintenance II – 2nd Ed.,

Industrial Press Inc. Kennedy, R (2006). Examining the Processes of RCM and TPM: What do they

achieve and are the two processes ultimately compatible?, Retrieved August 2012, from http://www.ctpm.org.au/resources/37/20090207%20Examining% 20RCM%20Vs%20TPM.pdf

Wiseman, M (date unknown), The Elusive P-F Interval, Retrieved August 2012, from http://www.omdec.com/articles/reliability/ElusivePF_files/image002.jpg &imgrefurl=http://www.omdec.com/articles/reliability/ElusivePF.html&h=237&w=273&sz=9&tbnid=hYyDvVesioTaGM:&tbnh=90&tbnw=104&prev=/search%3Fq%3Dp-f%2Binterval%26tbm%3Disch%26tbo%3Du&zoom=1 &q=p-f+interval&usg=__gGcnU-vjIEw9ZNDQWGQiHyxkzRs=&sa=X&ei= VmdWUOj4BKigywHPmYHoDg&ved=0CBsQ9QEwAg