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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
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