Reliability Centred Maintenance (RCM): Complete Guide
RCM is a structured methodology for determining the optimal maintenance strategy for each asset. Learn the seven questions of RCM, how it differs from PM, and how to implement it in your plant.
What is RCM?
Reliability Centred Maintenance (RCM) is a systematic approach to determining the optimal maintenance strategy for each asset based on its function, failure modes, and consequences. Rather than applying the same maintenance strategy to everything (e.g., 'PM every 3 months'), RCM tailors the strategy — preventive, predictive, or run-to-failure — based on the specific risk profile of each asset.
The Seven Questions of RCM
- What are the functions and performance standards of the asset? What is the asset supposed to do, and at what level of performance?
- In what ways can it fail to fulfill those functions? What are the failure modes — how can it stop doing what it's supposed to do?
- What causes each functional failure? What are the specific failure mechanisms — wear, fatigue, corrosion, overload, etc.?
- What happens when each failure occurs? What are the effects — downtime, safety risk, environmental damage, production loss?
- What are the consequences of each failure? How serious is it? Does it affect safety, the environment, production, or just costs?
- What can be done to predict or prevent each failure? What maintenance task (PM, PdM, inspection) can detect or prevent the failure?
- What should be done if no preventive task is appropriate? If the failure can't be predicted or prevented, what then? (Run-to-failure with redundancy, redesign, or procedure change.)
Maintenance Strategy Selection
RCM determines the optimal strategy based on the failure pattern and consequences:
| Failure Consequence | Preferred Strategy |
|---|---|
| Safety or environmental | Must be prevented — PM, PdM, or redesign. Run-to-failure not acceptable. |
| Hidden (no obvious indication) | Inspection or functional test to detect the failure |
| Operational (production impact) | PdM if cost-effective, PM if failure pattern is age-related, RTF if consequences are minor |
| Non-operational (repair cost only) | Run-to-failure if repair cost is less than prevention cost |
The Six Failure Patterns
RCM is based on research (the Nowlan and Heap study) showing that equipment failures follow six patterns:
- Pattern A (bathtub curve): High infant mortality, low constant failure, then wear-out. Only 4% of equipment.
- Pattern B: Constant failure rate with wear-out at end of life. 2% of equipment.
- Pattern C: Slowly increasing failure rate. 5% of equipment.
- Pattern D: Initial low failure, then constant. 7% of equipment.
- Pattern E: Constant failure rate throughout life. 14% of equipment.
- Pattern F: High infant mortality, then constant. 68% of equipment — the majority!
Key insight: Only 11% of equipment (Patterns A and B) benefits from time-based preventive maintenance (age-related failure). The other 89% fail randomly — meaning condition monitoring (PdM) is more effective than scheduled PM for most equipment.
Implementing RCM
- Start with critical assets: Don't try to RCM everything at once. Start with your most critical assets (A-class equipment) where the consequences of failure are highest.
- Assemble a team: Include operators, maintenance technicians, engineers, and the asset owner. Their combined knowledge is essential for accurate analysis.
- Document the analysis: Record the seven questions and answers in a structured format (spreadsheet or RCM software).
- Implement the strategies: Update the CMMS with the selected maintenance tasks, frequencies, and responsible persons.
- Review periodically: The RCM analysis should be reviewed when failure patterns change, new failure modes appear, or operating conditions change.