What is reliability-centered maintenance?
Reliability-centered maintenance (RCM) was developed in the airline industry in the 1960s and 1970s (Nowlan and Heap, 1978) and is defined today in SAE JA1011. It replaced the assumption that everything wears out on a schedule: most failure modes do not have a clear wear-out age, so the best maintenance is often to monitor condition, test hidden protective functions, or deliberately do nothing. RCM makes each of those choices explicit and justified.
Consequences and tasks
| Consequence | A task is worth doing if | If no task works |
|---|---|---|
| Hidden | It reduces the risk of a multiple failure to a tolerable level | Failure-finding task; redesign may be required |
| Safety / environmental | It reduces the risk to a tolerable level | Redesign is mandatory |
| Operational | It costs less than the operational loss plus repair | Run to failure, or redesign if worth it |
| Non-operational | It costs less than the repair | Run to failure |
RCM example
A team analyses cooling water pump P-101. It has four functions: pump 300–350 m³/h at 4 bar, contain the water, stop the pump on low flow (a protective function) and show the discharge pressure. Seven failure modes follow. Four are managed by condition monitoring (vibration analysis monthly, motor thermography quarterly, a six-monthly performance test for impeller wear, and a daily leak check for the seal, whose leak is a slip hazard). The coupling element is replaced every two years. The stuck flow switch is a hidden failure: nobody notices until the pump runs dry, so it gets a three-monthly function test. A broken pressure gauge has no operational effect and is run to failure.
Tips
- Start from functions with standards ("pump 300 m³/h at 4 bar"), not from the parts list.
- Do not forget protective functions: alarms, trips and relief valves are where hidden failures live.
- Base task intervals on the failure pattern: a Weibull analysis shows whether there is a wear-out age.
- For risk ranking of the failure modes, see FMEA; for the shop-floor programme, see TPM.
How to use this Reliability-Centered Maintenance tool
- Name the asset. Click the first box and name the asset in its operating context.
- List the functions. Click + to add each function with a performance standard, including protective and secondary functions.
- Add functional failures. For each function, add the ways it can fail: totally, partially, or outside the standard.
- Add failure modes. For each functional failure, add the causes, each with its effect.
- Classify and choose tasks. For each failure mode, set the consequence and choose a task type, task, interval and who does it.
- Check and export. Fix the issues the tool flags, then export the worksheet to PDF or Excel.
Frequently asked questions
What is reliability-centered maintenance (RCM)?
RCM is a structured process for deciding what maintenance an asset needs in its operating context. Instead of maintaining everything on a fixed schedule, it starts from what the asset must do (its functions), how it can fail, what the failures lead to, and then chooses the task that deals with each failure mode in a way that is technically feasible and worth doing.
What are the seven RCM questions?
From SAE JA1011: 1 What are the functions and performance standards? 2 In what ways can it fail to fulfil its functions? 3 What causes each functional failure (failure modes)? 4 What happens when each failure occurs (effects)? 5 In what way does each failure matter (consequences)? 6 What can be done to predict or prevent each failure? 7 What should be done if no suitable proactive task can be found?
What are the failure consequence categories?
Hidden failures are not evident to operators in normal operation (typically protective devices). Safety and environmental consequences could injure someone or breach a standard. Operational consequences affect output, quality or service. Non-operational consequences cost only the repair.
Which maintenance tasks does RCM consider?
On-condition tasks (condition monitoring, inspection), scheduled restoration (overhaul at a fixed age), scheduled discard (replace at a fixed age), failure-finding tasks (testing hidden functions), and default actions: run to failure when consequences are tolerable, or redesign when no task works and the consequences are not acceptable.
When is run to failure acceptable?
Only when the failure has non-operational or minor operational consequences and no proactive task is worth doing. It is never acceptable for safety or environmental consequences, and for hidden failures a failure-finding task is needed instead.
How is RCM different from FMEA?
RCM uses an FMEA-like analysis of functions, failures, modes and effects, but goes on to classify consequences and select maintenance tasks. FMEA ranks risks, often for design or process changes; RCM produces a maintenance programme.