RCM Basics - 7 Questions

In RCM we follow the 7 questions of RCM:

1. What are the functions and associated performance standards of the asset?
   1. Why do you have this asset?
2. In what ways can it fail to fulfill its functions?
   1. What failures do happen?
3. What causes each functional failure?
   1. Which Failure Modes are involved
4. What happens when each failure occurs?
   1. What is the Failure Scenario
5. In what way does the failure matter?
   1. What is the Criticality
6. What can be done to predict or prevent each failure?
   1. What Maintenance Tasks can we do?
7. What should be done if a suitable proactive task cannot be found?
   1. Is there enough risk reduction?  Is the Residual Risk too high?
   2. Is there economic benefit?   Is the MEI high enough?

Functions and Functional Failures

In this step we split up the process unit into Systems with specification of the expected performance. The defined Systems should enable an effective 'Failure mode and Effect Analyses' to assess the effects of equipment failures on the System functions. The functions and functional failures should relate to the performance production process, some examples to consider:

• Production Reference Plan
  • Production Targets, Reliability, Budget, Growth Plan
• License to operate requirements
  • Environmental, Health, and Safety requirements
  • Environmental Protection Act and Statutory Nuisances
• The production processes
  • Process phases, recycle loops and treating steps.
  • Main streams, auxiliary streams and utilities
• Production storage capability
• Product Quality Requirements (Off Spec effects)
• Redundancy of equipment
• TA strategy and interval
• Maintenance strategy
• Operational arrangements and Shifts (on shore / off shore)
• Repair time (maintenance response time) / Logistics/ Travel
• Spare parts status/ Lead times/ Logistics
• Economics (Production Loss Equation), Margin and Throughput
• Environment, seasonal conditions

Failure Modes

We typically focus on dominant Failure Modes (FM) which over longer time have proven to occur. The following steps are recommended to determine FM's:

• Check a picture of the equipment
• Check a cross sectional drawing of the equipment and identify wearable or degradable parts
• Check the equipment in the P&ID and verify the tag number, possible process conditions, indicators and instruments, auxiliary equipment. 

The FMs are anticipated on the expectation that the equipment runs on design conditions:

What happens when each failure occurs

Under the assumption 'No maintenance done' (= we put the hands in the pockets and observe the degradation to occur) a description is expected that indicates:

• Where the degradation of the FM involved starts,
• How the degradations develop,
• Where the degradation ends, in a stable failed state.

This can be done by articulating a sentence that describes the P-F curve. The P-F curve represents the degradation pattern from where the degradation can be detected - given by the point of Potential failure -to the point of Failure.

Such a P-F curve is a cause-and-effect pattern to the failed state, where various P-points might be involved. Each P-point is of interest in the definition of maintenance tasks.

'As found' conditions from maintenance history can help to identify how the degradations actually occurred.

Does the failure matter?

The probability and consequence of the failure is estimated, related to Asset (Economics), People (Health and Safety) and Environment.
This is shown in the criticality matrix in 6 levels from N to E:

For economic verification, the criticality is also calcualted in 'Annual price of non-conformance' (k$/yr).

What can be done to predict or prevent each failure?

A specification of maintenance tasks is provided, related to "What happens when each failure occurs", so the P-F curve plays an important role in determining and specifying the maintenance tasks.
The FM characteristics in terms of 'Age related degradation' or 'Non-Age-related degradation' is used to steer towards a time based maintenance strategy or a condition based maintenance strategy.
For proper economic balance between the 'No maintenance case' (described in the Failure Effects) and the 'Do maintenance case' (provided by the maintenance tasks) - the maintenance tasks should involve a restoration task.

What should be done if a suitable proactive task cannot be found?

The key word is here 'Suitable' and relevant in terms of:

• Is there enough risk reduction?
• Is the Residual Risk too high?
  Residual risk levels of MH, H or E are unacceptable and follow up investigation should be done to reduce the risk.

Next:

• Is there economic benefit?
• Is the MEI high enough?

The risk reduction provided by the maintenance tasks should 'pay' for the maintenance done.
Firstly the residual risk should be determined, based on the probability that the failure might happen after all. The risk reduction is determined by:
Base risk - Residual risk
the Maintenance Efficiency index (MEI) is: Risk Reduction/ Maintenance costs.
An MEI score below 1 indicates a low economic value of the tasks (so - too expensive) and suggests 'no scheduled maintenance' or 'Run to Failure'.