Reliability Centred Maintenance (RCM)

Reliability Centred maintenance is a process to determine the safe minimum set of maintenance tasks and frequencies for a group of assets. The approach is rigorous, transparent and auditable. It forces a structured review of the consequences of each and every failure and focuses attention on the maintenance activities which have the most effect on safety and environmental integrity and on equipment performance. Properly applied, RCM ensures that money spent on maintenance is spent where it will do the most good.

RCM has evolved from work carried out in the civil aviation industry from the 60's onwards. In 1978 Nowlan and Heap of United Airlines produced a paper called 'Reliability Centred Maintenance' for the US Department of Defence that became the basis for the US Air Transport Association's standard MSG-3, currently the accepted RCM standard.

The SAE standard JA1011 sets out criteria for determining whether a maintenance analysis method complies with the accepted understanding of what is RCM by testing whether it satisfies 7 specific questions, which are discussed in the section - RCM Concepts.

The RCM methodology adopted by Curtis Challen Ltd is Aladon RCM2, which satisfies the requirements of JA1011. (www.aladon.com)

RCM enables maintenance to be optimised to provide:

• The level of asset availability the organisation seeks
• Possible revisions to operating procedures where those in use reduce asset performance
• A list of one-off changes to asset design where an asset cannot provide the required performance in its present configuration.
• Avoidance of unnecessary maintenance and costs

RCM typically reduces maintenance man-hours by between 25% and 75% (assuming that all previously scheduled maintenance was actually being carried out). There can be many reasons why a maintenance schedule is not being achieved, but where this is the case, it is possible that the maintenance was unnecessary or that asset availability was being compromised. RCM can provide evidence to show where maintenance was unnecessary, which is particularly valuable where legislation or regulation requires organisations to demonstrate that they operate assets safely. If availability was being compromised by failure to achieve maintenance schedules, RCM will allow improvements to be determined.

Maintenance and operational personnel involved in RCM studies often find that participation clarifies details of the way particular equipment works and how it fails, which reinforces their expertise with these assets.

Reliability Centred Maintenance is a method of determining the maintenance tasks required to ensure that assets continue to function, taking into account the way they are configured and the conditions under which they operate. It also determines the frequency at which tasks must be carried out to secure the level of reliability required.

To understand this, RCM asks 7 questions:

1. What are the functions and associated performance standards of the asset in its present operating context?
2. In what ways does it fail to fulfil its functions?
3. What causes each functional failure?
4. What happens when each failure occurs?
5. In what way does each failure matter?
6. What can be done to predict or prevent each failure?
7. What if a suitable proactive task cannot be found?

The first four questions establish the functions required of assets, the way in which assets fail to fulfil those functions, the failure modes that lead to failures and the effects of each failure.

A typical example might be:

• Function - To continue pumping fluid when a main pump fails
• Failure - Does not continue pumping
• Mode - Standby pump seized
• Effect - Fluid is not pumped, process plant trips out causing loss of production. Main pump must be repaired before production can be resumed.

The remaining three questions establish what, if anything, should be done to prevent or predict the failure. If nothing can be done, then some change in design or in how the asset is operated may need to be found.

For each failure, the consequences are determined and these are generally:

• Revealed - the failure has an immediate effect on the state of the system which becomes apparent, i.e. there is some obvious sign that the failure has occurred.
• Unrevealed - the failure on its own will not be apparent until a subsequent failure.
• Safety - the failure will harm someone or harm the environment.
• Operational - the failures affects output or quality and has an effect on economic performance.
• Non-operational - the failure has no immediate effect on output other than the cost of repair.

Where failures affect safety, tasks that reduce risk to an acceptable level are found. Where failures have only economic consequences, the most cost effective tasks are sought.

The calculation of frequencies requires the organisation to specify the tolerable frequency of multiple failures that result in loss of production or to some harmful situation. It also requires an understanding of the frequency at which failures occur and the length of time they equipment is then out of service. This is usually determined by studying fault reports, however, where comprehensive failure information is not available within the organisation, external data and other techniques can be used to provide conservative results that can be revised as new failure data is accumulated.

The RCM process may reveal anomalies in asset design when no task can be found to detect or prevent failure. In this situation, analysis will conclude that a change in design or in the way the asset is operated is required. An example might be failure of a safety device due to freezing of water in the sensing mechanism. It would be impracticable to schedule a special maintenance task during cold weather, however by re-designing the atmospheric vent to prevent rainwater or condensate forming, the failure mode may be eliminated.

There are occasions also where a change in operating procedures is sufficient to improve reliability. An example of this can be found in the UK gas distribution network where prior to RCM analysis, the working and standby streams of pressure regulating installations were routinely swapped. This was a costly exercise and resulted on many occasions in problems with pressure settings during high demand and out of hours calls to site were required to re-set equipment. The practice was found to have no benefit to the reliability of equipment.

The RCM analysis process relies upon a team of asset operators and maintainers who are familiar with the asset, supported by an RCM facilitator who is an expert in the RCM process. The facilitator ensures that information about the asset and its operating conditions is collected to provide a common understanding of the equipment under review and seeks to provide the best environment and motivation for the group. The facilitator is able to maintain the flow of thought by explaining RCM terminology, and rephrasing or translating questions that cannot be resolved. The key role of the facilitator is to ensure that the RCM process and logic are applied correctly and that there is consensus over all decisions reached, however it is not intended that the facilitator contributes to the technical decisions reached.

• Familiarisation - Brief on RCM concepts, tools & techniques, likely effort and benefits.
• Test the water - A pilot study on a nominated Group asset is undertaken. The results are documented and used to ascertain the likely effort and benefits.
• Resources - Determine the asset groups to which RCM will be applied and the resources required to perform the analysis.
• Planning - A roll-out plan is formulated for the acquisition of skills and knowledge, the provision of data systems and a schedule of assets and a corresponding timetable for their analysis.
• Training - Train the required number of RCM review teams and facilitators. During early reviews to avoid costly pitfalls, retain Rune Associates as mentors until BG Group facilitators are confident in guiding review teams.
• Roll-Out - Carry out reviews to determine maintenance schedules. Record results and prepare new maintenance schedules. Use reviews as a basis for subsequent study of broadly similar assets, thus reducing effort as the project progresses.
• Audit - Ensure that the RCM process is being followed accurately, that results are recorded consistently and data used for calculation of maintenance schedule is reliable.
• Review - Carry out a review of asset performance following implementation of RCM to verify analysis findings and quantify benefits. Use information produced to revise maintenance schedules if required.

Attention to the following points may have a significant impact on the success of RCM implementation:

Issue	Mitigation
Lack of failure data	Whilst RCM analysis depends upon failure data to determine task frequencies, alternative information can be used conservatively to establish a schedule, which can be reviewed as new data is compiled.
Delaying application of results pending adoption of new computer systems	Some organisations have taken the opportunity to implement new data systems to support the maintenance management process, which can lead to delays in realising the benefits of analysis. Results can be applied immediately in most cases, using existing scheduling systems.
Retaining external advisors during early analysis	Newly trained facilitators can benefit significantly by having an advisor to consult over the correct application of RCM principles, so that consistent and accurate results are produced and optimum use is made of reviewer's time.
Training an optimum number of review teams	A sufficient number of review teams must be trained so that the schedule of assets can be studied in an acceptable period of time. Whilst training a high number of people has benefits in terms of fostering a wide understanding and acceptance of RCM principles, there is a danger of inconsistent analysis due to varying interpretation of RCM rules.
Pressure on 'expert's' time	RCM analysis demands that teams consist of people who are experts in the operation & maintenance of the assets under review. This can cause tension between the RCM process and operational pressures.
Attempting to modify recognised RCM programmes	RCM is a significant undertaking and many attempts have been made to 'streamline' the process or gain 80% benefits with 20% effort. Care must be taken to ensure that any such venture is well informed and does not lead to improper or inadequate maintenance schedules.
Not completing the project	Initially it is likely that RCM will be applied to the most widely occurring type of assets and as the project progresses, an increasing number of small reviews of 'one-off' systems is required. It is important that the project includes these items so that a consistent maintenance regime is applied and a robust audit trail is provided for the whole asset base.
Application of RCM to 'critical' assets only	It may be tempting to apply RCM only to assets described as 'critical' within a system. This leads to a two tier maintenance regime for an installation and requires some form of study to determine what items are considered critical and why. RCM seeks to determine the optimum maintenance regime for a complete system of assets and where this is not carried out, potential benefits will not be realised.