Myth 4. RCM does not support whole-of-life asset management

This posting continues the 10 part series on the 9 deadly Myths of RCM. Continuing to question commonly held beliefs throughout the maintenance engineering community regarding the application, implementation and evergreen processes involved in managing physical assets. Next Posting - Myth 5: RCM is Qualitative not Quantitative.

One of the first things taught by RCM practitioners in training courses around the world is the nature of failure, and the assignment of routine maintenance tasks. From the original RCM report we are provided with four basic routine maintenance tasks.

• Predictive Maintenance (PTIVE) – A task aimed at detecting the onset of failure or the potential failure. Often referred to as CBM or On-condition Maintenance the goal is to ensure that the occurrence of failure modes that have undesirable consequences are predicted so that they can be mitigated through planned activities. Within RCM PTIVE tasks are the preferred option.

• Preventive Restoration (PRES) – A task to restore a machines original resistance to failure based on some measure of hard time. (Such as calendar hours, hours run, or liters pumped for example) This task is generally applied to failure modes that can be restored without the need to replace the asset. Examples in this area include; re-machining, cleaning, flushing, sharpening, re-positioning, tightening and adjusting. Often PRES task can include calibration where this is done on a hard time basis. Within RCM PRES tasks are the second preferred option.

• Preventive Replacement (PREP) – A task to replace a physical asset in order to restore its resistance to failure. As with PRES tasks these are also hard time tasks. Common examples of PREP tasks include greasing bearings, changing oil filters and oil (if done on a time basis), and routine light bulb replacement (often but not always). Of the standard routine tasks PREP is the least preferred within an RCM framework.

• Detective Maintenance (DTIVE) – These are tasks that are done to detect whether an item has already failed so that action can be taken. These tasks are only used with items that have hidden functions. For example with protective devices such as circuit breakers, stand by pumps, lanyard switches on conveyor systems and High-high level switches. DTIVE tasks are only used within the four categories on the Hidden side of the RCM decision diagram and are not referred to in the four categories on the evident side at all. DTIVE tasks include proof testing of critical instrumentation and the occasional running of stand by pumps. Although often associated with safety related failures this is not always the case. Within RCM it provides the last line of defense for routine maintenance when a failure mode cannot be predicted or prevented.

The four routine tasks within RCM are generally well known and most of us with any exposure to this area of activity will have at least some understanding of them. This does leave out age exploration as this is a task aimed at increasing our level of knowledge rather than predicting, preventing or detecting a failure. It is relevant in terms of failure management policies but only so that we can decide the frequency of one of the tasks above.

But how does this help us when we start to look at whole-of-life asset management?

RCM provides the framework to define not only the 4 routine tasks, but also to define the three additional corrective tasks and calculate their expected frequencies.
For example, in a predictive maintenance task the PTIVE task is the task that we are applying at a given frequency in order to detect he onset of failure. However, there is also a corrective task. Once we have predicted that a component or asset is going to fail we need to plan, resource and execute a task to correct this situation. This is called the Predicted Task or PTED. (See Figure 1)

Figure 1 - Tasks Involved in Predictive Maintenance

Within the hard time tasks there is only one task, that of Preventive Restoration (PRES) or that of Preventive replacement (PREP). However, in Detective Maintenance tasks (DTIVE) there are also corrective actions. Once we have determined that a detective maintenance task is required, RCM enables us to derive a frequency based on managing the risk of a multiple failure to a tolerable level. The Detective task (DTIVE) is then performed on a routine basis to detect whether an asset has failed or whether it is still working.

Regardless of whether the asset is a switch, a circuit breaker, a sensor or a stand by pump, at some point we will detect that the asset has failed. This means that at some point there will be a corrective task, the Detected Maintenance task, which will normally be a replacement or repair of the failed asset. As with the Predictive Maintenance task (PTIVE) we have allowed this to happen because it is the best failure management policy available to us and wee are able to manage the consequences of the corrective task.
Figure 2 – Tasks involved in Detective Maintenance

The last of the corrective tasks that we can derive from a standard RCM analysis is that of run-to-failure. In this failure management policy we have eliminated the likelihood of either safety or environmental consequences and have determined that the most cost effective strategy is to allow the asset to fail. Any other action would cost more to carry out than to maintain the asset itself. In this case the only task that we need to consider is the Run-to-Failure task itself which is obviously a corrective action.
Figure 3 - Tasks involved in a Run-to-Failure Strategy

So once a comprehensive RCM Analysis is completed for an asset-system or an asset, it can include up to 7 planned tasks. 4 are routine tasks, 3 are corrective tasks, but all are proactive tasks. All are the result of careful decision making regarding maintenance policy and strategy. This allows us to build what is known as a Proactive Whole-of-Life Model.

• Predictive Maintenance (PTIVE) - Routine

• Predicted Maintenance (PTED) - Corrective

• Preventive Restoration (PRES) - Routine

• Preventive Replacement (PREP) - Routine

• Detective Maintenance (DTIVE) - Routine

• Detected Maintenance (DTED) - Corrective

• Run-to-Failure (RTF) – Corrective

The whole of life model is produced through calculating the resource burden of each individual task, then calculating this by the frequency of the task until the end of life event or threshold tine period. In the case of the routine tasks we can be pretty sure that our estimates are correct, however in the case of the corrective tasks these are often estimates based either on manufacturer’s data, our own maintenance history records and the experience of the people involved in the analysis.

As time goes on we begin to collect data that will enable us to become more accurate in our predictions.

For those familiar with attempts to calculate whole-of-life costs for assets there has always been a level of doubt regarding how to manage corrective tasks. This often results in some form of average of historical costs with an arbitrary cost reduction thrown in for improvement. When practiced rigorously,

RCM and the Proactive WoL models that it produces enables accurate lifecycle cost management for a given level of performance and risk.