Introduction to RCM
Traditional thinking that equipment failure can be determined by length of time in service is severely flawed, as most readers may be aware.
Research carried out by the airline industry and US Navy found that the traditional bathtub curve could account for only 4% of failures. It was established that there are in fact six common equipment failure patterns and when all failures are considered, only around 15% can be determined based on hours or cycles run. This means that carrying out scheduled replacement or restoration tasks based on hours or cycles run is inherently wasteful.
It is our role within maintenance to ensure the reliability of all assets, and to achieve this we must consider methods beyond simply setting up time-based scheduled repair or restoration tasks. One of the tools we can use to determine the correct maintenance for any asset is Reliability Centred Maintenance (RCM), which grew out of the aviation industry.
When the Douglas DC8 was in service back in the 1960s, around four million maintenance man-hours were expended between major 20,000 hour overhauls. With the introduction of the Boeing 747, a far more complex aircraft, it became obvious that a different approach was needed. This realisation prompted the industry to put together a series of ‘Maintenance Steering Groups’ (MSG) to re-examine everything they were doing to keep their aircraft airborne.
After much research and development a process was formed with a maintenance focus, based on the function and failure effects of components. This process, known as MSG 2, was released in 1970. The outcome was spectacular - the MSG maintenance programme on the 747 expended only 66,000 man-hours between major 20,000 hour overhauls, and this on a far more complex aircraft.
Unsurprisingly the MSG process was adopted by the wider aviation industry and shortly after by the military. In the early 80s the process was adapted for use by general industry by John Mowbray. It was renamed Reliability Centred Maintenance and has since been used successfully the world over.
Reliability Centred Maintenance enables the definition of a complete maintenance regime for any asset taking into account the context or environment in which it operates.
The initial part of the RCM analysis is to identify the operating context of the machinery, and write a Failure Mode Effects and Criticality Analysis, or FMECA. During this process the function(s) of the equipment is clearly defined and the ways in which it could fail to meet each function is considered. All possible causes of the failure (failure mode), and the effect that failure will have, are determined before the final part of the FMECA process, which is to consider the criticality of each failure mode.
The second part of the analysis is to apply the decision logic which is used to determine the most appropriate maintenance tasks for the failure modes identified in the FMECA. Once the logic is complete for all elements in the FMECA and all maintenance tasks have been identified, the resulting list of maintenance is packaged so that the periodicities of the tasks are rationalised to be called up in work packages.
Sounds simple enough! So why isn’t it carried out more widely? The reality is that to carry out an RCM analysis is a time consuming and detailed process, and requires a deep understanding of our equipment and the RCM process itself. Depending on the maturity of our current maintenance culture, bigger gains can also often be made by concentrating on the basics such as tightness of fasteners, lubrication, cleaning and alignment.
However, there should come a time within all organisations when RCM is the most appropriate way to progress reliability to the next level. Working on the premise that a little knowledge is a dangerous thing, the first step should be to obtain a thorough understanding of the RCM process through reading or attending a training course. This will allow the assets that are most likely to benefit from RCM to be identified and then provide the skills needed to get the process underway.
Reliability Centred Maintenance is a high level maintenance tool that will determine the most appropriate maintenance for any asset, taking into account the context or environment in which it is operating. It will not increase reliability if we are not paying attention to the basics, but used in context it has the potential to reduce the amount of man-hours we expend on maintenance while greatly increasing reliability.