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By Bill Hillman, CMRP, Ludeca
A successful reliability-centered maintenance (RCM) program or root cause analysis (RCA) is difficult to imagine without condition monitoring (CM). RCM is a process that has been around for a number of years and has proven successful because of the sheer logic of the process.
Just what is RCM? We will forgo any formal definitions and answer the question by looking at how RCM works. Succinctly, RCM draws clear and accurate boundaries around a physical asset. All things contained within these boundaries are then subjected to the RCM analysis. All of the functions of that asset are then identified. In other words, what does the asset do? Then all of the ways that those functions can fail are identified and analyzed. Once this is done, tasks are developed to prevent or minimize the consequences of the failures that are likely to occur and would have a negative consequence. Simply stated, an analysis is performed and then something is done (tasks) to keep the asset functioning to a required level. It is difficult to envision a process more logical than RCM for maintaining physical assets (machinery).
Features of RCM
Steps in performing RCM
Results of task analysis
Reasons for selecting maintenance tasks
Where does CM come into play in the RCM process? When all the RCM analyzing is complete, there comes a time in which something needs to be done. That something is the tasks that are selected for the reasons stated above. There is a preferred order by which tasks are selected. To prevent or minimize the consequence of failure the first type of task considered is a condition directed or predictive task (CM). Why would condition directed or predictive tasks (CM) be considered first? The answer is simply because CM tasks are usually the easiest to preform and, more importantly, least invasive. A large portion of equipment failures are self-induced. In “RCM — Gateway to World Class Maintenance,” Anthony M. Smith and Glenn R. Hinchcliffe state that as many as 50%t of machine failures are due to human error in maintenance work. Some studies put this number as high as 70%. In other words, we break things in our attempts to make them better.
“Equipment failure has played a major part in some of the worst accidents and environmental incidents in industrial history,” said RCM guru John Moubray. “As a result the processes by which these failures occur and what must be done to manage them are rapidly becoming very high priorities indeed. It becomes steadily more apparent just how many of these failures are caused by the very activities which are supposed to prevent them.” One of the greatest values of CM is that it helps us work only on the things truly in need of work. CM is about taking measurements and is much less invasive than using wrenches and can be done while the machines are running, reducing unnecessary downtime. The reason it is so easy to tie condition monitoring into RCM is because condition monitoring is already an integral part of RCM, as is evident in task selection requirements. RCM also provides a method for logically applying CM tools. Because failure modes are targeted, CM is not applied helter-skelter, but rather for specific purposes. Refer to the four categories below to learn more about task selection order.
RCM uses four categories of tasks to address failure modes:
1. condition-directed or predictive
2. time-directed (scheduled restoration and scheduled discard), also known as preventive maintenance
3. failure finding (functional checks)
4. redesign and run to fail.
RCA is any structured approach to identifying the factors that resulted in the harmful outcomes (consequences) of one or more past events in order to identify which behaviors, actions, inactions, or conditions need to be changed to prevent recurrence of similar harmful outcomes. There are many methods for doing a RCA, both informal and formal. The best methods have well-defined processes leaving very little to chance. Theoretically, we could take every root cause back to the beginning of the big bang. However, this would accomplish nothing even if it were possible. A root cause is rarely an initiating cause of a causal chain which leads to an outcome or effect of interest. Commonly, root cause is misused to describe the depth in the causal chain where an intervention could reasonably be implemented to change performance and prevent an undesirable outcome. In other words, we need only to progress back to an event where something can be identified that allows us to control or prevent the failure. How do you know when the root cause is found? A root cause has three identifying characteristics.