The core of reliability-centered maintenance (RCM) analysis lies in the answer to seven questions:
NOTE: For question number six, inspection techniques that adequately identify defects during normal operation are preferred over those that require downtime. Less invasive action is preferred over more invasive.
This is one of the fundamental concepts of any well-defined maintenance strategy.
Contained within question number three is the term failure mode. A failure mode is the condition that exists that will cause a functional failure. Another way to think of it is simply:
The "part" is a group of pieces that make up a component. Examples from the ISO standard include impeller, seal, shaft, bolt, nut, and bearing.
“What is wrong with the part” refers to the effect of the failure mechanism. Examples include failed, damaged, out of adjustment, abrasion, erosion, corrosion, fatigued, burnt, and broken.
The "reason" is the physical cause of the problem. This could be age, improper lubrication, misalignment, imbalance, or improper installation, among others.
One month, a misalignment condition is noted on a pump that is directly coupled to an electric motor. The pump was recently replaced due to wear on the impeller. The post-maintenance follow-up by the vibration analyst revealed that the alignment was performed improperly. The motor-pump combination is now running in a misaligned condition. The failure mode noted on the vibration analyst’s exception report would be Shaft – Misalignment – Improper Installation.
Just two months later, the misalignment condition having never been corrected, the vibration analyst now detects an outer race defect on the pump bearing. The failure mode noted on the exception report is now Bearing – Fatigued – Shaft Misalignment.
This example should help demonstrate how condition monitoring programs allow for the acceleration of root cause failure analysis (RCFA). Having the vibration analysis reports to review during the RCFA makes the process much faster because documented proof is readily available.
The above situation is an extremely typical example of defects creating increased maintenance labor and material costs while increasing the amount of unplanned (or even planned) downtime. Planned downtime is increased by the fact that replacing the pump bearings takes significantly longer than properly aligning the shafts, the initial failure that was noted.
This example also builds an excellent case for procedure-based maintenance and improved craft skills. Had the craftsmen aligned the shafts properly upon replacing the impeller, none of this would have occurred. This is also an excellent example of why the RCM analysis team should include a condition-based maintenance (CBM) specialist.
NOTE: The list of failure modes covered in an RCM analysis need not be an exhaustive list. It should only include the predominant failure modes that represent the failures that have previously occurred and the failures that are very likely to happen. This philosophy is decidedly different from the original system laid out by Nowlan and Heap, which John Moubray later formalized.
The biggest advantage of RCM is the fact that the analysis team, and by extension the organization, begin to think in a failure modes manner. They realize that there is a myriad of non-value-added tasks in a typical maintenance program that not only waste valuable crafts time but by means of intrusive inspections, increase their chances for infant mortality problems like improper reassembly or lubrication contamination.
The analysis team also realizes a clear set of guidelines for determining what tasks are to remain a part of the maintenance strategy. Any task that is to remain in the maintenance program must meet at least one of the following criteria:
This failure modes style of thinking quickly separates the value-added from the non-value added. Additionally, this type of analysis need not be limited to the creation of an equipment maintenance plan (EMP); it can also be applied to the redesign of an existing EMP.
Performing the preceding analysis on an already existing preventive maintenance (PM) strategy allows for the non-value-added tasks to be removed from the PM program and either deleted or reassigned to more appropriate personnel. It also calls out which PM tasks need to be kept and which ones need to be cleaned up in terms of wording and formatting to create a more quantitative, repeatable procedure. This exercise is called a preventive maintenance evaluation (PME).
A PME can be done in one of two ways. A sample PME can be done at the beginning of a reliability improvement initiative to build some momentum around the types of changes possible and start to define the size of the changes that could happen. This is typically performed on 200-300 PM tasks that are deemed to be representative of the entire PM program. The PM tasks should be selected from across 20-25 different equipment types in the plant and from a combination of monthly, quarterly, and annual PM tasks.
Secondly, a full PME can be done. This is typically performed on the entire PM library, towards the middle of a reliability improvement initiative. This is done to calculate precisely how many craft resources will be freed up and how many PM tasks need to be re-engineered into the proper format.
The organization does not have to implement the results of the PME right away. The output of the study can follow a staged implementation. For example,
Remember, this will not be as simple as throwing a light switch. Changes to the process workflows must be made and people need to be trained on changes in the workflow. Different metrics may need to be created to measure implementation effectiveness and overall system efficiency. All four of these steps can be done department by department, as the reliability improvement team tackles tasks and gets everything ready for rollout.
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