by: Douglas J. Plucknette of AlliedReliability
When I first began using Reliability Centered Maintenance as a tool to develop a complete maintenance strategy for a process or piece of equipment, I was bothered by the phrase “No scheduled maintenance”. I wasn’t that the phrase didn’t just come out and say what it means, “Run to failure”, it was that RCM as program leaves one with impression that nothing more can be done. It all stops here. Run it to failure. Fix it when it’s broke. Now, I understand the thought process Nowlan and Heap were using, if a components failure cannot be predicted through the use of on-condition maintenance, prevented by using a preventive maintenance task, or eliminated through redesign, the remaining strategy would be “no scheduled maintenance”. Fact is, if you’re an RCM analyst, you work should not end here.
It was clear to me that something had been left out of this process. Looking at the reality of a manufacturing environment, I asked myself this question:
Question: “How would our manufacturing director react if I told him the process was down because we made the decision to run that part to failure?”
Answer: He/she would first absolutely crazy. I can just hear it, “We planned on letting this part fail!” Then, he/she would want to know how long the process would be down and do we have that part.
You as the maintenance manager or supervisor would have some real explaining to do, especially, if you didn’t have the spare part on hand. The missing piece in the RCM process was right in front of my face on a daily basis. When your business is in a sold out condition, down time can be just as important as up time. RCM was designed to maintain the functionality of a process or piece of equipment. It never considered the function of reducing equipment downtime.
Analyzing equipment functionality on its own, RCM does a fantastic job of developing a maintenance strategy. However, it falls short of developing a complete maintenance strategy by failing to address the reduction of consequences when “no scheduled maintenance” is you strategy. Consequence reduction is a key expectation of maintenance in any manufacturing environment. Downtime is critical to our manufacturing partners and we are expected to reduce it in any way we can. So can consequence reduction be addressed as part of an RCM analysis? The answer is yes! It can be, and it should be!
Looking at the RCM decision diagram below, run the failure mode of a “Photo-eye fails” through the decision diagram. Making the assumption that the failure of this switch is evident to the operator and has no effect on health, safety or environment, we run the failure down through the operational consequences portion of the decision diagram.
As we run this failure through the diagram, we answer the following questions:
1. Is there an on-condition task that would detect the failure?
Answer: No - Failure of this electronic device occurs too quickly to be predicted.
2. Is there a scheduled rework, discard, or inspection task that would reduce the failure rate?
Answer: No - The failure is electronic in nature and random, simply looking at the device or checking its function will not indicate if failure is about to occur.
3. Is there a business case for redesign?
Answer: No - The component has been in service several years with no failures.
The decision process has leads us to “No scheduled maintenance”, this where RCM used to end. Note we have added to this box the words “Implement a consequence reduction strategy”. The tells the RCM team that making the decision to run to failure is ok, provided they now consider how to reduce the consequences of the failure or the mean time to restore. This can be accomplished several ways so I ask teams to take the following things into consideration when asked to reduce consequences:
1. Spare parts - If we are going to allow this component to run to failure, should we keep the part on hand? Run this part through a part decision diagram and make this decision.
2. Replacement Procedure - Is there a procedure in place that describes the most effective way to replace this part including, where is the part located, a lock-out, tag-out try-out procedure? Describe how the component can be changed and aligned to ensure functionality.
3. LOTOTO- Ensure a lock-out, tag-out, try-out procedure exists
Assessing each of these things can significantly reduce equipment down time or mean time to restore (MTTR). The assessment and reduction of failure consequences across an entire RCM analysis will result significant savings to your company and save your RCM program some serious grief.