Article extract from ReliaPlant newsletter:http://www.reliableplant.com/Read/28939/attain-reliability-maintainability
Do you have double vision? I hope you do, but not in the sense I bet that you are thinking. No, I’m not talking about having one too many or that splitting headache that sometimes results in double vision. I’m talking about driving availability. It’s a measure that is made up of two component measures — mean time before failure (MTBF) and mean time to repair (MTTR).
The equation is: Availability = MTBF / (MTBF + MTTR).
I hope you would agree that MTBF is a measure of reliability. Isn’t that one of the primary visions that you have for your organization, driving improved reliability? I recently worked with a client in the heavy industrial sector on just that, an equipment reliability improvement effort that involves failure modes and effects analysis (FMEA) and other techniques.
What about MTTR? It’s a measure of maintainability, or the average (mean) amount of time required to complete the repair or restoration of a failed component. It’s more than just a second part of the availability equation; it must be included as a separate integrated vision for your organization.
The reality is that very little attention is paid to making equipment easy to maintain in many organizations. Yet, it’s quite easy to justify simple, often inexpensive modifications to new or existing equipment to make it maintenance friendly.
A piece of equipment that I was asked to include in the FMEA effort makes for a great example. A large hydraulic reservoir sat right above two large hydraulic pump/coupling/motor combinations. The pumps were sandwiched between the reservoir and the floor, not to mention surrounded on the sides by the framework holding the reservoir. The pumps serviced critical production equipment that operated 24 hours a day, 7 days a week.
As the maintenance group was unable to service and align the assemblies, it experienced the replacement of six $40,000 pumps in the last two years. Yes, I know, sometimes the obvious escapes us, or we don’t feel empowered to make the change, but that’s a different topic for another day. Interestingly, you can actually build in addition parameters to your FMEA to create an index for maintainability that you can sort just like the risk probability number (RPN).
Everyone recognizes that there is a cost associated with downtime. Equipment that is difficult to maintain drives less reliability and only serves to extend the amount of downtime required to restore the equipment to operation. Create an environment that has double vision – that of both reliability and maintainability – for a more comprehensive and effective approach.
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