Thursday, August 18, 2011

The Basics of Reliability Series: Preventive, Predictive, and Precision Maintenance



With the Triple P M single point lesson, you can cover multiple topics with two diagrams. There are two key points to be driven home with these graphics: first, a solely time-based maintenance strategy is destined to leave you missing the performance mark; and two, precision maintenance concepts and craft skills are imperative to effective maintenance. Other points can be added as the audience allows.
The first diagram shows the six failure curves from the many Reliability Centered Maintenance texts. When you realize that only 11 percent of the failure modes tend toward time-based presentation, you quickly see why a maintenance strategy solely based on time-based preventive maintenance activities is flawed. You also see that doing everything right with precision maintenance is crucial if you want to reduce the number of infant mortality failures.
The second graphic to devote to memory is the I-P-F curve, which shows that the most effective downtime prevention tool is to postpone the failure with precision maintenance and the second most important downtime preventer is to catch the defect early enough using predictive tools to plan and schedule the repair. One more point to make that ties into a later single point lesson on materials is that if you do not store it properly and maintain it in stores, then point S (the point it is put in stores), point I, and point P can become one and the same.
On this single point lesson, you can also talk about how, based on recent studies of PM maintenance tasks, the following holds true for the average facility:
·         30% of the PM tasks add no value.
·         30% of the PM tasks in the average facility could be more effective and efficient if they were done with PdM tools.
·         30% of the PM tasks should be reengineered to address the failure modes of the asset.
·         10% of the PM tasks are fine the way they are.
This sheds a bit of light on another substantial area of waste that can be removed with a plan and some patience.

1 comment:

  1. Not denying the usefulness of P-F curve as a concept, it is hard to appreciate its usefulness as a practical tool. The reason? No engineering values on the axes. Theoretically they could be derived, but one needs to run a statistical study for each individual piece of equipment. Not a real scenario most of the time.