MAR-APR 2019

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34 INTECH MARCH/APRIL 2019 WWW.ISA.ORG The P-F curve: One of the first, yet hardest, things to learn By Kevin Clark, CMRP T he P-F curve is a way of representing an asset's behavior or condition before it has reached a failed state. It illustrates an as - set's progression toward failure. On the chart, the x-axis represents the time to failure, starting with an asset's installation, and the y-axis represents an asset or component's resistance to failure. Potential failure (PF) indicates a detectable state of failure, or the point at which degrada - tion begins. Functional failure (FF) is when the asset or component has reached a failed state or no longer performs satisfactorily. The most important part of the P-F curve is the P-F inter - val, which represents the time between when potential failure is detected in an asset and when it reaches the failed state. The length of the P-F interval is largely determined by the technology used to detect failure. Highly dependent on patterns "Most assets follow a curve in their life cycle, from good to progressively worse, until they completely fail," says John Bernet, a product application specialist at Fluke with decades of experience in vibration monitoring. "The P-F curve is a conceptual representation only and does not have any units or scale." The P-F curve is highly dependent on pat- terns. For example, if one motor ramps up to a specific rpm during operation, then an identical motor used on another asset should behave in the same way. The P-F curve is something that we—those of us in the maintenance and reli- ability space—depend on from a mature stand - point. As reliability engineers using the P-F curve, we have gotten to the point of trying to design out failure, of trying to indicate failure, rather than simply waiting for it to happen. The way motors are built today, they have onboard diagnostics indicating how they per- form—but not how they feel. Similarly, our human bodies are built to take care of them- selves—but when things go wrong, we need doctors to help us determine what is wrong and Improving maintenance by adopting a P-F curve methodology

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