MAR-APR 2019

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36 INTECH MARCH/APRIL 2019 WWW.ISA.ORG SPECIAL SECTION that the further away from the failed state you detect potential failure, the more sophisticated (and thus expen - sive, considering both equipment and training) the detection technology. Importance of timing Sometimes taking corrective action too soon can have bigger consequences, such as higher costs or more downtime, than not acting. If you are repairing things too quickly, you are going to be spending money on changing out com- ponents more often than necessary. In such cases, you either have inaccurate- ly identified the actual point of failure or have your parameters set incorrectly. By detecting failures when they are actionable but still early, you are able to plan the most advantageous time to take corrective action. When used in conjunction with condition monitor- ing, the P-F curve improves mainte- nance by allowing you to do more than just react. Oil analysis is one of the first indi- cators of potential failure. It tells you a lot about what is going on with a piece of equipment by indicating what kind of particles are in the oil. But not all assets have oil, so you cannot use oil analysis for everything. Vibration is typically the next earliest indicator. The most common thing to use the P-F curve on is equipment with ro tat- ing assets, which makes vibration a perfect technology to use. Rotation is something that is fairly consistent. When you have a consistently behav- ing piece of equipment, using the P-F curve makes a lot of sense. P-F curve and vibration monitoring All machinery vibrates, but excess vi bration in rotating equipment can make potential issues known early on. Vibration monitoring can measure changes in the amplitude, frequency, and intensity of forces that can cause damage to rotating equipment. "Compared to other technologies— like ultrasound, oil analysis, and thermography—vibration is kind of like Goldilocks," says Bernet. "Thermography can be too late, while ultrasound and oil analysis can be too early, but vibration is just right. With vibration, we can see indications of faults 12 to 18 months in advance— when there is still life left in the components—and not react too soon." The four most common vibration faults are imbalance, looseness, mis- alignment, and bearing wear. Rare ma chine faults do happen, but almost all vibration faults fall into these four categories. "Vibration is especially effective in diagnosing mechanical faults," Bernet continues. "Even a healthy machine is going to have vibra- tion, so it's easy to identify what is nor- mal for a good rotating machine and then to be able to look for patterns in the change in the vibration." Why condition monitoring pairs well with the P-F curve Condition monitoring is the use of continual screening technologies to detect changes in the operation of as sets, which means you are alerted to potential issues well before failure or downtime occur. It gives you real-time situational awareness of your opera- tion and enables you and your team to schedule maintenance and correc- tive actions in advance. Furthermore, condition monitoring can provide a longer P-F interval than other mainte- nance methods. "Reactive maintenance is all based on failures that have already occurred. Planned or calendar-based mainte- nance is based on taking some kind of corrective action globally but not hav- ing any indication of which machines actually need it," Bernet said. "Condi- tion monitoring is based on knowing that a fault is coming—but has not oc curred yet—and gives you some prewarning and the ability to schedule corrective repairs before the efficiency or capability of a machine is reduced." Identifying anomalies before they result in damage, downtime, or dis- ruptive repairs decreases costs, un- expected downtime, and production loss. Other benefits include extended equipment life and smaller spare parts inventories. And, when you have suffi- cient lead time to order parts on an "as needed" basis, you can even eliminate expedited costs. Other maintenance methods, such as calendar-based maintenance, simply do not fit as well with the P-F curve. The real-time data provided by condition monitoring lets you stay on top of where each critical asset is on the P-F curve. Tools to optimize Maintenance is neither about fixing everything the moment potential fail- ure is detected nor about waiting until

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