Condition-Based Maintenance: The P–F Curve

Paul shows the team the so-called maintenance potential failure to actual failure (P-F) curve (Figure 6.4): "Many of you may have seen this. I believe this is very important and like to use it to describe a common understanding of equipment failure. Every system or piece of equipment has something that can be detected when its performance is degrading. It could be a slight change in temperature, a high vibration, or a change in amperage. The P point on the curve represents the time that change is detected. Every system or equipment will also have a point when it fails; that is the F point on the curve. The time between these two points is our opportunity time to avoid a catastrophic failure. The farther up you can move the point of detection, the better opportunity you have to commercially plan around the market and schedule outages at the best financial time, while planning for acquiring parts and scheduling labor. You need proper instrumentation and real-time data availability on your critical equipment to have earlier detection of pending issues and move that up the curve."

Figure 6.4 profiles the equipment condition from initial detection to catastrophic failure. Measures detected that assist in assessing the equipment condition to define an action include ultrasonic detection, vibration detection, oil analysis, audible or sound, temperature change, mechanically


Condition-based predictive failure P-F curve.

loose, ancillary damage, and ultimately catastrophic failure, resulting in an unscheduled downtime, which can be very costly.

The "run to failure" portions of the graph in Figure 6.3 represent the risk of asset failure assuming the test method indicates a failure is near. The response time varies based on asset, type of test, and frequency of the testing method. Quite often, there is little time to respond, depending on plant conditions, time of the notification, and so forth. Most commonly, alarms for critical items are sent to the operations department to ensure that equipment can be moved into a safe condition prior to catastrophic failure. Although these predictive techniques technically indicate a condition of the asset, they are not often used by a computerized maintenance management system (CMMS) because they are not automatically forwarded to the CMMS.

A simple example of the workflow was presented in Chapter 4: The EIDI generates a notification, which is sent to operators and the maintenance team, who analyze the situation and schedule changing of the part at the appropriate time.

CBM replaces vendor recommended maintenance schedules with activity driven by equipment condition data. It allows planning and scheduling of maintenance activities or repairs before functional failure. With CBM, organizations perform maintenance only when needed to prevent operational deficiencies or failures, to eliminate costly and sometimes unnecessary periodic maintenance, and to significantly reduce the likelihood of equipment failures. CBM applications built on a real-time infrastructure detect potential failures more quickly and provide a rich environment for discovering cause-and-effect scenarios based on immediate availability of equipment operating data.

Condition-based monitoring focuses on increasing throughput by determining when to stop the equipment before it breaks down, thereby reducing unscheduled equipment downtime. Having real-time data enables initial indications of increasing standard deviation in a motor amperage or impeding problems with rotating equipment using lube chemistry analysis, thus increasing plant availability, reducing utility consumption, and stemming production losses. Condition-based monitoring coupled with digital CBM systems directly supports the elimination of waste, which is consistent with an operational excellence program (Pierce 2018).

Paul sees opportunities for coordination among all the teams with easy access to the equipment data. Internationally recognized standards, such as ISO 55001 and PAS 55, reinforce the idea that successful programs require participation from all organizational levels and alignment to core business missions. Delivering the information at the right time means people do not have to waste time searching for data. In fact, information flows enable increased visibility and awareness for continuous improvement. Collaboratively handling the notifications is imperative for a successful initiative.

Peter summarized: "The goal is to keep the flow of materials with the necessary information to maintain planed production flow at all times." Proclndustries can

  • • Gain visibility into all static process units and mobile equipment;
  • • Get raw material data from the receiving department;
  • • Deploy additional sensors to monitor speed and power;
  • • Adopt and streamline collaborative processes;
  • • Document best practices at the local and enterprise levels;
  • • Integrate process, equipment, and safety procedures with necessary information, data, methods, and analysis rules; and
  • • Build competence centers to maintain and transfer knowledge from older to younger workers.
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