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P-F curve explained: definitions and how it’s used to improve maintenance

The P-F curve represents an asset’s condition before it has reached a failed state. Let’s find out why it’s important in maintenance!

Industrial plants and machinery are not designed to last indefinitely, but they can definitely work longer if you adopt appropriate maintenance strategies.

In this article, we’ll take a look at the P-F curve, a graphical representation that aims at characterizing the behavior of assets over time. It’s a useful strategy that can really help professionals to develop reliable maintenance programs extending equipment life-span.

Before we move on to definitions and benefits of this Maintenance improvement approach, I suggest monitoring the operating conditions of your assets in order to get updated and reliable insights to create reliable and accurate maintenance plans. That’s basically why it’s worth discovering a professional Facility Management software.

What is a P-F curve in the field of maintenance?

The P-F curve is a two-dimensional Cartesian environment used in Facility Management to describe the behavior of an asset over time. This evaluation considers the maximum usage lifespan achievable from a given piece of equipment.

The P-F chart is an essential component of a reliability-based maintenance strategy. Reliability Centered Maintenance (RCM) allows the different departments of a production system to identify which are the most critical assets. Subsequently to establish the appropriate and effective maintenance program for each of them.

Using the information provided by the P-F curves, maintenance managers can gain a deeper understanding of the equipment and identify potential causes of failure. This allows you to determine the optimal timetable to perform maintenance interventions. It also give the possibility to define the most appropriate strategies to maximize the reliability of the systems, minimizing management costs.

How to Read a P-F Curve

The P-F graph shows the time variable on the abscissa and the “health” of the asset on the ordinate. The curve represents the behavior of the equipment from the moment it comes into operation until it reaches its ultimate operational limit.

The essential elements to consider within the graph are basically:

  • point P, represents the potential failure point. This point refers to the first signs of deterioration. Such deterioration will eventually lead to the failure condition shown at the instant “F”;
  • point F, represents the functional failure and refers to the moment when the equipment is actually damaged and is no longer capable of satisfactory performance;
  • the P-F time frame, measures the difference in time between the potential failure and the functional failure. Therefore, the moment when the problem becomes technically detectable and the instant in which the equipment stops working permanently. The wider the P-F range, the greater the time margin to plan and implement strategic maintenance interventions.
Chart showing the P-F curve

The P-F curve

How to Maximize the P-F Range

Depending on the type of equipment and its typical failures, there are several techniques that can be used to detect signs of deterioration in advance and therefore postpone the operational interruption of the asset as much as possible.

The most common techniques to maximize the time range between potential failure and functional failure include, for example:

  • visual inspections;
  • thermographies;
  • tracking temperature, pressure, speed, flow parameters, etc.;
  • corrosion monitoring;
  • sampling and lubricants analysis;
  • detection of noise emissions, such as ultrasound;
  • vibration measurement and analysis.

These techniques are extremely complex and require specific skills for their implementation. However, companies that develop maintenance strategies based on reliability and use of P-F curves, can significantly reduce maintenance costs while optimizing the functionality and productivity of their resources.

How to Use the P-F Curve to Improve Maintenance

Maintenance teams rely on P-F curves to monitor asset deterioration and implement more effective maintenance strategies. Thanks to the use of these graphs it is possible, in fact:

  • Plan preventive maintenance. The P-F curve allows to schedule maintenance activities before a fault occurs. By knowing the potential fails and identifying when the equipment is likely to stop working, you can procure replacements and earlier organize the resources to solve the problem. Operators can also determine which activities will require specialist and negotiate agreements in advance with third-party contractors. Overall, this strategy avoids over-maintenance of equipment, reduces operation costs, increases asset operational time range and prolongs its lifespan.
  • assessing the severity of risks: data history and in-depth knowledge of the operation of a technical system help companies to assess increasing levels of risk throughout the equipment life-cycle. By studying the trend of P-F curves, maintenance teams can predict when potential failures and functional failures will occur and establish the severity of the risks associated with the different problems. This allows you to choose the best maintenance strategy to follow to minimize unscheduled downtime and ensure maximum safety, efficiency and productivity over time;
  • maximize asset life-cycle: Using the information in the P-F charts, organizations are able to maximize and extend the functional life of their assets by replacing spare parts before the plant reaches a functional failure state. P-F curves also help set the control indicators needed to alert technicians and operators of the incoming failure and allow them to schedule repairs in advance;
  • combine different maintenance strategies: in most cases the use of a single approach is not sufficient to ensure effective maintenance. P-F curves allow companies and facility managers to find the right balance between different strategies. It also can determine when predictive maintenance and condition monitoring approaches are needed or, on the other side, when corrective maintenance is appropriate.
Uses of the P-F curve in maintenance

Uses of the P-F curve in maintenance

What Factors Affect the P-F Curve?

The P-F curve is an integral part of reliable maintenance. There are, however, several factors that can vary the failure identification and, consequently, change the trend of the P-F interval. These factors refer to:

  • equipment design: the different types of equipment are designed with multiple safety levels This can cause variations in failure modes (some equipment, for example, are designed to withstand overloads while others are unable to do so, affecting the type of maintenance required);
  • usage frequency: the high frequency of start/stop cycles and the excessive use of equipment may cause a reduction in the P-F range compared to the normal operating conditions of the asset;
  • accidental errors: during the installation, operation and maintenance of an equipment there may be accidental errors that inevitably affect the efficiency, functionality and durability of the entire asset or its component;
  • characteristics of the spare parts: when carrying out repairs, it is often preferred to replace the original components with poorer and cheaper spare parts, which can cause an overall reduction in the quality of the asset. This results in an increase in the probability of failure and a variation in the P-F interval that is less extensive than the conditions originally estimated.

For the P-F curve to be effective, companies and facility managers need to collect and analyze historical data on equipment operation and failure patterns. To monitor the operating conditions of your assets, I strongly recommend using Facility Management software, a powerful and reliable tool that allows you to manage all activities, processes and information regarding resource maintenance from a single centralized platform.

Try now a demo version to test the potential of this tool!