Glossary

P-F curve

In short

The P-F curve describes how an asset fails over time, from the point a developing failure first becomes detectable, called P, to the point of functional failure, called F. The gap between them is the P-F interval: the warning time you have to act once a problem can be spotted. Condition monitoring and inspections aim to catch the failure near P, while the interval is still long enough to plan a repair rather than react to a breakdown.

P-F curve

The P-F curve is a reliability model that describes how an asset fails over time. It plots the decline in an asset’s condition from the point where a developing failure first becomes detectable, labelled P for potential failure, to the point where the asset can no longer do its job, labelled F for functional failure. The shape of the curve, and especially the gap between P and F, tells you how much warning you get once a problem can be seen.

How the P-F curve works

Most failures do not happen all at once. A bearing wears, a belt frays, a seal degrades, and for a while the asset keeps working while the problem develops. At some point that developing failure becomes detectable, by a vibration reading, a temperature rise, an unusual noise, a visual sign. That detectable point is P. If nothing is done, the condition continues to fall until the asset reaches functional failure at F.

The distance between P and F, measured in time, is the P-F interval. It is the warning window: the period in which you can detect the problem and act before it becomes a breakdown. A long interval is a gift, because it gives you time to plan a repair, order parts and schedule the work. A short interval is unforgiving, because you have to be checking often to catch the failure inside the window at all.

What it tells you

The practical lesson of the P-F curve is about inspection frequency. To catch a developing failure near P, a check has to fall within the P-F interval for that failure mode. As a rule of thumb, the interval between inspections should be shorter than the P-F interval, so at least one check lands in the warning window. Inspect too rarely and you will keep arriving at F, dealing with breakdowns you could have prevented.

It also tells you where condition monitoring earns its keep. The whole point of monitoring vibration, temperature, wear or other measures is to detect failures as early in the curve as possible, close to P, where you have the most time and the most options. The earlier the detection, the calmer and cheaper the response.

How it relates to Cohiva Control

Cohiva Control gives you the tools to act on the P-F curve. Meter-based preventive maintenance lets you trigger checks on usage, which suits failure modes that track running hours or cycles. Inspection templates let you build the condition checks that detect the P point, and a failed inspection item can raise a work order automatically, so a developing failure spotted in the warning window becomes a planned repair rather than a reactive one. The append-only history of inspections and work orders builds the record you need to learn the real P-F interval for your assets and tune the inspection frequency accordingly. See preventive maintenance and MTBF for related measures.

Part of the Cohiva platform

Cohiva Control is part of the Cohiva platform. Leisure operators often run it with Cohiva Complex, and finance teams connect it to Cohiva Crunch for the general ledger. Explore the platform at www.cohiva.app.

Frequently asked questions

What do P and F stand for on the P-F curve?
P is the potential failure point, the moment a developing failure first becomes detectable by an inspection or a condition check. F is the functional failure point, where the asset can no longer do its job. The curve plots the decline in condition between them.
What is the P-F interval?
It is the time between P and F, the window in which you can detect a developing failure and act before it becomes a functional failure. A longer interval gives you more time to plan; a short one means you need to check more often to catch it.
How often should I inspect to catch the P point?
Often enough that a check falls within the P-F interval, so the developing failure is detected before it becomes functional. As a rule of thumb, inspection frequency should be shorter than the P-F interval for that failure mode. The right figure depends on the asset and the failure, so confirm it for your equipment.
How does the P-F curve relate to condition monitoring?
Condition monitoring exists to detect failures as close to the P point as possible, using measurements like vibration, temperature or wear. The earlier the detection within the interval, the more options you have to plan the repair calmly.