If you only ever learn one curve in maintenance engineering, make it the P-F curve. P is the point where a failure becomes detectable. F is the point where it becomes functional failure. The gap between them, the P-F interval, is your window to act.
Everything about inspection strategy follows from this one idea. Your inspection interval must be shorter than the P-F interval, or you can inspect diligently forever and still be surprised by failures. Inspecting a bearing monthly when its P-F interval is two weeks is theatre: the failure develops and completes between visits, and the inspection record shows healthy readings right up to the breakdown.
Getting the Interval Right
- The P-F interval is a property of the failure mode and the detection technique together. Vibration analysis, oil analysis, thermography and operator inspection each see the same degradation at different points, so each has its own effective P.
- Practical rules set the inspection interval at a fraction of the P-F interval, typically half or less, so at least one inspection reliably lands inside the window with margin to plan the repair.
- Detection is only half the value. The other half is estimating how long you have left once P is detected, which is the remaining useful life problem. The podcast episode Beyond the Curve: Making Sense of Remaining Useful Life covers what RUL estimates can and cannot honestly promise.
Why Condition Monitoring Changes the Game
Continuous monitoring, such as wireless vibration probes, changes the equation precisely because it drives the effective inspection interval toward zero. You catch the failure at P, or close to it, every time. The failure still happens eventually, but it happens on your schedule: planned, parted and crewed, instead of at 2am on a long weekend. And the economics are strikingly asymmetric: monitoring hardware keeps getting cheaper while the cost of an undetected functional failure on critical equipment keeps rising. On critical assets the business case is usually stronger than intuition suggests. The question is how to prove it with your own numbers rather than a vendor’s brochure.
How the Tools Help You Discover the Benefit
RCMCost and AvSim let you model the same failure mode two ways: with periodic inspection at a chosen interval against the P-F window, and with continuous detection. Compare the downtime, cost and risk outputs side by side and the value of the monitoring investment falls out as a number, in your consequence structure, on your equipment. We have seen this comparison settle debates that years of opinion could not. Our condition monitoring assessment service extends the analysis to reviewing which techniques and coverage your fleet actually warrants, mode by mode, rather than site-wide by fashion.
Go Deeper
- Software: RCMCost, AWB Availability Simulation
- Services: Condition Monitoring Assessment, Reliability Centered Maintenance
- White papers: Working on the Right Things
- Podcast: Beyond the Curve: Making Sense of Remaining Useful Life
- Next in the series: RCM as a Decision Engine and Risk Matrix Modelling
How can we help? Talk to us at contact@mantua.group.