P-F Interval
The time window between the first detectable sign of imminent failure (P) and functional failure (F).
Definition
The P-F interval is the period between the point at which a potential failure (P) becomes detectable and the point at which it becomes a functional failure (F). It sets the maximum useful inspection interval for a given failure mode.
Why the P-F interval matters
Inspections must happen more frequently than the P-F interval or detection comes too late. For a bearing failure with a 12-week P-F interval, a monthly vibration check finds it. A quarterly one may not. The right PM frequency is derived from the P-F interval of the failure modes you are trying to catch — not from manufacturer cadences in isolation.
Typical P-F intervals
- Bearing vibration: weeks to months
- Oil contamination (particle count): weeks
- Hot-spot thermography on electrical: days to weeks
- Crack propagation in structural steel: months
- Insulation breakdown in motors: hours to days (late-stage)
P-F interval in FacilityLane
FacilityLane lets you set condition-based PMs triggered by meter thresholds that sit inside the P-F window for each failure mode. LAYLA can surface which assets show signs of entering the P-F curve based on reading drift.
FAQ
Common questions about P-F Interval.
No. It is per failure mode, not per asset. One bearing on a motor may have a different P-F interval from the stator insulation on the same motor.
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