Predictive Maintenance(PdM)

The process of monitoring a parameter of condition in equipment (vibration, temperature, pressure, flow, oil quality, acoustic emission, electrical properties) to identify significant changes indicative of a developing failure. Condition monitoring is the technical enabler of predictive maintenance, detecting degradation at the P point on the P-F curve to allow planned intervention before functional failure.

Maintenance performed at predetermined intervals or according to prescribed criteria to reduce the probability of failure or functional degradation. Preventive maintenance includes time-based activities (replacement, overhaul, calibration at fixed intervals), usage-based activities (at fixed operating hours or cycles), and condition-based activities (when monitored parameters indicate intervention is needed). The goal is to prevent failures that would otherwise occur.

A deliberate maintenance strategy where no preventive or predictive maintenance is performed, and the item is allowed to operate until it fails, at which point it is repaired or replaced. RTF is a valid strategy for non-critical items where the consequence of failure is low, the item is not safety-related, redundancy exists, or the failure mode is random (no wear-out pattern). RTF is not the same as neglect — it is a conscious, risk-based decision.

The estimated time from the present until an equipment item reaches a condition where it can no longer perform its intended function safely and must be repaired, replaced, or retired. For static equipment, RUL is typically calculated from the current measured wall thickness, the minimum required thickness, and the corrosion rate. For rotating equipment, RUL may be estimated from degradation models fitted to condition monitoring data.

The time between the point at which a potential failure is first detectable (P — the onset of detectable degradation) and the point of functional failure (F — the point at which the item can no longer perform its required function). The P-F interval determines the maximum inspection interval for condition-based maintenance — inspections must occur at intervals shorter than the P-F interval to detect the developing failure before functional failure occurs.