Bearing decision-window estimator
A vibration report tells you a bearing is degrading. This tool tells you whether your spare can arrive before it fails — the four-stage P-F window against your supply lead time.
From failure stage to a spares decision
BPFO/BPFI/BSF families are unambiguous in the velocity spectrum with harmonics; the machine is still safely operable.
The four stages, and why the window shrinks
Rolling-element bearings fail through four recognised stages. Ultrasonic and high-frequency techniques (PeakVue, Spike Energy, Shock Pulse) catch the earliest evidence — sometimes months ahead. By the time defect frequencies are unmistakable in the ordinary velocity spectrum, the bearing is in Stage 3 and the literature puts the remaining window at roughly one to four weeks. The estimator maps your detected stage onto that progression, adjusts for speed, and weighs it against your spares lead time.
The verdict is the point: when the criticality-adjusted spare lead time exceeds the lower window estimate, the normal supply path is already too slow. That is the moment to expedite, plan a controlled stop, or de-rate — not to keep trending.
Questions reliability teams ask about the bearing window
What is the P-F interval for a bearing?
The P-F interval is the time between the first detectable sign of a potential failure (P) and functional failure (F). For rolling-element bearings it maps onto the four-stage model: ultrasonic evidence can appear months ahead, while clear velocity-spectrum defect frequencies (Stage 3) typically leave one to four weeks. ISO 17359 treats the interval as asset-specific — this tool gives planning bands, not a prediction for one machine.
How long do I have once bearing defect frequencies appear?
Once BPFO/BPFI/BSF families are clear and harmonic in the velocity spectrum, the bearing is in Stage 3 — the published window to functional failure is typically one to four weeks for a machine at moderate speed. Higher speeds shorten it. That window is exactly why this stage is the trigger to schedule a planned replacement rather than keep trending.
Does machine speed change the bearing failure window?
Yes, in calendar terms. Damage accumulates per stress cycle, so a 3,600 rpm machine works through the same stage faster than a 600 rpm one. The estimator shortens the window at high speed and lengthens it at low speed as a planning heuristic — the physical progression is still asset-specific and should be confirmed by trend.
Why factor in spares lead time?
Because the operations decision is not 'when will it fail' but 'do I have time to act before it does'. If your criticality-adjusted spare lead time is longer than the lower estimate of the window, ordering on the normal path is already too slow — you expedite, plan a controlled stop, or de-rate. Connecting the failure window to the supply constraint is the decision this tool exists to support.