Rolling-element ball bearing — Failure Modes & Failure Rate

Universal element wherever a shaft rotates with low friction. Bearing reliability is calculated, not measured: ISO 281 gives the L₁₀ life (90% survival) from load and speed. Field λ data must therefore be interpreted with the actual duty cycle in mind — generic-data values cited here are for a typical industrial service.

λ typical

5.0×10-7 / h

Range

1.0×10-7 – 5.0×10-6

Source

NPRD-2016 / ISO 281

Failure modes

Spalling (sub-surface fatigue)

Root causes: Cyclic Hertzian contact stress at the rolling-element / raceway interface generating sub-surface cracks that propagate to the surface; predicted by ISO 281 L₁₀ life.
Detection: Vibration spectrum shows characteristic ball-pass frequencies (BPFI / BPFO / BSF / FTF); shock-pulse or envelope-detection trend climbs steeply weeks before functional failure.
Mitigation: Size bearing for actual peak and average load with ≥3× L₁₀ design margin; condition-monitoring per ISO 17359 catches the failure 2-6 months ahead of seizure; replace at the early-warning detection rather than running to failure.

Lubricant degradation / contamination

Root causes: Particulate ingress (often from a failed seal or breather); water contamination promoting acid attack; thermal degradation of grease at high speed; oil oxidation in hot service.
Detection: Oil analysis (ISO 4406 particle count, water content, viscosity, acid number); grease analysis less common but available; bearing-cap temperature trend.
Mitigation: Sealed bearings (2RS, 2Z) for dirty environments; pressurised purge in motor bearings to prevent ingress; relubrication interval matched to service severity; oil-mist for high-speed.

Brinelling / impact damage

Root causes: Static-load impact (drop during installation, shock load in service); false brinelling from stationary-shaft vibration making the rolling elements wear flats on the raceway.
Detection: Vibration step-change after the impact event; visible indentation on disassembly; characteristic ball-pass-frequency spectrum.
Mitigation: Proper installation tooling — no hammer-on; rotate stored equipment monthly to spread the contact band; isolate stationary spares from neighbouring vibration.

Cage failure

Root causes: Cage wear from poor lubrication; cage damage from heavy axial loads on a deep-groove bearing not designed for it; cage breakage from severe vibration.
Detection: Erratic vibration; rolling-element pinch and seizure; characteristic spectrum (FTF — fundamental train frequency).
Mitigation: Specify the right bearing geometry for axial-thrust component; matched cage material to operating temperature; verify alignment and balance reduce cage stress.

Typical applications

Shafts in motors, pumps, fans, gearboxes, machine tools; spindles in CNC and grinding; conveyor rollers; vehicle wheel bearings; aircraft engines (with much higher quality grade).

How to model in a fault tree

For mechanical-equipment FTA, the ball bearing is the typical leaf for rotating-machinery branches — but its λ is highly application-specific. Don't use generic-data λ blindly: for a high-load, high-speed compressor bearing the actual rate may be 10× higher. Where rolling-element condition monitoring is in place (vibration trending per API 670), the bearing failure becomes an extension of λ_DD (revealed) rather than λ_DU, with a strong reduction in PFD contribution. See centrifugal pump for the typical context.