Bearing Failure Analysis

Understanding why a bearing failed helps prevent repeat failures and choose the right replacement. This guide covers the five most common bearing failure causes, how to recognize each one, and what to fix before you order a new bearing.

Why Bearing Failure Analysis Matters

A bearing rarely fails on its own. In most cases, the failure is a symptom of something else — a lubrication problem, a contamination path, a misalignment, or a load that exceeds the design rating. If you replace the bearing without fixing the root cause, the new bearing will fail the same way, often faster.

Bearing failure analysis is the process of examining the failed bearing (and its operating conditions) to identify the failure mode. The appearance of the raceways, rolling elements, cage, and seals is the primary evidence. Each failure mode leaves a characteristic pattern.

1. Fatigue spalling (30% of failures)

Appearance: Pitting or flaking on raceway surfaces. Cause: End of normal fatigue life, or overload beyond design limits. Fix: Confirm the load rating (Cr) meets the application requirement. Upgrade to a higher-capacity series if needed (e.g., 6205 to 6305).

Fatigue spalling is the only “natural” failure mode — it happens when the bearing simply reaches the end of its calculated L10 life. But premature spalling (well before expected life) usually means the actual load is higher than the design load, or the bearing was misapplied. Check the application load, not just the bearing.

2. Lubrication failure (25%)

Appearance: Discolored (blue/brown) rings and balls, smeared metal. Cause: Insufficient grease, wrong grease type, or grease breakdown from heat. Fix: Review relubrication interval. For high-temperature applications (>100°C), use synthetic grease.

Lubrication failure covers both starvation (not enough grease) and degradation (grease overheated, oxidized, or contaminated). The classic signs are blue or brown discoloration on the rings and balls, and smeared or welded metal on the raceways. If the bearing ran dry or hot, check the relubrication schedule and the grease selection before installing the replacement.

3. Contamination (20%)

Appearance: Abrasive wear, scoring, dull surfaces. Cause: Dirt, metal particles, or moisture entering the bearing. Fix: Switch from open to sealed (2RS) or shielded (ZZ). Improve housing seals.

Contamination is the most preventable failure mode. Abrasive particles entering the bearing act like grinding paste, producing dull, scratched, or scoured raceways. The fix is usually at the housing level: use sealed or shielded bearings, and improve the shaft and housing sealing arrangement.

4. Misalignment (10%)

Appearance: Wear path not centered on raceway, edge loading. Cause: Shaft deflection, housing misalignment, or bent shaft. Fix: Use self-aligning ball bearings (1200 series) or spherical roller bearings (22200 series) where misalignment is unavoidable.

When a bearing is misaligned, the load path moves to the edge of the raceway, producing an off-center wear pattern. Deep groove ball bearings tolerate only small misalignment (a few arc-minutes). If the application has shaft deflection or housing misalignment, consider a self-aligning type instead of a rigid deep groove bearing.

5. Corrosion (8%)

Appearance: Red/brown rust, etching on surfaces. Cause: Moisture ingress, condensation during storage. Fix: Store bearings in dry conditions. Use stainless steel bearings for wet environments.

Corrosion is usually a storage or sealing problem rather than an operating problem. Moisture entering the bearing — through damaged seals, condensation, or washing processes — etches the raceways and rolling elements. Once corrosion starts, it accelerates fatigue. For permanently wet environments, stainless steel bearings are the durable answer.

Failure Mode Quick Reference

Mode	Share	Key visual sign	Primary fix
Fatigue spalling	~30%	Flaking/pitting on raceway	Check load rating, upgrade series
Lubrication failure	~25%	Discolored rings, smeared metal	Relubrication schedule, grease type
Contamination	~20%	Dull, scratched surfaces	Sealed/shielded bearings, housing seals
Misalignment	~10%	Off-center wear path	Self-aligning bearings, alignment
Corrosion	~8%	Rust, etching	Dry storage, stainless steel

What to Document Before Ordering a Replacement

When you send a quotation request for a failed bearing, include:

1. The complete part number from the bearing itself (including all suffix letters).
2. The failure pattern — a photo of the raceway and rolling elements.
3. Operating conditions — speed, load, temperature, environment.
4. Time in service — how long the previous bearing lasted.

This information lets KIHOI confirm the right replacement bearing and the right closure (open, ZZ, or 2RS), so the new bearing does not repeat the same failure.