Bearing Damage: What It Is and How to Identify It!

Related Reading

• How to Prevent Bearing Contamination in High-Intensity Production
• Bearing Failure Modes: A Visual Identification Guide
• Bearing Removal Without Damage: Tools You Actually Need
• How to Diagnose a Failing Bearing in Under 10 Minutes
• Bearing Damage: Misalignment Diagnosis and Practical Remedies

The ISO Classification of Bearing Failure Modes

ISO 15243 catalogues bearing failure into six primary categories: fatigue (sub-surface and surface-initiated), wear (abrasive and adhesive), corrosion (moisture and fretting), electrical erosion (excess current and current leakage), plastic deformation (overload and indentation), and fracture/cracking (forced fracture, fatigue fracture, thermal cracking). Each category presents with a distinct visible signature on the raceway, the rolling elements and the cage. A technician who learns to recognise the patterns can identify the failure cause from inspection alone in maybe 70 percent of cases, without needing laboratory analysis. The remaining 30 percent — usually mixed-mode or root-cause-ambiguous cases — benefit from metallurgical or chemical analysis, but those are the exceptions rather than the rule.

Fatigue: Pitting and Flaking on the Raceway

Fatigue failure is the natural end-of-life condition for any bearing and presents as small pits coalescing into larger flakes on the raceway. Sub-surface fatigue starts beneath the surface and produces the classic pit-then-spall progression over weeks. Surface-initiated fatigue begins at a stress concentration — a small dent from poor handling, for example — and propagates outward. A bearing showing the early stages of fatigue should be tagged for replacement at the next maintenance window; left in service, the spalls grow and shed debris that accelerates wear elsewhere. The presence of fatigue on a bearing that has not yet reached its calculated rating life always indicates a root cause beyond simple operating hours: overload, lubrication failure, or contamination.

Lubrication Failure: Discoloration, Smearing, Glazing

Lubrication failures present in stages. The first visible symptom is discoloration of the raceway — gold becoming brown becoming blue — which corresponds to progressive heating of the surface. The next stage is smearing, where small areas of the raceway have been welded and torn apart by metal-to-metal contact under inadequate film thickness. Late-stage lubrication failure produces glazing, where the raceway surface looks polished but is actually heat-damaged at depth. Each of these stages corresponds to a recoverable or non-recoverable condition: discoloration alone may simply mean a relubrication is overdue; smearing means the bearing is approaching end of life; glazing means the bearing must be replaced and the lubricant system inspected before the replacement runs.

Contamination: Particles, Moisture, and Their Distinct Marks

Hard particles in the lubricant produce a characteristic set of small dents (true brinell marks) across the raceway in random positions, distinguishable from load-induced damage by their irregular distribution. Soft contamination produces abrasive wear that polishes the raceway uniformly. Moisture ingress produces rust spots, often in arc patterns that follow where the rolling elements paused at shutdown. Fretting corrosion produces reddish-brown deposits at the bearing-shaft or bearing-housing interface, indicating micro-motion in the fit. Each of these tells a story about the seal performance, the lubricant cleanliness, or the assembly tolerances, and addressing the symptom without addressing the upstream cause guarantees recurrence.

Electrical Erosion: The Failure Mode Born of the VFD Era

The proliferation of variable-frequency drives in electric-motor applications has made electrical bearing damage a category that maintenance teams now meet routinely. The mechanism is straightforward: high-frequency switching in the inverter creates common-mode voltages that find ground paths through the bearings, where micro-arcing across the lubricant film erodes the raceway in a characteristic fluted or frosted pattern. Detection is straightforward once the pattern is recognised. Prevention requires either grounded shaft brushes, insulated bearings (ceramic balls or insulated outer rings), or both. Any motor running on a VFD that has not been engineered for it will eventually develop electrical-erosion bearing damage; the question is whether the maintenance team catches it before the failure stops the line.

Related Resources from Eurobearing

For technicians who want to go deeper into bearing damage diagnosis, our editorial team has produced dedicated guides on adjacent topics. Each of the following articles complements the framework above with concrete examples, photographs, and selection tables built around real distribution scenarios:

• Bearing Failure Modes: A Visual Identification Guide
• Bearing Damage: How to Address Misalignment
• How to Address Bearing Overheating
• How to Prevent Bearing Contamination in High-Intensity Production Environments
• How to Address Bearing Overheating: Diagnosis and Remedies

Documenting What You See: Why the Inspection Photograph Matters

The most underused tool in bearing failure diagnosis is the smartphone camera. A high-resolution photograph of the failed raceway, the rolling elements and the cage, taken before any cleaning or handling, captures information that no written description can convey. Modern phone cameras resolve fine detail well enough to identify spalling patterns, discoloration gradients, contamination marks and electrical-erosion frosting from a metre away. Five photographs — raceway top-down, raceway oblique, rolling element close-up, cage condition, and housing-fit surface — are usually enough to settle the diagnosis even when the bearing is later discarded.

Plants that adopt photographic documentation as a standard inspection practice almost always discover that they had been misdiagnosing failures for years. The discovery is uncomfortable but valuable: it usually reveals that one or two root causes are responsible for the majority of premature removals, and addressing those root causes produces an outsized reduction in bearing-replacement frequency.

The Eurobearing technical desk reviews failure photographs as part of our customer support and provides written diagnostic responses for any customer who needs a second opinion on a difficult case.

One operational discipline that pays compound interest is requiring the technician removing a failed bearing to take a photograph, write a one-line diagnosis on the work order, and reference the work order in the procurement request for the replacement. This single-sentence linkage between failure and replacement is what turns scattered events into a longitudinal failure record. Over twelve to twenty-four months it reveals which assets fail repeatedly for the same reason, which lubrication points are quietly missing from the schedule, and which suppliers consistently deliver bearings that meet or exceed expectations — and those insights make the next budget cycle measurably easier to defend.

Need help with bearing selection?

Eurobearing is a European bearing and power-transmission distributor based in Northern Italy serving OEMs, MRO buyers, and industrial resellers across more than 40 countries. Our technical desk can help you cross-reference legacy part numbers, identify the correct dynamic load rating, choose the right cage material or seal type, and align lubricant intervals to your duty cycle. If you are evaluating bearing damage diagnosis for a specific machine — whether it is a continuous-process line, a packaging station, an agricultural drivetrain, or a marine winch — we are happy to review specs and propose qualified options from brands like SKF, FAG, INA, NSK, NTN, NMB, and Schaeffler. Contact the Eurobearing technical team for a free consultation, share the application photograph and the failed reference, and we will return a recommendation within one business day.