Bearing failure analysis: the six ISO 15243 failure modes

When a bearing breaks, the machine stops and the priority is getting back into production. The damaged component usually ends up in a bin. That gesture is expensive: with the dismounted bearing in hand there are ten to fifteen minutes of information available nowhere else, information that decides whether the next stoppage happens in three years or in three months.

ISO 15243 — Rolling bearings: damage and failures, terms, characteristics and causes — exists precisely so that this reading is repeatable and so that two different technicians give the same name to the same thing. Below are the six modes, what each one looks like and what has to be corrected.

Quick reference to the six modes

1. Fatigue: the only natural ending

Subsurface-initiated fatigue starts below the raceway surface, where shear stress peaks, and progresses until material breaks away as a crater. It is the mechanism the ISO 281 basic rating life L10 sets out to predict, and the only mode that corresponds to a bearing reaching the end of its useful life having worked as expected.

Surface-initiated fatigue is different and far more common: it appears when the lubricant film is too thin and the asperities of the two surfaces come into contact. The appearance is a more diffuse surface break-up, preceded by a greyish, dull look. If a bearing shows surface fatigue well before its calculated life, the problem lies in lubricant viscosity, operating temperature or relubrication interval.

2. Wear: abrasive and adhesive

Abrasive wear occurs when hard particles circulate between the surfaces. It produces dull, lustreless raceways and also wears the cage pockets. The sources are failed seals, unfiltered plant air, sand in aggregate operations, or dirt introduced during maintenance itself.

Adhesive wear appears when two surfaces slide under load without a sufficient lubricant film: material transfers from one to the other, with local heating and sometimes tempering of the steel. It is typical in roller bearings carrying too light a load, where the rollers skid instead of rolling as they enter the load zone.

3. Corrosion: moisture and fretting

Moisture corrosion leaves visible rust and pits which, as the rolling elements pass over them, become spalling initiation points. It arises from condensation in equipment that stops and starts, from pressure washing without protecting the seals, or from lubricant carrying dissolved or free water.

Fretting corrosion is different and sits on the seat, not on the raceway. It shows as a reddish-brown powder on the contact surface between the ring and the shaft or housing, and it means there is micro-movement where there should be a firm fit. The cause is almost always a loose fit or a worn seat. False brinelling is a particular case: evenly spaced marks matching the rolling elements, appearing in equipment subjected to vibration while stationary — typically during transport or in standby machines.

4. Electrical erosion: the mode that gets overlooked

Current passing through the bearing produces micro-discharges between rolling element and raceway. Excessive current forms craters with melted edges; continuous low-intensity leakage produces the transverse grooves known as fluting, an unmistakable washboard pattern.

The usual origin is motors driven by variable frequency drives, where fast switching generates shaft voltages. The fix is not primarily in the bearing but in the installation: shaft grounding through a conductive ring, shielded cabling and a proper return path. Where that is not possible, ceramic-insulated bearings or hybrid bearings with ceramic rolling elements are used.

5. Plastic deformation

These are permanent marks produced while the bearing was not rotating, or by a momentary overload. Classic brinelling leaves indentations spaced exactly like the rolling elements, caused by excessive static load or by a blow during mounting — including the classic hammer strike transmitted from one ring to the other. Particle indentations are far smaller and spread across the whole raceway, with raised edges that become stress concentrators.

6. Fracture and cracking

Forced fracture comes from overstress during mounting or dismounting — excessive interference, a puller bearing on the wrong ring — and thermal cracking from intense frictional sliding between surfaces. It is the least frequent mode and the easiest to trace: it almost always corresponds to a specific, documented intervention.

How to run the analysis on site

1. 01

   Do not wash the bearing yet

   The lubricant holds the evidence. Take a sample before cleaning and record its colour, smell and texture. A dark lubricant that smells burnt says as much as the raceway.

2. 02

   Photograph before dismounting

   With the bearing still in place, record orientation, load pattern and seat condition. Once separated, that information is gone.

3. 03

   Mark the angular position

   Before extraction, mark the outer ring position relative to the housing. A displaced load pattern reveals misalignment or abnormal load — but only if you know how it was oriented.

4. 04

   Classify per ISO 15243

   Identify the dominant mode and record it using the standard's terminology, not a free description. That is what allows comparison across equipment and over time.

5. 05

   Close with an action, not a diagnosis

   The analysis ends when you define what changes: relubrication interval, grease type, fit, seal, filter, grounding or alignment. A report without an action does not prevent the next failure.

When external support is worth it

When the same equipment fails more than once in under a year, when the dominant mode is not obvious, or when the failure hits a critical machine with no backup. In those cases the analysis has to be cross-referenced with lubrication history, real load conditions and vibration records. At Rodacaribe we support that work with the SKF bearing and seal portfolio, Q8 Oils lubricants and WIX filtration — the three fronts where the root cause usually sits.