Bearing damage: When is a dent not a dent?

When machinery failures happen, accurate identification of the true failure mechanism is crucial.

The image reveals blunt force impacts to the bearing ring and raceways. The hammer marks on the ring side face (ISO 15243:2004, Plastic Deformation / Indentation by Handling) are pretty easy to fix – take away the hammer. The triangular marks on the bearing raceway are something different, but the root cause is the same.


Under low-power (3x to 5x) magnification, the manufacturer's grinding and honing marks are easily seen inside and outside the dented area. Permanent, plastic deformation leaves the triangular shaped mark, but the impact damage remains clear (ISO 15243:2004: Plastic Deformation / Overload.) “True brinelling” is another term for this damage.

If we observed wear, perhaps rust, and an absence of hone marks in the bottom of the “dents”, we’re probably looking at false brinelling (ISO 15243:2004: Corrosion / Frictional Corrosion / False Brinelling.)

This wear process happens to stationary machines subject to vibration. The rollers break through the oil film and wear indentations in the raceway at roller spacing. This “dent” isn’t produced by impact, and the root cause - typically external vibration – must be tracked down and eliminated.

Understanding the origins of bearing damage allows us to develop and implement corrective actions to prevent recurrence of failure. Learn more in our instructor led WE204 Course, held worldwide, several times a year, by the SKF Reliability Maintenance Institute.