Surface-initiated fatigue (surface distress)

The oil film was too thin and the surface peaks started to touch. Urgency

The steel simply wore out from repeated stress, or was pushed there early by poor lubrication.

What surface-initiated fatigue (surface distress) looks like

• Dull grey or frosted band on the raceway or rolling elements, sometimes slightly crazed
• Fine pitting and micro-flakes a few microns across, clear only under magnification
• Progresses to larger flaking if the bearing keeps running

Rotec AI schematic illustration. It shows the typical pattern and is not a photograph of a real bearing.

How surface-initiated fatigue (surface distress) develops

When the lubricant film cannot fully separate the rolling surfaces, the microscopic peaks on the steel meet and shear. Tiny cracks start at the surface, then micro-flakes, then bigger spalls. Every rolling bearing has a little sliding in its contact; extra sliding or a weak film makes it much worse.

How fast it progresses: Often a slow burn. By the time flaking is obvious, the original cause (thin film, dirt, wrong lubricant) can be hard to prove.

Causes of surface-initiated fatigue (surface distress)

Lubrication

• Oil or grease base oil too thin for the speed and temperature
• Too little lubricant, or old and degraded lubricant
• Additives that turn aggressive when hot (some EP packages)

Environment & sealing

• Particles or water that roughen or dent the surfaces first

Operating conditions

• High temperature thinning the oil; sliding from light load or rapid speed changes

Bearing selection

• Viscosity chosen for the wrong speed or temperature

How to confirm it is surface-initiated fatigue (surface distress)

• Dull grey surface without clear dents, usually over much of the loaded track
• Check the lubricant itself: type, amount, age, contamination and operating temperature. The surface alone cannot tell you which was at fault
• Look for earlier damage (dents, wear) that may have started the breakdown

How to fix and prevent surface-initiated fatigue (surface distress)

• Pick lubricant viscosity for the real speed and temperature; aim for a film that comfortably separates the surfaces
• Right lubricant, right quantity, right interval: correct the regreasing schedule
• Improve sealing or filtering to keep contamination out
• Check lubricant condition at regular intervals, not only at breakdowns

Easily confused with

• Abrasive wear: Abrasive wear removes metal and leaves a worn, scratched track; surface fatigue leaves a dull, finely pitted one.
• Subsurface-initiated fatigue: Subsurface fatigue gives discrete flakes without the dull, frosted surround.

Worth knowing

Peeling is a lubrication warning

Micro-spalling, or peeling, shows up as a frosted band of tiny flakes. It means the oil film was too thin for the load: high load at low speed, high temperature, or a lubricant that is too thin. It is the first rung of the lubrication damage ladder in the Lubrication view.

Catching surface-initiated fatigue (surface distress) early

Early surface distress is hard to see with plain vibration trending. High-frequency or envelope methods pick it up much sooner.

Other fatigue modes

Questions about surface-initiated fatigue (surface distress)