Moisture corrosion
Water got in, and rust, etching or frosting followed. Urgency
Chemical attack from water, or micro-movement that keeps stripping the protective oxide.
What moisture corrosion looks like
- Reddish-brown or dark rust on rings and rolling elements, sometimes pitted
- Etched marks spaced exactly at rolling-element spacing when the bearing sat still in water-contaminated lubricant
- A fine, dull grey frosted texture across the whole track when water was in the lubricant while it ran
- Fingerprint-shaped rust patches from bare-hand handling
Rotec AI schematic illustration. It shows the typical pattern and is not a photograph of a real bearing.
How moisture corrosion develops
Water (liquid or condensing) sits at the contact points, especially at standstill, and chemically attacks the steel. Where each ball or roller rests, that spot corrodes, so the marks later line up with element spacing. The pits then become starting points for fatigue.
How fast it progresses: Even light corrosion roughens the surface and shortens life; once pitted, the damage is permanent.
Causes of moisture corrosion
Environment & sealing
- Seal failure, washdown, condensation from temperature swings, aggressive process fluids
Lubrication
- Grease that does not resist water, or lubricant already contaminated with it
Mounting, handling & storage
- Unprotected storage, unwrapping too early, bare-hand handling
How to confirm it is moisture corrosion
- Look at the lubricant for a milky appearance or free water, and check seals and breathers
- Marks at element spacing mean the bearing corroded while standing still
- A frosted (not blotchy) pattern means water was inside the lubricant, not just on the outside
How to fix and prevent moisture corrosion
- Upgrade sealing for the real moisture exposure and check breathers or vents
- Use a water-resistant grease suited to the environment
- Keep idle machines running periodically or protected from condensation
- Store bearings in their wrapping until mounting, and handle with clean gloves
Easily confused with
- False brinelling: False brinelling is mechanical wear from vibration; moisture corrosion is chemical etching, though rust can accompany both.
- Fretting corrosion: Fretting corrosion sits on fitted surfaces (bore or outside diameter), not on the raceways.
Other corrosion modes
Questions about moisture corrosion
What causes moisture corrosion in a bearing?
Seal failure, washdown, condensation from temperature swings, aggressive process fluids. Grease that does not resist water, or lubricant already contaminated with it. Unprotected storage, unwrapping too early, bare-hand handling.
How do you fix or prevent moisture corrosion?
Upgrade sealing for the real moisture exposure and check breathers or vents. Use a water-resistant grease suited to the environment. Keep idle machines running periodically or protected from condensation.
What does moisture corrosion look like?
Reddish-brown or dark rust on rings and rolling elements, sometimes pitted. Etched marks spaced exactly at rolling-element spacing when the bearing sat still in water-contaminated lubricant.