Effect of water contamination on anti-friction (ball) bearing life 

Q - What is the effect of water contamination on lubricating oil on the fatigue life of anti-friction (ball) thrust bearing?

A – Water, or moisture, contamination of lubricating oil reduces the oil‘s lubricating properties and efficiency because of oxidation, reduced viscosity, additive precipitation, etc.

A study conducted by a large multinational oil company on the effect of water contamination on lubricating oil shows the following estimated reduction in the fatigue life of anti-friction (ball) bearings on their pumps:

§ A 0.002% water contamination in oil, roughly the equivalent of one drop of water in one quart of oil, reduces the fatigue life of anti-friction bearings by 48%.

§ A 3% contamination reduces the fatigue life by 78%.

§ A 6% contamination reduces the fatigue life by 83%.

We do not know the actual operating environment under which the study was made so it should not be implied that most other pumps would experience the same adverse effect from water contamination. Among others, the type of oil used, the temperature and relative humidity, and whether the pumps run continuously or intermittently during the study are bound to affect the results.

For instance, other studies show that a 100 ppm water contamination in oil can reduce the bearing life by about 40% to 50%.

Regardless of what the exact figures are, it is fair to say that the detrimental effect is very drastic in reducing the fatigue life of ball bearings. That is why the use of bearing isolators, to prevent water contamination, is standard in API 610 and ANSI pumps, and their use in upgrades of older pumps is becoming increasing popular despite of the added cost.