Water in oil is a common, but often overlooked reliability problem. Water will not only destroy the oil film strength, but may also cause flash-vaporization which causes erosive wear if there is enough water content in the oil.
Oil containing about 0.1% (1000 ppm) water will turn cloudy in appearance. At this point, about 75% of the bearing life is gone (see graph).
As a rule of thumb we want as little water as possible in oil. For most oils and applications there should not be more than 0.01 – 0.03% (100-300 ppm) water content.
Preventing water content in oil can be done by for example:
- Making sure breathers on equipment are silica gel breathers
- Water extracting filters
- Store oil in completely enclosed containers
- Make sure to handle oils correctly
Finding water content can be done by visually inspect oil for cloudiness even though this isn’t the best method, it’s better than no inspection at all.
Water content can also be found by putting a sample of oil on a tablespoon and heat the spoon with a lighter.
A few small bubbles means a water content of 0.05 – 0.1% (500-1000), many larger bubbles indicate a water content of 0.1 – 0.2 % (1000-2000 ppm), while a crackling sound from the oil sample means a water content in excess of 0.2% (2000 ppm).
Oil analysis will also reveal water content.