Water contamination in oil can exist in three forms: dissolved water, emulsified water and free water.
There is always a small amount of dissolved water in oils that can range from about 200 to 600 ppm (0.02 to 0.06%) depending on the formulation and the time in service for used oils. Used oils that are near their drain interval can hold 3-4 times more water than the unused oil of the same formulation. This level of water contamination is too low to be seen when inspecting oil samples.
When the concentration of water in the oil increases to the point of saturation, the small droplets of water form an emulsion which produces a hazy or cloudy appearance to the oil. The tendency to form emulsions is more pronounced with detergent oils than non-detergent oils.
Increasing water concentrations past the cloudy or hazy appearance characteristic of emulsified water and oil will cause the mixture to separate into distinct layers. An oil layer and an emulsion layer are formed and, with higher levels of contamination, a layer of free water will appear on the bottom with PAO synthetics and petroleum based oils.
The presence of emulsified or free water causes the greatest detriment to lubrication performance and oil life. Water increases wear rate, decreases load carrying capacity and increases the rate of oil oxidation, reducing the life of the lubricant. Because of this, water levels in the oil should be well below the saturation point. For most in-service oils, the level should be approximately 500-1000 ppm or less depending on the type of oil and temperature in the application.
Water contamination can also have a detrimental effect on some oil additives causing a reaction between the additive and water called hydrolysis.
Water is measured in oil using several different test methods:
"Crackle" Test - A drop of the oil is placed on a hot surface at
about 320 F. Observation of a few bubbles indicates a level of 500 to 1000
ppm (0.05 to 0.1%), significantly more and larger bubbles indicates a range
of 1000 to 2000 ppm (0.1 to 0.2%) and an audible "crackle" sound
from the heated oil drop indicates a level over 2000 ppm (0.2%).
FT-IR - This analysis method has a lower detection limit of about 1000 ppm
which is acceptable for crankcase oils, but not sensitive enough for some
industrial oil applications.
Karl Fischer - The most accurate test that measures water contamination down
to a few ppm.
Water is a major cause of lubricant and equipment failure. Once detected, steps should be taken to remove it from the lubrication system and prevent further contamination of the oil.
Universal Lubricants, Inc.
Technical Services,
June, 2003 - 0603.2
For more information, please contact our Technical Services Dept. at 1-800-444-6457.
