Water is the most common contaminant found in lubricating oils. It is also one of the most damaging to bearings and other lubricated components. It causes corrosion to metal surfaces, lubricant degradation, and poor lubrication. Water can be present in three forms in lubricating oils:
Dissolved: There is a limited amount of solubility of water in oil which is very temperature dependent. At 120° F, about 100 ppm of water can be dissolved in oil. Dissolved water is not harmful nor does it affect the appearance or performance of the lubricant.
Emulsified: Water and oil can form tight bonds that are difficult to break. This form of water in oil is what causes oil to become milky and is the most harmful. Oil will begin to become ‘milky’ at about 150 – 300 ppm, depending on the base stock and additive in the lubricant.
Free Water: These are free water droplets, often suspended in the lubricant due to surface tension. This form of water in oil is also very harmful to lubricated parts, but is also the easiest to separate. Often free water is routinely drained from sumps and reservoirs. The ability of the oil to separate from the water is an important characteristic of the lubricant in many applications, such as steam turbines and centrifugal compressors.
The Karl Fischer Water Titration is the only suitable test for determining how much moisture is present in a lubricant at levels less than 500 parts per million (0.05%). Depending on the procedure used, accurate results can be obtained down to the 4 or 5 parts per million (ppm) level. Karl Fischer Water Titrations will determine the total amount of water present, regardless of the form it is in.