The Presence of Water in Lubricants

The ingress of water or moisture in lubricants is somehow unavoidable.  From the drums, exposure to extreme hot-cold cycles can introduce water.  Sometimes, water contamination may come from cooling system leaks; in metalworking fluids, prior processes using emulsions or alkaline cleaners can contribute to moisture content; with air compressors, the moisture content in the intake air can introduce water, too.

At levels of 0.02 to 0.06% (200 to 600 ppm), the moisture is at such a low-level that it is dissolved in the oil, and practically un-noticeable.  Exceeding this level, oil and water ‘mix’ forming an emulsion, exhibited by a hazy appearance of the lubricant.   Past the ‘emulsion’ stage is the saturation point wherein the lubricant is now unable to hold the water as dissolved, or as an emulsion, and thus a phase separation between the oil and water is easily observed.

As water, with a specific gravity of 1.0 kg/liter, is heavier than most lubricants, it typically settles at the bottom.

Utmost attention should be given to prevent or minimize water contamination, since it can contribute negatively to lubrication performance, to wit,

  1. Rust and Corrosion may be accelerated
  2. Wear on metal components will be evident
  3. Lubricant oxidation is hastened
  4. Acid and sludge formation
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