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Water
Table of Contents Physical & Chemical Properties Water in oil is detrimental to lubrication both physically, as discussed earlier, and chemically. The amount of water is expressed as ppm, percent by volume, or percent by weight. Water is soluble in base oils to 50 to 80 ppm, and in formulated oils to a few hundred ppm. Hazy oil is most often a result of undissolved water droplets. Low water content is especially important in hydraulic, gear, pneumatic tool, steam cylinder and circulating oil systems. Water catalyzes oil oxidation and acid formation, and reacts with or precipitates additives. Water corrodes many common tribological metals. For example, water reacts with ferrous alloys to form rust, the hydrated iron oxide. Rust creates solid debris in the oil and pits the metal surfaces. Pits may initiate contact fatigue in rolling element bearings, and contact fatigue or bending fatigue in gears. The literature states that water promotes contact fatigue in rolling element bearings. See Part 3 for methods of measuring water concentration in oil. Another indication of water contamination in lubricating oils may be increased sodium and chlorine content especially in marine applications, because salt (NaCl) is always present in large quantities in sea water and to some extent in all but distilled or rain water. Rust inhibitor is an additive that adsorbs on a metal surface in preference to water and therefore prevents rusting of ferrous alloys. Metal deactivators are additives which reduce metal corrosion by also preferentially adsorbing on the surface and protecting it from corrosion. For more information call 1-888-HERGUTH (437-4884) |
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