Water Contamination of lubricating oil

Water Contamination of lubricating oil

Water contamination is one of the most insidious factors in industrial applications. If the water content exceeds a certain level that the lubricating oil cannot accept, it may shorten the service of lubricating oil and damage machines gradually.

There are three forms of water: dissolved, emulsified and free.

Dissolved water is usually benign except in extreme cases that require exceptionally low moisture levels. This form of water generally enters the lubricant via humidity or a similar process. The lubricant simply absorbs the water up to the saturation point and does not exhibit any signs of water contamination such as clouding.

Emulsified water is the most damaging form of water contamination. It occurs when the amount of water is beyond the saturation point and has likely entered the lubricating stream. A mixing action in the equipment may have emulsified the water, or it may be a function of a lubricant additive. Regardless, the initial identifier of this type of water contamination is that the lubricant is usually cloudy. This cloudiness comes from the water becoming small droplets within the oil. Emulsified water is the most damaging because it is free flowing with all of the lubricant and will be in the load zone.

Free water is somewhat less damaging than emulsified water but is still problematic. Some lubricants will not hold water in suspension past the saturation point, so it falls to the bottom of the sump. Among the problems resulting from this type of contamination include allowing water to become part of the lubricating stream, impacting the lubricant’s ability to shed water (demulsibility) and letting it emulsify, initiating biological contamination that will further degrade the oil, and plugging the filter. There is also the possibility of a safety hazard if free water is allowed to continue to enter the sump and overflow it.

With water contamination, there is just as much if not more damage to the lubricant as there is to the equipment. The main source of equipment degradation will be rust. Any time you have a degraded lubricant with water contamination, there is the possibility of rust on nearly any iron/steel surface. Rust is very hard (harder than steel) and creates abrasive particles in addition to the existing water problem.

Another problem with water contamination involves hydrogen embrittlement. In this phenomenon, water is cracked into oxygen and hydrogen, and the hydrogen is absorbed into metal surfaces. This creates a harder but more brittle surface that is unable to flex as needed for rolling elements to work properly. This results in cracking of the rolling surfaces and spalling.