Page 213 - An Introduction To Predictive Maintenance

Tribology 203

and types of lubricants required to maintain plant equipment. Elimination of unnec-
essary duplication can reduce required inventory levels and therefore maintenance
costs.

As a predictive maintenance tool, lubricating oil and spectrographic analysis can be
used to schedule oil change intervals based on the actual condition of the oil. In mid-
size to large plants, a reduction in the number of oil changes can amount to a con-
siderable annual reduction in maintenance costs. Relatively inexpensive sampling and
testing can show when the oil in a machine has reached a point that warrants change.

The full benefit of oil analysis can only be achieved by taking frequent samples and
trending the data for each machine in the plant. It can provide a wealth of informa-
tion on which to base maintenance decisions; however, major payback is rarely pos-
sible without a consistent program of sampling.

9.1 LUBRICATING OIL ANALYSIS
Oil analysis has become an important aid to preventive maintenance. Laboratories rec-
ommend that samples of machine lubricant be taken at scheduled intervals to deter-
mine the condition of the lubricating film that is critical to machine-train operation.

9.1.1 Oil Analysis Tests
Typically, the following tests are conducted on lube oil samples:

Viscosity
Viscosity is one of the most important properties of lubricating oil. The actual vis-
cosity of oil samples is compared to an unused sample to determine the thinning or
thickening of the sample during use. Excessively low viscosity will reduce the oil film
strength, weakening its ability to prevent metal-to-metal contact. Excessively high vis-
cosity may impede the flow of oil to vital locations in the bearing support structure,
reducing its ability to lubricate.

Contamination

Contamination of oil by water or coolant can cause major problems in a lubricating
system. Many of the additives now used in formulating lubricants contain the same
elements that are used in coolant additives. Therefore, the laboratory must have an
accurate analysis of new oil for comparison.

Fuel Dilution
Dilution of oil in an engine, caused by fuel contamination, weakens the oil film
strength, sealing ability, and detergency. Improper operation, fuel system leaks,