Above: The Kittiwake Oil Test Centre test for TAN levels
Info Centre >> Fuel and Lube Oil Technical Manual >> 7. Lube Oil - Test Results >> 7.4 Enclosed Gears >> 7.4.3 Total Acid Number (TAN)
Measuring Total Acid Number (TAN) in Enclosed Gears Oil
The usual mechanism of oil degradation in gear oils is the ageing over time that arises through the effects of oxidation. This usually occurs very slowly because although gear oils tend to have high exposure to air, oil temperatures are usually low. The two key indicators of oxidation are increases in acidity and viscosity of the oil.
When considering the impact of oil oxidation on machinery operation, the most relevant consideration is that alongside the polymerisation processes that are mainly responsible for the viscosity increase, oxidation gives rise to lacquers and sludge as well as a rise in acidity. Lacquers and sludge ultimately translate to deposits on surfaces and acidity to corrosive activity, particularly when water is present. The effect of oil degradation by oxidation tends to be relatively slow-moving and initially at least is not likely to present any particular technical problems. Over time however, the effects described previously may start to become evident - initial discoloration of bright surfaces leading to darker deposition.
Comment
Effects of corrosive processes may take time to show up visually on surfaces, by the time such damage becomes obvious to the eye, considerable surface damage may have occurred.