In all of my years in oil analysis, I cannot recall a single time when data from a surface tension (ST) or interfacial tension test (IFT) appeared on a routine analytical report, aside from transformer oil analysis, for which the test is considered routine.

The reason this is so surprising is that many studies have reported that changes in an oil’s surface tension to be the earliest sign of contamination, sludge potential and oxidation. Quoting from the book “Lubrication of Industrial and Marine Machinery” by William G. Forbes, “The interfacial tension test is the most valuable single test that can be used to evaluate a turbine oil.

It is generally agreed that when the interfacial tension is between 15 and 20 dynes/cm, deposits may or may not be forming in the system. Safe practice would call for an oil change in this range.”

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