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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You may be surprised to learn that there are no less than five lubrication performance properties that are missing from nearly all in-service oil analysis reports. These are not esoteric properties that are of limited value or interest to those in charge of machine reliability. Instead, they represent the core foundation of a lubricant’s formulation and purpose. In other words, they relate to the essence of what we expect and need from a lubricant. And, these are the properties that are imparted by additives and commonly found on a lubricant’s product data sheet (spec sheet).

Don’t get me wrong; I am not suggesting that commercial oil analysis labs are duping their clients by shortchanging testing services. Many of these missing tests cannot be practically performed on routine oil samples because they are expensive, involve prolonged test periods and/or require large sample volumes. Yet it is important that the user community fully understand what they get and what they don’t get when they pay $35 for oil analysis.

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