What the TAN value reveals about the condition of a lubricant
TAN, the abbreviation for Total Acid Number, is a characteristic value that indicates the acid content in a lubricant. The value is measured in mg KOH/g oil (milligrams of potassium hydroxide per gram of oil) and indicates how much base is required to neutralize the acidic components contained in the oil. An increasing TAN value indicates oil ageing or contamination.
Relevance in the industry
The TAN value is a key analysis parameter for monitoring the condition of engine oils, turbine oils, hydraulic fluids and industrial lubricants. It helps to better plan oil change intervals, detect unusual chemical reactions at an early stage and prevent system damage. In industry and energy technology in particular, the TAN is regularly monitored via oil analyses in order to extend the service life of machines and oils.
What is a normal TAN value for engine or industrial oils?
That depends on the type of oil. Fresh oil often has a TAN value of 0.05-2.0 mg KOH/g. A strongly increased value (e.g. >4) can indicate oil ageing, oxidation or contamination and should be checked.
What does a rising TAN value mean in practice?
An increasing TAN value indicates chemical degradation of the oil – e.g. through oxidation, additive degradation or contact with water and acidic reaction products. This can lead to corrosion and damage to components.
How is the TAN value measured?
The determination is carried out titrimetrically according to ASTM D664. This determines how much potassium hydroxide is required to neutralize all acidic components present in the oil.
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