The Total Acid Number (TAN) is the number of milligrams of Potassium Hydroxide (mgKOH) required to neutralize the acidic compounds present in one gram of oil. It is represented in mgKOH/gram.
The TAN is an important parameter in lubricating oils and in hydraulic oils. At high temperatures, the rate of oxidation in oils increases. This can increase the TAN of the oil. The TAN can also increase with age.
Higher the TAN, greater is the deterioration in the oil. While analysing the Total Acid Number (TAN), both trend and absolute values should be considered.