Total Acid Number (TAN)

Total Acid Number (TAN)

Total Acid Number

The total acid number (TAN) is a measurement of acidity that is determined by the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil. It is an important quality measurement of crude oil. The TAN value indicates to the crude oil refinery the potential of corrosion problems. It is usually the naphthenic acids in the crude oil that causes corrosion problems. This type of corrosion is referred to as naphthenic acid corrosion (NAC).

TAN value can be deduced by various methods, including

  • Potentiometric titration: The sample is normally dissolved in toluene and propanol with a little water and titrated with alcoholic potassium hydroxide (if sample is acidic). A glass electrode and reference electrode is immersed in the sample and connected to a voltmeter/potentiometer. The meter reading (in millivolts) is plotted against the volume of titrant. The end point is taken at the distinct inflection of the resulting titration curve corresponding to the basic buffer solution

Some fluids are already acidic in their formulation; therefore, the most effective means to measure for acidity is in its change compared to a new fluid or to the previous sample
The GT-200 potentiometric titrator is a versatile allrounder that can control up to 12 burets. A 5.7 inch color LCD, operation by keypad or mouse and predefined parameter sets for various applications make the GT-200 a very easy to operate instrument.


Why we need to know?

  • Total Acid Number is an analytical test to determine the deterioration of lubricants.
  • The more acidic a lubricant is, the further its degradation has proceeded. As oils or hydraulic fluids breakdown, they generally form acidic byproducts that can be corrosive to metal components, accelerate wear, form deposits and increase viscosity.
  • As a fluid degrades, the levels of corrosive acids increase along with the danger of component failure.


Total Acid Number of general oil and Pentas Flora recovered oil


General Oil


Base Oil


Bunker Fuel




Heavy Oil


Light Fuel Oil 80 cSt


Medium Fuel Oil 180 cSt


Tyre Oil


Waste Engine Oil


Pentas Flora Recovered Oil


Eco Light Fuel Oil


Super Light Fuel Oil


Green Light Fuel Oil


Base Light Fuel Oil