Total Base Number (TBN)
Is a measure of a lubricant's reserve alkalinity. It is measured in milligrams of potassium hydroxide per gram (mg KOH/g).
TBN in oils generally range from :
- 6 to 80mg KOH/g in modern lubricants
- 7 to 10mg KOH/g in general automative lubricants
- 10 to 15mg KOH/g in diesel operations
- 10 to 50mg KOH/g in marine lubricants
It is generally believed that if the TBN in used or in-service oil has gone down to half (50%) or less than half of the new or fresh oil, the oil has to be changed. For example, an engine oil with a initial base number of 10mg KOH/g should be changed if the base number is less than 5mg KOH/g.
When you test an oils base number it means that you are measuring its alkaline reserve or its ability to nutralize corrozive and degradation acids. Though viscosity is one of the most important critera, base number indicates if the oil is suitable for continued use and is an important parameter for entending oil drain intervals. A decrease in base number is usually accompanied by an increase in viscosity, oxidation and nitration.
Base Number (TBN) is like a shield to the oil because :
- It effectively controls the acids formed during the combustion process by nutralizing them
- Suspends wear causing contaminants
- Prevents breakdown of the oil film
Testing of Total Base Number (TBN)
ASTM D2896 and ASTM D4739 is the test method which we are using for monitoring the degradation acid content of in-service oil or used oil. The base number test is performed by diluting the sample with a mixed solvent in a reaction beaker. While mixing, hydrochloric acid is titrated to chemically react with alkaline components (detergents) in the sample. When the end point of the chemical reaction is reached, the amount of titrant used is converted to the result and reported in milligrams of potassium hydroxide equivalent per gram of sample (mg of KOH/g).
Testing Equipment used by us in our laboratory: Mettler Toledo G20