This standard specifies two test methods for the determination of acidic constituents in petroleum products, lubricants, biodiesel and blends of biodiesel.
Test Method A is applicable to petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and propan-2-ol. It is applicable for the determination of acids whose dissociation constants in water are larger than 10-9; extremely weak acids whose dissociation constants are smaller than 10-9 do not interfere. Salts react if their hydrolysis constants are larger than 10-9. The range of acid numbers included in the precision statement is 0.1 mg/g KOH to 150mg/g KOH.
Test Method B is applicable to determination of acid number of biodiesel and biodiesel blends with low acidity and greatly different solubility.
Note: In new and used oils, the constituents that may be considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak bases, acid salts of polybasic acids, and addition agents such as inhibitors and detergents.
This standard may be used to indicate relative changes that occur in oil during use under oxidizing conditions regardless of the color or other properties of the resulting oil. Although the titration is made under definite equilibrium conditions, this standard is not intended to measure an absolute acidic property that can be used to predict performance of oil under service conditions. No general relationship between bearing corrosion and acid number is known.
Note 1: The acid number obtained by this standard may or may not be numerically the same as that obtained in accordance with GB/T 4945 and SH/T 0163. There has not been any attempt to correlate this method with other non-titration methods.
Note 2: A few laboratories have made the observation that there is a difference in the standard results when aqueous versus nonaqueous buffers are used.
1. Scope
2. Normative References
3. Terms and Definitions
4. Summary of Test Method
5. Methods and Use
6. Apparatus
7. Reagents
8. Electrode System
9. Standardization of Apparatus
10. Preparation of Sample of Used Oil
11. Test Method A
12. Test Method B
Appendix A (Informative) Check for Electrode Performance
Appendix B (Informative) Determination of Acid Number of Synthetic Oil
