Total Acid Number
Total Acid Number (TAN), also known as Acid Number (AN), measures the acidity of non-aqueous lubricants in milligrams of potassium hydroxide per gram of oil (mg KOH/g). It quantifies mineral and organic acids from oxidation, contamination, and additive depletion via titration, unlike pH which applies only to water.
In shop floor maintenance, TAN is a trending tool within CMMS systems like ServiceGrid to monitor fluid service life and detect oxidation by-products before visible wear. Maintenance teams track TAN values over time; a significant increase (e.g., >0.3 mg KOH/g rise) signals the need for remedial action to prevent system failure. It is primarily applied to non-engine oils such as hydraulic fluids, gear oils, and transmission lubricants, enabling proactive asset reliability.
Why is TAN being replaced by AN in industry nomenclature?
The term 'Total Acid Number' is misleading because the test does not detect all acidic components, specifically extremely weak acids/bases with dissociation constants <10⁻⁹; 'Acid Number' (AN) is more accurate.
How does TAN differ from Total Base Number (TBN)?
TAN measures acidic content from oxidation and contamination, while TBN measures alkaline reserve from additive depletion; both monitor lubricant effective life.
What is the standard test method for TAN?
Common standards include ASTM D974 and ASTM D664 (potentiometric titration).