ASTM D943 Oxidation Characteristics of Inhibited Mineral Oils
Oils exposed to atmospheric oxygen may form sludge and carboxylic acids in a reaction catalyzed by water and metals. To lessen the rate of oxidation, antioxidants are added to these oils. This test predicts the effectiveness of antioxidants, particularly in steam turbine oils, hydraulic fluids and circulating oils.
Oxygen is bubbled through heated sample oil containing an iron-copper catalyst and water. After three weeks, a small aliquot of oil is removed and the acid number is determined. Aliquots are removed and tested periodically thereafter. The time it takes for the acid number to reach 2 mg KOH/g oil is reported. We routinely run this test up to 2000 hours. If you would like a longer period of time, please let us know.