ASTM D6971-22

SIGNIFICANCE AND USE 5.1 The quantitative determination of hindered phenol and aromatic amine antioxidants in a new turbine oil measures the amount of these compounds that has been added to the oil as protection against oxidation. Beside phenols, turbine oils can be formulated with other antioxidants such as amines which can extend the oil life. In in-service oil, the determination measures the amount of original (hindered phenol and aromatic amine) antioxidants remaining after oxidation has reduced its initial concentration. This test method is not designed or intended to detect all of the antioxidant intermediates formed during the thermal and oxidative stressing of the oils, which are recognized as having some contribution to the remaining useful life of the in-service oil. Nor does it measure the overall stability of an oil, which is determined by the total contribution of all species present. Before making final judgment on the remaining useful life of the in-service oil, which might result in the replacement of the oil reservoir, it is advised to perform additional analytical techniques (as in accordance with Test Methods D6224 and D4378; see also Test Method D2272), having the capability of measuring remaining oxidative life of the in-service oil. 5.1.1 This test method is applicable to non-zinc type of turbine oils as defined by ISO 6743 Part 4, Table 1. These are refined mineral oils containing rust and oxidation inhibitors, but not antiwear additives. 5.2 The test is also suitable for manufacturing control and specification acceptance. 5.3 When a voltammetric analysis is obtained for a turbine oil inhibited with a typical synergistic mixture of hindered phenol and aromatic amine antioxidants, there is an increase in the current of the produced voltammogram between 8 s to 12 s (or 0.8 V to 1.2 V applied voltage) (see Note 1) for the aromatic amines, and an increase in the current of the produced voltammogram between 13 s and 16 s (or 1.3 V to 1.6 V applied voltage) (se... SCOPE 1.1 This test method covers the voltammetric determination of hindered phenol and aromatic amine antioxidants in new or in-service type non-zinc turbine oils in concentrations from 0.0075 % by mass up to concentrations found in new oils by measuring the amount of current flow at a specified voltage in the produced voltammogram. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.