EXPLANATION
Degradation of fluid lubricants because of oxidation or thermal breakdown can result in fluid thickening or in the formation of acids or insoluble solids and render the fluid unfit for further use as a lubricant. This test method can be used for estimating the oxidation stability of oils. It can function as a formulation screening tool, specification requirement, quality control measurement, or as a means of estimating remaining service life. It shall be recognized, however, that correlation between results of this test method and the oxidation stability of an oil in field service can vary markedly with field service conditions and with various oils.
This test method is designed to complement Test Method ASTM D5846 and is intended for evaluation of fluids which do not degrade significantly within a reasonable period of time at 135° C. It covers evaluating the oxidation of inhibited lubricants in the presence of air, copper, and iron metals. Although this test method was developed and used to evaluate the high temperature oxidation stability and deposit forming tendency of oils for steam and gas turbines, it has also been used for testing other lubricants made with mineral oil and synthetic basestocks for compressors, hydraulic pumps, and other applications, but these have not been tested in cooperative testing.
TEST SUMMARY
After determining the viscosity at 40° C and the acid number of a sample, a test specimen is stressed at 155° C for 96 hours. After cooling, the test specimen is vacuum filtered for the determination of total insolubles formed during the test. Total insolubles are reported as low, medium, or high. The viscosity and the acid number of the filtrate are determined and compared with the initial values to ascertain any increase in those values. Both the changes in acid number and the increase in viscosity at 40° C are reported. The glass cell in which the test specimen was stressed is rinsed with heptane and dried. Residual deposits are compared with ASTM Adjunct ADJD6514, and the results are reported.
TEST PRECISION
Where X is the mean value.
This test method has no bias because the value of the oxidation life is defined only in terms of this test method.