EXPLANATION
Degradation of hydraulic fluids and turbine oils, because of oxidation or thermal breakdown, can result in the formation of acids or insoluble solids and render the oil unfit for further use. This test method covers a procedure for evaluating the oxidation stability of such oils. Correlation between the results of this test method and the oxidation stability in use can vary markedly with service conditions and with various oils.
TEST SUMMARY
An oil sample is contacted with air at 135° C in the presence of copper and iron metals. The acid number and spot forming tendency of the oil are measured daily. The test is terminated when the oxidation life of the oil has been reached. The oil is considered degraded when either its acid number (measured by Test Methods ASTM D664 or ASTM D974) has increased by 0.5 mg KOH/g over that of new oil; or when the oil begins to form insoluble solids as evident from a clearly defined dark spot surrounded by a ring of clear oil when a drop of the oil is placed on a filter paper.
TEST PRECISION
Where X is the mean value of the oxidation test life.
This test method has no bias.