ASTM D942 standard test method for oxidation stability of lubricating greases by the oxygen pressure vessel method
8. Procedure
8.1 Fill each of the five dishes with 4.00 more or less 0.01 g of grease. Distribute the samples in the dishes in a uniform layer with a smooth level upper surface. Place the filled dishes on the five bottom shelves of the holder, leaving the top shelf to act as a cover to prevent condensing volatile products from dropping into the grease samples. When assembling the pressure vessel, place a small ball of glass wool in the bottom of the stem.
8.2 Place the dish holder in the pressure vessel with a sealing gasket in place, and close the pressure vessel by tightening the bolts slowly and uniformly. Clear the air from the pressure vessel by introducing oxygen slowly until a pressure of 100 psi (689 kPa) is attained, then allow the oxygen to escape slowly; repeat four times. Bring the oxygen pressure to a value as shown in the following table:
Allow the pressure vessel to stand overnight to make sure there are no leaks.
NOTE 4 - It has been found that pressure readings as shown above will result in a pressure reading of 110 more or less 2 psi (758 more or less 14 kPa) when the pressure vessel is placed in the bath in the following step, 8.3, and consequently no release of oxygen will be required in most cases. This minimizes the chance of a leak developing at the valve after the overnight check for leaks has shown the pressure vessel to be satisfactory.
8.3 Place the pressure vessel in the oil bath maintained at a temperature of 99 more or less 0.5°C (210 more or less 1.0°F). As the pressure rises, if needed, intermittently release oxygen from the pressure vessel until a constant pressure of 110 more or less 2 psi (758 more or less 14 kPa) is obtained and maintained for at least 2 h. A gradual drop in pressure indicates a continuous leak in the pressure vessel. Observe and record the pressure at least every 24 h. In case a leak develops, do not report the results but repeat the test.
8.4 Start timing at the moment of immersion of the pressure vessel in the oil bath, and continue the oxidation for the time period specified.
NOTE 5 - Specifications are usually given in terms of pressure drop in pounds per square inch, or kilopascals at one or more time intervals, for instance, after 100, 200 h, and so forth.