Abstract
Turbine and other large machines require lubrication where considerable volumes of oil remain in service for numerous years between replacements. The service life for these applications is primarily influenced by oxidation stability and the residues that this degradation creates. Oxidation stability is one of the most critical factors used in assessing the performance of fresh and in-service oils. A primary condition monitoring test method utilized to measure the oil oxidative stability is the rotating pressure vessel oxidation test (RPVOT), which is described in ASTM D2272. The oxidative resistance of modern turbine oils has increased dramatically over the last 50 years. Advances in lubrication technologies such as improved base oil formulations, additive synergy and synthetic oils have extended RPVOT test times from less than 300 min to over 3,000 min. This has caused extended testing runtime that exceeds the original intent of the method and the long test durations have potentially introduced errors that affect the accuracy and predictive capability of the test. As a result, the ability to properly trend and assess the relative oxidative health of the oil may be compromised. The D2272 Test Method was examined using alternative reporting criteria expected to improve test precision and provide a more accurate assessment of a lubricants condition. Reporting criteria based upon the true induction point and pressure drop at a specified time were examined. Efficacy of using pressure loss from the test maximum at 1,400 minutes for condition monitoring purposes was evaluated and holds promise. These changes would be expected to improve accuracy for full induction tests or lead to laboratory cost savings in that tests can be terminated earlier and without an induction occurring; effectively increasing laboratory throughput and provide the end user with more informative data that is more befitting for long life oils in use today.
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