Dry RPVOT as a Performance Test for Condition Monitoring of Gas and Steam Turbines

Since its original approval in 1964, the rotating pressure vessel oxidation test (RPVOT; ASTM D2272) has been the primary oxidation performance test for turbine oils. When this test was developed the steam turbine was the primary power-generation equipment in the market, and water levels were commonly in the 1,000-ppm (mg/kg) range. Today those trends have changed. Gas turbines are now the primary power-generation equipment, and water levels are commonly less than 50 ppm (mg/kg)—even for steam turbines. This trend has led to concerns about the performance correlations between the RPVOT (ASTM D2272) and real-life in-service operations. The RPVOT is an oxidation test that uses 20% water as part of the test itself. As ASTM D6224 states: “Some oils may undergo degradation leading to insoluble contaminants and deposit formation prior to reaching the warning limits (for example, the 25 % RPVOT warning limit). … This issue appears to be most prevalent in large frame industrial gas turbines.” This issue can be related to the fluid's water level now not being properly represented in the test as it is in operation. The trend is to study testing in the absence of water. For example, the turbine oil oxidation stability test (TOST; ASTM D943) now has a dry TOST (ASTM D7873). Differences between the oxidation of lubricants with and without water have been reported. Thus, there is a need for a performance test that resembles current operation conditions and serves condition monitoring purposes. This paper discusses the application of a dry RPVOT and how it compares to the standard version. New and in-service fluids are compared using both the dry and wet version of this oxidation performance test—along with intermediate chamber extraction samples having supported chemical testing.