Volume 3, Issue 5 (May 2006)
Evaluation and Comparison Between Oxidation Stability Test Methods for Turbine Oils
Traditionally, long established oxidation tests such as TOST (ASTM D 943-03) and RPVOT (ASTM D 2272-02) in combination with the acid number (ASTM D 974-03) test has been used to screen the oxidation stability of turbine oils. Lately, nevertheless, a new voltammetric method has been applied to measure the remaining useful life (RUL) of turbine oils, RULER™ (ASTM D 6971-03) as it uses microlitre amounts of sample and needs only a short testing time. The aim of this study is to examine the correlation between the RULER™ voltammetric test in comparison to the standing oxidation turbine methods, TOST and RPVOT. Three fully formulated commercially available oils were studied; two were based on synthetic esters and one was mineral oil based. In addition, other oils were tested in our laboratories in Norway and Sweden in order to investigate the correlation between RULER™ and RPVOT oxidation stability tests. Field samples were also used to evaluate those methods. Although those studies have been worthwhile, reaching a definite conclusion regarding correlations has proven to be somewhat difficult. It is clear, however, that by a careful methodology, a useful correlation for the investigated oil types may be obtained. For example, guide limits for RULER™ results and their correlation to RPVOT values were established.