Comparison of the Tandem Conductivity Tester (TCT) and the Complete Oil Breakdown Rate Analyzer Model 2 (COBRA 2) for Detecting Synthetic Aircraft Oil Degradation

摘要

At the request of the U.S. Air Force Oil Analysis Program Office (AF OAP) at Tinker AFB, two commercial instruments were evaluated for comparability in the analysis of jet engine oil synthetic ester (polyol)): the Complete Oil Breakdown Rate Analyzer (COBRA 2) from NAECO, LLC and the Tandem Conductivity Tester (TCT) from Spectro, Inc. The two instruments were compared by using each to test a single source of thermally degraded aircraft lubricant (Mil-7808 grade 3). The calibration of each instrument was set using a COBRA standard tricresyl phosphate (TCP) in 1,1,1-(trimethylol) propane triheptanoate (TMPTH)) that was obtained from the Joint Oil Analysis Program Technical Support Center (JOAP TSC). Approximately 2 gallons of thermally degraded lubricant obtained from a Tinker engine shop hot oil tank was used as a source of samples throughout the testing process. Since the COBRA 2 unit is currently used by the Air Force to monitor oil degradation it was to be used as a baseline for measuring TCT performance. Precision was similar for both instruments. In our opinion, the TCT instrument provided acceptably similar results to COBRA when measuring the same bulk sample using the Field boat cleaning method and the Laboratory boat cleaning method. The Field and Laboratory TCT boat cleaning methods appeared to produce nearly identical TCT measurement results as indicated by the 1200 sample results obtained with the use of ten different boats. TCT provided stable results when exposed to changing environmental conditions whereas; the COBRA 2 produced relatively unstable readings when exposed to those same short-term temperature changes. The TCT sample boats appeared to be very rugged with no significant damage observed resulting from the prolonged TCT only testing and cleaning cycles. Some slight surface scuffing on the connector pads was observed.