Ferrographic and spectrometer oil analysis from a failed gas turbine engine

Abstract

An experimental gas turbine engine was destroyed as a result of the combustion of its titanium components. It was concluded that a severe surge may have caused interference between rotating and stationary compressor parts that either directly or indirectly ignited the titanium components. Several engine oil samples (before and after the failure) were analyzed with a Ferrograph and with plasma, atomic absorption and emission spectrometers to see whether this information would aid in the engine failure diagnosis. The analyses indicated that a lubrication system failure was not a contributory factor in the engine failure. Neither an abnormal wear mechanism nor a high level of wear debris was detected in the engine oil sample taken just prior to the test in which the failure occurred. However, low concentrations (0.2–0.5 ppm) of titanium were evident in this sample and samples taken earlier. After the failure, higher titanium concentrations (more than 2 ppm) were detected in oil samples taken from different engine locations. Ferrographic analysis indicated that most of the titanium was contained in spherical metallic debris after the failure. Attempts to pinpoint the failure initiation site were inconclusive, but the oil analyses did eliminate a lubrication system bearing or shaft seal failure as the cause of the engine failure.