Investigation of Compressor Rear Frame Cracking of United States Navy LM2500 Gas Turbine Engines

In December 2000, a 7” long axial crack was visually identified on the compressor rear frame of an LM2500 propulsion gas turbine engine aboard the USS MITSCHER (DDG 57). This was originally thought to be a unique failure mode possibly caused by misaligned brackets external to the engine imparting undo thermal stresses onto the engine casing and flange. Since that time, 17 additional engines in the Navy fleet have been identified with either the large axial crack on the compressor casing or a small craze crack on the CRF flange, which appears to be the origination point prior to crack propagation. This paper discusses the extent of the cracking problem in the US Navy, the engineering investigation undertaken by the OEM and Navy to determine the root cause of the cracks and development of a field repair strategy to mitigate the impact of these cracks. The focus of the paper includes metallurgical analysis of failed compressor rear frame hardware, vibratory evaluation of the engine’s external piping system as a contributory failure mode and results of strain gage testing of the mid flange region.