Root Cause Analysis for the Failure of an Air Compressor Impeller

This study examines the reason of failure of a three-stage air compressor, which failed during service. The as-cast component consisted of 15-5 martensitic stainless steel. The alloy satisfied ASTM standards for alloy chemistry, mechanical properties, and phase constituents in microstructure. During structural investigation, distinctive chemical heterogeneities in the form of embedded carbonaceous flakes were found near surface/sub-surface of the as-cast component. The probable origin for the formation of such carbon-rich phases was inappropriate casting process, which perhaps involved improper mould preparation. These flaky carbon-rich locations acted as stress concentrators leading to crack initiation. The crack propagated under cyclic loading during high-speed rotation of the impeller, and ultimately leading to premature failure of the component.