Metallurgical Failure Analysis of a Rotating Blade in the Compressor Section of a Gas Turbine

A metallurgical failure analysis was performed for the stage 17 gas turbine rotating blade and stationary vane. Four pieces including the failed rotating and stationary blades were removed from the air compressor section of a gas turbine. The damaged components were found during a borescope examination. The objectives were to determine the failure mechanism and to estimate an inspection interval. The measured chemical compositions of the rotating blade and stationary vane are consistent with that of 403 stainless steel. The failure mechanism for the rotating blade is fatigue based on the beachmarks on the fracture surface and the transgranular cracking. The fatigue crack initiated at the trailing edge of the blade. The crack at the trailing edge is due to impact damage. The probable root cause of failure for the rotating blade is the loss of axial clearance between the stationary and rotating blades. Fatigue crack growth calculations were performed using the NASGRO computer program and the corner cracked plate geometry to estimate the inspection interval. The estimated inspection interval is of order of magnitude hours to days for failure by high cycle fatigue crack growth.