Root Cause Analysis of Failure of 40th Stage Moving Blade of Single Cylinder Condensing Turbine

Blade failures in steam and gas turbines are quite a common occurrence. The last stages of steam turbines are designed to have the lowest possible fluid temperature. In view of the longest blade length in the last stages, the blades are subjected to highest bending moment forces and susceptible for erosion-corrosion phenomenon owing to the low service temperature environment. The failure analysis of last stage blade of 54 MW direct condensing type gas turbine are presented. The blade was made of martensitic grade stainless steel. Detailed analysis of the blade surface, lacing wire hole as well as the fracture morphology was analyzed using SEM-EDX. The probable reason for the failure of the blade was brought out based on the detailed investigations of the failed blade as well as the vibration signature analysis at the time of failure incidence.