Application of fracture mechanics in the failure analysis of a last stage steam turbine blade

This paper describes the application of fracture mechanics principles in the failure investigation of a last stage steam turbine blade of the nuclear power plant at Narora in India. The machine failed in the early morning hours on 31 March, 1993. The failed parts include two bearings and several blades in the fifth stage of flow path 2 of LP turbine. Blade #52 in this stage revealed three clear zones of fracture, the first with a crack initiating at the strain raiser point and propagating at a low rate, a second where the blade was subjected to multiple impacts with initiation of fresh cracks and propagating at high rates and the third one consisting of unstable fracture. Stress Intensity Factor approach is used to identify the three crack zones and establish the mechanism of the machine failure.