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The failure of a LP (low pressure) turbine blade of a 220 MW thermal power plant is presented. The blade was made of martensitic stainless steel and the structure was tempered martensite. There was no evidence of degradation of blade material. The fracture took place at the aerofoil region, 113-mm from the root. Throughout the blade surface Si rich phases were detected. Several pits/grooves were found on the edges of the blades and chloride was detected in these pits. These were responsible for the crevice type corrosion. The probable carriers of Cl− were Ca and K, which were found on the blade. The failure mode was intergranular type. Possibly the ultimate failure was due to corrosion-fatigue.

The failure of two adjacent platen super heater tubes of a thermal power plant has been analysed. One tube fractured with a fish mouth opening and another thinned down considerably. A significant amount of oxide layer was observed in the inner side of the failed tube. In the other tube the inner oxide layer was very small and the tube was thinned down due to fireside corrosion. The unexposed tube from the same lot revealed a ferritic bainitic microstructure. The failed tube also showed a ferrite bainite microstructure but most of the bainitic carbide had transformed to globular form. Considerable carbide precipitation both in grain boundary (GB) and inside grains were observed. A large number of cavities and micro-cracks were observed along the grain boundaries. A similar microstructure was observed on the same tube 10 cm away from the failed region. The micrograph at the fracture location showed a similar microstructure but the grains are very much elongated. The formation of globular oxide on the other tube was compared to that of the failed tube. Due to breakage of oxide scale of the failed tube, the metal surface of the failed tube was exposed to steam at a higher temperature and this accelerated the oxide growth. This led to creep damage of the material. Ultimately, failure occurred due to rapid overheating of the tube material.

Studs in the interceptor valve of a 110 MW unit failed after a service life of 148,700 h. The studs were operated under a steam pressure of 35 kg/cm2 and a temperature of 535°C. The studs were fractured at one end of the threaded end. Various techniques were employed to analyse the failure of the studs. It has been concluded that the failure of the studs was due to reverse temper embrittlement. The failure was delayed due to the presence of Mo and V. To reduce the tendency to this kind of failure, the following steps were recommended: (a) reduce the phosphorus content in the steel to a low level or (b) reduce the grain size to about 10 μm.

The premature fatigue failure of a compression spring during service has been analysed. Optical and scanning electron microscopy, hardness and tensile testing and X-ray diffraction techniques were employed. Quench cracks, presumably due to improper quenching, were observed across the cross-section of the spring. It is established theoretically that the diameter of the spring rod was smaller than the critical diameter for this composition of steel. X-ray diffraction showed the presence of a small amount of retained austenite (average grain size of 2 μm).