Abstract
An analysis of the failure of LP turbine blades of a 210 MW thermal power plant has been presented in this paper. The blade material is of 12% Cr steel with tempered martensitic microstructure. Microstructural analysis as well as hardness and tensile tests did not indicate any degradation in terms of microstructure and mechanical properties. Physical discontinuities were observed in the braze joint which might have been formed due to improper brazing operation. Failure of the brazed joints between the blade and lacing rod was found to be due to improper brazing operations and corrosion effects during service. Fractographic evidence showed that the cracks were initiated from various points on the blade surface, which were at the interface with the lacing rod. Striations and beach marks were also observed which indicated the occurrence of high cyclic loading on the blades. Frequency data obtained from plant indicated the possibility of excessive vibration generated due to fluctuation in grid frequency during operation. Thus, the situation was aggravated due to a resonant condition of vibration, facilitating the propagation of cracks which were initiated earlier.
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