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To improve the reliability, and extend the life, of high-temperature gas turbines, the residual life assessment method and the repair technology of hot gas-path components have been developed as steps for preventive maintenance.
The residual life assessment methods are based on the damage investigation of the turbine nozzles, buckets and combustors in service. The damage mechanisms have been clarified as crack growth behavior and the evolution of material degradation. The maximum surface crack growth prediction method is described for the nozzles, and the coating degradation of the buckets in service is examined by means of a small punch testing method. The validity of these methods is verified by assessing the inspection date.
To extend the life of the components, an appropriate repairing technology for the damaged parts has been developed. This paper also describes the life management system which is used to optimize the operating costs and the reliability, availability and maintainability of the gas turbines.