On the service performance of refurbished turbine blades in a power station

Due to initial high cost, refurbishment of turbine blades is of particular importance to the power generation industry to reduce operating costs. In particular, there is a growing interest in developing heat treatment processes capable of restoring most of the original microstructure and corresponding properties of used blades. Toward this objective, it is important to develop an understanding of the behavior of refurbished blades exposed to actual service conditions. Therefore, this investigation was undertaken to analyze the damage produced in a blade refurbished after 40,000 hours of operation at about 800 °C (Westinghouse W501D5A Engine). However, after about 900 hours of operation at the same temperature, the blade was fractured by a ductile intergranular mode. Electron microscopy and computational modeling were used to develop a one-to-one correspondence between microstructure and temperature distribution. Although there was no evidence for overheating during service, the results showed that the blade initially contained y' precipitate-free zones alongside grain boundaries, which could accelerate intergranular failure during service. It was concluded that the blade was damaged by improper heat treatment during refurbishing