Novel repair technique for life-extension of hydraulic turbine components in hydroelectric power stations

A significant number of hydraulic turbines operated in Japan were installed around the decade of the 1930s. Today, aging degradation and flaws are observed in these turbine equipments. So far, Japanese engineers have applied NDI technology of Ultrasonic Testing (UT) to detect the flaws, and after empirical evaluation of the remaining life they decided an adequate moment to replace the equipments. Since the replacement requires a large-scale field site works and high-cost, it is desirable a life-extension of the equipments by implementing repair services. We have been working in order to enhance the accuracy of results during the detection of flaws and flaws dimensioning, in particular focusing on the Tip-echo technique, TOFD and Phased-array UT, accompanied by the conventional UT. These NDI methods made possible to recognize the entire image of surface and embedded flaws with complicated geometry. Then, we have developed an evaluation system of these flaws based on the theory of crack propagation, of the logic of crack growth driven by the stress-intensity factor of the crack tip front. The evaluation system is constituted by a hand-made software and database of stress-intensity factor. Based on these elemental technologies, we propose a technique of repair welding to provide a life-extension of hydraulic turbine components.