Development of Surface Modification System using Ultrasonic Shot Peening for Improving the Fatigue Strength of Pump-Turbine Runner

Abstract

In pump-turbine runner, fatigue cracks after welding works are occasionally found. To avoid the generation of cracks, we developed ultrasonic shot peening system to improve fatigue life by introducing to the runner surface with beneficial compressive residual stress. This developed system consists of supporting frames, movable frames, peening machine and its chamber, and the ultrasonic transmitter. This system has been applied to a pump-turbine runner which had been damaged with fatigue cracks and repaired by welding. We confirmed high compression residual stress by portable X-ray analyzer.