Cavitation erosion – corrosion behavior of some hydraulic turbine runner steels

Abstract

Cavitation erosion is still a phenomenon which causes severe damages to hydraulic turbine runners. A lot of effort has been deployed in the scientific community to understand the materials response to this kind of solicitation. Part of researches which are conducted at Research Institute of Hydro-Quebec are focused on determining the materials behavior laws. For this, the classical ASTM G32 standard is used. Mass losses are followed during the exposure time. Also degradation parameters i.e mean depth of erosion and erosion rate are determined. Furthermore, a lot of effort has gone into the determination of the evolution of surface damages in terms of pitting, surface cracking and material removal. For this, microscopy techniques have been used to link the microstructure to the material removal mechanisms. Furthermore, another part of the researches is focused on enlightening and quantifying the deleterious effect of the environment. In some cases, a synergistic effect can establish between cavitation erosion mechanisms and corrosion kinetics and increase the material degradation. In the present study the ultrasonic cavitation rig has been coupled with electrochemical techniques to determine the contribution of corrosion to this phenomenon in natural river freshwater. The electrochemical behavior of three commonly used materials in hydraulic turbine runners, ASTM A27, E309L and UNS S41500 are studied in condition of quiescence and also in cavitation conditions.