Mechanical and electrochemical interactions during liquid–solid impingement on high-alloy stainless steels

Abstract

The erosion–corrosion behaviour of three high-alloy stainless steels (UNS S31245, UNS S32654 and UNS S32750) under aggressive liquid–solid impingement conditions has been assessed using a combination of electrochemical tests and weight-loss analysis. The material loss occurring under conditions of varying solid loading (900 mg/l), and at a temperature of 18°C, velocity of 17 m/s and impingement angle of 90° has been scrutinised as a function of time. Post-test examination has identified material loss mechanisms and the physical relevance of erosion and corrosion interactions has been illustrated. In this paper it has been shown that the resistance to material loss for the three materials does not follow the expected trend of increasing resistance as hardness increases. Through electrochemical measurements the pure corrosion component of the material can be isolated and it has become clear that corrosion (through direct and indirect effects) plays an important role in the erosion–corrosion process of even high-grade stainless steels due to depassivation–repassivation events corresponding to solid impact in the corrosive medium. Although the pure corrosion process (direct corrosion effect) constitutes only a small part of the total material loss, there is an important synergistic factor defined as the effect of corrosion on erosion which means that corrosion-related processes can be significant in erosion–corrosion.