Influence of electrochemical descaling treatment in simulated cooling water on the corrosion behavior of stainless steel

Abstract

The electrochemical descaling treatment of circulating cooling water can effectively reduce the content of scaling ions, chloride ions and produce strong oxidizing substances with bactericidal properties in the water, which is beneficial for operation at high concentration ratio (N) of circulating water, meets the goal of clean production and has a good prospect. However, changes in ion concentration and type in water can have an impact on the corrosion behavior of metals. Currently, there is limited understanding of the impact of electrochemical treatment on the corrosion behavior of stainless steel, a commonly used material in cooling water systems, which increases the application risk of this technology. In this study, the effects of electrochemical treatment of simulated cooling water on the corrosion behavior and the passive film properties of Type 304 stainless steel with different N values were investigated by analysis of water composition, polarization curve and X-ray photoelectron spectroscopy. The results showed that the pitting potential of stainless steel decreased with the raise of N in untreated simulated water, while the pitting potential increased with the raise of N in electrochemically treated simulated water, and the highest pitting potential was observed when N was 10. The electrochemical treatment effectively reduced the Cl− content in the simulated water. With the increase of N, the concentration ratio of [Cl−]/[SO42−] decreased, and the content of ClO− generated by Cl− oxidation in the water increased, which affected the corrosion behavior of stainless steel. Appropriate concentrations of the ClO− can effectively inhibit pitting corrosion of the stainless steel in simulated water, and the best inhibitory effect observed when ClO− concentration was 50 mg⋅L−1. The inhibition of pitting corrosion by ClO− was attributed to the effective improvement of the Cr/Fe ratio and the oxides/hydroxides ratio in the passive film on the surface of stainless steel, thus the compactness and the protection performance of the passive film was enhanced. The results can provide reference for the design of electrochemical treatment devices and processes.