Effect of Chloride Ion Concentration on the Corrosion Behavior of 304 Stainless Steel Used in the Electric Water Heater

Abstract

In this paper, the effect of chloride ion concentration on the corrosion behavior of 304 stainless steel used in the electric water heater at 25° and 80° is investigated, by using open circuit potential tests, electrochemical impedance spectroscopy (EIS), polarization curves tests. It is found that the passive film can be spontaneously formed at the corrosion potential. The Eocp values of 304 stainless steel progressively stabilize at 25°, while the Eocp values are unstable at 80°. The chloride ion in the solution is detrimental for forming protective oxides passive film both at 25° and 80°, due to the increase of Q1-Y values and the decrease of R1 values with the increase of chloride ion concentration. However, the impedances increase with the immersion time at 25°, while the impedances increase at the beginning of the immersion (1 hour→1 day), and then gradually decrease with the increase of immersion time at 80°. In addition, the Ecorr and Epit tend to noble with the decrease of the concentration of chloride ion at the same temperature. The Epit at 25° is much nobler than that at 80° in the same solution. The radius and depths of the pits formed on the surface after polarization curve tests increase with the increase of concentration of chloride ions.