Effect of chloride threshold on pitting behavior of 316LN stainless steel in sour water solution by electrochemical analysis
Si Chen, Li Sun, Weihua Li
Abstract
Abstract The effect of chloride threshold (CT = [Cl − ]/[SO 4 2− ]) on the pitting behaviors of 316LN in the sour water was studied by using electrochemical tests. The result shows that the pitting resistance of 316LN decreases with the increase in CT and temperature. The critical chloride threshold (CCT) decreases from 3 at 40°C to 1.5 at 70°C and then remains unchanged when further increases the temperature. The EIS experiment manifests that the protectiveness of the passive film reduces with the increase of CT, and the variation of the charge transfer resistance ( R ct ) is in keeping with the pitting potential ( E pit ). Increasing the CT or raising the temperature from 40°C to 80°C enhances the donor (point defect) density, resulting in a thinning of the protective film. Methods to raise the value of the CCT, that is, to improve the chlorine corrosion resistance of the pipelines were proposed.