Influence of chloride ion concentration on the corrosion behavior of 304 austenitic stainless steel in sulfuric acid

The corrosion behavior of 304 austenitic stainless steel in sulfuric acid (H 2 SO 4 ) solutions was investigated as a function of chloride ion (Cl - ) concentration. The steel exhibited distinctive electrochemical behaviors governed by both acid and chloride concentrations. In H 2 SO 4 solutions (≤ 1 M), the corrosion current density ( i corr ) increased, while the polarization resistance ( Rₚ ) decreased with increasing Cl - concentration, indicating accelerated corrosion rate. In contrast, in ≥ 2 M H 2 SO 4 solutions, i corr decreased and Rₚ increased with increasing Cl - concentration up to approximately 0.5-1.0 M, followed by a reversal in trend at higher chloride levels (≥ 1 M NaCl). The pitting susceptibility of the steel was strongly influenced by both parameters, increasing with Cl - concentration but diminishing with higher H 2 SO 4 concentrations. These results demonstrate a competitive interaction between Cl - and SO 4 ²⁻ ions, where sulfate ions inhibit pitting, thereby improving the corrosion resistance of 304 stainless steel in relatively high acidic concentration media.