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 (H₂SO₄) 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 H₂SO₄ 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 H₂SO₄ 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 H₂SO₄ concentrations. These results demonstrate a competitive interaction between Cl^- and SO₄²⁻ ions, where sulfate ions inhibit pitting, thereby improving the corrosion resistance of 304 stainless steel in relatively high acidic concentration media.