Corrosion studies of Ni-free austenitic stainless steel in methanol containing H₂SO₄, HCl and LiCl

Abstract

The corrosion behaviour of an austenitic stainless steel containing nitrogen with negligible amount of nickel has been investigated in methanol-H₂SO₄, methanol-HCl, and methanol-LiCl solutions using potentiostatic polarization technique. The cathodic reaction was the hydrogen evolution reaction. Active, passive and transpassive behaviours were observed only at high concentrations of H₂SO₄ (0.01-1.0 M) in methanol, and passivity was due to the high inherent water content in sulphuric acid. Pitting was also observed on the steel surface. The pitting potential became nobler as the concentration of H₂SO₄ increased. In 0.1 and 1.0 M H₂SO₄, a cathodic loop, characterized by measured negative current in the anodic region, was also observed. In methanol-HCl and methanol-LiCl solutions, the steel dissolved actively and no active-passive transition was observed. The corrosion rate was significantly higher in methanol-HCl solution as compared to methanol-LiCl due to the synergistic effects of acid and chloride ion.