Effects of dithionite ion on corrosion of type 304 stainless steel in sulphuric acid solution

Corrosion behaviour of type 304 stainless steel was investigated, with particular attention to additive effects of hydrosulphite (Na2S2O4) on corrosion in 0.1 mol/l H2SO4 solution with various amounts of Na2S2O4 up to 60 mmol/l. Corrosion of SUS304 occurred below pH 3.0 at 30 °C in a 0.1 mol/l H2SO4 solution in which Na2S2O4 was added to 0.1–20 mmol/l. The maximum corrosion rate at 30 °C was measured as 7.2 g/m2 h (7.9 mm/y) in 0.1 mol/l H2SO4–10 mmol/l Na2S2O4 at pH 1.2. Microscopic surface observation revealed that active dissolution was accompanied by intergranular corrosion at the metal surface. The SUS304 was easily passivated in 0.1 mol/l H2SO4 solution with more than 30 mmol/l Na2S2O4. NiS was detected in the passivated film.