Corrosion of nickel-containing stainless steel in concentrated sulphuric acid

The corrosion of UNS S30403 stainless steel was investigated in 93.5 wt% sulphuric acid at temperatures from 40 to 100 °C. Time-dependent free corrosion potential measurements demonstrate that the steel is subject to spontaneous active–passive oscillation. Studies on the effect of temperature and electrode rotation speed indicate that the oscillation is activation and transport controlled over different segments of the oscillations. It is concluded that the oscillation is caused by reversible changes in the exchange current for the cathodic reduction of sulphuric acid, depending on the presence or absence of nickel sulphide on the steel surface.