Electrochemical Behaviour of AISI 316 Austenitic Stainless Steel in Acidic Media Containing Chloride Ions

The electrochemical behaviour of AISI 316 austenitic stainless steel (SS) was investigated in deaerated hydrochloric and sulphuric acid solutions using the open-circuit potential, cyclic voltammetric and chronoamperometric techniques. Enhanced corrosion of steel samples occurred with bigger HCl concentrations, as the potential range of passivity was shortened and both the pitting (E(pit)) and the protection potentials (E(prot)) became less noble. Conversely, the SS electrodes exhibited a greater corrosion resistance in solutions containing sulphuric acid of the same concentration. The aggressive effect of chloride ions towards steel corrosion was also investigated through controlled additions of NaCl to both electrolytic media and the analysis of the corresponding effects on the shape of the voltammetric curves. Chronoamperometric measurements run by setting different potential values to steel electrodes allowed the determination of the induction time for pit initiation, and the rates of pit nucleation and pit growth.