The use of cyclic polarization method for corrosion resistance evaluation of austenitic stainless steel 304L and 316L in aqueous sodium chloride solution

Corrosion behavior of austenitic stainless steels 304L and 316L types in various concentrations of aqueous sodium chloride solutions were investigated related to its pitting corrosion resistance. Experimental testing was carried out by using cyclic polarization method at room temperature (27°C) to evaluate the corrosion mechanism by considering breakdown potential (E_b) and protection potential (E_p). Aqueous sodium chloride solutions were prepared with various concentration i.e. 1%, 2%, 3.5%, 4% and 5% w/v. The testing results were represented by cyclic potentiodynamic polarization curves for both alloys which showed potentials that indicated the onset of potentials E_b and E_p respectively. The results were influenced by sodium chloride concentrations and the chemical composition of alloys. Rank of the values of E_b and E_p of 304L and 316L at various sodium chloride concentrations from the highest to the lowest were 1%, 2%, 5%, 4%, 3,5% w/v NaCl consecutively. It was observed that the lowest corrosion resistance of both alloys was at 3,5% w/v NaCl which was similar to typical seawater solution with maximum dissolved oxygen solubility. It was shown that 316L has more positive potentials for both E_b and E_p as well as its difference values compared to SS 304L at all concentrations of aqueous sodium chloride solution.