A comparative H2S corrosion study of 304L and 316L stainless steels in acidic media

H2S corrosion of 304L and 316L in oxygen-free Na2SO4 + Na2S solution at pH 3 and temperature of 60 °C were investigated by EIS, potentiodynamic polarisation, multi-component Pourbaix diagrams and microstructure characterization. At similar conditions, lower corrosion rate was observed on 316L, attributed to its denser (1.5 times) and smoother (6%) surface layer and confirmed by SEM micrograph. During polarisation, H2S increases significantly the critical current density on 304L and passivation current density, ip, on 316L. Higher ip on 316L was associated to simultaneous FeS2–MoS2 preservation, confirmed by XRD examination. H2S could have an inhibiting effect on 304L in passivity region.