Corrosion Behaviour of 316L Stainless Steel in Hot Dilute Sulphuric Acid Solution with Sulphate and NaCl

The corrosion behaviour of 316L stainless steel (316L SS) in 10% H2SO4 solution (94 degrees C) with various concentrations of NaCl (0-0.085 mol/L) was studied by immersion corrosion test and polarization methods, combined with SEM/EDS, XPS and XRD tests. The influence of NaCl on the corrosion of 316L SS was investigated. The results showed that at lower NaCl contents (0-0.0085 mol/L), the steel presented a general corrosion characteristic with a higher corrosion speed and the corrosion rate increased with the NaCl content. At higher NaCl contents (0.017 mol/L), the corrosion rate decreased remarkably due to the protective corrosion products precipitation which contained metallic sulphates and NaHSO4. However, the higher concentration of chloride ions caused micron pitting-like local dissolution on the surface. The addition of Na2SO4 effectively inhibited general corrosion of the steel because of a dense and continuous products layer enriched with more NaHSO4 and metallic sulphates formed.