Compositional design of low carbon sulphuric acid dewpoint corrosion resistant steel and corresponding anticorrosive mechanism

The optimal contents of C, S, Cu and Sb in a new low alloy steel for the purpose of improving the sulphuric acid dewpoint corrosion resistance were investigated by weight loss and potentiodynamic polarisation in 50 wt-%H₂SO₄ at 70°C. The optimal elemental contents of C, S, Cu and Sb in the low carbon sulphuric acid dewpoint corrosion resistant steel (SADPS) are 0·09, 0·016, 0·3 and 0·09 respectively. The corrosive products of Fe₂(SO₄)₃ and FeSO₄ were found on the surface of plain low carbon steel while corrosive products of (Cu,Fe)SO₄, FeSbO₄, FeSb₂O₄, CuSbO₄ and CuO were found on the surface of SADPS. Potentiodynamic polarisation test also revealed that the higher corrosion resistance of SADPS was due to inhibition of the cathodic reaction due to surface enrichment by the alloying elements.