Corrosion behaviour of duplex SAF2507 in aqueous organic acid solutions

This paper reports on mass loss and electrochemical polarization behaviour of duplex SAF2507, in aqueous solutions of acetic acid, formic acid and their mixtures, in the presence of specific contaminants, such as sulphuric acid. The effect of temperature and redox couples was also investigated. SAF2507 withstands corrosion in acetic acid solutions in a wide temperature and concentration range. The corrosion rate is higher in the more dissociated formic acid at the same concentration. Uniform corrosion with selective dissolution of the austenitic phase was observed in all tested solutions, the selectivity being strictly connected to solution aggressiveness. The presence of sulphuric acid in organic acid aqueous solutions is severely detrimental to the corrosion resistance of the duplex: the corrosion rate increases almost linearly with H2SO4 concentration. Few tens of ppm of Fe3+ or Cu2+ improve the corrrosion performance markedly, causing often the corrosion rate to decrease to very low values. The addition of H2O2 has a strong effect favouring the increase of the corrosion potential up to the passivity of duplex due to the possible formation of peracids.