Electrochemical behaviour of duplex stainless steels in caustic environment

Research highlights: → Corrosion rates for tested DSS alloys are less than 0.2 mm/year in NaOH solution. → Temperature increases the corrosion rates of DSS in caustic solutions. → Polarisation behaviour of DSS at lower potentials is affected by Fe, Ni and Cr. → Presence of molybdenum can be detrimental to its corrosion in caustic environments. → Corrosion films of DSS alloys consisted of spinel oxides of Fe, Ni and Cr. - Abstract: Recent studies have shown that duplex stainless steels can be susceptible to general corrosion and stress corrosion cracking in high pH caustic environments. This difference in the corrosion resistance can be attributed to changes in the electrochemical behaviour of steels. The present study has shown that the corrosion rates of duplex stainless steels increase with an increase in temperature and sulphide addition to caustic environments. Moreover, alloying Fe with Cr and Ni helps to raise the corrosion potential and lower critical current density of DSS in an alkaline environment whereas Mo can be detrimental to the corrosion resistance of the steel.