Author Description

Corrosion resistance of austenitic-ferritic (duplex) stainless steels (DSS) in atmosphere in presence of chloride deposits was studied in order to promote their safe application for construction of storage tanks and other facilities. Laboratory tests of pre-stressed specimens demonstrated clear superiority of DSSs over reference austenitic stainless steel (ASS) grades in terms of the resistance to stress corrosion cracking (SCC). SCC initiated at temperatures as low as 20 and 30 °C in ASS grades EN 1.4306 (304L) and EN 1.4404 (316L), respectively, whereas the only occurrence of SCC in duplex stainless steel samples was recorded at 70 °C. It was found that the initiation of SCC and selective/pitting corrosion is governed by the equilibrium chloride concentration in solution formed in contact of chloride surface deposits with air at given relative humidity. The propagation rate of selective corrosion of the ferritic phase in duplex stainless steel structures was maximal at the chloride concentration between 6 and 9 mol/L and it increased with the pH of the salt solution. Threshold levels of chloride concentrations and relative humidity in presence of specific deposits leading to localised corrosion were defined. Additional experiments and results of field exposures showed that deposits formed on real structures under washing conditions were benign in terms of the SCC initiation in view of both the surface chloride concentration and composition. If storage tanks are designed properly, DSSs are optimal materials for their construction due to superior corrosion resistance, mechanical properties and lower life cycle cost.