Is duplex stainless steel more corrosion resistant than 316L in aqueous acid chloride-containing environments at temperatures higher than 100°C?

Abstract

The influences of temperature and chloride content on the corrosion resistance of stainless steels (SS) in acid solution were investigated employing polarisation curves (PC) and electrochemical impedance spectroscopy measurements. Although the duplex SS presented a higher pitting resistance equivalent number than that of 316L SS, the PC for the duplex SS in solution containing 250 ppm chloride ions showed a surprisingly large positive hysteresis loop, suggesting that there was damage to the passive film caused by localised intergranular corrosion at 120^oC. In contrast, it was interesting to note that the 316L SS immersed in an acid solution containing 250 ppm chloride did not exhibit pitting corrosion. The oxides naturally formed on both steels at open circuit potential at 120^oC had double layer structures and their thicknesses were obtained from constant phase element calculations.