Improvement of pitting corrosion resistance of AISI 444 stainless steel to make it a possible substitute for AISI 304L and 316L in hot natural waters

The pitting corrosion resistance of AISI 444, 304L and 316L stainless steels in two tap waters with different chloride concentrations at 80 °C was studied. Cyclic potentiodynamic polarization tests were carried out starting from Ecorr - 30 mV until the current density reached 0.1 mA cm-2 (scan rate 0.166 mV s-1); the scan was then reversed and continued until new passivity conditions were achieved. The corrosion potential was measured before the polarization experiments. From the E-log i plots, the values of pitting and protection potential were obtained; from these potentials, the perfect and the imperfect passivity regions were defined to compare the corrosion resistance of the studied steels. Cyclic potentiodynamic polarization tests were performed both on as received stainless steel samples and on samples submitted to different cleaning-passivation treatments to improve their corrosion resistance. The results indicate that, for industrial production, AISI 444 stainless steel can substitute the more expensive AISI 304L or 316L after a cleaning-passivation treatment that reduces the presence of inclusions.