Abstract
Localized corrosion of stainless steel particularly SS316 is not totally understood in aqueous systems. However, localized corrosion of SS 316 in non-aqueous solutions is even less understood or explained. The present effort is aimed at developing an understanding of localized corrosion of stainless steel in methanolic solutions. Potentiodynamic polarization curves on SS316 were performed in methanol-water-1M LiCl at different methanol concentrations ranging from (0 - 99 wt%). The pitting potential decreased from +350 mV SCE to -100 mV SCE as the concentration of methanol increased from 0 wt% to 99 wt%. Dissolution kinetics were determined as a function of methanol concentration from 0 wt% to 90 wt%, in a saturated pit environment. The overvoltage for active dissolution decreased with decreasing methanol (increasing water) content. This however, doesn’t explain the decrease in pitting potential with increasing methanol content. Repassivation transients were determined by pulsing the potential to -150 mV SCE at different concentrations of methanol. The time to repassivate increases with increasing methanol content, suggesting that the critical concentration for repassivation decreases with methanol content. This may indicate that pit growth is stabilized at lower concentration of metal ions with increasing methanol (decreasing water) content. The decrease in critical concentration for repassivation explains the decrease in pitting potential with increasing methanol (decreasing water) content.
