EFFECT OF WATER ON CORROSION BEHAVIOR OF STAINLESS STEEL UNDER HIGH-TEMPERATURE AND HIGH-PRESSURE METHANOL SOLUTION CONTAINING CHLORIDE IONS

摘要

The effect of water in a methanol solution containing 0.42 wt% LiCI on the corrosion behavior of type 316L stainless steel was evaluated by anodic polarization and electrochemical impedance spectroscopy (EIS) at 423K and 473K. The addition of water to the methanol solution increased the anodic dissolution potential (E_a) at both temperatures. At 423K, an increase in the corrosion potential (E_(corr)) was observed and the passive region was reduced by the addition of even small amounts of water. The specimen surface structure after anodic polarization measurements changed from a localized tarnish to pitting with an increase in the amount of added water. A random plot of electrochemical impedance spectroscopy (EIS) results showed typical pitting corrosion at an initial stage caused by an autocatalytic process. The water impurity increased the risk of chloride attack at 423K. Corrosion was activated as the added water volume increased. At 473K, no corrosion occurred, regardless of the water concentration.