Comparison of Corrosion Behaviors of Carbon Steel in Simulated Reverse Osmosis Product Water and Seawater

The corrosion morphology and electrochemical characteristics in simulated reverse osmosis (RO) product water and seawater were investigated by wire beam electrode (WBE),electrochemical impedance spectroscopy (EIS) techniques and coupon weight loss method. The results show that the corrosion potential decreased with time both in simulated RO product water and seawater. In the fifteen days experiments in simulated RO product water,the biggest potential difference between micro-cathode and micro-anode on the carbon steel surface was always greater than 110 mV;the positions of cathode/anode areas were basically unchanged,and corrosion always took place on the local anode area during the experiments;the impedance spectrum of carbon steel shows one time constant. In the experiments in simulated seawater,the biggest potential difference between micro-cathode and micro-anode on the surface of carbon steel was smaller than 10 mV after two days immersion;the positions of cathode/anode areas kept changing,leading to uniform corrosion;the corrosion process began to be controlled by diffusion as the appearance of Warburg impedance in the EIS of carbon steel electrodes,which might be aroused by the compact corrosion product on the surface of carbon steel and therefore restrained the further corrosion and reduced the corrosion rate to some extent. The apparent corrosion rate of carbon steel in simulated RO product water was slightly greater than that in simulated seawater. But the actual corrosion rate on the local anode area in simulated RO product water was much more greater than that in simulated seawater due to the smaller actual corrosion area.