Study of the effects of hydrogen on the pitting processes of X70 carbon steel with SECM

The effects of hydrogen on the pitting processes of X70 carbon steel in neutral chloride ions containing solution are investigated by using the scanning electrochemical microscope (SECM) technique. The tip of the SECM monitors the Fe²⁺ ions produced by the specimen during its anodic dissolution processes, thus the initiation and the propagation of the pitting processes can be observed. Pitting is much more easily observed after the specimen has been pre-charged with hydrogen, for the oxidation of the hydrogen in the X70 decreases the pH value at the X70/solution interface, which retards the formation of an oxide film and subsequently promotes the pitting processes. The observed behaviour is further verified by the decrease of the solution's pH.