Effect of pH value on the galvanic corrosion behaviour of Q235-304L couples in sulfur environment

The galvanic behaviour of a Q235-304L couple was studied by the electrochemical method and immersion test. Surface morphologies of the samples were observed by SEM after rust cleaning. The results showed that both the cathodic and anodic processes of 304 L were controlled by the electrochemical activation step in all the three solutions with pH values of 4.0, 7.0 and 13.3, and both the cathodic and anodic processes of Q235 in the solutions with pH values of 4.0 and 7.0 were controlled by the electrochemical step, while the anodic process of Q235 exhibited an apparent characteristics of diffusion control when the pH value of the solution was 13.3. As the area ratio increases, the galvanic effect increased in all the three solutions accordingly, but the correlation between the galvanic current and the cathode/anode area ratio did not accord to the rule of logarithm. With the elevation of pH value, the galvanic corrosion rate of Q235 would greatly decrease, but the change of the galvanic effect was not so obvious.