Effects of AC interference on the corrosion behavior of X70 steel in seawater and acidic solutions

The effect of alternating current (AC) and pH on the corrosion behavior of X70 steel was studied by electro-chemical measurements and morphological analysis. With increasing pH value, the effects of AC on the cathodic reaction of X70 steel were different. At pH = 3, the hydrogen evolution reaction enhanced with increasing AC current density. When the pH moved to the neutral, the formed OH- and corrosion product inhibited the hy-drogen evolution reaction and promoted the oxygen reduction reaction. The enhancement of AC on the corrosion rate of X70 steel in solutions with pH <= 4 was much less than that in solutions with pH ranging from 5 to 7. Moreover, as the pH value increased from 3 to 7, the corrosion current density of X70 steel increased after an initial decrease with AC. The corrosion products formed at different pH values possessed different structures and affected the corrosion resistance of the X70 steel. The application of AC modified the surface corrosion mor-phology of X70 steel. With increasing AC current density, the corrosion form of X70 steel changed from uniform to pitting. With decreasing pH value, pitting further developed, indicating an increased corrosion sensitivity to AC.