Corrosion Potentials and Their Change Rules for Ferrous Metals in Natural Seawater

The corrosion potentials of ferrous metals such as iron castings, carbon steels, low alloy steels in Qingdao and Zhoushan seawater for 120 days were measured by a self-made multi-channel potential data acquisition device. The change rules of corrosion potentials and steady corrosion potentials for these materials in the natural seawater were analyzed. The results show that the corrosion potentials of ferrous metals in seawater followed a process of "decreased-increased-steady". The initial potentials were higher than the steady potentials. The steady corrosion potentials of ferrous metals with more alloying elements were higher, and with less alloying elements were lower. Grain refining and purification for steels had less influence on the steady corrosion potential. The numerical values of steady corrosion potentials in Qingdao seawater were different from those in Zhoushan seawater for such ferrous metals, but the order of steady corrosion potentials was similar in these two kinds of seawater.