Effects of Fe₃O₄ Film, Dissolved Oxygen and Water Velocity on Corrosion and Rest Potential of Carbon Steel in High Purity Water at Room Temperature

Abstract

Effects of preautoclaved Fe₃O₄ film, dissolved oxygen and water velocity on corrosion and rest potential of carbon steel were examined in high purity water at room temperature. Although the preautoclaved carbon steel with defective film suffered slight pitting in static water saturated with air, corrosion of carbon steel with the preautoclaved Fe₃O₄ film was prevented in any high purity water. Rest potential of the preautoclaved carbon steel was similar to that of sintered Fe₃O₄ electrode. Release rate of iron corrosion product from Fe₃O₄ powder was less than that from Fe powder. In the case of a polished carbon steel, the corrosion rate and the rest potential were strongly controlled by water quality conditions. In static water, the corrosion rate increased with increasing dissolved oxygen levels, and also the rest potential slightly shifted towards noble value but never exceeded -0.5V (vs. SCE). In flowing water, however, the corrosion rate decreased by the addition of oxygen, and then the rest potential remarkably shifted towards noble value near 0V (vs. SCE). Carbon steel can be passivated in flowing water saturated with air at velocity higher than 0.1cm/sec. Pitting in the preautoclaved carbon steel with defective film was prevented with this passivation.