Effects of Cr content and environmental factors on FAC rate of carbon steels

Combined effects of Cr content and environmental factors, pH and dissolved oxygen concentration, on removal rate of carbon steels due to flow accelerated corrosion have been examined by experiments. The effects of environmental factors on FAC rate have been attempted to interpret based on oxide solubility, which has been precisely evaluated by separate experiments and numerical estimations. pH dependency of the FAC rate has been found to be directly related to solubility of magnetite. Cr content holds a strong impact on the FAC rate regardless of pH values from 6.84 to 10.4. Addition of 1% Cr to a carbon steel reduces the FAC rate by one order of magnitude under the environmental conditions, where magnetite forms. Addition of oxygen up to 1200ppb changes the oxide from magnetite to hematite, resulting in significant improvement in corrosion resistance. Oxide film characteristics, e.g. compositional distributions and types of oxide compound, have been also examined and their correlation to the FAC rate has been discussed.