Use of the Polarization Technique To Study Corrosion in Aqueous Ammonia Systems

Abstract

Abstract Severe internal corrosion of certain carbon steel storage tanks in Honolulu which contained aqueous ammonia solutions, 25 percent by weight ammonia, prompted investigation of this unusual corrosion problem in the laboratory by the polarization technique. Interpretation of polarization curves obtained with steel electrodes exposed to different environments indicated that oxygen is the major factor in the corrosion of steel by aqueous ammonia solutions. However, corrosion of carbon steel can occur in both oxygen-containing and oxygen-depleted solutions. Corrosion of carbon steel in oxygen-containing solutions is caused by activation through removal of oxygen, or by the presence of large areas of mill scale on carbon steel in oxygen-depleted solutions. Anodic polarization curves revealed that carbon steel in both oxygen-containing and oxygen-depleted ammonia solutions can be made passive. A stable passive potential or state was observed for carbon steel in the oxygen-containing system, but not in the oxygen-depleted system. Laboratory data for these environments indicated that anodic or cathodic protection can be applied to control the corrosion. 2.3.5, 4.3.3