Corrosion of Lead by Alternating Current

Abstract

Abstract From laboratory tests, it appears that corrosion of buried, lead-sheathed cables by alternating current is due to current leakage through breaks in the insulating coating. Even though the current flow in the lead sheathing may be small, it becomes concentrated, i.e., its density increases considerably at small openings through which the current is grounded into the soil. In tests in which direct current was superimposed on alternating current flowing to lead electrodes immersed in tap water, the corrosion of the electrode acting as anode was increased; corrosion of the cathode was decreased. Lead may also be cathodically protected by connecting it with a less noble metal, such as Fe, Zn or Mg. In the case of Mg, when connected so that it conducts the current rectification occurs which results in increased corrosion of the lead. The morphology of corrosion of lead by alternating current is characterized according to whether the anions present form soluble lead compounds (nitrate or acetate, for example) or insoluble products (sulfate or carbonate).