10. Cathodic and Anodic Protection

The cost of corrosion in the U.S. in 1986 was estimated to be close to $180 billion. Furthermore, estimates show that $70 billion worth of corrosion loss could have been prevented in 1986 by applying modern corrosion control technology. This section discusses the corrosion of metal in contact with moist soil or water, and the tendency of some metals to corrode preferentially with respect to other metals when located in the same environmental conditions. The use of a superimposed current to prevent or reduce the rate of corrosion by making the entire metal surface the cathode of an electrochemical cell and providing a separate anode is called cathodic protection. This section discusses the mechanisms of cathodic protection and the types of cathodic protection systems available for corrosion control. The different types of cathodic interferences are covered along with the safety considerations. A glossary of cathodic protection terms is also included. Sections 1200-1600 discuss specific applications of cathodic protection systems. The best cathodic protection system in the world is of no value if not properly checked and maintained. See Section 1800 on maintenance for details. Contents

This paper presents the most significant information on the corrosion of steel structures, which can be a source of environmental pollution. It has been recognised that early detection of the hazard and application of appropriate protection are the basic conditions of elimination of pollution as a result of corrosion processes. Basic information has been given on principles of cathodic protection, scope of application of the technique and its practical aspects. It has been stated that this highly effective anticorrosion technology can guarantee trouble-free operation of objects such as underground and underwater tanks, steel pipeline storage, or transporting oil products and aggressive chemical media.