4.21 - Practical Application of Cathodic Protection

Abstract

In principle, cathodic protection can be used for a variety of applications where a metal is buried, immersed, or encased in an aqueous solution of an electrolyte, which can range from soils, relatively pure water, seawater, and dilute solutions of acids to concrete. Whether the method is applicable will depend on many factors and, in particular, economics; cathodic protection of steel immersed in a highly acidic solution is theoretically feasible but is generally too costly to be practicable. It should be emphasized that as the method is electrochemical, both the structure to be protected and the anode used for protection must be in both metallic and electrolytic contact. Cathodic protection cannot therefore be applied for controlling atmospheric corrosion, since it is not feasible to immerse an anode in a thin condensed film of moisture or in droplets of rain water. Further, cathodic protection to the external surfaces of a pipeline will not provide corrosion protection to the internal surfaces. This section deals exclusively with the practical application of cathodic protection principally using the impressed-current cathodic protection. The application of cathodic protection using galvanic (or galvanic) anodes of aluminum, zinc, and magnesium, which themselves corrode preferentially to the material being protected and do not require an external (or impressed) current source, is considered separately.