4.18 - Principles of Cathodic Protection

Abstract

Cathodic protection is unique among all the methods of corrosion control in that, if required, it is able to stop corrosion completely, but it remains within the choice of the operator to accept a lesser, but quantifiable, level of protection. Manifestly, it is an important and versatile technique. In principle, cathodic protection can be applied to all the so-called engineering metals. In practice, it is most commonly used to protect ferrous materials and predominantly carbon steel. It is possible to apply cathodic protection in most aqueous corrosive environments, although its use is largely restricted to natural, near-neutral environments (soils, sands, and waters, each with air access). Thus, although the general principles outlined here apply to virtually all metals in aqueous environments, it is appropriate that the emphasis, and the illustrations, relate to steel in aerated natural environments. The text seeks to show why cathodic protection is apparently so restricted in its scope of application despite its apparent versatility. Nevertheless, having recognized the restricted scope, it is important to emphasize that the number and criticality of the structures to which cathodic protection is applied is very high indeed.