Steel products such as pipe, storage tanks, and utility or communication equipment housings which are buried before use are subjected to long-term exposure to underground corrosion. To prevent possible failure due to corrosion damage, buried steel structures are protected against corrosion. Present protective systems may be classified either as active, in which applied voltages are used to maintain the steel structure cathodic in relation to its environment, or passive, in which barrier coatings are applied to the steel to interrupt the electrical corrosion path. Passive systems, such as extruded plastic coatings or hot melts and tapes, can and do give satisfactory protection if properly applied. These are, however, prone to premature failure because of factors such as poor coating application, inadequate chemical or physical properties, and damage during transit and/or installation in the field. Active protection systems are commonly used in conjunction with passive systems to provide corrosion protection for steel areas exposed by localized coating failure. Whether or not active systems are used, the goal is to minimize the area of steel exposed to corrosive conditions in underground service.
