Abstract
The combined use of coatings and cathodic protection (CP) for corrosion protection for submerged steel offshore structures is increasing. The combination of coatings and CP has several advantages for offshore structures: (1) total current demand is reduced, (2) an even current distribution is readily achieved, and (3) polarization to a protective potential is achieved within a few days. A concern for the design of such protection systems for very long design life (30 to 50 years) is the uncertainty in the current demand with progressive coating deterioration. To better quantify the coating deterioration, a mathematical expression incorporating the term "coating half-life" has been introduced. It has been found that coating deterioration data can be fitted to this mathematical expression with the "coating half-life" as the variable. The rate of the progressive coating deterioration resulting in increasing current demand will depend on the coating system chosen. A high performance coating can have a "coating half-life" of 50 years or more. The economics of coated and uncoated structures will be discussed in relation to coating quality, service life, the concept of precoated tubulars, and a model for predicting coating breakdown is proposed.
