L51178 Cathodic Protection Monitoring for Offshore Pipelines

In the search for new sources of fossil fuels, the offshore gas and oil fields continue to be among the most promising areas. Corrosion protection for offshore pipelines is provided by a combination of coatings and cathodic protection. While this combination is similar to that for buried onshore pipelines, several characteristics of offshore environments favor effectiveness and lessen degradation of corrosion protection compared to onshore service. Coatings are not exposed to alternate wet/dry conditions or soil stresses. Effective cathodic protection is favored by both the relatively low resistance of seawater and marine soils and the uniformity of environment. The former enhances the range of influence of a protective anode, and the latter enhances desirable current distribution. These favorable characteristics are opposed by the generally more corrosive nature of marine environments and presence of concrete coatings for buoyancy control. The objective of this study was to determine techniques to evaluate the cathodic protection status of existing and future offshore pipelines; to make a preliminary analysis of the probable success of each technique; and to recommend a program to develop and demonstrate feasibility of one or more of the techniques. The program was to survey existing information with emphasis on personal contact with those pipeline companies and cathodic protection companies engaged in the protection of offshore pipelines.