Cathodic Protection of Bottom Plates of Above Ground Crude Oil Storage Tanks

摘要

Safety and environmental considerations call for implementation of a reliable Cathodic Protection system to effectively eliminate the soil side corrosion of tank bottom plates. Tank integrity continues to be adversely affected due to existence of soil side corrosion even with Cathodic Protection systems. The protection of these buried structures from external corrosion requires providing efficient Cathodic Protection systems, combined with external coatings. Designing effective Cathodic Protection system for these tank bottoms is a real challenge due to the large and complex geometries involved and the proximity of the anodes to the tank bottom. Special considerations such as unprotected areas, with preferential corrosion, occurring at the heat-affected zones (HAZ) of the base metal near welds, unprotected areas in contact with soil and normal coating breakdown overtime, require careful corrosion mitigation Cathodic Protection system. This paper discusses the role of passive barrier (primary coating) in prevention of soil side corrosion of tank bottoms. The paper presents the details and benefits of the soil side corrosion prevention measures provided at five locations. The installed Cathodic Protection Systems are effectively protecting 26 numbers of tank bottoms at three locations for 5-15 years. Various anode configurations have also been discussed to examine the limitations of the conventional Cathodic Protection systems.