Abstract
Steel is commonly used for marine structures. However steel is easily corroded under marine environment, therefore various protection methods against steel corrosion have been developed. Among them, paint coating and cathodic protection are often used together. When cathodic protection is applied to defective paint-coated steel, cathodic protection may lead to paint degradation around defects. Namely, paint coating is blistered or disbonded by the generation and accumulation of hydroxide ions induced by cathodic reaction. Cathodic protection can control corrosion reaction under submerged zone. However in tidal zone, there is a dry period in which paint-coated steel is exposed in air. At that time cathodic protection cannot work. So paint degradation in tidal zone may lead to severe corrosion. Based on the above backgrounds, the following items were investigated in the present study; (1) investigation of influence of defect existence on paint degradation on paint-coated steel with cathodic protection, (2) investigation of influence of paint type, paint thickness and current density on paint degradation on defective paint-coated steel with cathodic protection, (3) clarification of paint degradation and corrosion on defective paint-coated steel with cathodic protection under tidal zone. Experimental results obtained in this study indicated that the paint degradation and severe corrosion around defects might be occurred due to cathodic protection but could be controlled by using proper paint conditions.
