陰極 防蝕法이 適用된 塗裝鋼板의 防蝕特性 硏究

Abstract

Cathodic protection and coatings are both engineering disciplines with the primary purpose of mitigating and preventing corrosion. Each process is different: cathodic protection prevents corrosion by introducing electrical currents from external sources to counteract the normal electrochemical corrosion reactions; coatings form a barrier to prevent the flow of corrosion current between the naturally occurring anodes and cathodes or within galvanic couples. So the combination of coatings and cathodic protection provides maximum corrosion protection for immersed steel structures. In this work, anticorrosive properties of painted steel subjected to cathodic protection were studied using EIS (electrochemical impedance spectroscopy), open circuit potential measurement and calculation of electrochemical capacity of sacrificial anode. Exterior observation of the specimens was also conducted after the completion of experiment. Painted steel specimens having various coating thickness (180, 280, 450, 650, 800㎛) were prepared. Thermal cycling tests, which can accelerate coating degradation, were carried out to decrease the test-time duration because immersion test of defect-free specimens requires very long periods. It was shown that the paint system applied on steel substrate has a good compatibility with cathodic protection and painted steel subjected to cathodic protection indicated good anticorrosive property due to cathodic protection mechanism. So, in this case, thick coating is not needed. In case of specimens with defect, anticorrosive property of painted steel subjected to cathodic protection is affected by the defect size than the coating thickness.