Being a resource-poor country, Japan needs oil storage steel tanks to store oil imported from overseas. In general, an electrolyte solution accumulates in bottoms of tanks because the oil contains water, chloride ions, sulfate ions and oxygen. Therefore, corrosion occuring in the inner surfaces of the bottom plates is a serious problem. Presently, the inner surfaces are usually coated with a heavy-duty coating to inhibit the corrosion. Since the heavy-duty coating has exceptional durability, it is often difficult to monitor the aging degradation by a laboratory immersion test, and the long-term degradation behavior is unclear. In a present work, the impedance characteristics of the heavy-duty coating used for a long period is analyzed to develop an evaluation method for the degradation of the heavy-duty coating applied to large steel structures by focusing on the recent studies in terms of the CPE.

Acknowledgement: This research was performed with financial support from Japan Oil, Gas and Metals National Corporation.