Relation between Surface Appearance and Corrosion Depth Distribution of Carbon Steel under Atmospheric Corrosion Environment

Degradation due to atmospheric corrosion is an important problem for steel structures such as bridges. In order to maintain steel structures safely over a long period of time, there is a need for a low-cost and easy-to-use method to evaluate corrosion degradation. In this study, corrosion morphology under atmospheric corrosion environment was focused on. The relation between the surface appearance and the distribution of corrosion depth of the carbon steel specimen after atmospheric exposure was analyzed, and the prediction of corrosion morphology under rust layers by surface observation of steel specimens was examined. It was found that deeply-corroded areas were possible to be located within the dark brown regions in the rusted specimen after the atmospheric exposure. As the exposure period increased, the correspondence between the dark brown regions in the rusted specimen and deeply-corroded areas became clearer. Since the corrosion progressed more locally as the exposure period increased, it is considered that the surface appearance of the rusted specimen showed traces of the deeply-corroded areas.