Electrochemical investigation on mutual interaction effects between multiple adjacent coating defects in steel structures

Abstract For painted steel structures, coatings can deteriorate due to factors like ultraviolet radiation, water accumulation, and salt exposure, thereby leading to corrosion. This kind of corrosion tends to originate not only from isolated coating defects but also from multiple adjacent defects. Previous research by the author’s group demonstrated that the presence of adjacent defects can amplify corrosion on steel substrates. However, the precise interaction mechanism between these adjacent defects remains unclear. In this study, circular defects of varying sizes were created on coated steel electrodes to simulate coating defects. The macrocell currents between these defects were measured in an immersion environment using a zero-resistance ammeter (ZRA). The results indicated that when environmental conditions lead to stable anodic and cathodic regions at the defect sites, the anodic corrosion rate increased, while corrosion at the cathodic site was inhibited due to cathodic protection from the anode. Furthermore, when the electrode at a smaller defect became cathodic, the increased protection current density may even prevent any corrosion at that site.