FUNDAMENTAL STUDY ON ELECTROCHEMICAL PROPERTIES OF MACROCELL CORROSION BETWEEN ADJACENT PAINT COATING DEFECTS

Abstract

 For the painted steel structures exposed to highly corrosive environments, especially where under the air-borne sea salt deposition, most of the localized corrosion initiates from coating flaws and defects. These corrosion cases would often progress with the mutual interaction between adjacent defects, because of the occurrence of the electrical short circuit around the multiple coating defects due to the stagnated rainwater or dew. This study focused on those regions in steel structure where the rainwater accumulated, and wetdry cycles repeated caused by dew. The objective is to investigate the electrochemical properties of corrosion between adjacent coating defects during the initial stage. Therefore, the model specimens embedded with a plurality of electrodes were fabricated to simulate coating defects, and the time-dependent macrocell currents were monitored between the electrodes. Based on the test results, an estimation method of the corrosion current density was proposed by investigating the electrochemical properties of the three coating defects in the water stagnated environment. Additionally, for the cyclic wet-dry environment, it was clear that the corrosion occurred in small-area defect would be easier to progress than that of a large-area defect.