Electrochemical behavior of a fusion bonded epoxy coating with linear defects/carbon steel X70 system in 3.5% NaCl solution

The electrochemical behavior of a fusion bonded epoxy (FBE) coating with linear defects/carbon steel X70 system in 3.5% NaCl solution was studied by electrochemical impedance spectroscopy (EIS) technique. The defects were made on samples at right angle by scribing the sample through the paint down to the bare metal to form a 20 mm×20 mm cross. Experimental results show that corrosion process can be divided into three stages. In the initial stage of eroding, the electrochemical behavior is similar to that of bare steel. In the interim stage, corrosive outgrowth accumulates in the interior of linear defects. It makes pH of solution in the interior of linear defects fall down and causes the coating bonded joint rupture. In the final stage, EIS data show that along the seams, the FBE coating peels off steel substrate. EIS data had been interpreted and discussed in terms of the time dependence of electrical (paint coating) and electrochemical (steel substrate) parameters. The parameters were associated with interracial processes describing deterioration of the carbon steel/fusion bonded epoxy coating with linear defects system.