Corrosion study of carbon steel protected by a primer, by electrochemical impedance spectroscopy (EIS) in 3% NaCl medium and in a soil simulating solution

The corrosion of underground structures, such as pipelines, depends on soil aggressiveness towards the metals. Two different methods of protection are used: (a) cathodic protection and (b) polymer coatings. The assessment of the degradation of buried structures is not easy because of the complex composition of the soil and its resistivity, and the risk of bacterial corrosion. Corrosion phenomena are generally studied in artificial solutions. The objective of the present paper is to study the protective capacity of coatings on pipeline steel using a "primer" paint exposed to conditions which are simulating the soil (soil simulating solution). The electrochemical behavior of uncoated and coated plates are estimated by means of electrochemical impedance spectroscopy (EIS) in two solutions: a reference media: 3 % NaCl solution; and a "soil simulating solution". Appropriate models for impedance are used to fit the experimental data and extract the parameters which characterize the corrosion process.