CORROSION STUDY OF CARBON-STEEL PROTECTED BY A PRIMER, BY ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY (EIS) IN 3-PERCENT 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 prot ection are used: (a) cathodic protection and (b) polymer coatings. The assessment of the degradation of buried structures is not easy becaus e 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 stu dy the protective capacity of coatings on pipeline steel using a ''pri mer'' paint exposed to conditions which are simulating the soil (soil simulating solution). The electrochemical behavior of uncoated and coa ted plates are estimated by means of electrochemical impedance spectro scopy (EIS) in two solutions: a reference media: 3 % NaCl solution; an d a ''soil simulating solution''. Appropriate models for impedance are used to fit the experimental data and extract the parameters which ch aracterize the corrosion process.