Evaluation of paint systems on A36 steel through electrochemical techniques: Corrosion resistance of container tanks

In this research work, the corrosion resistance of plate steel used in the construction of cylindrical container tanks of seawater was evaluated. These container tanks are usually used for fighting fires on the coast of the Arequipa-Peru region, where the shortage of drinking water is significant. The study was based on immersion tests of 2 × 2 cm square test plates in 3.5 wt.% NaCl solution. Five paint systems were studied, varying only in the primers: P1-860 (inorganic zinc silicate); P1-ZC (epoxy-zinchromate); P1-850 (organic rich in zinc); P1-600 (reinforced inorganic zinc) and P1-SP1000 (high solids epoxy-amine). All systems consisted of a primer coat, an epoxy middle coat and a polyurethane topcoat. To characterize the behaviour of each system, the electrochemical impedance spectroscopy (EIS) was mostly used. In addition, the scanning Kelvin probe (SKP) and scanning electro­che­mical microscopy (SECM) were used as local techniques. The first three paint systems (P1-860, P1-ZC and P1-850) showed an invariable value of impedance modulus up to 3360 h of immersion in NaCl. The last two paint systems (P1-600 and P1-SP1000) showed a decrease in impedance modulus by more than one order of magnitude. This research provides a clear contribution of results obtained by global electrochemical techniques such as EIS, estab­lishing excellent tools for monitoring the performance of organic anticorrosive coatings