Testing of Acrylic Polyurethane-Coated Carbon Steel for Immersion Service Using Electrochemical Impedance Spectroscopy

This study was carried out on acrylic polyurethane coating deposited on carbon steel substrate. Electrochemical impedance spectroscopy (EIS) was used to investigate the interfacial impedance of polyurethane coated carbon steel and examine the effect of primer application. The coating material was applied using air-spray technique and its thickness varied between 35& 150 m. Impedance data were collected using three-electrode cell arrangement while test samples were submerged in aerated 0.5 M NaCl solution at room temperature. A Gamry instrument Reference600 with dedicated EIS300 software served as the Potentiostat for EIS testing of acrylic polyurethane coated carbon steel samples. In order to minimize the external interference, all EIS measurement were carried out in a faraday cage. In the initial stages of testing the coating system proved to have high dielectric properties of the order of giga ohm (G) but this does not persist with time. After three weeks immersion, coating resistance has decreased to lower values and the coating capacitance was of the order of micro-farad; indicative of considerable electrochemical instability. This was for coated samples with and without primer. Determination of the delamination ratio has proved much lower delamination levels (less than 1 %) for coated sheets with primer in comparison to those without primer.