Electrochemical behaviour of X80 pipeline steel with alumina coating

Abstract

X80 pipeline steel was firstly aluminised at a relative low temperature then treated by a microarc oxidation process. Electrochemical behaviour of X80 pipeline steel before and after the combined treatment was evaluated by electrochemical tests in different solution. Results show that ceramics coating composed of α-Al₂O₃ and γ-Al₂O₃ can be obtained on the surface of X80 pipeline steel by the combined treatment. In neutral 3·5% NaCl solution and alkaline solution (pH = 9), X80 pipeline steel with ceramics coating shows a higher corrosion potential and a lower corrosion current density than pure steel and the X80 pipeline steel treated by one-step aluminising. However, aluminising coating presents a better corrosion protection for X80 pipeline steel than that of ceramic coating in acidic solution with pH = 5. γ-Al₂O₃ is considered as the main reason for the corrosion resistance degradation of ceramic coating in acidic solution.