Electrochemical behaviour of X80 pipeline steel with alumina coating

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 alpha-Al2O3 and gamma-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. gamma-Al2O3 is considered as the main reason for the corrosion resistance degradation of ceramic coating in acidic solution.