Evaluation of the corrosion resistance of thermal sprayed aluminum coatings in sulfidric acid

The production of H2S acid and cyanide during the catalytic cracking of petroleum is the main cause of major corrosion events taking place in refineries. In order to improve the reliability of the materials, thermal sprayed coating is used to protect equipment from corrosion. This paper describes the performance of thermal sprayed aluminum coatings deposited by electric arc (ASP) on carbon steel and then exposed to either a wet H2S saturated acid or alkaline environment. The acid environment consisted of a NACE TM 0284 solution whereas the alkaline environment consisted of either 2M (NH4OH) + 2M((NH4)(2)SO4) + 100 ppm Cl- or 10M (NH4OH), Tests were performed using Electrochemical Impedance Spectroscopy (EIS) and Linear Resistance Polarization (LPR) techniques. Optic Microscopy images were obtained prior to and following the electrochemical tests. The results are discussed in order to evaluate the protectiveness against corrosion provided by the thermal sprayed aluminum layer.