Steel Of The Heat Exchanger Corrosion And Protection

With the increasing of the amount of high acid and sulfur petroleum import in China, equipment corrosion problems become more and more serious in refinery and chemical factories. Heat exchanger is widely used in petrochemical industry and becomes as one of the main corrosion equipments. The corrosion always occurred at portion such as the tube-tube sheet, shell, tube, shell cover, tube plate and flange connection, especially at the tube portion. In this work, such measures as the electroplating of pure Ni and Ni-Fe alloys are taken for improving the corrosion resistance of Cr-Mo steel widely used in manufacture of heat exchanger.Ni and Ni/Fe alloy coatings were prepared by using pulse electroplating. The surface morphology and chemical of the as-deposited coatings were characterized by using SEM technique together with EDS. X-ray diffraction method was used to identify the grain size.The anodic polarization curves and electrochemical impedance spectroscopy of the coatings were measured on the PARSTAT2273electrochemical station in3.5wt.%NaCl solution. It indicates that:â‘ . The reverse ratio and the current density can affect surface morphology, resulting in different texture with (111) or (200) or (220) of Ni coatings and the coating with (200) texture exhibits the best corrosion resistance while the coating with (111) texture exhits corrosion resistance in between and the coating with (220) texture exhibits the worst in corrosion resistance.â‘¡. The addition of saccharin, frequency and reverse ratio can affect the grain size, surface morphology and the Fe wt.%, resulting in the different corrosion resistance of the coatings.â‘¢. The Ni and Ni/Fe alloy as electroplated on the Cr-Mo steel are compact and uniform nanocrystalline coatings, which obviously improve the corrosion-resistance as compared to the conventional Cr-Mo steel in3.5wt.%NaCl solution.