Effects of Sulfuric Acid Concentration and Alloying Elements on the Corrosion Resistance of Cu-bearing low Alloy Steels

During the process of sulfur dioxide removal, flue gas desulfurization equipment provides a serious internal corrosion environment in creating sulfuric acid dew point corrosion. Therefore, the utilities must use the excellent corrosion resistance of steel desulfurization facilities in the atmosphere. Until now, the trend in developing anti-sulfuric acid steels was essentially the addition of Cu, in order to improve the corrosion resistance. The experimental alloy used in this study is Fe-0.03C-1.0Mn-0.3Si-0.15Ni-0.31Cu alloys to which Ru, Zn and Ta were added. In order to investigate the effect of $H_2SO_4$ concentration and the alloying elements, chemical and electrochemical corrosion tests were performed. In a low concentration of $H_2SO_4$ solution, the major factor affecting the corrosion rate of low alloy steels was the exchange current density for $H^+/H_2$ reaction, while in a high concentration of $H_2SO_4$ solution, the major factors were the thin and dense passive film and resulting passivation behavior. The alloying elements reducing the exchange current density in low concentration of $H_2SO_4$, and the alloying elements decreasing the passive current density in high concentration of $H_2SO_4$, together play an important role in determining the corrosion rate of Cu-bearing low alloy steels in a wide range of $H_2SO_4$ solution.