Corrosion Characteristics of Downstream Metal Material of Boiler System in Solution of By-product Ammonium Bisulfate from SCR Denitrification

Abstract: The corrosion behavior of the boiler tail material which is made of carbon steel and stainless steel in solutions of ammonium bisulfate (ABS) and H2SO4 respectively was studied by means of mass loss measurement and potentiodynamic polarization curve as well as SEM/EDS and XPS. The results showed that: stainless steel has better corrosion resistance to ABS, and with the increase of ABS solution concentration, corrosion becomes more intensive. The corrosion products consist of Fe2O3, FeOOH, Fe3O4, iron sulfate and a small amount of iron carbon oxide. The corrosion process of carbon steel and stainless steel is similar in the solutions with the same concentration of ABS and sulfuric acid. It can be concluded that ABS has stronger corrosivity. The corrosion mechanism is that hydrogen depolarization first may occur during the corrosion of carbon steel, and then generate hydrogen. As the acid consumption, as well as the effect of dissolved oxygen in the solution, the oxygen depolarization corrosion will happen on metal surface, Fe2+ is then further oxidized to Fe3+, produces a series of secondary reaction, to generate iron oxide and sulfate, etc.