Corrosion Behavior Of Stainless Steel In Desulfurization Environment

In recent years,with the strengthening of environmental protection in China and the implementation of relevant national environmental protection policies,the flue gas desulfurization system(FGD)has become a basic facility in thermal power plants and refineries with the aim of reducing SO2 and other acid gas emissions.In the process of flue gas treatment,SO2,HCl,etc.in the flue gas form a highly corrosive acidic condensate with water,causing serious corrosion damage to the desulfurization system equipment.Therefore,it is very important to study the corrosion resistance of FGD system materials in strong acid media,and to guide the selection of FGD system.Aiming at the strong acid corrosion environment of flue gas desulfurization system in thermal power plant,this paper discusses the electrochemical corrosion behavior of 255,316 stainless steel at different concentrations of Cl-,F-,sulfuric acid and hydrochloric acid at 55?;on this basis,The electrochemical corrosion behavior in acidic chloride environment at different temperatures was investigated.In this paper,the corrosion resistance and corrosion law of two stainless steels in different acid corrosive environments are analyzed and compared by electrochemical test methods such as open circuit potential,polarization curve,AC impedance,Mott-Schottky curve and cyclic polarization curve.The paper also studied the mass loss of two kinds of stainless steel after hanging for 21 days in 55? acid chloride by weight loss coupon method.The corrosion morphology of the sample was observed by metallographic and SEM,and the elements of corrosion products were analyzed by energy spectrum.kind.Through the above research,the following conclusions are drawn:(1)The corrosion current density of two stainless steels increases with the increase of Cl-and F-concentrations in the dilute sulfuric acid solution with pH value of 2,55?,the Rct and Eb decrease,and the corrosion resistance decreases;different Cl-255 stainless steel is more resistant to corrosion at F-concentration.(2)255 stainless steel at 55?,0.05mol/L to 1.5mol/L sulfuric acid solution,with the increase of sulfuric acid concentration,corrosion current density increased,Ret value decreased corrosion resistance;when the sulfuric acid concentration reached at 2mol/L,the corrosion resistance is greatly improved.The corrosion resistance of 316 stainless steel decreased with the increase of sulfuric acid concentration;the corrosion resistance of both stainless steels decreased with the increase of hydrochloric acid concentration;255 staiuless steel showed better corrosion resistance in different concentrations of sulfuric acid and hydrochloric acid solution.(3)In the acid chloride solution,as the temperature rises,the corrosion current density of the two stainless steels increases,the Rct value decreases,and the corrosion resistance decreases;compared to the alloy at 20?,high temperature(55? or 40?)The element content has a significant effect on the blunt current density and corrosion current density of the two stainless steels,and the effect on the blunt current density value is significantly smaller.When the scanning potential is about 0.75V,the n-type semiconductor film of the two stainless steels is generated to the p-type.The transformation of the semiconductor film,as the temperature increases,the donor density ND and the acceptor density NA of the two stainless steels increase,and the stability of the passivation film decreases.(4)The Rct and icorr values of 255 and 316 stainless steels in acid chloride solutions at different temperatures show that 255 stainless steel is more resistant to corrosion,and the corrosion rate measured after 21 days of hanging in this solution at 55? shows 316 stainless steel corrosion resistance,better sex.Therefore,the electrochemical corrosion data should be combined with the coupon corrosion weight loss data to reflect the corrosion resistance of stainless steel in some environments.According to the energy spectrum analysis,the content of Cl and O is obviously increased after the corrosion of the sample,and Cl-is the main erosion ion.