Study On The Corrosion Resistance Of Stainless Steels In FGD System Of Thermal Power Plant

Limestone gypsum wet flue gas desulfurization has become the dominant technology indomestic for several of advantages, included a wide accommodate of coal quality, largetreatment capacity of flue gas, high desulfurization efficiency, long stable operation cycle,mature technology and so on. Slurry react with waste flue gas in countercurrent with CaCO3as absorbent in limestone-gypsum wet flue gas desulfurization. There is a combination ofgas, liquid and solid in absorber system. Serious corrosion will be occured in the inner walland the equipment of the absorption tower if it has an unreasonable select of materials.Compared to most organic and inorganic anti-corrosion materials, the use of corrosionresistant metal materials have a high investment cost, however, if has a reasonable select ofmaterial, the maintenance time and the long-term repair costs will be reduced.In this paper, stainless steel316L,317LMN,2205and255has been selected. The effectof the concentration of Cl-and SO₄^2-has been studied on the corrosion behavior of stainlesssteel. In order to research the corrosion resistance of stainless steel material, the test materialwas hanged in the slurry tank of the dynamic simulation device. Then, the loss of the fourstainless steel material was measured and their morphology was observed. In addition, inthree electrode system, with one of four stainless steel as the working electrode respectively,the corrosion current density, corrosion potential, breakdown potential, electrochemicalimpedance and other electrochemical parameters of stainless steel has been measured by Tafelmethod and AC impedance measurement.The test of dynamic simulation was performed in the concentration of2.2g/L and22g/Lrespectively. When the experiment of hanging the test material was complished, the surface ofthe metal was observed by optical microscope, the microscopic structure of four kinds ofmaterials showed that the surface condition of duplex stainless steel255,2205was better thanthe austenitic stainless steel316L,317LMN. The weight-loss sequence of the four kinds ofthe material was316L>317LMN>2205>255, therefore, the sequence of the corrosionresistance of stainless steel material in the slurry is255>2205>317LMN>316L.The electrochemical experiments results showed that: with the increase of Cl-concentration in the solution, the corrosion resistance of four stainless steel dropped as thecorrosion current density of four stainless steel increased gradually, the breakdown potentialand electrochemical impedance decreased when pH value was5.5, temperature was50℃.Further more, the pH value was5.5, temperature was50℃, and the concentration of chloride ion was10g/L fixed, with the increase of concentration of sulfate ions, corrosioncurrent density of four kinds of stainless steel decreases, the breakdown potential rise,electrochemical impedance values increased. The results revealed that: if the solution wasadded with sulfate ion, the corrosion of stainless steel material will be inhibited. The corrosionresistance of stainless steel316L,317LMN,2205, and255was consistent with experimentsof dynamic simulation.