| The main form of power source is coal-fired power gerneration in our country. It is imminent to control coal-fired power release air pollutant and protect the environment. Now the country has issued the "on strengthen fired power plant sulfur dioxide pollution control work notice "and" thermal power plant air pollutant emission standards ". The country has also mandatory provisions that the thermal power plants must use flue gas desulfurization device (FGD). So far, most of our power plants in China are using limestone-gypsum wet desulphurization to control SO2 emissions from coal-fired power plants. The equipment in the FGD system will be corroded seriously because the flue gas has SO2, HF, HCl, NOx and other corrosive substances. The main corrosion form are pitting and crevice corrosion. So the selection of material in FGD system has become an important research task.This paper analyzed the corrosive environment at the outlet of the FGD system.Regarding 317LMN, Al-6XN, alloy 625 as the main studing object.Using static coupon experiments、atomic absorption spectroscopy experiments and electrochemical experiments to study the corrosion behavior of alloy in FGD outlet systems. As well as analyzing and evaluating the strength of the corrosion resistance of the three materials. Using electrochemical (Tafel polarization curves and AC impedance) experimental studied the corrosion mechanism and corrosion laws of metallic materials in corrosive environments. Considering the corrosion behavior of three metallic materials in the different pH, Cl", F’ solution according to the analysis on the environmental. As well as obtaining the pitting corrosion different between the three kinds materials in the Cl’conditions.A separate study of the Al-6XN corrosion behavior was conducted under the synergistic of Cl-, SO42-. The atomic absorption spectroscopy experiments and coupon experiment drew the following conclusions:Three kinds materials’resistance corrosion size relations was alloy625>Al-6XN>317LMN in the two kinds of gas simulation condensate solution. By metallographic microscope figure,317LMN and Al-6XN obviously appeared pitting corrosion in the pH=1、Cl=20g/L、F-=lg/L、Mg2+=0.5g/L, Ca2+=0.0563 g/L and other com-ponents’gas simulation condensate liquid. Alloy 625 also had a certain degree of corrosion. But it had no obviously pitting corrosion.The degree of corrosion of metallic materials in the pH=2、Cl-=10g/L、F-=0.5g/L、Mg2+=0.5g/L、Ca2+=0.0563 g/L and other components’ gas simulation condensate liquid was lower than in the pH=1 simulated solution. In the two simulated solution, Fe、Ni、Cr elements of three kinds metal hanging slice were dissolved. Three kinds element’s leaching total amount relations were 317LMN> Al-6XN> alloy 625. These results showed corrosion resistance of the alloy 625 was the best.The electrochemical test drew the following conclusion:With the decreased of pH and Cl-, F-concentration increased, the corrosion current density of three kinds materials increased. However Rp value decreased. Meanwhile the pitting potential of three electrode materials constantly shifted negatively with the increasing of Cl-, F- concentration. It was prone to occur pitting corrosion. It showed that SO42- could inhibit the pitting corrosion of metal material through analyzing the electrochemical parameters in the same Cl-concentration and different SO42- concentrations. While the higher SO42- concentration was, the stronger the effect of inhibition the pitting corrosion was. The inhibition effect of SO42- may be due to the competitive adsorption of ion. Material surface may mainly occur overall corrosion when SO42- concentration was very high. |
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