Research On Corrosion Behavior Of S2205 Stainless Steel In Denitrifier Solution

S2205 stainless steel is widely used in more demanding working conditions because of its two-phase structure of ferrite and austenite,excellent mechanical properties and corrosion resistance.The circulating fluidized bed boiler?CFB?widely uses the COA denitration process.The denitration solution delivery pipeline uses relatively corrosion-resistant S2205 stainless steel,which has leaked many times during operation,threatening production safety.The main component of the denitration agent is Na Cl O₂,which has strong oxidation and contains certain Na Cl impurities.In this paper,the research work on the following aspects of S2205 stainless steel in the denitrifying agent solution corrosion environment was carried out,and the corrosion mechanism of S2205 stainless steel in the denitrifying agent solution was discussed.This article aims at the corrosion of S2205 stainless steel in the denitration agent solution,macroscopic analysis is used to observe the failed pipe fittings,metallographic microscope is used to observe the polished and eroded metals,the grid counting method is used to count the ferrite phase and the austenite phase,and the electron scanning microscope?SEM?is used to observe the pit and the microscopic morphology of the corrosion products,X-ray diffraction?XRD?is used to analysis the passivation film.Using electrochemical methods such as potentiodynamic polarization,AC impedance,Mott-Schottky curve,potentiostatic polarization to study the corrosion differences of S2205 and S316L stainless steel in the denitrifier solution and the single factor conditions such as temperature,roughness,Na Cl O₂concentration,etc.on corrosion resistance,and orthogonal experiments were designed to explore the optimal level and optimal combination.This experiment also studied the different passivation time and the effect on the corrosion resistance in different media after passivation,the effect of different roughness,denitration agent concentration and Cl O₂^-concentration on metastable pitting corrosion was studied by slow dynamic potential scanning.The main conclusions drawn are as follows:The failure mode of the denitration solution delivery pipeline S2205 stainless steel is severe pitting corrosion,the metallographic structure is ferrite with twin austenite structure,the local area preferentially corrodes ferrite,the proportion of ferrite phase is normal,and corrosion products are characterized by loose pores.It is not ideal for self-passivation of S2205 stainless steel in denitrifying agent.Compared with S316L stainless steel,S2205 stainless steel has lower I_corrand higher corrosion resistance than S316L stainless steel.As the roughness decreases,the corrosion resistance increases,the temperature increases,the O₂solubility decreases,the passivation film repair ability decreases,the Cl^-thermal motion strengthens,and corrosion accelerates.When the concentration of the denitration agent is 6%,it may be a critical value of the concentration,and the corrosion is the fastest.Temperature has the greatest influence on the corrosion rate,roughness has the least influence,and the best combination with the strongest corrosion resistance is:25?-400#-3%.Increasing the concentration of denitrifying agent promotes the transformation of pitting corrosion from metastable pitting to stable pitting,and promotes the nucleation and growth of metastable pitting.The smoother the metal surface,promote the occurrence of metastable pitting corrosion,inhibit metastable pitting nucleation,and promote the growth of metastable pitting.The introduction of Cl O₂^-,its strong oxidizability promotes the dissolution of high-valent oxides in the passivation film,the corrosion resistance is reduced,metastable pitting is not easy to occur but it is easier to transform into stable pitting,the introduction of Cl O₂^-suppresses the metastable The pitting nucleation has little effect on the growth rate of metastable pitting corrosion.Later,with the increase of Cl O₂^-concentration,the number of metastable pitting nucleation increases slightly,the growth rate does not change significantly.On the one hand,the potential increases,it inhibits metastable pitting nucleation,on the other hand,it promotes the growth of metastable pitting.