The Study On Corrosion Behavior Of WB36CN1 Steel In Simulated Secondary Circuit Of PWR

In the secondary circuit of PWR,various factors will have a greater impact on pipeline corrosion,and each factor has a different mechanism on the pipeline corrosion process.At present,there is still insufficient understanding about the corrosion behavior of pipeline in PWR secondary circuit.Therefore,it is of great significance for nuclear power industry to explore the corrosion behavior of material in high temperature fluid.This paper explores the effects of alkalizing agent,flow rate,temperature and sodium chloride concentration on the corrosion behavior of WB36CN1 steel in the simulated secondary circuit environment.The effects of various factors on the corrosion rate,corrosion type and corrosion mechanism of WB36CN1 steel were analyzed by electrochemical impedance spectroscopy,polarization curve and electrochemical noise.SEM and XPS were used to characterize the changes of corrosion morphology and corrosion products.At a temperature of 170?and a flow rate of 0.42m/s,it is indicated the effect of different alkalizing agents(Na OH,ETA,NH₃·H₂O,Na₃PO₄)on the corrosion behavior of WB36CN1 steel is different by analysis results.The corrosion rate order is v_corr(Na OH)<v_corr(ETA)<v_corr(NH₃·H₂O)<v_corr(Na₃PO₄)in different medias,and the corrosion inhibition effect of ETA is good,with stable physicochemical properties.At a temperature of 270?and a flow rate of 0.42m/s,as the ETA concentration increases(0ppm,3ppm,6ppm,12ppm,24ppm),the R_tobtained from the EIS becomes larger,the i_corrobtained from the polarization curve becomes smaller,the sample corrosion rate becomes smaller.The reason is that the effect of ETA concentration on the corrosion rate is related to the solution p H.From the XPS and SEM results,it can be seen that the composition of the oxide film does not change with ETA concentration increasing,but the structure of the film becomes denser.At a temperature of 170?and an ETA concentration of 6ppm,as the flow rate increases(0.42m/s,1.05m/s,2.09m/s),the noise resistance R_nand charge transfer resistance R_tbecomes smaller,which indicates that the corrosion rate becomes larger.According to the corrosion morphology and EDS results,as the flow velocity increases,the effect of the fluid on the sample surface increases,the oxide content on the surface decreases.Noise current PSD curve has a constant value in the entire frequency domain,the energy in the EDP is mainly distributed in the high-frequency region,and there are no obvious local corrosion characteristics on the sample surface,which indicate that the corrosion type of WB36CN1 steel is uniformly corrosion.At a flow rate of 0.42m/s and an ETA concentration of 6ppm,as the temperature increases(230?,240?,250?,260?,270?),the charge transfer resistance R_tbecomes smaller,the corrosion rate increases,the sample surface becomes rougher,and corrosion pit appears on the sample surface at 260?and 270?.Which indicates that the density and protective effects of oxide film decreases with increasing temperature.Under the same conditions(270?,0.42m/s,6ppm ETA),as the sodium chloride concentration increases(100?g/L,1mg/L,5mg/L,20mg/L,80mg/L),the number of corrosion pits on the sample surface increases,noise resistance R_ndecreases,the current PSD curve and the energy distribution in the EDP have changed.Which indicates that the corrosion type of WB36CN1 steel has changed from local corrosion with low corrosion rate to uniform corrosion with high corrosion rate.