Research On Pitting Corrosion Behavior Of 2205DSS In Sulfurand Chlorine-containing Solutions

As China's demand for crude oil continues to increase,many of our country's refineries purchase crude oil with high sulfur and acid content from foreign,which makes the corrosion problem of oil refinery plant very serious.Especially,the upper plate tower and some volatile lines of atmospheric tower are corroded at low temperature,which belongs to HCl-H2S-H2O environment medium corrosion,and the corrosion situation is the most serious and complex.2205DSS has good corrosion resistance,many refinery equipment has adopted good corrosion resistance of 2205DSS,but in recent years,some reports on the problem of corrosion failure of 2205DSS,the corrosion resistance of 2205 dual-phase stainless steel at home and abroad is also increasing year by year,but on the corrosion mechanism of HCl-H2S-H2O environment media in the refinery is rarely reported.In this thesis,the corrosion resistance of 2205DSS in the typical environment of atmospheric tower was research by using the potentiodynamic cyclic polarization curve method,electrochemical impedance spectroscopy method,potentiostatic polarization method,Mott-Schottky,scanning electron microscope morphology analysis,X-ray photoelectron spectroscopy method and so on.The results are as follows:(1)With the increase of test temperature,the resistance to pit corrosion of 2205DSS decreases,the critical corrosion temperature of 2205DSS in 3.5%NaCl solution with pH=7 is 59.1?.(2)The greater the Cl-concentration,the worse the pitting resistance of 2205DSS.When the concentration of Cl-reaches 0.4 mol/L,there is no passivation potential in 2205DSS,which indicates that the pitting corrosion of the broken passivated film cannot be recovered,and the sensitivity to pitting corrosion is enhanced.(3)With Na2S concentration increasing,the resistance to pit corrosion and re-passivation ability of 2205DSS die away and then strengthen.Mott-Schottky results show that when the Na2S concentration is lower than 0.22 g/L,the impurity density in the 2205DSS passivation film is relatively large,and the structure inside the passivation film is not uniform.With the increase of Na2S concentration,the aggressive anions in the test solution are dominated by S2-,the corrosion of the solution decreases,and the internal impurity density of the passivation film is reduced,and the internal structure of the passivation film is uniform.(4)Increasing the test pH,Eb of 2205DSS becomes larger,and the pitting sensitivity die away,the nucleation resistance and re-passivation capacity of 2205DSS increased.Mott-Schottky results show that with the increase of pH value,both the density and the band potential of the donator decrease,indicating that the defect area of the outer passivation film of 2205 dual-phase stainless steel decreases,and the corrosion resistance of 2205DSS is better.XPS results show that the metal will selectively dissolve at different pH values,the passivation film is mainly composed of oxides and hydroxides of both Fe and Cr.When pH=9 and 11,FeS exists.