Research On First-principles Calculations And CO₂Corrosion Resistance Of Rare Earth Element Doped Cr13Steel

Carbon dioxide corrosion is a common type of corrosion in petrochemical industry，oil pipelineor casing pipe and other equipment will be causing serious corrosion if carbon dioxide gasdissolved in water or crude oil. Cr13stainless steel is a very potential corrosion material inpetroleum chemical industry for its low price and good comprehensive performance. Cr13stainlesssteel has some fatal flaws, such as uniform corrosion at high temperature, pitting corrosion atmedium temperature, sulfide stress cracking(SSC) at low temperature. Adding proper amount ofrare earth elements in Cr13stainless steel will improve the corrosion resistance against carbondioxide.In this thesis, the effects of rare earth element Ce in Cr13steel about corrosion resistanceagainst carbon dioxide had been systematically studied. Setting up six kinds of absorptionconsidering that the CO2molecules on Fe(100) surface adsorption mode. The variation ofadsorption energy after Ce doped Cr13stainless steel had been calculated by the first principlesmethod, the effect of Ce in Cr13steel about corrosion resistance against carbon dioxide had beenanalyzed from the micro aspect. Cr13stainless steel doped with different amount of Ce had beenrefined using plasma arc furnace. The phase and microstructure of experiment steels had been testedby means of metallographic microscope and scanning electron microscope, the effect of Ce on themicrostructure of Cr13stainless steel had been analyzed. For analyzing the effects of Ce in Cr13steel about corrosion resistance of carbon dioxide, the electrochemical impedance spectroscopy andpotentiodynamic polarization curve of experiment steels in3.5%NaCl solution and Daqing oilproduction plant six Poly produced liquid within saturated carbon dioxide gas had been tested byelectrochemical workstation.The adsorption energy calculation shows that the variation of adsorption energy before andafter doping revealing that the absorption energy increases after Ce doped Cr13steel, decreases thestability of adsorption structure, enhances the corrosion resistance against carbon dioxide. Thecorrosion resistance against carbon dioxide is not increases with the content of Ce, The absorptionenergy of adsorption structure has a maximum value, the stability of adsorption structure is minimal,the corrosion resistance against carbon dioxide is maximal, when the content of Ce is0.1%(wt%).The metallographic microscope and scanning electron microscope observation shows that themicrostructure of Cr13is improved by the addition of reasonable content of Ce. With the increaseof Ce content, the grain size of ferrite in matrix is refined, uniform, and equally distributed. The size and number of carbides are decreased without segregation of alloy elements. The optimalmicrostructure can be obtained for0.1%(wt%) Ce. The grain is coarsening and inhomogeneous forfurther raising Ce content, and the segregation of alloy elements generated.Electrochemical studies shows that the corrosion resistance of carbon dioxide for Cr13steel isgreatly improved by adding appropriate amount of Ce. When the content of Ce is0.1%(wt%), thepassive region of Cr13steel is the widest, which indicates that the corrosion resistance of carbondioxide is the best. The passive region’s width decreases with the increasing content of Ce and thecorrosion resistance decreases. The corrosion resistance of experiment steel in produced fluid isbetter than3.5%NaCl solution.