CO_(2)和H_(2)S对镍基合金028点蚀敏感性及点蚀生长动力学的影响

Effects of CO_(2) and H_(2)S on Pitting Sensitivity and Pitting Growth Kinetics of Nickel-based Alloy 028

目的探明CO_(2)和H_(2)S对镍基合金028钝化膜性能和点蚀敏感性的影响。方法采用循环动电位极化(CPP)、电化学阻抗谱(EIS)、莫特-肖特基(M-S)等测试方法,研究Cl-环境、CO_(2)-Cl-环境和H_(2)S-Cl-环境中镍基合金028的钝化膜性能。通过制备一维人工凹坑电极模拟点蚀坑的稳态生长,采用向负向电位扫描法,研究镍基合金028在局部点蚀环境中的金属溶解动力学,明确CO_(2)和H_(2)S对点蚀生长动力学的影响。结果CO_(2)和H_(2)S都会使镍基合金028钝化膜性能变差,而H_(2)S的影响更为显著,具体表现为:在H_(2)S-Cl-环境中具有更高的钝化电流密度jp、更低的点蚀电位Eb和再钝化电位Erp。H_(2)S-Cl-环境中的钝化膜电阻Rf、电荷转移电阻Rt和钝化膜厚度均低于CO_(2)-Cl-环境中的,此外,钝化膜在H_(2)S-Cl-环境中具有更高的点缺陷密度。在最大点蚀坑溶解电流密度jdiss,max相同的条件下,H_(2)S-Cl-环境中点蚀稳态生长所需的驱动力Emax明显低于CO_(2)-Cl-环境中的;在相同Emax下,H_(2)S-Cl-环境中的jdiss,max高于CO_(2)-Cl-环境中的。结论CO_(2)和H_(2)S通过增加钝化膜溶解速率、降低钝化膜电阻和增加点缺陷密度,不同程度地增加了镍基合金028的点蚀敏感性,而H_(2)S更容易造成钝化膜损伤。在点蚀稳态生长阶段,镍基合金028点蚀的稳态生长遵循塔菲尔规律,相比于CO_(2),H_(2)S更容易促进点蚀从亚稳态向稳态发展,并且在H_(2)S环境中具有更高的点蚀生长稳定性。

In the development process of sour oil and gas fields,the presence of corrosive substances such as CO_(2),H_(2)S and Cl–poses a major threat to the service safety of underground pipes,and also puts higher requirements for the service performance of materials.Nickel-based alloys are widely used in highly sulfuric acid oil and gas fields due to their excellent corrosion resistance.Despite this,the protective properties of surface films can be seriously affected in harsh corrosive environments.Local damage to the surface film can induce the initiation and development of pitting corrosion,and ultimately leading to material failure.Therefore,local corrosion dominated by pitting corrosion will be the biggest corrosion problem faced by nickel-based alloys.In this study,nickel-based alloy 028 was examined as the research object.The effects of surface passivation films and pitting steady-state growth on the pitting corrosion performance of nickel-based alloy 028 were considered comprehensively.The passivation film properties and metal dissolution kinetics of nickel-based alloy 028 in CO_(2) and H_(2)S environments were studied by in-situ electrochemical test and one-dimensional artificial pit electrode technology.Additionally,the effects of CO_(2) and H_(2)S on pitting sensitivity and pitting growth kinetics of nickel-based alloy 028 were discussed.The work aims to investigate the effects of CO_(2) and H_(2)S on the passivation film properties and pitting sensitivity of nickel-based alloy 028.Cyclic potentiodynamic polarization test(CPP),electrochemical impedance spectroscopy test(EIS),and Mott-Schottky test(M-S)were adopted to study the passivation film properties of nickel-based alloy 028 in the Cl–environment,the CO_(2)-Cl-environment and the H_(2)S-Cl-environment.The steady-state growth of pitting was simulated by one-dimensional artificial pit electrode,and the metal dissolution kinetics of nickel-based alloy 028 in the local pitting corrosion environment was studied by downward potential scan.The effects of CO_(2) and H_(2)S on the pitting growth kinetics of nickel-based alloy 028 were clarified.Both CO_(2) and H_(2)S would worsen the stability of nickel-based alloy 028 passivation films,and the effect of H_(2)S was more significant,which was manifested in higher passivation current density(jp),lower pitting potential(Eb)and repassivation potential(Erp)in the H_(2)S-Cl-environment.The passivation film resistance(Rf),charge transfer resistance(Rt)and passivation film thickness in the H_(2)S-Cl–environment were lower than those in the CO_(2)-Cl-environment,and the passivation film had a higher point defect density in the H_(2)S-Cl-environment.Under the same condition of the maximum pit dissolution current density(jdiss,max),the presence of CO_(2) and H_(2)S would reduce the threshold value(Emax)of nickel-based alloy 028 to achieve steady growth of pitting corrosion,while the Emax of the H_(2)S-Cl-environment would be lower.At the same pitting driving force(Emax),the H_(2)S-Cl-environment had a higher maximum pit dissolution current density(jdiss,max)than in the CO_(2)-Cl-environment.In the pitting initiation stage without stable pitting corrosion,the addition of CO_(2) and H_(2)S reduces the protective performance of the passivation film,enhances the nucleation ability of the pitting corrosion,and ultimately increases pitting susceptibility,among which the role of H_(2)S is more obvious.In the steady-state growth stage of pitting corrosion,the steady-state growth of nickel-based alloy 028 pitting corrosion follows the Tafel's law.When the maximum pit dissolution current density is same,the threshold value for steady-state pitting corrosion of nickel-based alloy 028 in the H_(2)S-Cl-environment is lower than that in the CO_(2)-Cl-environment,which is easier to promote the development of metastable pitting to steady-state pitting corrosion.Under the same driving force of pitting growth,H_(2)S can cause a higher maximum pit dissolution current density of nickel-based alloy 028 than CO_(2),so nickel-based alloy 028 has higher pitting growth stability in the H_(2)S-Cl-environment,which in turn reduces the pitting resistance of nickel-based alloy 028.