CO2和H2S对镍基合金028点蚀敏感性及点蚀生长动力学的影响OA北大核心CSTPCD

In the development process of sour oil and gas fields,the presence of corrosive substances such as CO2,H2S 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 CO2 and H2S environments were studied by in-situ electrochemical test and one-dimensional artificial pit electrode technology.Additionally,the effects of CO2 and H2S on pitting sensitivity and pitting growth kinetics of nickel-based alloy 028 were discussed. The work aims to investigate the effects of CO2 and H2S 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 CO2-Cl-environment and the H2S-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 CO2 and H2S on the pitting growth kinetics of nickel-based alloy 028 were clarified.Both CO2 and H2S would worsen the stability of nickel-based alloy 028 passivation films,and the effect of H2S was more significant,which was manifested in higher passivation current density (jp),lower pitting potential (Eb) and repassivation potential (Erp) in the H2S-Cl-environment.The passivation film resistance (Rf),charge transfer resistance (Rt) and passivation film thickness in the H2S-Cl-environment were lower than those in the CO2-Cl-environment,and the passivation film had a higher point defect density in the H2S-Cl-environment.Under the same condition of the maximum pit dissolution current density (jdiss,max),the presence of CO2 and H2S would reduce the threshold value (Emax) of nickel-based alloy 028 to achieve steady growth of pitting corrosion,while the Emax of the H2S-Cl-environment would be lower.At the same pitting driving force (Emax),the H2S-Cl-environment had a higher maximum pit dissolution current density (jdiss,max) than in the CO2-Cl-environment. In the pitting initiation stage without stable pitting corrosion,the addition of CO2 and H2S 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 H2S 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 H2S-Cl-environment is lower than that in the CO2-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,H2S can cause a higher maximum pit dissolution current density of nickel-based alloy 028 than CO2,so nickel-based alloy 028 has higher pitting growth stability in the H2S-Cl-environment,which in turn reduces the pitting resistance of nickel-based alloy 028.