Corrosion Law And Protective Coating Of X65 Pipeline Steel Under Multi-factor Coupling Action

X65 steel is often used as pipeline steel in the process of natural gas transportation,and its service life is 8-12 years.However,because the transportation of natural gas generally adopts the wet gas transportation technology,there will be a certain amount of water vapor,corrosive gas,corrosive ions and microorganisms in the pipeline,which will cause serious corrosion of pipeline steel.The weight of coupling corrosion factors in the corrosion process is an important prerequisite for the design of pipeline steel composition modification and surface protection.In this paper,a high-pressure reactor was used to simulate the actual working conditions of X65 pipeline steel,and the corrosion law of X65 pipeline steel under the coupling action of multiple factors was studied,and the leading factors affecting the corrosion and the corresponding corrosion mechanism were revealed.The Ni-Zn/CuO coating was designed and prepared according to the corrosion condition of X65 pipeline steel.The effects of constant current,Ni content and CuO NPS content on the morphology,corrosion resistance and hardness of the Ni-Zn/CuO coating were studied.The antibacterial properties and corrosion resistance of the Ni-Zn/CuO coating were characterized.Under the condition of pressure of 6MPa and water content of 1.1 ‰,CO₂ accelerated the corrosion,and the corrosion product was FeCO₃.The greater the partial pressure of CO₂,the more serious the corrosion was.Under the synergistic action of CO₂ and Cl',Cl' promotes the dissolution of CO₂ and corrosion reaction.When Cl-content is 5 g/L,the corrosion rate of X65 pipeline steel increases by about 30%.Under the coupling action of CO₂,Cl-and SRB(sulfate reducing bacteria),CO₂,as the electron donor of SRB growth,leads to the corrosion reaction,which increases the corrosion rate of X65 pipeline steel by 70?90%.Cl-promotes the electron flow in the corrosive liquid and catalyzes the whole corrosion process.The corrosion rate of X65 pipeline steel increases by 22%.Compared with the synergistic effect,the corrosion rate of X65 pipeline steel increases by about 28%.Under the coupling effect,the leading corrosion factors of X65 pipeline steel are CO₂>SRB>Cl-.Under the conditions of constant current of 800mA,Ni content of 0.6mol/L and CuO NPS of 0.01g/L,Ni-Zn/CuO coating with uniform surface distribution,complete microstructure,good corrosion resistance and high hardness was prepared.The results of antibacterial test showed that the CuO NPS in the coating had the ability to inactivate SRB,and the antibacterial rate of the coating was about 60%.The Ni-Zn/CuO coating exhibits high corrosion resistance under both synergistic and coupling effects.The protective efficiency is about 54%under the synergistic action of CO₂ and Cl-,and 58%under the coupling action of CO₂,Cl-and SRB.The CuO NPs in the coating can inhibit the metabolism of SRB at the pressure of 6MPa,and the NiO₃ formed after corrosion of the coating can reduce the corrosion rate of X65 pipeline steel.