Study On Erosion Law Of X65 Friction Stud Welded Joints In Seawater

The problem of seawater erosion has a greater impact on the safety of oil and gas gathering and transmission.X65 pipeline steel has good tensile strength,welding performance and other advantages,and is widely used in subsea oil and gas pipelines.However,the complex marine environment makes the subsea pipelines need regular maintenance and repair.Friction stud welding is a relatively mature repair method for submarine pipelines,the quality of welded joints is an important guarantee of the long cycle of safe service of submarine pipelines,so the development of X65 friction stud welded joints（FRSW）in seawater corrosion law research for the safety of marine engineering is particularly important,this paper intends to X65 friction stud welded joints in 3.5%Na Cl sand-containing simulated seawater solution to carry out dynamic and static erosion and corrosion behavior study.Main Research the content is as follows:（1）Study on the effect of flow velocity on the erosion of FRSW in simulated seawaterA dynamic erosion-corrosion coupling experimental system was built to simulate the real working conditions,and the erosion-corrosion coupling law of FRSW with different flow rates（0.2 m/s,0.4 m/s and 0.6m/s）was dynamically studied.After 168h of immersion,the corrosion resistance decreases with the increase in flow rate,and the polarization resistance reaches a maximum of 369.78Ω·cm²at 0.2 m/s.The static study of the corrosion pattern of FRSW shows that the corrosion resistance increases with the increase in immersion time,and the polarization resistance reaches a maximum of 206.58Ω·cm²at 168h.The static and dynamic corrosion products are mainly composed ofα-Fe OOH,γ-Fe OOH,Fe₃O₄and Fe₂O₃,and the corrosion product film formed at 0.2m/s flow rate is thicker,and there are scouring grooves on the joint surface at 0.6 m/s.Compared with the static corrosion conditions,simulating the real working conditions of dynamic erosion-corrosion coupling conditions better reflect the marine service environment.（2）Study of sea sand mass fraction on the erosion of FRSW in simulated seawaterThe dynamic erosion-corrosion coupling law of FRSW with different sea sand mass fractions（2wt%,3wt%and 4wt%）at 0.4m/s was investigated,and the results showed that:the change of sea sand mass fraction under simulated working conditions has a large effect on the polarization resistance of the joint,and the corrosion resistance of the joint increases and then decreases with the increase of sea sand mass fraction after 1h immersion in simulated real working conditions,and the polarization resistance is 118.63Ω·cm²at 2wt%,214.54Ω·cm²at 3wt%and 96.97Ω·cm²at 4wt%.The polarization resistance was lower than that at 3wt%because the mass transfer rate between ions in the solution was slower for a short period of time when the mass fraction of sea sand was4wt%.After soaking for 168 h,the joint corrosion resistance decreased with the increase of the sea sand mass fraction,and the polarization resistance reached the minimum value of 101.07Ω·cm²at 4wt%and the maximum value of 163.83Ω·cm²at 2wt%,with a difference of about1.62 times.（3）Simulation mechanism analysis of seawater erosion of welded jointsSimulation and experimental means,considering the impact of the secondary current distribution between the various regions of the joint,the study of static conditions between the FRSW areas of the electric coupling corrosion,the results show that:the highest corrosion resistance in the weld area,the joint is expected to have a remaining life of at least65 years;consider the flow field distribution,secondary current distribution and the impact of particle tracking,the study of FRSW in the simulation of seawater dynamic erosion-corrosion The results show that the erosion rate increases with the increase of the flow rate,and the dynamic erosion-corrosion experimental results are consistent with the results presented in the simulation.The experimental results of dynamic erosion-corrosion are consistent with the simulated results.