Unveiling the inhibition of high-pressure CO2 flow accelerated corrosion at gradual contraction and gradual expansion tubings

The different inhibition behavior of imidazoline quaternary ammonium salt for high-pressure CO ₂ flow accelerated corrosion of carbon steel gradual contraction and gradual expansion tubings was unveiled combing high pressure dynamic in situ electrochemical methods and microstructure characteristics analysis. It is manifested that there is no noticeable inhibition effect in high CO ₂ partial pressure environments at extremely low inhibitor concentration. At low inhibitor concentration, the polarization resistance and inhibition efficiency increase firstly and then decrease along the flowing direction of gradual contraction tubing. However, the polarization resistance generally drops along the gradual expansion tubing. As the inhibitor concentration of the corrosion inhibitor is further increased, the polarization resistance and inhibition efficiency are reduced in a whole along the gradual contraction tubing. Nevertheless, the polarization resistance is raised, followed by a fall along the flowing direction of gradual expansion tubing. The inhibition effect at the top and the bottom of gradual contraction tubing exhibits symmetry while it is asymmetrical at the top and the bottom of inclination section in gradual expansion tubing. The distinct inhibition effect at different inhibitor concentration is relevant to flow characteristics of fluid at gradual contraction tubing and gradual expansion tubing. The findings could provide valuable guidance for the protection of flow accelerated corrosion at gradual contraction tubing and gradual expansion tubing under high CO ₂ partial pressure conditions.