Comparative investigation on high-pressure flow accelerated corrosion at gradual contraction and gradual expansion pipes

In current study, the flow accelerated corrosion behaviors of X65 steel gradual contraction and gradual expansion pipes under high-pressure conditions were comparatively investigated by establishing dynamic in situ electrochemical tests under high CO ₂ partial pressure conditions in a loop apparatus. The findings indicate that the corrosion rate is reduced along the flowing direction of gradual contraction pipe. Nevertheless, the corrosion rate firstly descends and subsequently ascends along the flowing direction of gradual expansion pipe, and the lowest corrosion rate is presented in inclination segment close to the straight pipe with large diameter. The corrosion rate at the top wall of gradual contraction pipe is symmetrical to that at the bottom wall, while it is asymmetrically distributed at the top wall and the bottom wall of inclination segment in gradual expansion pipe. The distribution of corrosion rate is correlated with the flow fields at gradual contraction and gradual expansion pipes. Furthermore, the special corrosion rate distribution at inclination segment of gradual expansion pipe is ascribed to the formation of secondary flow and vortexes.