Mesoscopic transformation at initial corrosion stage of 20# steel in aqueous solution under gas–liquid two-phase stratified flow condition

This study aims to investigate the initial corrosion behavior in aqueous solution of 20# seamless steel under (CO₂/aqueous solution) gas–liquid two-phase stratified flow conditions.

The initial corrosion behavior was studied through the weight loss methods, scanning electron microscopy with energy-dispersive x-ray spectroscopy and x-ray diffraction.

The corrosion rate of 20# steel obviously increases with the increasing gas pressure at different corrosion time when the CO₂ pressure is less than 0.11 MPa, and the increase of corrosion rate tends to be steady when the pressure exceeds 0.11 MPa. With the increase of CO₂ pressure, the corrosion products changed from flocculent to acicular, granular and scaly. A four-stage model for the growth of the corrosion product layer was proposed, namely, the diffusion reaction stage, the local film formation stage, the complete film formation stage and the densification stage of the product film.

A four-stage model for the growth of the corrosion product layer on the pipe wall surface under this condition was proposed, namely, the diffusion reaction stage, the local film formation stage, the complete film formation stage and the densification stage of the product film. The growing process and densification mechanism of corrosion products layer were discussed.