Corrosion Behavior and Corrosion Prediction Model of X65 Steel under Flowing Conditions in Oxygen-Containing Systems

Abstract

The medium of X65 steel injection sea pipe contains dissolved oxygen, causing severe corrosion inside the pipeline. Regarding this issue, based on the basic data of the on-site water injection subsea pipeline, considering the effects of flow rate, temperature, dissolved oxygen and Cl- concentration on the corrosion behavior of X65 steel, 9 sets of orthogonal tests were designed, and the weight loss test and corrosion product characterization were carried out by using high temperature autoclave, scanning electron microscope and X-ray diffractometer. Combined with multiple linear regression method, a corrosion prediction model was established. Results showed that the order of the degree of influence of the four influencing factors on corrosion rate from large to small was: dissolved oxygen concentration > temperature > flow rate> Cl- concentration, and dissolved oxygen concentration was the main control factor of corrosion. The corrosion rate increased with the increases of flow rate, temperature, dissolved oxygen concentration and Cl- concentration. The characterization results of corrosion products showed that the corrosion products were mainly Fe3O4 and Fe2O3. Considering the influence of the above four factors, a corrosion prediction model was established based on seven groups of uniform corrosion rate values. Furthermore, the remaining two groups of uniform corrosion rate values were used to validate the corrosion prediction model, and the maximum error was 8.9%, indicating that the corrosion rate prediction model was accurate.

Keywords

• water injection subsea pipeline; oxygen-containing system; high-temperature autoclave test; corrosion behavior; corrosion prediction model