Effect of Velocity on the Under-Deposit Corrosion and Its Corrosion Mechanism

The causes of perforation of an oil pipeline were analyzed by macro and micro morphology observation, chemical composition analysis, and the corrosion mechanism was also studied by indoor weight loss test and FLUENT software simulation. The results show that the perforation of pipeline was mainly the result of the combination of erosion and under-scale corrosion. When the flow rate of the medium was increased from 0 to 2.5 m/s, the deposition rate of the scale layer on the surface of samples first increased and then tended to be gentle. The shear stress of the fluid caused uneven accumulation of scale layers and severe perforation, which was caused by Cl^- and oxygen in the environment. The FLUENT software simulation results show that the areas where the scale corrosion was more likely to occur in actual production were the areas where the pipe was bent and where the pipe diameter was reduced. This was because in these areas, the formed scale layer was peeled off by relatively high shear force and carried away by the fluid, and the medium was more likely to react with the matrix through the loose product layer, so the corrosion under the scale was severe. In addition, at the exit position of the pipe, a fine turbulent flow occurred on the inner arc side, which tended to cause the accumulation and uneven coverage of scale layers, and uneven scales could form a concentration cell and increased corrosion.