Effect of Velocity on the Under-Deposit Corrosion and Its Corrosion Mechanism
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摘要: 采用宏、微观形貌观察，化学成分分析等方法对输油管线穿孔原因进行了分析，并通过室内失重试验和FLUENT软件模拟研究了腐蚀机理。结果表明：管道穿孔主要是冲刷和垢下腐蚀共同作用的结果；当介质流速从0增加到2.5 m/s时，试样表面的垢层沉积率先增大后趋于平缓；流体的切应力导致垢层堆积不均，穿孔严重，这是由Cl-和氧气在环境中引起的。通过FLUENT软件模拟找到实际生产中较易发生垢下腐蚀的区域——在管道弯曲处及管径减小处，这是因为在这些区域，已形成的腐蚀垢层被较高的剪切力剥离并被流体带走，介质更容易透过疏松的产物层与基体反应，因此垢下腐蚀严重，此外，在管道出口处，内弧侧发生明显细湍流，容易造成水垢堆积，使垢层覆盖不均，构成浓差电池，加剧腐蚀。Abstract: 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.
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Keywords:
- flow rate /
- under-deposit corrosion /
- scale layer morphology /
- pitting
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