冲蚀作用下CO2分压对集输气管线内腐蚀的影响规律——以大庆油田徐深6集气站集输管线为例

我国部分油气田集输管线中CO₂与水含量较高，同时由于提高输运流速，集输管道CO₂腐蚀日趋严重，掌握流场诱导下CO₂腐蚀速率的变化规律对腐蚀防护与定期检测具有重要意义。为此，以大庆油田徐深6集气站一集输天然气管线为分析对象，首先基于Norsok腐蚀模型预测CO₂分压对其内腐蚀速率的影响，再应用计算流体动力学方法（CFD）对管道内流场进行分析，并结合现场的内腐蚀测厚数据，得出冲蚀作用下CO₂分压对集输天然气管线内腐蚀的影响规律：集输天然气管线内，湍流作用在内流道剧烈变化区域（弯头、T形管处），湍动能升至最大75 m²/s²，对CO₂局部腐蚀具有明显的促进作用；流体介质的流型与流速会对管道内壁的CO₂均匀腐蚀产生较强促进作用；管道内壁在CO₂分压重腐蚀区间内（0.02~0.20 MPa），CO₂的腐蚀程度随CO₂分压的增大呈线性加剧，随后其最大腐蚀速率保持在0.75 mm/a，并趋于平缓，而最小腐蚀速率保持在0.62 mm/a，稳中有升。研究结果可作为预测集输管线重点部位运行寿命的参考依据，使得管道腐蚀防护与定期检测更为精确省时。

Effect of CO2 partial pressure on the corrosion in flow and transport lines under the erosion action:A case study from the Xushen-6 Gas Station in the Daqing Oil Field

The content of CO₂ and water is rather high in the gathering and transportation lines in some oil and gas fields. Moreover, the operating pressure needs to be enhanced at the gathering and transmission stations to improve the flow rate in the lines. This leads to the increasingly serious result of the CO₂ dominated corrosion in the lines. Therefore, to master the changing law of CO₂ dominated corrosion induced by flow field is of great significance to corrosion prevention & control and regular inspection. In view of this, a case study was made of a pipeline at the Xushen 6 Gas Station in the Daqing Oil Field. First, based on the Norsok corrosion model, the effect of CO₂ partial pressure was predicted on the corrosion rate at the inner side wall of this pipeline. Then, the computational fluid dynamics (CFD) module was used to analyze the flow field in the pipeline; and in combination with the pipe wall thickness, it is disclosed that how the partial CO₂ pressure influences the internal corrosion in a pipeline under the erosion action. In a pipe line, erosion accelerates the partial CO₂ corrosion distinctly in the specific parts such as tees or elbows with a violent change of turbulent flow, the kinetic energy of which increases to the maximum value of 75 m²/s²; flow patterns and velocity exacerbate the CO₂ corrosion evenly at the inner wall of the pipe. With the CO₂ partial pressure increasing, the average CO₂ corrosion rate sharply rises in the pipe line; but when the CO₂ content reaches a saturation value in a gas water transport line, the CO₂ corrosion will tend towards stability and the expected CO₂ corrosion rate rises on the whole. During the severe CO₂ corrosion interval (0.02 ~ 0.20 MPa), the CO₂ corrosion level enlarges linearly with the increase of CO₂ partial pressure, subsequently, the maximum of the corrosion rate holds a value of 0.75 mm/year and the minimum of the corrosion rate is kept at 0.62 mm/year. This study will provide a reference for predicting the life span of the key parts of a pipeline and also help improve the efficiency of corrosion prevention & control and regular inspection of pipelines.