冲蚀作用下CO_2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

Effect of CO_2 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

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75m2/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0.75mm/a,并趋于平缓,而最小腐蚀速率保持在0.62mm/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。

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 iqow 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 COz corrosion distinctly in the specific parts such as tees or elbows with a violent change o{ 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 sharp- ly rises in the pipe line; but when the C~ 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.