含酸性溶解气的气液两相流管道流致腐蚀模拟

Flow-assisted Corrosion Simulation of Natural Gas Pipeline Flow Containing Sour Dissolved Gas

目的研究天然气输送管道中的酸性溶解气(CO_(2))与水相冲刷作用共同影响下形成的流致腐蚀(FAC)现象。方法基于计算流体力学理论,确定了不同条件下影响流致腐蚀的气液体积分数和壁面剪应力分布情况。结果对于上倾管道,水相主要积聚在管道底部,并且水相的积聚厚度与流速呈反比、与含水率呈正比。当流速小于3 m/s、含水率大于30%时,水相会发生回流现象,即弯管前、后直管段的液体会向弯管处积聚,从而使弯管处积聚水相的厚度大幅度增加。对于下倾管道,水相积聚的位置及与流速和含水率的关系与上倾管道相同,区别在于下倾管道并未出现回流现象。相同条件下,上倾管道的壁面剪切力始终大于下倾管道。当含水率与弯曲角度恒定时,上倾管道的最大剪切力出现在弯管底部,但随着流速的增加,最大壁面剪切力逐渐向弯管后直管段迁移,而下倾管道的最大壁面剪切力出现在弯管的顶部且不随流速的增加而发生变化。当流速和弯曲角度恒定时,上倾管道与下倾管道的最大壁面剪切力规律与含水率恒定的规律相同。当流速与含水率恒定时,弯曲角度对上倾管道壁面剪切力的影响较大,对下倾管道的影响较小;对于上倾管道,随着弯曲角度的增大,最大壁面剪切力的集中位置由弯管底部逐渐向弯管后直管段延伸且遍布管道周身;对于下倾管道,最大壁面剪切力主要集中在弯管及弯管后直管段的顶部,并且随着弯曲角度的增加,数值有所增大而位置不变。结论通过分析积聚水相分布和壁面剪切力集中位置可知,上倾管道两者作用区域近似重合,即会受到严重的流致腐蚀影响;下倾管道两者作用区域并不重合,管道的上部主要受局部冲刷腐蚀的影响,下部主要受局部电化学腐蚀的影响,即下倾管道不会受到流致腐蚀的影响。

To study the flow-assisted corrosion(FAC)phenomenon formed under the combined influence of acid gas(CO2)and water phase in natural gas pipelines.Based on the theory of computational fluid dynamics,the gas/liquid integrals and wall shear stress distributions that affect FAC under different conditions are determined.For upwardly inclined pipelines,the water phase mainly accumulates at the bottom of the pipeline,and the thickness of the water phase is inversely proportional to the flow velocity and proportional to the water content.When the flow velocity is less than 3m/s and the water content is greater than 30%,the water phase will flow back.The liquid in the straight pipeline before and after the elbow will accumulate toward the elbow,which greatly increases the thickness of the water phase accumulated at the elbow.For downwardly inclined pipelines,the location of water phase accumulation and the relationship with the flow velocity and water content are the same as those of upwardly inclined pipelines.The difference is that there is no backflow phenomenon in downwardly inclined pipelines.Under the same conditions,the wall shear stress of the upwardly inclined pipeline is always greater than that of the downwardly inclined pipeline.When the water content and the bending angle are constant,the maximum wall shear stress of the upwardly inclined pipeline appears at the bottom of the elbow,but as the flow velocity increases,the maximum wall shear stress gradually migrates to the straight pipeline after the elbow.The maximum wall shear stress of the downwardly inclined pipeline appears at the top of the elbow and does not change with the increase of the flow velocity.When the flow velocity and the bending angle are constant,the law of the maximum wall shear stress of the upwardly inclined pipeline and the downwardly inclined pipeline is the same as the law of constant water content.When the flow velocity and water content are constant,the bending angle has a greater influence on the wall shear stress of the upwardly inclined pipelines and has a smaller influence on the downwardly inclined pipelines.For upwardly inclined pipelines,with the increase of the bending angle,the concentrated position of the maximum wall shear stress gradually extends from the bottom of the elbow to the straight pipeline after the elbow and spreads all over the pipeline.For downwardly inclined pipelines,the maximum wall shear stress is mainly concentrated on the top of the bend and the straight pipeline after the elbow,and as the bending angle increases,the value increases but the position does not change.By analyzing the distribution of the accumulated water phase and the concentration position of the wall shear stress,it can be known that for the upwardly inclined pipeline,the two action areas approximately overlap,that is,the upwardly inclined pipeline will be severely affected by FAC.For downwardly inclined pipelines,the two action areas do not overlap.The upper part of the pipeline is mainly affected by local erosion and corrosion,and the lower part is mainly affected by local electrochemical corrosion,that is,the down-dip pipeline will not be affected by FAC.