含错边焊缝缺陷弯管气固两相流冲蚀磨损研究

Erosion wear of gas-solid two-phase flow in a curved pipe with a misaligned welding defect

在天然气输送系统中,当考虑弯管焊接缺陷时,结构特征差异导致的流场变化会使弯管产生不同的冲蚀特性。采用Computational Fluid Dynamics-Discrete Phase Model(CFD-DPM)方法研究不同颗粒参数、弯管导向、缺陷高度及颗粒入射角度下无错边焊缝弯管、外错边焊缝弯管、内错边焊缝弯管的介质流态特征与冲蚀规律。研究结果表明:(1)气体在弯管部位出现二次流动现象,速度分布出现扭曲,其中外错边焊缝弯管速度分布曲线扭曲幅度大,二次流作用效应最明显;(2)流体速度对冲蚀速率的影响最大,两者呈幂指数函数关系,质量流量次之,与冲蚀速率呈线性函数关系,颗粒粒径的影响最小,与冲蚀速率近似呈线性函数关系;(3)外错边焊缝弯管会在弯头处形成第二冲蚀磨损严重区域,而内错边焊缝与无错边焊缝弯管冲蚀效果相似,均只有1个冲蚀严重区域;(4)当流体在竖直管流向一致时,“H-V”导向弯管最大冲蚀速率均大于“V-H”导向弯管,在不同弯管导向下外错边焊缝弯管冲蚀速率最大;(5)弯管最外侧最大磨损位置随着错边高度发生变化,在一定高度下会使弯头内壁形成第二冲蚀磨损严重区域,且错边高度越大,弯头最外侧所受冲蚀速率越大;(6)颗粒的入射角度会影响弯管的冲蚀效应,其影响程度需结合入口直管长度与颗粒运动状态分析。

In a natural gas transmission system,when welding defects at the elbow are considered,the flow field changes caused by the different structural characteristics will lead to different erosion characteristics at the elbow.The Computational Fluid Dynamics-Discrete Phase Model(CFD-DPM)method has been used to study the media flow characteristics and erosion laws at an elbow without an internal defective edge weld,an elbow with an external defective edge weld and an elbow with an internal defective edge weld under the influence of different particle parameters,bend guides,defect heights and particle incidence angles.The results show that:(1)There is a secondary flow phenomenon in the elbow,and the velocity distribution is distorted.The curvature of the velocity distribution curve of the elbow with the external defective edge weld is larger,and the secondary flow effect is the most obvious.(2)The effect of fluid velocity on erosion rate is the largest,having a power exponential function,followed by mass flow rate,which is a linear function,and particle size,which is approximatively a linear function.(3)Severe erosion wear areas are formed in the elbow of the bend with the external edge defect.In contrast,the erosion effect of the internal defective edge weld is similar to that of the bend without a defective edge weld,which both only have one serious erosion area.(4)When the flow direction of the vertical pipe is the same,the maximum erosion rate of the“H-V”guide pipe is greater than that of the“V-H”guide pipe,and the erosion rate of the external misaligned weld pipe is a maximum for different bend guides.(5)The maximum wear position on the outermost side of the elbow changes with the height of the defect side.The inner wall of the bend will form a second area of serious erosion wear at a certain height.The higher the height of the defect side,the greater the erosion rate on the outermost side of the bend.(6)The particle incidence angle will change the erosion effect of the bend,and the influence degree should be analyzed in combination with the length of the inlet straight pipe and the particle motion state.