Numerical study of fillet weld leg height of sleeve repair welding for in-service pipeline

This paper presents a mechanical calculation and numerical simulation of the fillet weld of sleeve repair.The mechanical analysis based on the yield criteria is performed to obtain the minimum value of the fillet weld leg height to ensure the strength and loadbearing capacity of the weld. Within the framework of numerical simulation,the parameters of double ellipsoid heat source are determined by fitting method and the simulated molten pool morphology agrees well with the practical weld. Finite element models with various weld leg height are performed to predict the distribution and magnitude of the deformation and stress. The simulation takes into account thermal,metallurgical and mechanical factors,and the maximum value of the fillet weld leg height is obtained based on the magnitude of the deformation and stress.The mechanical calculation and numerical simulation results show that 1.2-2 times wall thickness is an optimal range of fillet weld leg height. And reasonable parameters of sleeve repair for in-service welding are provided for engineering field,which can improve the service life of the weld and production efficiency.     

微缺陷对在役焊接接头力学性能的影响

为了从原子层次揭示裂纹、空位等微缺陷对在役焊接接头力学性能的影响,从而得到焊接接头中最易失效的区域,本文采用焊接模拟软件SYSWELD对在役焊接过程进行模拟,计算熔池周围的温度场和应力场分布,然后利用LAMMPS软件建立含微缺陷的结构模型,以在役焊接过程中熔池下方区域的瞬时温度、应力状态作为计算条件,研究其在服役环境下的力学性能及微缺陷积累、扩展的动态演化机理.结果表明:在役焊接烧穿是一个宏观、微观结合的多层次过程;焊接电弧经过时,烧穿失稳更易发生在熔深最大处后方;熔池下方的各微区中,熔合线附近力学性能较差,在焊接热和应力的作用下最先失效;管壁材料烧穿时经历了微缺陷的形核、积累及扩展,整个失效过程伴随着空位、微裂纹的形成和扩展;空位、裂纹等微缺陷显著降低了结构的强度,在应力集中的作用下沿缺陷处起裂,严重破坏了结构的稳定性,大大加速了失效进程.