Prediction And Safety Evaluation Of Welding Seam Formation Of X70 Pipeline Welded In Service

Pipeline transportation is an efficient,low-cost,low-loss,and environmentally friendly mode of transportation.It is also the main mode of transportation for oil and gas.However,up until now,the accumulated service time of pipelines in China has been relatively long,and pipeline damage is quite severe.In order to ensure the normal operation of pipelines and ensure economic benefits,in-service welding technology will play an increasingly important role.This article uses a combination of experimental research,numerical simulation,and theoretical analysis to study the forming simulation and safety evaluation of in-service welding seams of X70 steel.In order to solve the problem that the geometric shape of the weld seam involved in the safety evaluation of in-service welding of natural gas pipelines is difficult to obtain,a three-dimensional dynamic model of the forming of in-service welding seams of natural gas pipelines was established through Fluent software as the platform.The influence of arc pressure,droplet transition,electromagnetic force,and free deformation of the molten pool were comprehensively considered,and the program development of energy equation,momentum equation,and mass equation source terms was carried out using the C language.The influence law of welding current and pipe wall heat dissipation coefficient on the temperature and flow fields of the molten pool and the geometric parameters of the weld seam was analyzed.The results show that the established model can reflect the dynamic evolution process of the temperature and flow fields of the droplets falling and mixing with the molten pool to form the weld seam.At the same time,in order to improve modeling efficiency and simplify operation processes,a parameterized finite element modeling plugin for thermal coupling in-service welding of natural gas pipelines was developed based on Abaqus software.The rapid and automatic establishment of a parameterized finite element model was realized,and the establishment of geometric models,material and section property settings,mesh partitioning,analysis step establishment,weld seam element life and death control,and boundary condition imposition were completed quickly and automatically.This significantly reduces the workload of finite element simulation for in-service welding of pipelines and improves modeling efficiency.Finally,a BP neural network was used to predict the remaining strength and radial deformation peak value of pipelines during in-service welding,and the relative error curve shows that the accuracy of the neural network is relatively high.