Numerical Simulation Of Burnthrough During In-service Welding Of Oil And Gas Pipelines

Compared with the traditional pipeline repair methods, the transportation of medium inpipeline is not stopped during the process of the in-service welding repair. Therefore, thisrepair method can generate enormous economic benefits. Because of the potential danger ofin-service welding research by experimental methods, the thesis analyzes the influence of sizeof molten pool on burnthrough and the mechanism of burnthrough during in-service weldingby ANSYS.The result shows that when the temperature field remains constant and the internalpressure in the pipe is low, the value of radial deformation of the node, which has the highesttemperature on inner surface of the pipe, is negative for one given molten pool. With theincrease of pressure, the value of radial deformation of the node becomes positive and theradial deflection increases linearly. But when the pressure exceeds a certain value, the linearchange vanishes and the radial defomation increases seriously. For different size of moltenpool, when the penetration and pressure remain constant, with the decrease of the size ofwidth and length of molten pool, instability temperature increases. When the penetration andthe highest temperature of inner surface of the pipe remain the same, buckling pressureincreases with the decrease of the size of width and length of molten pool. When the lengthand width of molten pool remain the same, with the decrease of the remain wall thickness ofpipeline, the capability of resisting pressure must be weakened. Compared with the moltenpool which has the big length, big width and small penetration, the capability of resistingpressure of the molten pool which has the small length, small width and big penetration maybe stronger. The size of molten pool can be reduced by adopting small welding parameters,small diameter welding electrode. When the inner surface of pipeline is under high pressure, the node, which has thehighest temperature on inner surface of the pipe, undertakes compressive stress and the node,which locates on maximum penetration, undertakes tensile stress. When the tensile stresssurpasses the yield stress on this node, burnthrough will take place. The hoop stress canpromote the happen of burnthrough.