Numerical Simulation On Welding Residual Stresses Of The X80 Pipeline Steel

Large-caliber& high-voltage transmission and the use of high-level pipeline steel is an inevitable trend in the international pipeline project development .Through the use of high-grade pipeline steel which could increase pressure on transportation (natural gas), enhancing transmission efficiency and thinning pipeline wall thickness, reducing consumption of the corresponding welding materials , thereby saving the investment on the pipelines building. However, the higher level of pipeline steel intensity, the greater the residual stresses, it is necessary to understand the size and distribution of the residual stresses and thus to control residual stress.X80 Pipeline is the controlled rolling and cold-alloy steel. It has the high strength and good anti-ductile fracture performance, and it is the high-grade steel of increasingly extensive application in transmitting gas pipeline. The topics which study the X80 pipeline steel is based on metal physics, mechanics and welding heat transfer and other basic theory. Simulating the X80 pipeline steel butt joint welding thermal and stress field by the means of a combination with the physics experiments and numerical simulation.Applicating SYSWELD project finite element analysis software and using a dual ellipsoid heat source model, taking into account the the non-linear relationship of heat physical properties and temperature , as well as the impact to temperature field which the latent heat of the phase transition lead, simulating the multi-layer welding process of X80 pipeline steel, getting the heat cycle curve of coarse grain area of HAZ under the different welding process parameters, and implementing the three coupling of welding temperature, organizational status and stress-strain field .Getting the distribution and changes of welding residual stress under a different welding process parameters by the numerical simulation.Laying the foundation for further coupling calculation to the spread and the concentration of local hydrogen in welded joints.In addition, fitting analysis the linear relationship of residual stress about the welding heat-affected zone, welding center and welding line energy,the preheating temperature by using linear regression analysis ,the result shows the linear relationship between largest residual stress and welding line energy, preheat temperature. A variety of factors on the impact of residual stress are revealed at the macro,which provid the theoretical basis for optimizing the welding process parameters.