Simulation Study On Bending Forming Technology Of Large Diameter Pipe

With the increasing of oil and gas pipeline projects in China,the demand of large diameter elbow increases.Large diameter elbow pipe is usually made by medium frequency induction heating pipe bender,its forming mechanism is very complex,and the precision is not easy to control.The production technology of large diameter elbow pipe is lower than the world advanced level,some model bends are still dependent on foreign imports.Therefore,in order to improve the forming quality of large diameter elbow and reduce dependence on foreign imports,it is important to study the bending forming technology of large diameter pipes.The main defects of large diameter pipe are flat flattening,corrugation inside the elbow and uneven thickness change rate of the elbow.At present,the research of scholars focuses on the quality defects of tube bending under the action of pure bending.The bending method of medium frequency induction heating pipe bender belongs to the heat push bending process,in view of this,this paper will focus on the analysis of the impact of the thrust on the pipe neutral layer angle and flat flattening in the bend,and explore the control method of wall thickness change rate.The specific research content and results are as follows:(1)According to the heat conduction theory,the temperature field on the bending pipe is calculated.Combined with the plastic bending theory and the mechanical model of bending process,the theoretical value of the tube bending is calculated.According to the model simplification rule and mechanics equivalent theory,the finite element model of pipe bender and pipe is established.Using the finite element analysis software,the effect of the applying temperature range on the inner wrinkle of the elbow and the influence of thrust on the pipe neutral layer angle and flat flattening is analyzed.(2)This paper introduces the effect of neutral layer angle and flat flattening on wall thickness reduction,and revises the calculation formula of wall thickness of elbow,greatly improving the accuracy of wall thickness measurement.At present,the most representative wall thickness control method is resistance method,this paper discusses the influence of resistance size on the wall thickness of the elbow.(3)In this paper,the fabrication process of non-uniform wall thickness tube is introduced,and the initial wall thickness of non-uniform wall thickness tube is deduced according to the target wall thickness of uniform wall thickness elbows.The ultimate goal of non-uniform wall thickness pipe bending is to achieve the uniform wall thickness of the bended pipe,and avoid the problem of the outside wall thickness thinning.Compared with resistance method,the non-uniform wall thickness pipe forming process greatly reduces the stress peak of the main structures of the pipe bender.