Multiple Pressure Straightening Process Of Roll Type Four Point Bending For Large Longitudinal Welded Pipe

With the development of natural gas and oil resources all over the world,the energy resources are transferred to unconventional oil and gas,so the construction and design of pipelines are required to meet the severe development environment.Large-scale straight seam submerged arc welding pipe based on good welding technology and forming technology has been widely used in the cold area and deep seabed pipeline laying and construction in the harsh environment.Because the traditional three-point bending straightening process has its limitations:the straightening times are more,usually 4-6 times,and the straightening efficiency is low.The upper roller of three-point bending exerts a large load on the pipe,and the pipe is easy to produce cross-section distortion.Based on this,this paper puts forward a new technology of roll four point bending multiple pressure straightening for large longitudinal welded pipe.Based on the finite element simulation analysis,the straightening load is calculated by theoretical straightening moment according to the geometric parameters and material properties of the pipe.The four roll straightening model is established by using symmetrical roll system,and the simulation analysis is carried out.The tube needs only three straightening times,and the straightening efficiency is high.Through comparative analysis,the load of four point bending straightening is smaller than that of three-point bending straightening,and the cross section of straightened pipe is not easy to produce distortion.The straightening mechanism of roller four point bending multiple pressure straightening process is revealed,that is,the trapezoidal broken line distribution bending moment approximates the theoretical straightening bending moment smooth curve.According to the initial deflection distribution,the process parameters required for roller four point bending straightening are given.Finally,a large-scale roll type four point bending multiple pressure straightening experimental equipment system for longitudinal welded pipe is built.The equipment includes deflection detection device,electro-hydraulic control system and mechanical system,which can measure the initial deflection of the pipe to be straightened online.The feasibility and accuracy of the new process are verified by finite element simulation and experimental analysis of small-size test pipe.