Research On Three-roller Continuous And Synchronous Adjusting Straightness And Roundness Process For Lsaw Pipes

Oil and gas have become the most promising energy source.With the development of oil-gas resources to unconventional transfer,the remote and harsh development environment and the development trend of super-large transmission volume put forward high demands on pipeline construction.Longitudinally Submerged Arc Welding(LSAW)pipes are made from high steel-grade wide plates,which are suitable for long-distance oil and gas pipeline transportation and for laying pipes in deep-sea or cold areas.By the interference of welding thermal stress,material properties,technical equipment and other factors,the straightness and roundness of forming pipes cannot meet the industrial standards and need to be straightened and rounded.The existing straightening and straightening processes are completed independently,which leads to the increase of process flow and the decrease of production efficiency.The rounding and straightening deformation are involved in each other,the flattening of LSAW pipes cannot be solved,so it is difficult to adjust the straightness and roundness to the optimal standard at the same time.Therefore,the co-regulation of straightness and roundness has become the key technology of short-process production of LASW pipes,and it is also the bottleneck that restricts the construction of oil and gas pipelines with high pressure and long-distance oversized transmission.In view of the above problems,this paper combines straightening process with rounding process,and proposes a new process of three-roller continuous and synchronous adjusting straightness and roundness for LSAW pipes based on the bidirectional reciprocating bending.The process,roller shape distribution and loading parameters are introduced.According to the springback theory of small curvature plane bending and the unified curvature theory of reciprocating bending,the springback analysis of axial reciprocating bending straightening and circumferential reciprocating bending rounding are established.The springback analysis reveals the deformation mechanism of the process and proves that reciprocating bending can eliminate the difference of initial curvature of pipes,so that the axial and circumferential curvature are unified in the same direction and value,respectively.It provides theoretical support for the process.By means of the finite element software ABAQUS,it is proved that the continuous and synchronous adjusting straightness and roundness process of pipes is mainly affected by axial stress and circumferential stress.Based on the statics analysis and elastoplastic analysis of pipes,the mechanical model of the primary statically indeterminate problem in the calibrating roundness stage is established and solved.To analyze the influence of loading parameters on the process of calibrating roundness,a finite element model of "three-stage" roller shape composed of the loading stage,calibrating roundness stage and unloading stage is proposed and simulated.The simulation results are compared with the theoretical analytical results to verify the correctness of the model.The variation of horizontal section force,bending moment,maximum bending curvature,minimum bending curvature and loading force with radial reduction is predicted theoretically,which provides a theoretical guidance for setting loading parameters.Depending on the roller shape and radial reduction,the equivalent stress and equivalent strain of any element of pipes are solved.The distribution of equivalent stress and equivalent strain in the major deformed area,that is,roundness calibration stage and roundness and straightness calibration stage,is described.The effectiveness of stress-strain analysis and solution is proved by the simulation results,which provides a reference for the setting of loading parameters.In addition,by comparing the axial and circumferential deformation curves of the theoretical results with the experimental and simulation results,it is proved that the mathematical description of the axial and circumferential deformation curves is reasonable.The axial and circumferential deformation curves of pipes can be predicted according to different roller shape,which provides a shortcut for optimizing roller shape.Using numerical simulation technology,with the minimum value of residual roundness,residual straightness and residual stress as the design goal,the roller shape design of the process is proposed,which provides a reference for the optimization of roller shape.The simulated results show that when the "five-stage" roller design scheme is adopted,the roller is divided according to the design proportion of 1?2?4?2?1,the elastic zone ratio is 0.6 or 0.8,and the roundness and straightness calibration stage is designed as a continuous change curve in the form of a hyperbolic curve,the residual straightness of the pipe can reach 0.12%,and the residual roundness can reach 0.06%,which meets the API standard of LSAW pipes.The feasibility of the new process is preliminarily verified.Finally,an experimental equipment of the process is developed.The experimental equipment can realize two functions of LSAW pipes: continuous straightening and continuous rounding.Taking the minimum value of residual roundness and residual straightness as the goal,the effect of process parameters such as radial reduction,initial roundness,initial straightness,reciprocating bending times and diameter-thickness ratio is investigated by experimental methods.According to the experimental equipment,roller shape design,material and geometric dimension of pipes during the process,a strategy of continuous and synchronous adjusting straightness and roundness is put forward,that is,the range of process parameters such as radial reduction,roller rotation speed and pipe feed speed can be determined.It provides technical guidance for the application of the process in practical production.The semi-automatic experimental platform of the process can realize the co-regulation of straightness and roundness of LSAW pipes.It builds a groundwork for promoting the intelligence of adjusting straightness and roundness process.The experimental results show that the residual straightness can reach less than 0.17% and the residual roundness can reach less than 0.4%.The reliability and feasibility of the new process are proved.It provides technical guarantee for the construction of super large oil and gas pipeline in China.