Research On Pre-bending And Forming Theory And Process Technology Of Small Diameter Thickwalled Longitudinal Welded Pipe

Under the background of carbon peak and carbon neutral,the direction of "de-coalization" of energy structure is obvious,and according to the overall requirements of national oil and gas pipeline network,the scale of oil and gas transportation in China is planned to exceed 200,000 km by 2025,and the oil and gas transportation will form a "trunk interconnection and regional network" mode.At present,the global stainless steel pipe industry is growing rapidly,the level of production technology and equipment technology have been greatly enhanced,characterized by new processes and new equipment to improve the quality and increase the number of new products.But China’s stainless steel pipe production and the international advanced level,compared to the development of new varieties of technology,size specifications and other aspects of a large deficiency pointed out,which requires us to start this technical transformation to enhance the efficiency and quality of our economic development.At the same time,stainless steel because of the characteristics of high pressure resistance,low temperature resistance,corrosion resistance and weather resistance,can meet the special needs of harsh environments,and its long life can save resources to a greater extent.For the harsh environment of the ocean,desert and other requirements for the quality of the finished welded pipe,stainless steel material tissue properties can be a perfect fit,especially duplex stainless steel,nickel-based alloys,etc.This paper starts from the study of rolling forming theory and sheet forming process,combines the characteristics of cold rolling deformation of small diameter welded pipe and the basic principle of plastic bending theory,gives the calculation method of plate edge pre-bending process deformation of steel plate,uses mathematical analysis method,establishes the theoretical model of prebending forming process,and carries out theoretical analysis of plate edge bending deformation.At the same time,by establishing the relationship between the pre-bending upper and lower dies and the plate material,the calculation of the upper and lower die spacing,pre-bending edge length,pre-bending force,prebending roll angle and curvature after rebound solution formulas that meet the preparation of small-diameter thick-walled pipe.By adjusting the forming process to obtain different thicknesses of the plate edge pre-bending model,analyze the influence law of different thicknesses on the bending roll angle and stress at the transition section during the plate pre-bending process.The design method and optimization technology of the transition section of the pre-bending tool based on the transition area of the straight and curved edges of the thick-walled pipe are constructed.If the design of this area is too short,it is very easy to cause stress concentration in the bending radical change of the sheet,and too long will occupy the forming length of the curved section and cause low productivity,so the optimized design of the transition section of the mold under pre-bending is crucial.By establishing a three-dimensional geometric model of plate edge prebending forming and using DEFORM-3D finite element simulation software,finite element simulation of cold-rolled plate edge pre-bending process with different slab thickness is carried out to obtain important data such as the distribution of rolling forces,stress clouds and metal flow direction of the rolling process,so as to analyze the reasonableness and accuracy of the plate edge prebending process parameters and optimize the process parameters;the study of the influence of the relevant parameters of the lower die transition section on the stress-strain of the pre-bending coil transition area with different sheet thickness is carried out;To study the influence law of the relevant parameters of the transition section of the lower die on the stress-strain in the transition area of the straight and curved edges of the sheet,and to make reasonable optimization of the transition section parameters;to study the influence law of the pre-bending rebound on the pre-bending roll angle for different sheet thicknesses through theoretical calculations and simulation results.The actual rolling experiment of nickel-based alloy N08810 was carried out by using a universal testing machine to check the dimensional data after bending and deformation,and the comparison and analysis with the theoretical analysis results and the rolling force data obtained after finite element simulation finally confirmed that the theoretical model derived in this paper,the die optimization model,the deformation after rebound and the finite element simulation results are relatively consistent and can be applied to the actual production.