CHANGES IN PIPE GEOMETRY DURING SEQUENTIAL CREATION OF STRESSES ON THE INNER SURFACE UNDER EXTERNAL THERMOMECHANICAL EFFECTS

In  modern  high-tech  industry,  flexible  pipe  technology  is  widely used. Pipe benders are an integral part of pipeline systems.  The most widely used are methods of pipes cold bending, which are  accompanied by a number of negative phenomena – such as reduction in the crackle of the wall on outer side of the bend, ovalization  of the cross section and formation of bumps. The article presents a  study of influence of deformation technology of pipe billets by rolling with high tension on the structure and properties of the billet’s  material. The method of pipe deformation by rolling with tension  allows obtaining radial bending of the billet without its destruction  and without causing obvious defects of the surface and microstructure. The tests were carried out on the samples from steel of 3sp and  12Kh18N10T grades. Research of the microstructure was performed  in  accordance  with  GOST  5639  –  82,  of  mechanical  properties  –  with GOST  1397  –  84, of microhardness  – with GOST  9450  –  76.  The article examines the effect of changes in geometry of the pipe  billet on its structure and properties. The process of pipe deformation  by rolling leads to changes in the mechanical properties of the tested  materials. The values   of micro hardness and strength increase, while  the grain points decrease. In the process of deformation, it is possible  to change the microstructure of the material as a result of structural  transformations (quenching). In the thermomechanical method of deformation, plastic flow of metal suggests possible change in structure  of pipe walls as a result of recrystallization and heat treatment of material of the bend area. Therefore, it requires further study and more  in-depth analysis of this technology.

pipe billet,  rolling,  pipe bender,  deformation,  microhardness,   mechanical properties,  microstructure

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