A Study Of Mechanical Expanding Process For Lsaw Pipe End

LSAW pipes, made by thick steel plates through compacting, are main pipeline products for long-distance transportation of oil, natural gas.Expanding is an important part of the production process of LSAW pipe, which is used, on one hand, to calibrate the welded pipe in order to improve its straightness and roundness, on the other hand, to meet the need to connections of two pipes. Therefore, the study of LSAW pipe expanding technology has great significance.In this paper, X52 LSAW pipes were adopted as the subject investigated to carry out the research on mechanical expanding process of LSAW pipe end with large diameter and thick-wall. Static equilibrium theory and the principal stress method were combined, on the first place, to analyse and deduce the expanding force formula of pipe port expanding, which provides a basis for the selection of equipment. On the second place, detailed analysis was implemented for the pipe end deformation process during mechanical expanding, and forming criterion was also obtained. In addition, formula of springback deformation after unloading was given by analysing the calibration and expanding stage. At last, using the finite element software MSC.Marc to develop the two-dimensional and three-dimensional simulation of port expanding, the regularities of distribution of the stress, strain, thickness and radial size had been gained.The study shows that plastic deformation of the elliptical tube which has a significant local characteristic mainly concentrates in the vacant section, when expanding using several expanding punches. The cross-section outline and wall-thickness of the products present uneven distribution.As to the cross section, in both the region contacted with the punch edge angle and the vacant area, the wall-thickness reduces greatly and there is a phenomenon of depression during the expanding process. In addition, the billet will be straightened with the expanding rate increases. However, the deformation is more uniform with regard to billet in contact with the work surface of punch, material thickness decreases less, therefore, the purpose of calibration has been reached.In the longitudinal section, it can be divided into port deformation zone, transition zone and undeformed zone along the z-axis, according to the morphology of deformation zone. The end is restricted by the tensile stress in the axial deformation zone on account of the existence of undeformed zone, so length of port deformation zone is smaller than that of the punch, that is the expanding length. Consequently, it is necessary to ensure the minimum expanding length while doing the line-pipe port mechanical expanding.The minimum length in this case is 60 mm.The inner radius can generally meet docking requirements after the mechanical expanding. Nevertheless, the inner diameter of the port reduces in local area, as a result of the depression in vacant section, therefore, docking will be influenced in a certain extent, resulting in the misalignment. Secondary expanding is suggested as a solution.