The influence of boss welding on residual stress of electric welding longitudinal pipes
Date:2019-04-29 View(s):100 Tag:The influence of boss welding on residual stress of electric welding longitudinal pipes
Valves, meters and flanges need to be tapped in the main pipeline during site construction of natural gas and oil pipelines. At present, it is difficult to identify the straight seam position of high frequency resistance welding pipe. Some of the bumps are installed very close to the welded pipe seam. Therefore, it is very necessary to study and analyze the influence of the installation of the owner on the foundation pipeline. The distribution of residual stresses in boreholes of high frequency straight seam resistance welded pipes and the influence of original residual stresses in different welding positions of high frequency straight seam resistance welded pipes are analyzed. The stress rises sharply after the bump is installed on the resistance welded pipe, and the effect of the residual stress in the longitudinal weld is much greater than that of the main pipe.
The distribution of residual stress in HFW welded pipe is closely related to the welding and forming process. HFW resistance welding is a circular tube blank with fracture section formed after rolling. Skin effect and proximity effect of high frequency current are used to concentrate the induced current on the edge of the billet opening angle. The temperature is rapidly raised to the welding temperature and extruded by the extrusion roll. The dimension and hydraulic test after welding are both important processes leading to the value of axial residual stress greater than that of circumferential residual stress. After high frequency welding, the microstructures and properties of welds and heat-affected zones are improved by on-line heat treatment, resulting in the residual stresses in the welds and their vicinity being lower than the area of the pipe body. The total residual stress of HFW resistance welded pipe is small and its axis is small. The value of residual stress is larger than that of circumferential residual stress, and the maximum values of axial and circumferential residual stress are about 38% and 29% of the yield strength of basic materials. The residual stress of HFW welded pipe and its adjacent longitudinal weld is lower than that of the pipe body. The range of axial and circumferential variation is about 24.5%~33.6% and 16.4%~21.5% of the yield strength of base metal. There is no stress concentration in the welding area.
The horizontal line represents the average residual stress in the welded zone of welded pipe, and the curve is the axial and circumferential residual stress of welded pipe. It can be seen that the influence law and degree of original residual stress amplitude on HFW longitudinal weld are basically the same when the welding bump of 26mm and 50mm holes is opened by thermal cutting in the weld center. With the increase of opening size, the stress concentration area increases. The value of residual stress near the bump on longitudinal weld of HFW welded pipe increases, and the increase of axial residual stress is much larger than that of axial residual stress. The residual stress increases with the increase of the distance from the bump weld. In these two cases, the amplitudes of axial residual stress are 444 MPa and 427 MPa respectively, which are about 3.86-3.71 times higher than the original state of HFW resistance welded pipe, and about 84% of the yield strength of base metal. The circumferential residual stresses are 201 MPa and 260 MPa, which are about 3.10-2.33 times higher than the original state of HFW resistance welded pipe, and about 49% of the yield strength of base metal. Relative to the original distribution of residual stress in HFW resistance welded pipe, the stress concentration in longitudinal weld under two conditions is based on the variation of axial residual stress.
Sound range: 92 mm and 167 mm.