ERW pipe boss welding

Posted by zora li on November 21st, 2022

ERW pipe boss welding

During the construction of oil and gas pipelines in the station, the installation of valves, instruments and flanges all require openings in the main pipeline. The position of the straight seam of the high-frequency resistance welded base pipe is difficult to visually identify. Some bosses are installed very close to the seam of the electric welded pipe. Therefore, it is very necessary to conduct in-depth research and analysis on the influence of boss installation on the foundation pipeline. The residual stress distribution of the drilled high-frequency straight seam electric resistance welded pipe and the influence of different boss welding positions on the original residual stress of the erw pipe are analyzed. After the boss is installed on the erw pipe, the stress rises sharply, and the influence of the residual stress of the longitudinal weld is much greater than that of the parent pipe.

The distribution of residual stress in erw tube is closely related to its welding forming process. HFW resistance welding is to roll the strip through a circular tube blank with a cross-section, and use the high-frequency current skin effect and proximity effect to make the induced current highly concentrated on the edge of the opening edge, so that the temperature of the tube rises rapidly to the welding temperature, extrusion The pressing roller extrusion is completed. Both dimensional and hydrostatic testing after welding are important processes that lead to axial residual stress values ​​greater than circumferential residual stress values.

After high frequency welding, in-line heat treatment improves the microstructure and properties of the weld and heat affected zone, thereby reducing residual stress in and near the weld. The overall residual stress on the erw tube is small, the residual stress value is larger than the circumferential residual stress value, and the maximum axial and circumferential yield strength is about 38% and 29% of the base metal. The residual stress of the erw pipe and its adjacent longitudinal welds is lower than that of the pipe body. The axial and circumferential variation ranges are about 24.5%-33.6% and 16.4%-21.5% of the yield strength of the base metal, and there is stress concentration.

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