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The basic situation of pre-welding and welding of straight seam steel pipes

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Pre-welding of straight seam steel pipe:

Pre-welding includes seams and welds.

1. The joint seam (that is, the forming seam) has no wrong edge or the wrong edge is less than the specified value. Generally, the amount of the wrong edge is less than 8% of the plate thickness, and the maximum is not more than 1.5mm.

2. To ensure that the weld has an appropriate penetration depth and deposition amount, it is necessary to ensure that there is no cracking or burn-through after welding, and the height of the weld must be controlled so that the external welding weld height does not affect the weld.

3. The welding bead is continuous and shaped to ensure the external welding afterward.

4. The welding seam does not have defects such as welding deviation, pores, cracks, slag inclusion, burn-through, and back welding bead, and the center deviation of the welding seam is required to be ≤1mm.

5. No arc burns, little splash, and no influence on the bevel and surface of the pipe end.

6. The welding seam is matched with the base metal, and the physical and chemical properties of the welding seam metal meet the requirements.


The essentials of straight seam steel pipe welding:

The forming methods for manufacturing large-diameter longitudinally welded pipes include UOE forming method, roll forming method (CFE), CE forming, and so on. For most farming methods, the latter process is to perform a full-length expansion of the welded tube blank to improve the shape of the welded steel tube. Diameter expansion has become an important process in the production of large-diameter longitudinally welded pipes to ensure finished pipes. Diameter expansion is a pressure processing technology that uses hydraulic or mechanical means to apply force from the inner wall of the steel pipe to expand the steel pipe radially outward. The mechanical method is simpler and more efficient than the hydraulic method. The expansion process of several large-diameter longitudinally welded pipelines in the world has been adopted. The mechanical expansion uses the split sector block at the end of the expander to expand in the radial direction. , Make the tube blank step by step along the length direction to realize the plastic deformation process of the whole tube length in sections.


1. The preliminary rounding stage. The fan-shaped block is opened until all the fan-shaped blocks touch the inner wall of the steel pipe. At this time, the radius of each point in the inner tube of the steel pipe within the step length is almost the same, and the steel pipe is initially rounded.

2. Nominal diameter stage. The sector block starts to reduce the movement speed from the previous position until it reaches the required position, which is the required inner circumferential position of the finished pipe.

3. Rebound compensation stage. The fan-shaped block will further slow down at the position of stage 2 until it reaches the required position, which is the position of the inner circumference of the steel pipe before rebounding as required by the process design.


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