Pre-welding and welding method of straight seam steel pipe

Pre-welding of straight seam steel pipes: Pre-welding includes joints and welds.
1. There is no wrong edge or the wrong edge is smaller than the specified value. Generally, the amount of the wrong edge is ≤8% of the plate thickness, and the maximum is not more than 1.5mm.
2. It is necessary to ensure that the welding seam has a suitable penetration depth and deposition amount. It is necessary to ensure that there is no cracking after welding and no burn-through phenomenon, but also to control the height of the welding seam so that the excess height of the external welding seam will not be affected.
3. The weld bead is continuous and formed, to facilitate the guarantee of external welding.
4. There are no defects such as welding deviation, pores, cracks, slag inclusions, burn-through, and back welding flashes in the welding seam, and the center deviation of the welding seam is required to be less than or equal to 1mm.
5. There is no arc burn, or little splash, and does not affect the groove and surface of the pipe end.
6. The weld seam is matched with the base metal, and the physical and chemical properties of the weld metal meet the requirements.

The essentials of straight seam steel pipe welding:
The forming methods for manufacturing large-diameter straight seam welded pipes include UOE forming method, row roll forming method (CFE), CE forming, and so on. For most forming methods, the last process is to expand the full length 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 straight seam welded pipes to ensure finished pipes. Diameter expansion is a pressure processing process that uses hydraulic or mechanical means to add 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. Several large-diameter straight seam welded pipe expansion processes are used in the world. The mechanical expansion uses the split sector block at the end of the expander to expand radially. , so that the tube blank can realize the process of plastic deformation of the whole tube length in a step-by-step manner along the length direction.

1. Preliminary rounding stage. The fan-shaped blocks are opened until all fan-shaped blocks are in contact with the inner wall of the steel pipe. At this time, the radius of each point in the inner circular pipe of the steel pipe within the range of the step size is almost the same, and the steel pipe is initially rounded.
Second, the nominal inner diameter stage. The fan-shaped block starts to reduce the movement speed from the front position until it reaches the required position, which is the required inner circumference position of the finished pipe.
3. Repetition compensation stage. The fan-shaped block starts to further reduce the speed at the position of stage 2 until it reaches the required position, which is the inner circumference position of the steel pipe before the rebound required by the process design.