Introduction to pre-welding and welding essentials of straight seam steel pipes

Pre-welding of straight seam steel pipes: Pre-welding includes joints and welds.

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

2. It is necessary to ensure that the weld seam has 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 seam must be controlled so as not to affect the weld reinforcement height of the external welding seam.

3. The welding bead is continuous and shaped to facilitate subsequent external welding.

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

5. No arc burn, small splash, and no impact on the pipe end bevel and surface.

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

Essentials of straight seam steel pipe welding: The forming methods for manufacturing large-diameter straight seam welded pipes include UOE forming, roller forming (CFE), CE forming, etc. For most forming methods, the last step 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 apply force from the inner wall of the steel pipe to expand the steel pipe outward in the radial direction. The mechanical method is simpler and more efficient than the hydraulic method. It is used in the expansion process of several large-diameter straight seam welded pipe pipelines around the world. The mechanical expansion uses the segmented sector block at the end of the expansion machine to expand in the radial direction. , the process of achieving plastic deformation of the entire pipe length in sections in a stepwise manner along the length direction of the pipe blank.

1. Preliminary rounding stage. The sector blocks are opened until all the sector blocks are in contact with the inner wall of the steel pipe. At this time, the radius of each point in the inner circular tube of the steel pipe within the step range is almost the same, and the steel pipe is initially rounded.

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

3. Rebound compensation stage. The sector block starts from the second stage position and further reduces the speed until it reaches the required position. This position is the inner circumferential position of the steel pipe before rebound is required by the process design.