Longitudinal Welded Steel Pipe Diameter Expansion

The welding current in the swing welding of the straight seam steel pipe is slightly larger than that of the traditional welding method; secondly, the tungsten extreme elongation in the swing welding of the straight seam steel pipe is determined according to the tube wall thickness, usually 4-5mm; the argon flow is slightly larger than the traditional welding method, About 8-10l/min; after the swing welding of the straight seam steel pipe, the swing amplitude is 2mm of the blunt edge of the fusion bevel on both sides; the left and right hands are flexibly matched, the swing is even, and the wire is fed evenly. The swing welding technology of straight seam steel pipes is generally used for welding thick-walled straight seam steel pipes. The technical parameters of the swing method of straight seam steel pipe welding are slightly different from those of the traditional linear welding method. First, the end of the porcelain nozzle of argon arc welding is slightly thicker than that of the traditional linear welding method. Secondly, there is also a gap between the welding joints. The difference, taking the 00Cr19Ni10 weld of φ89×5 as an example, the gap of the traditional straight welding method is 0~3mm, while the swing method is 4mm, and the welding specifications are also different.

Longitudinally welded pipe 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 process is:

The mechanical expansion utilizes the split sector block at the end of the expander to expand in the radial direction so that the tube blank is stepped along the length direction to realize the plastic deformation process of the entire tube length in sections. Divided into 5 stages

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 round.

2. Nominal 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 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 rebound required by the process design.

4. Pressure maintaining and stable stage. The sector block remains stationary for some time before rebounding on the inner circumference of the steel pipe. This is the pressure-holding and stable stage required by the equipment and the diameter expansion process.

5. Unloading and returning stage. The sector block rapidly retracts from the position of the inner circumference of the steel pipe before the rebound, until it reaches the initial expansion position, which is the small contraction diameter of the sector block required by the diameter expansion process.