Straight seam steel pipe welding essentials

The forming methods for manufacturing large-diameter straight seam welded steel pipes include UOE forming, row forming (CFE), CE forming, etc. For the last process of most forming methods, the full-length diameter expansion of the welded tube blank is performed again to improve the shape of the welded steel tube. Diameter expansion has become an important process to ensure the finished pipe in the production of large-diameter longitudinal welded pipe. 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 radially outward. Compared with the hydraulic method, the mechanical method has simpler equipment and higher efficiency. It has been adopted in several large-diameter straight seam welded pipe pipeline expansion processes around the world. The mechanical expansion uses the split fan-shaped block at the end of the expansion machine to expand radially. , the process of making the tube blank along the length direction in a stepwise manner to realize the plastic deformation of the full tube length in sections.

1. Preliminary full circle stage. The fan-shaped blocks are opened until all fan-shaped blocks touch the inner wall of the steel pipe. At this time, the radii of all points in the inner circular pipe of the steel pipe within the step range are almost the same, and the steel pipe obtains a preliminary full circle.

2. The nominal inner diameter stage. The fan-shaped block starts to reduce the moving speed from the front position until it reaches the required position, which is the required position of the inner circumference of the finished tube.

3. It is the recovery compensation stage. The fan-shaped block starts to lower the speed at the position of the second stage until it reaches the required position, which is the position of the inner circumference of the steel pipe before the spring back is required by the process design.