The current forming methods of large-diameter longitudinal submerged arc welded steel pipes include UOE forming method, row roll forming method (CFE), CE forming, and so on. For most of the forming methods, the last process is to carry out a full-length diameter expansion on the welded tube blank to improve the quality of the welded tube shape. Diameter expansion has become an important process in the production of large-diameter straight seam welded steel pipes to ensure the quality of finished pipes.
The diameter expansion of straight seam welded steel pipe 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 is used in the diameter expansion process of several of the most advanced large-diameter straight seam welded steel pipelines in the world. The process is as follows: The fan-shaped block of the petal expands in the radial direction, so that the tube blank is stepwise along the length direction, and the process of realizing the plastic deformation of the whole tube length is segmented. divided into 5 stages
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. Nominal ID stage. The fan-shaped block starts to reduce the moving speed from the front position until it reaches the required position, which is the inner circumference position of the finished tube required by the quality.
3. Springback 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.
4. Stable pressure holding stage. The fan-shaped block remains stationary for some time at the inner circumference of the steel pipe before springing back, which is the pressure-holding and stable stage required by the equipment and diameter-expanding process.
5. Unloading regression phase. The fan-shaped block retracts rapidly from the inner circumference of the steel pipe before springing back, until it reaches the initial diameter expansion position, which is the minimum shrinkage diameter of the fan-shaped block required by the diameter expansion process.
In practical application, in process simplification, steps 2 and 3 can be combined and simplified, which does not affect the diameter expansion quality of steel pipes. In China, Bestar Steel can produce X120 straight seam welded steel pipes and has adopted the above five stages of mechanical diameter expansion technology in their diameter expansion.
Post time: Jun-25-2023