Several Stages of The Mechanical Expansion Process of Large-diameter Steel Pipes

The steel plate is first pressed into a U shape and then into an O shape in the forming mold, and then internal and external submerged arc welding is performed. After welding, the diameter is usually expanded at the end of the entire length, which is called UOE welded pipe, and the diameter without expansion is called UO welded pipe. The steel plate is rolled and bent into shape (Roll Bending), and then internal and external submerged arc welding is performed. After welding, the diameter is expanded to RBE welded pipe or not to RB welded pipe. The steel plate is formed in the order of J type - C type - O type, and after welding, it is expanded into a JCOE welded pipe or not expanded into a JCO welded pipe. Among the above-mentioned LSAW welded pipes, UOE is commonly used. The diameter expansion process of large-diameter steel pipes starts with the 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. 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. The diameter expansion process stage of large-diameter steel pipe is the 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. The sector-shaped block remains stationary in the inner circumferential position of the steel pipe for some time before springing back. This is the pressure-maintaining and stable stage required by the equipment and diameter expansion process. The last step is the unloading return stage of the diameter expansion process of large-diameter steel pipes. The sector-shaped block rapidly retracts from the inner circumferential position of the steel pipe before rebounding until it reaches the initial diameter expansion position, which is the minimum contraction diameter of the sector-shaped block required by the diameter expansion process.