Several stages of the mechanical expansion process of large-diameter steel pipes

The steel plate is first pressed into a U shape in the forming die, and then pressed into an O shape, and then internal and external submerged arc welding is carried out. Roll Bending the steel plate, and then performing internal and external submerged arc welding. After welding, the diameter is expanded to RBE welded steel pipe or non-expanded to RB welded steel 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 steel pipe or not expanded into a JCO welded steel pipe. Among the above-mentioned LSAW welded steel pipes, UOE is commonly used. The expansion process of large-diameter steel pipes is the initial rounding stage. The fan-shaped blocks are opened until all the fan-shaped blocks are in contact with the inner wall of the steel pipe. At this time, the radius of each point in the inner circular pipe of the steel pipe within the range of the step size is almost the same, and the steel pipe is initially rounded. 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 circumference position of the finished pipe. The expansion process stage of large-diameter steel pipe is the elastic compensation stage. The fan-shaped block starts to further reduce the speed at the position of stage 2 until it reaches the required position, which is the inner circumference position of the steel pipe before the rebound is required by the process design. The inner circumference of the steel pipe remains stationary for some time before the sector block is bounced back, which is the pressure-holding and stable stage required by the equipment and the expansion process. The latter is the unloading and regression stage of the expansion process of large-diameter steel pipes. The fan-shaped block quickly retracts from the inner circumference of the steel pipe before the rebound until it reaches the initial diameter expansion position, which is the small shrinkage diameter of the fan-shaped block required by the expansion process.