Stages and standard parameters of mechanical expansion process for large diameter steel pipes

The 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.

Qualified standard parameters for flaw detection of large-diameter steel pipes:
In the production of large-diameter steel pipes, a single circular inclusion and pore with a weld diameter not exceeding 3.0mm or T/3 (T is the specified wall thickness of the steel pipe) is qualified, whichever is smaller. Within the range of any 150mm or 12T weld length (whichever is the smaller value), when the distance between a single inclusion and a pore is less than 4T, the sum of the diameters of all the above-mentioned imperfections that are allowed to exist alone should not exceed 6.0mm or 0.5 T (whichever is smaller). A single bar-shaped inclusion with a length not exceeding 12.0mm or T (whichever is smaller) and a single bar-shaped inclusion with a width not exceeding 1.5mm is qualified. Within the range of any 150mm or 12T weld length (whichever is the smaller value), when the interval between individual inclusions is less than 4T, the maximum cumulative length of all the above-mentioned imperfections that are allowed to exist individually should not exceed 12.0mm. A single undercut of any length with a maximum depth of 0.4mm is qualified. A single undercut with a maximum length of T/2 a maximum depth of 0.5mm and no more than 10% of the specified wall thickness is qualified as long as there are no more than two in any 300mm weld length. All such undercuts shall be ground. Any undercut that exceeds the above range should be repaired, the offending area removed, or the entire pipe rejected. Undercuts of any length and depth that overlap each other longitudinally on the same side of the inner and outer welds are unacceptable.