The 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 performed. After welding, the diameter is usually enlarged at the end of the entire length, which is called UOE welded pipe, and the one without diameter expansion is called UO welded pipe. The steel plate is rolled into shape (RollBending), and then internal and external submerged arc welding is carried out. After welding, the diameter is expanded into RBE welded pipe or RBE welded pipe without expansion. The steel plate is formed in the order of J type-C type-O type, and after welding, the diameter is expanded into JCOE welded pipe or JCO welded pipe without diameter expansion. Among the above-mentioned LSAW welded pipes, UOE is commonly used. The diameter expansion process of large-diameter steel pipes is first a 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. 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. The expansion process stage of large-diameter steel pipe is the spring back 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 springback required by the process design. 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. Afterward is the unloading return stage of the diameter expansion process of large-diameter steel pipes. 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.
Qualified standard parameters for flaw detection of large-diameter steel pipes:
In the production of large-diameter steel pipes, single circular inclusions and pores with a weld diameter not exceeding 3.0mm or T/3 (T is the specified wall thickness of the steel pipe) are qualified, whichever is smaller. Within any weld length of 150mm or 12T (whichever is smaller), when the interval between single inclusions and pores is less than 4T, the sum of the diameters of all the above-mentioned imperfections allowed to exist alone shall not exceed 6.0mm or 0.5 T (whichever is smaller). A single bar-shaped inclusion whose length does not exceed 12.0mm or T (whichever is smaller) and a single bar-shaped inclusion whose width does not exceed 1.5mm are qualified. In any weld range of 150mm or 12T length (whichever is smaller), when the interval between individual inclusions is less than 4T, the maximum cumulative length of all the above-mentioned imperfections allowed to exist alone should not exceed 12.0mm. A single undercut of any length with a maximum depth of 0.4mm is acceptable. 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 places within any 300mm weld length. All such undercuts shall be ground. Any undercut beyond the above range shall be repaired, the problematic part shall be cut off or the whole pipe shall be rejected. Undercuts of any length and depth that overlap each other longitudinally on the same side of the inner and outer welds are disqualifying.
Deviation of large-diameter steel pipes in production:
Common large-diameter steel pipe size range: outer diameter: 114mm-1440mm wall thickness: 4mm-30mm. Length: according to customer requirements can be made in fixed length or indefinite length. Large-diameter steel pipes are widely used in various industrial sectors such as military, energy, electronics, automobiles, and light industry, and are important welding processes. The main processing methods of large-diameter steel pipes are: forging steel: a pressure processing method that uses the reciprocating impact force of a forging hammer or the pressure of a press to change the blank into the shape and size we need. Extrusion: It is a processing method for steel to place metal in a closed extrusion box and apply pressure at one end to make the metal extrude from the specified die hole to obtain a finished product with the same shape and size. It is mostly used for the production of non-ferrous metal steel. Rolling: A pressure processing method in which the steel metal billet passes through the gap between a pair of rotating rolls (various shapes), and the cross-section of the material is reduced and the length is increased due to the compression of the rolls. Pulling steel: It is a processing method in which the rolled metal blank (type, pipe, product, etc.) is pulled through the die hole to reduce the cross-section and increase the length. Most of them are used for cold working. Large-diameter steel pipes are mainly completed by tension reduction and continuous rolling of hollow base metal without a mandrel. On the premise of ensuring the spiral steel pipe, the whole spiral steel pipe is heated to a high temperature above 950°C and then rolled into seamless steel pipes of various specifications through a tension-reducing machine. The standard-setting documents for the production of large-diameter steel pipes show that there are allowable deviations in the manufacture and production of large-diameter steel pipes: length allowable deviation: the length allowable deviation of steel bars when delivered according to the specified length shall not exceed +50mm. Bending degree and end: The bending deformation of the straight steel bar should not affect normal use, and the total bending degree should not exceed 40% of the total length of the steel bar; the end of the steel bar should be cut straight, and the local deformation should not affect the use. Length: steel bars are usually delivered according to the fixed length, and the specific delivery length should be specified in the contract; when the steel bars are delivered in coils, each coil should be one steel bar, and 5% of the coils in each batch are allowed to consist of two steel bars composition. The weight and diameter of the plate are negotiated and stipulated by the supply and demand sides.
Post time: Mar-02-2023