First, 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, then pressed into an O shape, 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 non-expanded diameter is called UO welded pipe. The steel plate is roll-bent (RollBending), and then internal and external submerged arc welding is performed. After welding, the diameter is expanded to RBE welded pipe or RB 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 to JCOE welded pipe or JCO welded pipe without expansion. Among the above-mentioned LSAW welded pipes, UOE is commonly used. The expansion process of large-diameter steel pipes is first 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 round pipe of the steel pipe within the step range 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 pipes is the rebound 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 required by the process design. The fan-shaped block remains stationary for a period at the inner circumference position of the steel pipe before the rebound, which is the pressure-maintaining and stable stage required by the equipment and the expansion process. The last is the unloading and return stage of the expansion process of large-diameter steel pipes. The fan-shaped block starts to shrink rapidly from the inner circumference position of the steel pipe before rebounding until it reaches the initial expansion position, which is the minimum shrinkage diameter of the fan-shaped block required by the expansion process.
Second, the qualified standard parameters of the 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 150mm or 12T length of weld (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 defects that are allowed to exist separately should not exceed 6.0mm or 0.5T (whichever is smaller). Single strip inclusions with a length not exceeding 12.0mm or T (whichever is smaller) and a width not exceeding 1.5mm are qualified. Within any 150mm or 12T length of weld (whichever is smaller), when the interval between single inclusions is less than 4T, the maximum cumulative length of all the above-mentioned defects that are allowed to exist separately 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 not exceeding 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 should be ground. Any undercut beyond the above range should be repaired, the problematic part should be cut off or the entire steel pipe should be rejected. Undercuts of any length and depth that overlap on the same side of the inner weld and the outer weld in the longitudinal direction are unqualified.
Third, the deviation of large-diameter steel pipes in production:
Common large-diameter steel pipe size range:
Outer diameter: 114mm-1440mm Wall thickness: 4mm-30mm.
Length: can be made into fixed length or non-fixed length according to customer requirements.
Large-diameter steel pipes are widely used in various industrial sectors such as aviation, aerospace, energy, electronics, automobiles, and light industry, and are one of the important welding processes.
The main processing methods for large-diameter steel pipes are:
Forged steel: A pressure processing method that uses the reciprocating impact force of the forging hammer or the pressure of the press to change the blank into the shape and size we need.
Extrusion: It is a processing method in which the metal is placed in a closed extrusion cylinder, and pressure is applied at one end to extrude the metal from the specified die-hole to obtain a finished product with the same shape and size. It is mostly used to produce non-ferrous metal steel.
Rolling: A pressure processing method in which the steel metal billet passes through the gap (various shapes) of a pair of rotating rollers, and the material cross-section is reduced and the length is increased due to the compression of the rollers.
Drawing steel: It is a processing method in which the rolled metal billet (profile, tube, product, etc.) is drawn through the die hole to reduce the cross-section and increase the length. It is mostly used for cold processing.
Large-diameter steel pipes are mainly completed by tension reduction and continuous rolling of hollow parent materials without mandrels. Under the premise of ensuring the spiral steel pipe, the spiral steel pipe is heated to a high temperature of more than 950℃ as a whole and then rolled into seamless steel pipes of various specifications through a tension-reducing mill.
The standard document for the production of large-diameter steel pipes shows that deviations are allowed in the manufacture of large-diameter steel pipes: Length allowable deviation: The length allowable deviation of steel bars when delivered in fixed length shall not be greater than +50mm. Bending and ends: The bending of straight steel bars should not affect normal use, and the total bending should not exceed 40% of the total length of the steel bars; the ends of the steel bars should be sheared straight, and local deformation should not affect use. Length: Steel bars are usually delivered in fixed lengths, and the specific delivery length should be specified in the contract; when steel bars are delivered in coils, each coil should be a steel bar, and 5% of the coils in each batch are allowed to consist of two steel bars. The coil weight and coil diameter are determined by negotiation between the supply and demand parties.
Post time: Dec-26-2024