In terms of the welding process, the welding method of spiral welded pipe and straight seam steel pipe is the same, but the straight seam welded pipe will inevitably have a lot of T-shaped welds, so the probability of welding defects is also greatly increased, and the welding residue at the T-shaped welds The stress is large, and the weld metal is often in a three-dimensional stress state, which increases the possibility of cracks. Moreover, according to the technical regulations of submerged arc welding, each weld should have an arc starting point and an arc extinguishing point, but each straight seam welded pipe cannot meet this condition when welding a circular seam, so there may be more welding defects. When the pipe is subjected to internal pressure, two main stresses are usually generated on the pipe wall, namely radial stress δ and axial stress δ. The resultant stress δ at the weld, where α is the helix angle of the weld of the spiral welded pipe. The helix angle of the spiral welded pipe weld is generally 100 degrees, so the synthetic stress at the spiral welded seam is the principal stress of the straight seam welded pipe. Under the same working pressure, the wall thickness of the spiral welded pipe with the same pipe diameter can be reduced to that of the straight seam welded pipe.
Expanding technology of straight seam welded pipe:
1. In the preliminary rounding stage, the fan-shaped blocks are opened until all the fan-shaped blocks touch the inner wall of the steel pipe. At this time, the radii of all points in the inner tube of the steel pipe within the step range are almost the same, and the steel pipe is initially rounded.
2. In the stage of nominal inner diameter, 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.
3. In the spring back compensation stage, the fan-shaped block starts to move at a lower speed in the second stage until it reaches the required position. This position is the inner circumference position of the steel pipe before the springback required by the process design.
4. In the pressure-holding and stable stage, the fan-shaped block remains motionless for some time in the inner circumference of the steel pipe before springing back. This is the pressure-holding and stable stage required by the equipment and diameter expansion process.
5. In the stage of unloading and return, the sector block starts to retract 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 sector block required by the diameter expansion process.
Classification of straight seam steel pipe:
1. Straight seam high-frequency welded pipe: Straight seam high-frequency welded pipe is a welded pipe that is continuously produced on the production line by using steel strip (coil) as raw material and adopting a high-frequency welding process. The material strength is generally below 450MPa, and the materials include J55, L450, X60, Q235, Q345, Q420, and Q460. The diameter range of longitudinal welded pipe is 14-610mm, and the wall thickness is 1-23.8mm. Straight seam high-frequency welded pipe adopts a multi-frame continuous forming process, which has high production efficiency (production speed 15-40m/min). The production line has complete equipment for sizing, straightening, and rounding. Better for welding.
2. Longitudinal submerged arc welded pipe: Longitudinal submerged arc welded pipe is produced by using a single steel plate as raw material, through JCO or UO forming, submerged arc welding, or a combination of submerged arc welding and other welding processes. The common ones are X70, X80, X120, and so on. The diameter range of the LSAW pipe is 406-1422mm, and the wall thickness is 8-44.5mm. In terms of welding edge processing, edge milling is used for processing; in terms of forming, in addition to conventional JCO and UO technologies, some manufacturers adopt progressive forming (PFP) technology and roll bending (RBE) technology; welding, the automatic pre-welding machine with argon or CO2 gas protection and special multi-wire (4 wire and 5 wire) internal and external submerged arc welding equipment, and square wave power supply and power wave power supply device; in terms of diameter expansion, Mechanical diameter expansion is adopted for the entire pipe length; in terms of inspection, on-line flaw detection should be carried out on the plate, automatic ray wave flaw detection hydraulic test should be carried out on the steel pipe after welding, and secondary on-line or off-line ray wave flaw detection should be carried out after diameter expansion.
Sandblasting and de-rusting of straight seam steel pipe is to drive the spraying blade to rotate at high speed through a high-power motor, so that steel shot, steel sand, iron wire segment, minerals, and other abrasives are sprayed on the surface of straight seam steel pipe under the powerful centrifugal force of the motor, which can not only Oxide, rust and dirt, and the straight seam steel pipe can still achieve the required uniform roughness under the action of violent impact and friction of abrasives.
Sandblasting and de-rusting of straight seam steel pipe is to drive the spraying blade to rotate at high speed through a high-power motor, so that steel shot, steel sand, iron wire segment, minerals, and other abrasives are sprayed on the surface of straight seam steel pipe under the powerful centrifugal force of the motor, which can not only Oxide, rust and dirt, and the straight seam steel pipe can still achieve the required uniform roughness under the action of violent impact and friction of abrasives.
After spray de-rusting, not only the physical adsorption on the surface of the pipe can be expanded, but also the mechanical adhesion between the anti-corrosion layer and the surface of the pipe can be enhanced. Therefore, spray rust removal is an ideal rust removal method for pipeline corrosion. Generally speaking, shot blasting is mainly used for the inner surface treatment of pipes, and shot blasting is mainly used for the outer surface treatment of straight seam steel pipes.
Post time: Mar-07-2023