Introduction to large diameter welded pipes

Introduction to large diameter welded pipes

After both ends of the large-diameter welded pipe blank are heated to the welding temperature, under the squeeze of the squeeze roller, the single metal grains formed penetrate and crystallize with each other to form a strong weld. If the extrusion force is too small, the number of single crystals formed will be small, the strength of the weld metal will decrease, and cracks will occur after stress is applied. If the extrusion force is too large, the molten metal will be squeezed out of the weld, which not only increases the strength of the weld, but also produces a small amount of internal and external burrs, and even causes problems such as the number of welding turns. The strip steel is sent to the welded pipe unit, and is coiled by multiple rollers. The strip steel is gradually rolled up to form a round tube blank with tooth gaps. Adjust the reduction amount of the squeeze roller so that the weld gap is controlled at 1~3mm and both ends of the weld are flush.

The high-frequency induction coil of large-diameter welded pipe should be as close as possible to the position of the extrusion roller. The induction coil is far away from the extrusion roller, the effective heating time is longer, the heat affected zone is wider, and the strength of the weld is reduced; otherwise, the edge of the weld is not heated enough and the shape after extrusion is poor. The welding temperature of large-diameter welded pipes is mainly affected by high-frequency eddy current thermal power. According to the formula, it can be seen that the high-frequency eddy current thermal power is mainly affected by the current frequency, and the eddy current thermal power is proportional to the square of the current excitation frequency. The frequency of current excitation is affected by the excitation voltage, current, capacitance and inductance.

What are the design features of large diameter welded pipes?
1. The appearance is more beautiful, especially the pipe truss composed of welded pipe fittings, without redundant node connections, and has a strong modern feel.
2. The pipe section has good geometric properties, the pipe wall is generally thin, the cross-section material is distributed around the center of mass, the cross-section radius of gyration is large, and it has good torsional stiffness. As a compression, bending and two-way bending member, its load-bearing capacity is relatively good. The straightness and cross-sectional size of cold-bent pipes are better than those of hot-rolled open sections.
3. The welded steel pipe has a closed section. When the average thickness and cross-sectional area are the same, the exposed surface area is about 50% to 60% of the opening cross-sectional area, which is conducive to corrosion and can save coating materials.
4. From the perspective of hydrodynamic resistance, the cross-section of the circular pipe is acceptable, and the influence of wind and water flow is greatly reduced. Rectangular tube sections are similar to other open sections in this respect.
5. Concrete can also be poured into the pipe to form a composite component.

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