The high-frequency welding process of straight seam steel pipes is completed in high-frequency welded pipe units. High-frequency welded pipe units usually consist of roll forming, high-frequency welding, extrusion, cooling, sizing, flying saw cutting, and other components. The front end of the unit is equipped with a storage loop, and the rear end of the unit is equipped with a steel pipe turning frame; The electrical part mainly consists of a high-frequency generator, DC excitation generator, and instrument automatic control device. Thermal expansion straight seam steel pipe refers to the expansion of the straight seam steel pipe through diameter expansion technology to achieve the purpose required by the customer. There are two processes for straight seam steel pipes: double-sided submerged arc welding and high-frequency welding. Double-sided submerged arc welding can produce straight seam steel pipes with a diameter of about 1,500. What we call pipe expansion now mainly refers to high-frequency welded pipes. There are two points. The reason is that the production diameter of high-frequency welded pipe itself is relatively small, so it needs to be expanded.


There are many types of straight seam steel pipes, according to their uses: generally welded pipes, oxygen-blown welded pipes, galvanized welded pipes, wire casings, roller pipes, metric welded pipes, automotive pipes, deep well pump pipes, transformer pipes, electric welded special-shaped pipes, electric welded thin-walled pipes.


General welded pipe: General welded pipe is used to transport low-pressure fluid. Made of Q235 grade, L245, Q235B steel.
Galvanized steel pipe: It is to coat the surface of the black pipe with a zinc layer. Divided into hotness and coldness. The hot zinc layer is thick and the cold temperature is cheap.
Oxygen-blown welded pipe: Generally a small diameter welded steel pipe, commonly used for oxygen blowing in steelmaking.
Wire casing: It is a pipe for a power distribution structure, which is an ordinary electric welded carbon steel pipe.
Electrically welded thin-walled tube: It is a small-diameter tube used for furniture and lamps.
Idler tube: Electrically welded steel tube on the belt conveyor, with required ovality.
Transformer tube: It is an ordinary carbon steel tube. Used in the manufacture of transformer heat pipes and other heat exchangers.


Appearance requirements of straight seam steel pipes:
1. No cracks, lack of fusion, pores, slag inclusions, or spatter are allowed.
2. There must be no undercut on the weld surface of pipes with a design temperature lower than -29 degrees, and stainless steel and alloy steel pipes with a greater tendency to harden. The undercut depth of welds of pipes made of other materials should be greater than 0.5mm, the continuous undercut length should not be greater than 100mm, and the total undercut length on both sides of the weld should not be greater than 10% of the total length of the weld.
3. The weld surface shall not be lower than the pipe surface. The weld reinforcement shall not be greater than 3mm (it is the maximum width of the groove after the welding joint assembly).
4. The misalignment of the welded joint should not be greater than 10% of the wall thickness and not greater than 2mm.


Methods for preheating deformation of straight seam steel pipes:
1. Reasonable material selection. For precision complex molds, micro-deformation mold steel with good quality should be selected. Mold steel with serious carbide segregation should be reasonably cast and subjected to quenching and tempering heat treatment. Solid solution double-refining heat treatment can be performed on larger and uncastable mold steel. Reasonably select the heating temperature and control the heating speed. For precision and messy molds, slow heating, preheating, and other balanced heating methods can be used to reduce mold heat treatment deformation.
2. Correct heat treatment process operation and reasonable tempering heat treatment process are also effective ways to reduce the deformation of precision and messy molds. The causes of the deformation of precision complex molds are often complicated, but as long as we understand the deformation rules, analyze the causes of their occurrence, and use special methods to prevent the deformation of the mold, the deformation of the mold can be reduced and controlled.
3. Precision and complex molds must be preheated to eliminate residual stress generated during machining. For precision and complex molds, if conditions permit, vacuum heating quenching and cryogenic treatment after quenching should be used as much as possible. On the premise of ensuring the hardness of the mold, try to use pre-cooling, graded cooling quenching, or warm quenching processes.
4. The design and design of the mold should be reasonable, the thickness should not be too different, and the shape should be symmetrical. For molds with large deformation, the deformation rules should be controlled and machining allowance should be reserved. For large, precise, and complex molds, combined design can be used. For some precision and complex molds, pre-heat treatment, aging heat treatment, and quenching and tempering nitriding heat treatment can be used to control the accuracy of the mold. When repairing mold defects such as blisters, pores, and wear, use equipment with little thermal impact such as cold welders to avoid the occurrence of deformation during the repair process.