Different types and appearance requirements of straight seam steel pipes

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, 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.

③The surface of the weld shall not be lower than the surface of the pipe. The weld reinforcement shall not be greater than 3mm (it is the maximum width of the groove after the welding joint assembly).

④The 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 selection of materials. For precision molds, micro-deformation mold steel with good quality should be selected. Mold steel with severe carbide segregation should be reasonably cast and subjected to quenching and tempering heat treatment. For larger and uncastable mold steel, solid solution double-refining heat treatment can be performed. Reasonably select the heating temperature and control the heating speed. For precision 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 useful methods to reduce precision mold deformation. Precision molds are deformed, but as long as we understand their deformation rules, analyze their causes, and use special methods to prevent mold deformation, the deformation of the mold can be reduced and controlled.

③Precision molds must be preheated to eliminate residual stress generated during machining. For precision 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. Combined planning can be used for large and precision molds. For some precision molds, pre-heat treatment, aging heat treatment, and tempering and nitriding heat treatment can be used to control the accuracy of the mold. Repairing mold blisters and pores

⑤ When there are defects such as wear and tear, use equipment with small thermal impact such as cold welding machines to avoid the occurrence of deformation during the repair process.