Steel pipes can be divided into two categories according to production methods. One is seamless steel pipes and the other is welded steel pipes. Welded steel pipes are longitudinally welded pipes. According to the welding method, welded steel pipes can be further divided into high-frequency welded pipes and double-sided buried pipes. Arc welded pipe.

First of all, let us focus on the high-frequency welded pipe. The diameter of the high-frequency welded pipe is usually very small and does not need to pass through the welding wire, so the possibility of cracking during expansion is small. As far as the welding speed is concerned, the speed can be as high as 200 meters per minute for those with a smaller outer diameter, such as less than 1 inch. There are usually two crimping methods, one is welding, and the other is fusion welding. High-frequency welding is the first welding method. From the processing point of view, welding welded pipe is mainly to bend the steel plate into a cylinder and then weld it to form. The method is simple and efficient.

According to the principle of electromagnetic induction and the skin effect, proximity effect and eddy current heat effect of the AC charge in the conductor, the steel at the welding edge is heated and melted, and then squeezed by a roller to realize the intercrystalline connection of the butt weld, thereby achieving the purpose of welding. High-frequency welding is a kind of induction welding, which does not require welding fillers, no welding spatter, narrow welding heat-affected zone, beautiful welding appearance, and good welding mechanical properties. It has been widely used in the production of steel pipes.

The high-frequency welding of steel pipes uses the skin effect and proximity effect of alternating current. After the steel (strip) is rolled and formed, a circular tube blank with a broken section is formed. Rotate one or a group of resistors (magnetic rods) near the center of the tube blank induction coil. The resistor and the opening of the tube form a Electromagnetic induction loop. Under the skin effect and proximity effect, a strong and concentrated heat effect is generated at the edge of the tube blank opening, so that the edge of the weld is quickly heated to the temperature required for welding. After being squeezed by the pressure roller, the molten metal realizes intergranular bonding and cooling Then a firm butt weld is formed.

Double-sided submerged arc welded pipes need to use welding wire. The welding seam is much longer than that of straight seam pipes. The production efficiency will be much lower, but it may be stronger in terms of strength and compression resistance. It also has other advantages, such as a very good realization of automation. Secondly, based on two aspects of relatively strong performance, so the final product welding quality is higher, on the one hand is heat exchange, on the other hand is the protection performance.

The production process based on high-frequency welded pipe is relatively simple, so relatively speaking, the production efficiency of high-frequency welded pipe is higher, but on the basis of the continuous development of double-sided submerged arc welded pipe, its production efficiency has also been further improved. In short, these two welding methods have their own advantages and disadvantages. High frequency welded pipe has the advantages of small cracking possibility, fast welding speed, simple welding forming method and high production efficiency. The main advantages of double-sided submerged arc welded pipes are automation and high welding quality. In practical applications, which welding method should be selected, also needs to be analyzed according to specific conditions.