Detailed explanation of straight seam steel pipe

Straight seam steel pipe refers to a steel pipe in which the welding seam is parallel to the length direction of the steel pipe. Usually divided into metric electric welded steel pipes, electric welded thin-walled pipes, transformer cooling oil pipes, etc. The production process of longitudinal welded pipes is simple, with high production efficiency, low cost and rapid development. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Narrower blanks can be used to produce larger diameter welded pipes, while billets of the same width can also be used to produce welded pipes of different diameters, but compared with straight seam pipes of the same length, the welding length is increased by 30-100% and the production speed is reduced. .

Straight seam steel pipe: used to transport low-pressure fluid. Steel pipes need to undergo hydraulic pressure, bending and other experiments, and have certain requirements for surface quality. Usually, the delivery length is 4-10m, and delivery is usually required in fixed length (or double length). The specifications of welded pipes are expressed in nominal diameter (mm or inches). The nominal diameter is different from the actual diameter. According to the specified wall thickness, welded pipes are divided into ordinary steel pipes and thickened steel pipes.
Straight seam steel pipes can be divided into high-frequency straight seam steel pipes and submerged arc welded straight seam steel pipes according to the production process. Submerged arc welded straight seam steel pipes are further divided into UOE, RBE, JCOE steel pipes according to their different forming methods. The most common ones are introduced below. Forming process of high frequency straight seam steel pipe and submerged arc welded straight seam steel pipe.

High frequency welding
Straight seam welded steel pipes are made by rolling long strips of steel strips of certain specifications into round tubes through high-frequency welding units and then straight seam welding them into steel pipes. The shape of the steel pipe can be round, square or special-shaped. It Depends on the sizing rolling after welding. The main materials of welded steel pipes are: low carbon steel and low alloy steel or other steel materials with σs≤300N/mm2, σs≤500N/mm2. The production process of high-frequency welding of straight seam steel pipes is as follows:
High-frequency welding is based on the principle of electromagnetic induction and the skin effect, proximity effect and eddy current heating effect of AC charges in the conductor, so the steel at the edge of the weld is locally heated to a molten state, and the butt weld is squeezed by the rollers. together to achieve the purpose of seam welding. High-frequency welding is a type of induction welding (or pressure contact welding) that requires no weld filler, no welding spatter, a narrow welding heat-affected zone, beautiful welding shape, and good welding mechanical properties. Therefore, it has many advantages in steel pipe production and has a wide range of applications.
High-frequency welding of steel pipes utilizes the skin effect and proximity effect of AC. After the steel (strip) is rolled and shaped, a circular tube blank with a cross-section is formed, and rotates in the tube blank near the center of the induction coil. Or a set of resistors (magnetic rods) that form an electromagnetic induction loop with the opening of the tube blank. Under the action of skin effect and proximity effect, the edge of the opening of the tube blank produces a strong and concentrated thermal effect. After the edge of the weld is rapidly heated to the temperature required for welding and squeezed by a pressure roller, the molten metal achieves intergranular bonding and forms a strong butt weld after cooling.