Straight seam steel pipes can be divided into high-frequency straight seam steel pipes(ERW steel pipes) and submerged arc welded straight seam steel pipes(SSAW steel pipes) according to the production process. The following describes the most common high-frequency straight seam steel pipe and submerged arc welded straight seam steel forming process.

Submerged arc welding

After the steel plate used to manufacture the large-diameter submerged arc welded straight seam steel pipe enters the production line, the entire steel plate must be ultrasonically inspected; the two edges of the steel plate are milled on both sides with a milling machine to achieve the required plate width and plate edge Parallelism and groove shape. Use a pre-bending machine to bend the edge of the plate so that the edge of the plate has the desired curvature; press the first half of the pre-bent steel plate into a "J" shape on the JCO forming machine. Then, the other half of the steel plate is also bent and pressed into a "C" shape, and finally an open "O" shape is formed.

The formed longitudinal welded steel pipes are connected together and continuously welded by gas shielded welding (MAG); longitudinal multi-wire submerged arc welding (up to four wires) is used to weld the inner side of the longitudinal steel pipe; longitudinal multi-wire submerged arc welding is used in LSAW steel pipe is carried out on the outside. After the welding is completed, perform the first ultrasonic inspection (mainly the inspection of the weld and the base materials on both sides), the first X-ray inspection (the inspection to ensure the sensitivity of flaw detection), the diameter expansion and the water pressure test (water pressure tester) Records will be saved automatically).

Then, the qualified steel pipe is processed into the required size, and then the second ultrasonic inspection, the second X-ray inspection, the tube end magnetic particle inspection, anti-corrosion and coating treatment are carried out in order to complete the entire treatment process.

High frequency welding

High frequency welding is based on the principle of electromagnetic induction and the skin effect of AC charges in the conductor, proximity effect and eddy current heating effect. The steel at the edge of the weld is heated to a molten state, and then squeezed with a roller to achieve the intergranular bonding of the butt weld, so as to achieve the purpose of seam welding. High frequency welding is a kind of induction welding (or pressure contact welding). It does not require welding seam fillers, no welding spatter, narrow welding heat-affected zone, beautiful welding shape and good welding mechanical properties. Therefore, it is widely used in the production of steel pipes. Wide range of applications.

The high-frequency welding of steel pipes uses the skin effect and proximity effect of AC. After rolling the steel (strip), a circular tube blank with a cross section is formed, which is rotated in the tube near the center of the induction coil. Or a set of resistors (magnetic rods), which form an electromagnetic induction loop with the opening of the tube blank. Under the skin effect and proximity effect, the edge of the tube blank produces a strong and concentrated heat effect, so that the edge of the weld is rapidly heated to the temperature required for welding and squeezed by the pressure roller, and the molten metal realizes the intergranular bonding , After cooling, a firm butt weld is formed.