Straight seam steel pipes can be divided into high-frequency straight seam steel pipes(ERW) and submerged arc welded straight seam steel pipes (LSAW) according to the production process. The most common forming process in the process of submerged arc welded steel pipes and straight seam forming will be explained below.
Submerged arc welding
After the steel plates used for the production of large-diameter submerged arc welded straight seam steel pipes enter the production line, we must first perform ultrasonic inspection on the entire steel plate. Use a milling machine to analyze and mill the two edges of the steel plate on both sides at the same time to achieve the required plate width, plate edge parallelism and groove shape. Use an edge pre-bending machine to pre-bend the plate to make the edge of the plate with the required curvature; the front half of the pre-bent steel plate is pressed into the JCO "J" 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 can be formed.
The formed longitudinally welded steel pipes are connected together and continuously welded by gas shielded welding (MAG). The longitudinal multi-wire submerged arc welding (up to four wires) is used for welding the inner side of the longitudinal steel pipe; the longitudinal multi-wire submerged arc welding is performed outside the LSAW steel pipe. When welding, in the first ultrasonic inspection (and to inspect the welding on both sides of the substrate), after the first X-ray inspection (in order to ensure the detection sensitivity inspection), the diameter is enlarged, and the water pressure test (hydraulic pressure tester) The record will be saved automatically).
Then the qualified steel pipe is processed into a size that meets the design requirements, and then the second ultrasonic inspection can be carried out in turn. The second X-ray inspection, anti-corrosion and coating treatment, tube end magnetic particle inspection, to complete our entire system processing work process.
High frequency welding
High-frequency welding is based on the principle of electromagnetic induction and the skin effect, proximity effect and eddy current heating effect of the AC charge in the conductor. The steel at the edge of the weld is heated to a molten technical state, and then squeezed with a roller to achieve corporate butt joints and welds. The intercrystalline bonding can achieve the purpose of seam welding. High-frequency welding is a kind of induction welding (or pressure contact welding). It has no welding filler material, no welding spatter, narrow welding heat affected zone, and a very good shape. Therefore, it is widely used in the production of steel pipes.
The high-frequency welding technology of steel pipes uses skin effect and proximity effect. After rolling steel (strip), a round tube blank with a cross-section is formed, which rotates in the tube near the center of the induction coil; The magnetic induction tube split ring. 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 quickly heated to the temperature required for the welding work and is squeezed by the pressure roller. Metal can realize intercrystalline bonding, and after cooling, a firm butt weld is formed.