Processing and manufacturing technology of straight seam steel pipe

After the steel plates used to produce large-diameter submerged arc welded straight seam steel pipes enter the production line, we first need to conduct ultrasonic inspection of the entire steel plate. Use an edge milling machine to analyze and mill the two edges of the steel plate on both sides at the same time to achieve the desired plate width, plate edge parallelism and groove shape. An edge pre-bender is used to pre-bend the plate so that the edge of the plate has the desired curvature; the front half of the pre-bent steel plate is pressed into JCO’s “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 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 for welding on the inside of the longitudinal steel pipe; longitudinal multi-wire submerged arc welding is performed on the outside of the LSAW steel pipe. When welding, after the first ultrasonic inspection (and is to inspect the welding on both sides of the substrate), after the first X-ray inspection (to ensure detection sensitivity inspection), the diameter is enlarged, and the hydraulic pressure test (the hydraulic pressure tester will Automatically save records).

The qualified steel pipe is then processed into a size that meets the design requirements, and then the second ultrasonic inspection can be carried out in sequence. Second X-ray inspection, anti-corrosion and coating treatment, pipe 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 thermal effect of AC charges in the conductor. The steel at the edge of the weld is heated to a molten state, and then extruded with rollers to achieve corporate butt joints and welds. Intergranular 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, a narrow welding heat affected zone, and a pretty good shape. Therefore, it is widely used in the production of steel pipes. 

The high-frequency welding technology of steel pipes uses the skin effect and proximity effect. After rolling the steel (strip), a circular tube blank with a cross-section is formed, which rotates in the tube near the center of the induction coil; or in a set of resistors (magnetic rods), an electric current is formed. The magnetic induction tube is composed of a split ring. Under the skin effect and proximity effect, the edge of the tube blank opening produces a strong and concentrated heat effect, causing the weld to proceed. After the edge is quickly heated to the temperature required for welding work and squeezed by the pressure roller, the molten The metal can achieve intergranular bonding and form a strong butt weld after cooling.