Detailed explanation of large-diameter straight seam steel pipe welding process: Double-wire automatic welding of straight seam steel pipe is a welding technology developed in recent years. In addition to the characteristics of semi-automatic single-wire welding, it also has welding characteristics such as energy concentration and high deposition efficiency. The main and auxiliary wires are provided with welding current by separate ordinary welding power supplies, which are independently adjustable and can achieve the best optimization configuration of welding process parameters. The spacing and welding angle between the two wires is always maintained, which effectively controls the electromagnetic interference between the double arcs and has excellent static and dynamic characteristics. The two separate power supplies rely on the welding software to coordinate and supply power to the main and auxiliary wires. At the same time, the main and auxiliary wires are melted, and the transition metal is transferred to the weld to form a stable molten pool, which effectively guarantees the strength of the welded joint. It can not only use conventional melting electrode welding power supplies to achieve welding, but also reduce equipment costs, make the welding heat highly concentrated, the deposition speed fast, the welding efficiency is high, the deformation after welding is small, the labor intensity is low, and the organization and performance of the straight seam steel pipe weld are effectively improved, especially for the welding of high thermal conductivity materials, the effect of energy concentration is outstanding.
1. Control of weld gap: The strip is fed into the welded steel pipe unit, and after multiple roller rolling, the strip is gradually rolled up to form a round tube with an open gap. The pressing amount of the extrusion roller is adjusted to control the weld gap to 1~3mm, and the two ends of the weld are flush. If the gap is too large, the proximity effect is reduced, the eddy current heat is insufficient, and the intercrystalline bonding of the weld is poor, resulting in confusion or cracking. If the gap is too small, the proximity effect is increased, the welding heat is too large, causing the weld to burn; or the weld forms a deep pit after extrusion and rolling, affecting the weld surface.
2. Welding temperature control: When the input heat is insufficient, the edge of the heated weld cannot reach the welding temperature, and the metal structure remains solid, resulting in confusion or incomplete penetration; when the input heat is insufficient, the edge of the heated weld exceeds the welding temperature, resulting in overburning or molten droplets, causing the weld to form a molten hole.
3. Regulation of the position of the high-frequency induction coil: The high-frequency induction coil should be as close to the position of the extrusion roller as possible. If the induction coil is far away from the extrusion roller, the effective heating time is longer, the heat-affected zone is wider, and the weld strength decreases; on the contrary, the weld edge is not heated enough, and the forming is poor after extrusion.
4. Control of extrusion pressure: After the two edges of the large-diameter straight seam steel pipe billet are heated to the welding temperature, under the extrusion of the extrusion roller, a common metal grain is formed to penetrate and crystallize each other, and finally a solid weld is formed. If the extrusion pressure is too small, the number of common crystals formed is small, the weld metal strength decreases, and cracks will occur after the force; if the extrusion pressure is too large, the molten metal will be squeezed out of the welded steel pipe, which not only reduces the weld strength, but also produces a large number of internal and external burrs, and even causes defects such as welding overlap.
5. The impedance is a special magnetic rod for welding steel pipes or a group of them. The cross-sectional area of the impedance should usually not be less than 70% of the inner diameter cross-sectional area of the steel pipe. Its function is to make the induction coil, the edge of the pipe billet weld, and the magnetic rod form an electromagnetic induction loop, produce a proximity effect, and the eddy current heat is concentrated near the edge of the pipe billet weld so that the edge of the pipe billet is heated to the welding temperature. The impedance is dragged in the tube with a steel wire, and its center position should be relatively fixed near the center of the extrusion roller. When the machine is turned on, due to the rapid movement of the tube, the impedance is greatly worn by the friction of the inner wall of the tube and needs to be replaced frequently.
6. After welding and extrusion, the weld will produce weld scars, which need to be fixed on the frame. The method is to fix the tool on the frame and scrape the weld scars flat by the rapid movement of the welded steel pipe. The burrs inside the welded steel pipe are generally not.
Large-diameter straight seam steel pipe production method:
1. Introduction to the production process of large-diameter straight seam steel pipe: Coiler → Uncoiler → Uncoiler → Feeding and leveling machine → Vertical roller centering → Shearing and welding → Strip position control (double-headed vertical roller) → Disc shear → Strip position control (double-headed vertical roller) → Milling machine (fine milling X-shaped groove) → Double-headed vertical roller → Strip surface debris cleaning → Double-headed vertical roller → Delivery machine → Strip introduction and strip position control → Forming machine → Internal welding → External welding → Steel pipe straightening device → Plasma cutting → Straight seam steel pipe outlet
2. Detailed explanation of the production process of straight seam steel pipe
1) Pre-forming work of large-diameter straight seam steel pipe: Raw materials are strip coils, welding wires, and fluxes. They must undergo strict physical and chemical inspections before being put into use. The head and tail of the strip are butt-jointed, and single-wire or double-wire submerged arc welding is used. After the steel pipe is rolled, automatic submerged arc welding is used for repair welding.
2) Forming process of large-diameter straight seam steel pipe: The pressure of the oil cylinder on both sides of the conveyor is controlled by an electric contact pressure gauge to ensure the smooth conveying of the strip. The main machine is centrally positioned, so the vertical rollers should be checked and adjusted frequently (especially before and after the head) to ensure that the edge of the strip delivery strictly follows the route specified by the process and passes through the designed meshing point. Use external or internal control roller forming to check whether the circumference, ovality, straightness, etc. of the steel pipe meet the standard requirements. If not, continue to adjust until the requirements are met.
3) Welding process of large-diameter straight seam steel pipe: A weld gap control device is used to ensure that the weld gap meets the welding requirements. The pipe diameter, misalignment, and weld gap are strictly controlled. The forming seam condition should be observed continuously. If misalignment, open seam, etc. are found, the rear axle angle should be fine-tuned in time to ensure forming; when the situation is abnormal, the working width of the steel strip, the edge pre-bending condition, the delivery line position, the small roller angle, etc. should be checked for changes, and corrective measures should be taken in time. At present, the internal and external welding of Hebei straight seam steel pipe manufacturers are all carried out by Lincoln electric welding machines for single-wire or double-wire submerged arc welding, to obtain stable welding. Straight seam steel pipe manufacturers should continuously observe the condition of the forming seam. If the misalignment, seam opening, etc. are found, the rear axle angle should be fine-tuned in time to ensure the forming; when the situation is abnormal, the working width of the steel strip, the edge pre-bending condition, the delivery line position, the small roller angle, etc. should be checked for changes, and corrective measures should be taken in time.
4) Inspection of large-diameter straight seam steel pipes: The welded welds are all inspected by online continuous wave automatic flaw detectors to ensure 100% non-destructive testing coverage of spiral welds. If there are defects, the alarm will be automatically alarmed and sprayed with marks, and the production workers will adjust the process parameters at any time to eliminate the defects in time. When the nominal diameter D≥426mm, the internal defects of the steel pipe should be repaired and welded inside; when D≤426mm, the internal defects are allowed to be repaired from the outside. The welds after repair are ground, and the remaining wall thickness after grinding should be within the specified wall thickness tolerance range. Before the repaired steel pipe enters the next process, it should be carefully checked for any defects that have been missed or missed. Only after confirmation can it be transferred to the next process. The strip butt welds and the pipes where the T-joints intersect with the spiral welds are all inspected by X-ray television or film. Each steel pipe undergoes a hydrostatic pressure test, and the pressure is radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. The test parameters are automatically printed and recorded.
Post time: Jan-03-2025