Large Diameter Straight Seam Steel Pipe Welding Process And Production Method

A detailed explanation of the welding process of large-diameter straight seam steel pipes: Double-wire automatic welding of straight seam steel pipes 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 a separate ordinary welding power source and are independently adjustable, which can achieve the best-optimized configuration of welding process parameters. The spacing and welding angle between the two wires is always maintained, effectively controlling the distance between the double arcs. It has excellent electromagnetic interference and excellent static and dynamic characteristics. The two independent power sources 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 metal is transferred into the weld to form a stable molten pool, which ensures the strength of the welded joint. It can not only use conventional molten electrode welding power sources to achieve welding, but also reduce equipment costs, making the welding heat highly concentrated, fast deposition speed, high welding efficiency, small post-weld deformation, low labor intensity, and effectively eliminate straight seam steel pipe welds. Structural properties, especially for welding of high thermal conductivity materials, the effect of energy concentration is outstanding.

1. Control of the weld gap: The strip is fed into the welded steel pipe unit. After being rolled by multiple rollers, the strip is gradually rolled up to form a circular tube blank with an opening gap. Adjust the pressing amount of the extrusion roller so that The weld gap should be controlled at 1~3mm, and both ends of the weld should be flush. If the gap is too large, the proximity effect will be reduced, the eddy current heat will be insufficient, and the inter-crystal bonding of the weld will be poor, resulting in a lack of fusion or cracking. If the gap is too small, the proximity effect will increase and the welding heat will be too high, causing the weld to burn out; or the weld will form a deep pit after being extruded and rolled, affecting the surface of the weld.

2. Welding temperature control: When the input heat is insufficient, the heated weld edge cannot reach the welding temperature, and the metal structure remains solid, resulting in incomplete fusion or incomplete welding; when the input heat is insufficient, the heated weld edge The edge exceeds the welding temperature, resulting in overburning or molten droplets, causing the weld to form a molten hole.

3. Control of the position of the high-frequency induction coil: The high-frequency induction coil should be as close as possible to the position of the squeeze roller. If the induction coil is far away from the extrusion roller, the effective heating time will be longer, the heat-affected zone will be wider, and the strength of the weld will decrease; on the contrary, the edge of the weld will not be heated enough and the shape will be poor after extrusion.

4. Control of extrusion force: After the two edges of the large-diameter straight seam steel pipe blank are heated to the welding temperature, under the squeeze of the extrusion roller, common metal grains are formed to penetrate and crystallize with each other, and finally form a strong weld. seam. If the extrusion force is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracking will occur after stress; if the extrusion force is too large, the molten metal will be extruded out of the weld steel pipe, not only The strength of the weld is reduced, a large number of internal and external burrs are produced, and even defects such as welding overlaps are caused.

5. The resistor is one or a group of special magnetic rods for welded steel pipes. The cross-sectional area of the resistor should usually not be less than 70% of the cross-sectional area of the inner diameter of the steel pipe. Its function is to make the induction coil, the edge of the tube blank weld, and the magnetic rod form an electric current. The magnetic induction loop produces a proximity effect, and the eddy current heat is concentrated near the edge of the tube blank weld, causing the edge of the tube blank to be heated to the welding temperature. The resistor is dragged inside the tube blank with a steel wire, and its center position should be relatively fixed close to the center of the extrusion roller. When starting up, due to the rapid movement of the tube blank, the resistor suffers from large losses due to friction on the inner wall of the tube blank and needs to be replaced frequently.

6. The weld seam will produce weld scars after welding and extrusion, which is required. The method is to fix the tool on the frame and rely on the rapid movement of the welded steel pipe to smooth the weld scar. There are generally no burrs inside welded steel pipes.

The production method of large diameter straight seam steel pipe:

1. Introduction to the production process: Coiler → Uncoiler → Uncoiler → Lead-in leveler → Vertical roller centering → Shearing butt welding → Strip position control (double-headed vertical roll) → Disc shear → Strip position Control (double-head vertical roller) → edge milling machine (precision milling X-shaped groove) → double-head vertical roller → strip surface debris cleaning → double-head vertical roller → delivery machine → strip introduction and strip position control → forming Machine → Internal welding → External welding → Steel pipe centralizing device → Plasma cutting → Straight seam steel pipe outlet

2. Detailed explanation of the production process of straight seam steel pipes

1) Pre-forming work: raw materials are strip steel coil, welding wire, and flux. They must undergo strict physical and chemical inspections before being put into use. The head and tail of the steel strip are butt-joined using single-wire or double-wire submerged arc welding. After being rolled into a steel pipe, automatic submerged arc welding is used for repair welding.

2) Forming process: Electric contact pressure gauges are used to control the pressure of the cylinders on both sides of the conveyor to ensure smooth conveying of the strip. The main machine is centered, so the vertical rollers should be checked and adjusted frequently (especially before and after the opposite end) to ensure The strip delivery edge follows the exact route of the process and passes through the designed meshing points. Use externally controlled or internally controlled roller forming to check whether the circumference, ovality, straightness, etc. of the steel pipe meet the standard requirements. If it does not meet the requirements, continue to adjust until the requirements are met.

3) Welding process: The weld gap control device is used to ensure that the weld gap meets the welding requirements. The pipe diameter, offset amount, and weld gap are strictly controlled. The forming seam condition should be continuously observed to detect misalignment and opening. If there are seams and other conditions, the rear axle angle should be fine-tuned in time to ensure the molding; when the situation is abnormal, the working width of the steel strip, edge pre-bending status, delivery line position, small roller angle, etc. should be checked for changes, and corrective measures should be taken promptly. Hebei straight seam steel pipe manufacturers currently use electric welding machines for single-wire or double-wire submerged arc welding for both internal and external welding to obtain stable welding. Manufacturers of straight seam steel pipes should continuously observe the condition of the forming seams. If they find misaligned edges, open seams, etc., they should promptly fine-tune the rear axle angle to ensure forming; when the situation is abnormal, they should check the working width of the steel strip, edge pre-bending status, and delivery line position. , small roller angle, etc., and take corrective measures promptly.

4) Inspection: All completed welds are inspected by an online continuous wave automatic flaw detector, ensuring 100% non-destructive testing coverage of spiral welds. If there is a defect, it will automatically alarm and spray mark, so that production workers can adjust the process parameters at any time to eliminate defects in time.

When the nominal diameter D ≥ 426mm, internal defects of the steel pipe should be repaired and repaired inside; when D ≤ 426mm, internal defects are allowed to be repaired and repaired from the outside. The welds after repair welding shall be ground, and the remaining wall thickness after grinding shall be within the specified wall thickness tolerance range. Before entering the next process of repairing welded steel pipes, you should carefully check whether there are any missed repairs or defects on the steel pipes. Only after confirmation can you move to the next process.

The butt welds of the strip and the pipes where the T-shaped joints intersect with the spiral welds are all inspected by X-ray television or film. Each steel pipe is hydrostatically tested and the pressure is radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. Test parameters are automatically printed and recorded.