Welding process and production method of large diameter straight seam steel pipe

A detailed explanation of the welding process of large diameter straight seam steel pipe:

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 supplied with welding current by a separate ordinary welding power source, which can be independently adjusted to achieve the optimal configuration of welding process parameters. The distance between the two wires and the welding angle is always maintained, effectively controlling the gap between the double arc Electromagnetic interference, with unique static and dynamic characteristics, the two independent power supplies rely on the joint coordination of welding software to 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 ensures the strength of the welded joint to the greatest extent. It can not only use the conventional melting electrode welding power supply to realize welding, but also reduce the equipment cost, make the welding heat highly concentrated, the deposition speed is fast, the welding efficiency is high, the deformation after welding is small, the labor intensity is low, and the straight seam steel pipe weld seam is effectively improved. Tissue performance, especially for welding of high thermal conductivity materials, the effect of energy concentration is the most prominent.

1. Control of weld seam gap: The strip steel is sent into the welded steel pipe unit, rolled by multiple rollers, and the strip steel is gradually rolled up to form a round tube billet with an opening gap. Adjust the reduction of the extrusion roller so that The welding seam gap is controlled at 1~3mm, and the two ends of the welding joint are flush. If the gap is too large, the proximity effect will be reduced, the heat of the eddy current will be insufficient, and the intergranular 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 large, causing the weld to burn; or the weld will form a deep pit after extrusion and rolling, which will affect the surface of the weld.

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, forming incomplete fusion or incomplete penetration; when the input heat is insufficient, the heated weld The edge exceeds the welding temperature, resulting in overheating or molten droplets, causing the weld to form a molten hole.

3. Adjustment 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 extrusion roller. 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 strength of the weld seam decreases; otherwise, the edge of the weld seam is insufficiently heated, and the shape after extrusion is poor.

4. Control of extrusion force: 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, the common metal grains are formed to penetrate and crystallize each other, and finally form a firm 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 cracks will occur after being stressed; if the extrusion force is too large, the molten metal will be squeezed out of the welded steel pipe, not only The strength of the weld is reduced, and a large number of internal and external burrs will be generated, and even defects such as welding laps will be caused.

5. The impedance is one or a group of special magnetic rods for welding steel pipes. The cross-sectional area of the impedance should usually not be less than 70% of the inner diameter of the steel pipe. The magnetic induction circuit produces a proximity effect, and the eddy current heat is concentrated near the edge of the weld seam of the tube blank, heating the edge of the tube blank to the welding temperature. The impedance is dragged in the tube blank by a steel wire, and its central 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 is worn out by the friction of the inner wall of the tube blank and needs to be replaced frequently.

6. Weld scars will be produced after welding and extrusion. 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.

The production method of large diameter straight seam steel pipe:

1. Introduction of production process: Coiler → Uncoiler → Uncoiler → Lead leveler → Vertical roll centering → Shear butt welding → Strip position control (double-headed vertical roll) → Disc shears → Strip position Control (double-headed vertical rolls) → edge milling machine (fine milling X-shaped bevel) → double-headed vertical rolls → strip surface debris cleaning → double-headed vertical rolls → 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

A) Work before forming: Raw materials are strip steel coil, welding wire, and flux. Before putting into use, they must go through strict physical and chemical tests. The head-to-tail butt joint of strip steel adopts single-wire or double-wire submerged arc welding, and automatic submerged arc welding is used for repair welding after being rolled into steel pipes.

B) Forming process: Electric contact pressure gauges are used to control the pressure of the cylinders on both sides of the conveyor to ensure the smooth conveying of the strip steel. The main machine is positioned at the center, so the vertical rollers should be checked and adjusted frequently (especially before and after the opposite end) to ensure The strip delivery edge runs strictly on the route established by the process and passes the designed engagement point. Use external control or internal control roll forming to check whether the circumference, ellipticity, straightness, etc. of the steel pipe meet the standard requirements. If it does not meet the requirements, continue to adjust until it meets the requirements.

C) Welding process: The weld gap control device is used to ensure that the weld gap meets the welding requirements. The pipe diameter, misalignment amount, and weld gap are strictly controlled. The condition of the forming seam should be continuously observed to find misalignment, open If the situation is abnormal, check the working width of the steel strip, the edge pre-bending condition, the position of the delivery line, and the angle of the small roller, etc., and take corrective measures in time. Hebei straight seam steel pipe manufacturers currently use Lincoln welding machines for single-wire or double-wire submerged arc welding for internal and external welding, to obtain stable welding. Manufacturers of straight seam steel pipes should continuously observe the condition of the forming seam and fine-tune the angle of the rear bridge in time to ensure the forming if they find the wrong side, open seam, etc., Small roll angle, etc. have changed, and take corrective measures in time.

D) Inspection: The welded seams are all inspected by the online continuous wave automatic flaw detector, which ensures 100% non-destructive inspection coverage of the spiral welds. If there is a defect, it will automatically alarm and spray the mark, and the production workers can adjust the process parameters at any time according to this to eliminate the defect in time. When the nominal diameter D is greater than or equal to 426mm, the internal defects of the steel pipe should be welded and repaired inside; when D is less than or equal to 426mm, the internal defects are allowed to be repaired from the outside. The weld seam after repair welding shall be ground, and the remaining wall thickness after grinding shall be within the specified wall thickness tolerance range. Before the welded steel pipe enters the next process, it is necessary to carefully check whether any defects on the steel pipe have not been repaired or missed, and it can be transferred to the next process after confirmation. The tubes where the strip steel butt welds and the D-joints intersected with the spiral welds are all inspected by X-ray TV 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. The test parameters are automatically printed and recorded.