Ultra-large-diameter spiral welded pipe and manufacturing method

Abstract

According to the manufacturing method of the ultra-large-diameter spiral welded pipe, when forming is conducted at the large forming angle of 80 degrees or above, a forming device formed by combining three lower rollers, three upper rollers and four externally-controlled adjustable single rollers is built, a double-end welding pad roller and two forming device auxiliary outer rollers are additionally arranged on the forming device, and it is guaranteed that the geometric dimension of a large-diameter spiral welded pipe body is high in precision, and the residual stress of the welded pipe is low. Meanwhile, laser penetration spot welding is adopted for pre-welding, laser welding and CMT welding are adopted for internal welding, laser welding and SAW welding are adopted for external welding, the welding wire filling amount of the ultra-large-diameter thick-wall pipe is reduced, the depth-to-width ratio of a laser penetration welding seam is large, and during laser welding, under the condition of the same flow, He gas is adopted as shielding gas to deepen the laser welding depth; according to the online normalizing heat treatment method, the welding seams are completely fused after laser welding of the inner welding seams and the outer welding seams is ensured, laser welding joints after online normalizing heat treatment are refined in welding seam structure, the problems of softening and embrittlement of a thick-wall submerged-arc welding heat affected zone are solved, and the impact toughness of the laser welding joints, especially the heat affected zone, is higher than that of base metal.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing spiral welded pipes, and more particularly to an ultra-large diameter spiral welded pipe and a manufacturing method thereof.

Background Art

[0002] Nowadays, steel pipes used in water conservancy and hydropower projects have tended to develop in the direction of ultra-large diameter and ultra-large diameter-thickness ratio. Ultra-large diameter spiral submerged arc welded pipes have begun to be applied in the water conservancy and hydropower water conveyance industry. Conventional large diameter spiral welded pipes generally refer to those with an outer diameter of 1016 mm or more in the oil and gas industry. However, the outer diameter of large diameter welded pipes used in the water conveyance field generally refers to welded pipes with an outer diameter of 1219 mm to 3000 mm. When the outer diameter of the project exceeds 3000 mm, it is called an ultra-large diameter welded pipe. The working pressure of ultra-large diameter welded pipes is generally 0.8 Mpa to 2.5 Mpa. Affected by the capacity of the plate rolling mill, currently, only coils for spiral welded pipes with a maximum wall thickness of 25.4 mm can be rolled. However, for pipe factories, the geometric accuracy of ultra-large diameter spiral welded pipes with a nominal outer diameter greater than 3000 mm, a wall thickness of more than 16 mm and less than 25.4 mm is poor after forming, and all use submerged arc welding. Some pipe factories use double-sided welding, and both the inner weld and the outer weld need to be beveled, and the amount of filler wire filled is large. Some pipe factories use single-sided welding, and the outer weld needs to be beveled with a larger V-shaped or U-shaped groove, and the amount of filler wire filled is even more.

[0003] The above-mentioned forming and submerged arc welding methods will cause large deformation of the welded pipe, high residual stress in the welded pipe, poor geometric dimensional accuracy, and there are softening and embrittlement phenomena in the heat affected zone of thick-walled submerged arc welded pipes. The impact toughness of the heat affected zone has been unstable and low. During hydrostatic testing, ultra-large diameter welded pipes require several hours of water filling time. After water filling, together with the self-weight of the welded pipe, it exceeds more than 100 tons, and the base will be crushed during testing on an ordinary hydrostatic testing machine.

[0004] In view of this, the present invention provides a method for manufacturing an ultra-large diameter spiral welded pipe.

Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for manufacturing an ultra-large diameter spiral welded pipe. After forming with a lower three-roll, an upper three-roll and 4 externally controlled adjustable single rolls, the geometric dimensional accuracy of the pipe body is high and the residual stress is small. After adding laser welding, the amount of filler wire in the weld is small, and the toughness of the welded joint, especially the heat affected zone, is higher than that of the base material.

[0006] The present invention is realized through the following technical solutions. A method for manufacturing an ultra-large diameter spiral welded pipe is provided, including the following steps: uncoiling, leveling, edge milling, pre-bending, large-angle forming, laser pre-welding, length cutting, laser welding + CMT internal welding, laser welding + SAW external welding, weld normalizing heat treatment, pipe end expanding, ultrasonic inspection, X-ray inspection, hydrostatic test, pipe end chamfering, finished product inspection, wherein:

[0007] Edge milling: When manufacturing spiral submerged arc welded pipes using cut-to-length coils, the width of the coil should be not less than 1500 mm and not greater than 1650 mm, and the thickness of the coil is 16 mm - 25.4 mm. During edge milling, the inner-weld area in the middle of the wall thickness at both ends of the coil is milled into a type I shape, and the height of the type I root face is 8 mm - 16 mm; the inner-weld groove is milled into a small V-shaped groove, and the groove angle after jointing is 55° - 65°, and the height of the inner-weld groove is 2 mm. The outer-weld groove is milled into a large V-shaped groove, and the groove angle after jointing is 55° - 65°, and the height of the outer-weld groove is 6 mm - 10 mm. Thus, a type I groove beneficial for laser penetration welding and a V-shaped groove for CMT and SAW wire filling are obtained; the width of the plate after edge milling is increased by about 1 mm of allowance based on the calculated plate width to compensate for the shrinkage deformation of the thick-wall weld during laser welding, eliminating the "inner tight and outer loose" phenomenon generated after jointing of extra-large diameter spiral welded pipes.

[0008] Large-angle forming: To reduce the influence of self-weight on the pipe shape and welding quality, the original three-roll forming and externally controlled adjustable form of the former forming machine is removed and reconfigured into a combined former consisting of three lower rolls, three upper rolls, and 4 externally controlled adjustable single rolls. Among them, both the lower three-roll forming and the upper three-roll forming adopt the three-roll plate bending deformation effect to control the pipe diameter accuracy. Among the lower three rolls (approximately located at the 6 o'clock position), roll 1# is an externally controlled roll, roll 2# is an internal pressure roll, and roll 3# is an externally controlled roll. Among the upper three rolls (approximately located at the 12 o'clock position), roll 6# is an externally controlled roll, roll 7# is an internal pressure roll, and roll 8# is an externally controlled roll. Rolls 4# (approximately located at the 8 o'clock position), 5# (approximately located at the 10 o'clock position), 9# (approximately located at the 2 o'clock position), and 10# (approximately located at the 4 o'clock position) are successively externally controlled adjustable rolls that are nearly symmetric on the circumference. Using the principle of two sets of three-roll plate bending, the inner layer of the coil is extruded and the outer layer is stretched to continuously bend and roll into the billet of an extra-large diameter welded pipe. The deformation distance between rolls 1# and 3# is increased, and the overpressure amount of roll 2# on the extra-large diameter welded pipe is increased, thereby strengthening the auxiliary deformation function of the guide plate. Appropriately adjust the deformation distance between rolls 6# and 8# and the roll-down amount of roll 7# in the upper three-roll forming, thereby assisting in correcting the roundness of the extra-large diameter welded pipe. At the same time, the support of roll 7# as an internal pressure roll prevents the welded pipe from deforming significantly due to gravity. At the same time, double-headed welding pad rolls are added, combined with the auxiliary outer rolls of the 4#, 5#, 9#, and 10# formers to support and deliver the edge, preventing the edge curling phenomenon of extra-large diameter spiral welded pipes, alleviating the problem of extra-large diameter overpressure amount, and making the dynamic deformation of the former billet more stable. The straightener is modified from a gantry cantilever structure to a gantry frame structure to ensure the stability of the forming process of extra-large diameter steel pipes with a large diameter-thickness ratio and low-strength material welded pipes; the width of the first section of the rear axle body is changed from the original 2500 mm to 4600 mm to meet the installation of straighteners with specifications above Ф3000 mm; finally, a large forming angle of more than 80° is adopted to ensure high dimensional accuracy and low residual stress of extra-large diameter spiral welded pipes; after large-angle forming, a gap of ≤0.2 mm is reserved between the inner and outer welds of the formed pipe.

[0009] Laser pre-welding: After the lower three-roll forming and the upper three-roll forming, laser pre-welding is carried out at the bottom of the V-shaped groove of the outer weld. Small laser spot welding with a power below 2kW is used for pre-welding. Laser penetration backing welding with a length of 2 - 3mm is spot-welded at intervals of 100mm. Without wire filling, the forming speed can reach 5m / min using the two-step method, fully releasing the capacity of the forming machine.

[0010] Laser welding + CMT internal welding: A laser with a laser power of 5kW - 10kW and a defocus amount of -1.5mm - +1.5mm is used to complete 5mm - 10mm laser penetration backing welding on the type I root face area from the inner weld joint side. During the laser welding process, pure He gas with a flow rate of 5L / min - 10L / min is introduced as the shielding gas. The laser is in the front and the He shielding gas is in the rear. After the laser penetration backing welding is stable for 0.5s, for the inner weld with a groove depth of 2mm after milling the edge, the CMT welding machine is used to start arc and cover the surface with 1 pass of welding. An equal-strength wire with a diameter of 0.8mm is selected, the voltage is 20.5 ± 2V, and the current is 205 ± 20A. The CMT welding torch is also protected by He gas, and the flow rate is 0.4MPa - 0.6MPa. Finally, the common movement of the laser head and the CMT welding torch is controlled to complete the inner weld welding process, and the welding speed is about 1.6 ± 0.2m / min.

[0011] Laser welding + SAW external welding: A laser with a laser power of 5kW - 10kW and a defocus amount of -1.5mm - +1.5mm is used to complete 5mm - 10mm laser penetration backing welding on the type I root face area from the outer weld joint side. During the laser welding process, pure He gas with a flow rate of 5L / min - 10L / min is introduced as the shielding gas. The laser is in the front and the He shielding gas is in the rear. After the laser penetration backing welding is stable for 0.5s, for the outer weld with a groove depth of 6mm - 10mm after milling the edge, before the SAW twin-wire submerged arc welding starts, 1 pass of wire filling by the front wire and surface covering by the rear wire is carried out. Both wires use equal-strength wires with a diameter of 4.0mm. The first wire uses DC straight polarity, the current is 1300 ± 200A, and the voltage is 30 ± 4V. The second wire uses DC reverse polarity, the current is 800 ± 150A, and the voltage is 36 ± 2V. Finally, the common movement of the laser head and the SAW twin-wire welding torch is controlled to complete the outer weld welding process, and the welding speed is synchronized with the inner weld welding speed at about 1.6 ± 0.2m / min.

[0012] Normalizing heat treatment of the weld: After the laser hybrid welding of the inner and outer welds of the welded pipe, normalizing heat treatment is carried out on the laser-welded seam. A 1000℃ intermediate frequency inductor is used to heat the weld from the inner weld side for 2S - 5S. The weld temperature reaches 930 ± 20℃, and the welded joint is naturally cooled in the air, transforming the microstructure mainly composed of martensite in the weld area after laser welding into a microstructure mainly composed of fine-grained ferrite, ensuring the toughness of the weld and the heat-affected zone.

[0013] Hydrostatic test: On the hydrostatic testing machine platform of the multi-functional water storage and subsidence pit newly built independently, place the extra-large diameter spiral welded pipe into the prefabricated water-containing pit. The water in the pit quickly flows into the welded pipe by gravity. Calculate the thickness of the blind plates at both ends of the extra-large diameter spiral welded pipe, block both ends of the extra-large diameter spiral welded pipe with the blind plates and plugs, and then add pressurized water into the extra-large diameter welded pipe through the union on the plug. Soon when the water pressure reaches 80% of the minimum yield strength of the welded pipe, keep the pressure for 15S to complete the hydrostatic test.

[0014] Ultrasonic inspection and X-ray inspection: Conduct non-destructive testing on the welded joints and pipe nipples of the extra-large diameter spiral welded pipe.

[0015] Pipe end bevel machining (i.e., pipe end chamfering): Machine the bevels at both ends of the extra-large diameter spiral welded pipe with a vertical milling machine according to the required dimensions. The bevel angle should be 30°, and the perpendicularity of the pipe end should not be greater than 3mm.

[0016] Finished product inspection (appearance dimension inspection): Measure the appearance dimensions of the finished extra-large diameter spiral welded pipe according to the requirements, and measure the out-of-roundness, misalignment, straightness, etc. of the extra-large diameter welded pipe.

[0017] Performance testing of the extra-large diameter welded pipe.

[0018] The present invention also provides a large diameter spiral welded pipe manufactured by the above manufacturing method. The nominal outer diameter of the large diameter spiral welded pipe is greater than 3000mm, and the wall thickness is 16mm - 25.4mm.

[0019] The present invention provides a manufacturing method for super-large diameter spiral welded pipes. When forming at a large forming angle above 80°, a combined former consisting of a lower three-roll, an upper three-roll, and 4 externally controlled adjustable single rolls is assembled. A double-headed welding pad roll and two auxiliary external rolls for the former are added to ensure high-precision geometric dimensions of the pipe body of the super-large diameter spiral welded pipe and low residual stress in the welded pipe. At the same time, laser penetration spot welding is used for pre-welding, laser welding + CMT welding is used for internal welding, and laser welding + SAW welding is used for external welding, reducing the wire filling amount of super-large diameter thick-walled pipe materials. The laser penetration welding seam has a large aspect ratio of depth to width. When laser welding, under the condition of the same gas flow rate, the penetration depth obtained using He gas as the shielding gas is greater than that of other gases, which can deepen the laser welding depth and ensure complete fusion of the weld seam after internal and external welds are welded by laser. After normalizing heat treatment of the laser welded joint, the weld seam structure is refined, overcoming the softening and embrittlement problems in the heat affected zone of thick-wall submerged arc welding. The impact toughness of the laser welded joint, especially in the heat affected zone, is higher than that of the base material. The laser welding stress is small, further improving the dimensional accuracy of the super-large diameter spiral welded pipe. For CMT surfacing, compared with MIG / MAG welding, the movement of the welding wire and the droplet transfer process are digitally coordinated, the welding heat input can be reduced by more than 50%, and the tendency of joint softening and embrittlement is improved, reducing welding deformation. For SAW welding, double wires are used for one-time filling and surfacing, greatly reducing the wire filling. A multi-functional water storage and pit water pressure testing machine platform is selected for the hydrostatic test of super-large diameter spiral welded pipes, changing the long-time water filling of the welded pipe to quickly filling the welded pipe with water by sinking it into the water pool, greatly shortening the water injection time and improving the hydrostatic test efficiency.

Specific Embodiments

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following combines specific embodiments: Q355D steel grade Super-large diameter spiral welded pipes and their manufacturing are further described in detail for the present invention.

[0021] A manufacturing method for super-large diameter spiral welded pipes, which includes the following steps:

[0022] 1) Raw materials

[0023] The combined steel mill developed Q355D coil plates with a thickness of 24 mm, and the width of the coil plate blank is 1670 mm.

[0024] 2) Edge milling of coiled sheet: Load and unwind the Q355D coiled sheet with a width of 1670 mm and a thickness of 24 mm. After unwinding, start edge milling. When edge milling, mill the middle part of both ends of the sheet width near the inner wall into a type I shape, with a blunt edge height of 13 mm for the type I. Mill the inner welding groove into a 60° V-shaped groove with a depth of 2 mm for the small inner welding groove, and mill the outer welding groove into a 60° V-shaped groove with a depth of 9 mm for the large outer welding groove. After edge milling, the width of the Q355D coiled sheet is 1651 mm, with an additional 1 mm allowance compared to the theoretically calculated sheet width of 1650 mm to compensate for the shrinkage deformation during the laser welding process and eliminate the "tight inside and loose outside" phenomenon generated after the seams of the extra-large diameter spiral welded pipe are joined.

[0025] 3) Large-angle forming of coiled sheet; Utilize the principle of three-roll plate bending for the lower three rolls and the upper three rolls respectively, so that the inner layer of the coiled sheet squeezes the outer layer and is continuously bent and rolled into a pipe blank with the engineering outer diameter Increase the overpressure of the 2# roll on the extra-large diameter welded pipe by 1.2 mm, increase the deformation spacing of the 1# and 3# rolls by 1.5 mm, and strengthen the auxiliary deformation function of the guide plate. Adjust the deformation spacing of the 6# and 8# rolls and the pressing-down amount of the 7# roll during the upper three-roll forming to assist in correcting the roundness of the pipe diameter. At the same time, the 7# roll supports the deformation of the formed pipe due to gravity. Adjust the double-head welding pad roll, and combine the 4#, 5#, 9#, and 10# forming devices that are basically symmetrically distributed to assist the outer roll to support the delivery side and prevent the edge curling phenomenon of the extra-large diameter spiral welded pipe, relieve the problem of the extra-large diameter overpressure, and make the dynamic deformation of the formed pipe blank more stable. The aligner is a gantry frame structure to ensure the stability of the forming process of the extra-large diameter steel pipe with a large diameter-thickness ratio of Q355D steel grade and low-quality welded pipes. The width of the first section of the rear axle is 4600 mm, meeting the installation requirements of the aligner for the specified welded pipe. Finally, adopt a large forming angle of about 81° to ensure the high dimensional accuracy and low residual stress of the extra-large diameter spiral welded pipe. After pipe manufacturing, the measured pipe ring springback of the extra-large diameter welded pipe is only -20 mm, ensuring that the extra-large diameter spiral welded pipe of Q355D steel grade has good roundness and low residual stress after forming.

[0026] 4) Laser pre-welding; The inner and outer welds are in contact. After forming on the upper three-roll forming machine, perform laser pre-welding at the bottom of the outer weld groove. The pre-welding adopts spot welding, with a spot welding spacing of 100 mm, a spot welding length of 2 mm, and a forming speed of 4 m / min, so as to fully release the capacity of the forming machine and cut the welded pipe to length.

[0027] ​​5) Laser welding + CMT internal welding: Select a fiber laser with a maximum power of 10 kW and a defocusing amount of +1.0 mm. Set the laser power to 6 kW. Perform 6 - 7 mm laser penetration back welding on the Type I area from the inner weld joint area. During the laser welding process, introduce pure He gas with a flow rate of 6 L / min as the shielding gas. The laser is in the front and the He shielding gas is in the rear. After the laser penetration back welding stabilizes for 0.5 s, start the CMT welding machine produced by Fronius to perform 1 pass of surfacing welding. Use ER50 - 6 welding wire with a diameter of 0.8 mm, a voltage of 20 V, and a current of 206 A. The CMT welding torch is also protected by He gas with a flow rate of 0.45 MPa. Finally, control the common movement of the laser head and the CMT welding torch to complete the welding process, and the welding speed is 1.6 m / min.

[0028] 6) Laser welding + SAW external welding: Select a fiber laser with a maximum power of 10 kW and a defocusing amount of +1.2 mm. Set the laser power to 7 kW. Perform 8 - 9 mm laser penetration back welding on the Type I area from the inner weld joint area to ensure that the inner weld laser and the outer weld laser overlap to penetrate the entire weld, and the measured overlap of the laser weld is 2 mm. During the laser welding process, introduce pure He gas with a flow rate of 9 L / min as the shielding gas. The laser is in the front and the He shielding gas is in the rear. After the laser penetration back welding stabilizes for 0.5 s, start the SAW twin - wire welding to perform 1 pass of filling and surfacing welding. Both wires use H08C welding wire with a diameter of 4.0 mm, combined with SJ101G welding flux. According to the 9 mm depth of the outer groove, the first wire uses DC straight polarity with a current of 1300 A and a voltage of 32 V, and the second wire uses DC reverse polarity with a current of 850 A and a voltage of 36 V. Finally, control the common movement of the laser head and the SAW twin - wire welding torch to complete the welding process, and the welding speed is 1.6 m / min.

[0029] 7) Normalizing heat treatment of the weld: After the laser hybrid welding of the welded pipe, use an intermediate - frequency inductor to heat the weld from the inner weld side for 2 s until the weld temperature reaches 930 °C. Perform air - cooling normalizing heat treatment on the laser - welded joint to change the martensite microstructure in the pure laser weld area and refine it into ferrite grains to ensure the mechanical properties of the weld.

[0030] 8) Hydrostatic test: On the hydrostatic test machine platform of the multi - functional water - storage and subsidence pit built through independent innovation, place the super - large - diameter spiral welded pipe into the pre - fabricated pit. The water in the pit flows into the welded pipe by gravity. Add blind plates and plugs with a calculated thickness of 80 mm to both ends of the super - large - diameter spiral welded pipe, and then add water through the union of the plug to increase the pressure until the water pressure reaches 80% of the minimum yield strength of the welded pipe. Hold the pressure for 15 s to quickly complete the hydrostatic test.

[0031] 9) Ultrasonic inspection and X - ray inspection: Perform non - destructive testing on the welded joints and pipe nipples of the super - large - diameter spiral welded pipe. ​

[0032] 10) Groove machining at the pipe ends: Machine the grooves at both ends of the extra-large diameter spiral welded pipe with a vertical milling machine according to the required dimensions. The groove angle is 30°, and the perpendicularity of the pipe end is less than 2 mm.

[0033] 11) Appearance dimension inspection: Measure the appearance dimensions of the finished extra-large diameter spiral laser composite welded pipe according to the requirements. The out-of-roundness of the pipe body is 6 - 8 mm, the misalignment is ≤ 0.5 mm, the straightness is ≤ 3 mm, etc., far exceeding the actual geometric dimension accuracies of the out-of-roundness of 8 - 16 mm, misalignment of 0.5 - 2 mm, and straightness of 3 - 4 mm in the conventional forming and welding of extra-large diameter spiral submerged arc welded pipes.

[0034] The following conducts tests on the mechanical properties of the Q355D steel grade extra-large diameter spiral submerged arc welded pipe manufactured by the above method through experiments.

[0035] ① Transverse tensile properties

[0036] Table 1 Results of transverse tensile tests

[0037]

[0038] ② Charpy impact toughness, DWTT, and bending test results

[0039] Table 2 Impact, DWTT, and bending test results

[0040]

[0041] ③ Vickers hardness of the welded joint

[0042] Table 3 Vickers hardness (HV 10 ) of the pipe mother, weld, and heat-affected zone

[0043]

[0044]

[0045] As can be seen from Tables 1 - 3, the main performance table of the Q355D steel grade extra-large diameter spiral welded pipe prepared by the present invention. Thus, it can be seen that the extra-large diameter spiral submerged arc welded pipe prepared by this method far exceeds the technical requirements of conventional extra-large diameter spiral submerged arc welded pipes. Therefore, this method is truly feasible and can be applied to the manufacture of extra-large diameter spiral welded pipes for water conveyance in water conservancy and hydropower projects. The welded pipe manufactured by this method has the advantages of high geometric dimension accuracy, small residual stress, and no softening and embrittlement phenomena in the heat-affected zone.

Claims

1. A manufacturing method for super-large diameter spiral welded pipes, comprising the following steps: Uncoiling, leveling, edge milling, pre-bending, large-angle forming, laser pre-welding, sizing cutting, laser welding + CMT internal welding, laser welding + SAW external welding, weld normalizing heat treatment, pipe end expanding, ultrasonic inspection, X-ray inspection, hydrostatic test, pipe end chamfering, and finished product inspection. It is characterized in that, During edge milling, both ends of the coil plate need to be milled into an I-shape in the middle of the wall thickness, and the internal welding groove is milled into a small V-shaped groove, while the external welding groove is milled into a large V-shaped groove; In large-angle forming, the forming machine is composed of a combined lower three-roll, upper three-roll, and 4 externally controlled adjustable single rolls. Among them, both the lower three-roll forming and the upper three-roll forming use the three-roll plate bending deformation effect to control the high-precision pipe diameter. After large-angle forming, the gap between the internal and external welds of the formed pipe is ≤0.2 mm; Laser pre-welding needs to be carried out at the bottom of the V-shaped groove of the external weld. The pre-welding uses a small laser spot welding with a power of less than 2 kW, and laser penetration backing welding with a length of 2 - 3 mm is spot welded at intervals of 100 mm without wire filling; Laser welding + CMT internal welding: Use a laser to complete 5 mm - 10 mm laser penetration backing welding on the I-shaped root face area from the inner weld joint side, and introduce a shielding gas. After the laser penetration backing welding is stable for 0.5 s, for the internal weld with a groove depth of 2 mm after edge milling, use a CMT welding machine to start arc and cover the surface with 1 pass of welding. Finally, control the common movement of the laser head and the CMT welding torch to complete the internal weld welding process, and the welding speed is 1.6 ± 0.2 m / min; Laser welding + SAW external welding: Use a laser to complete 5 mm - 10 mm laser penetration backing welding on the I-shaped root face area from the outer weld joint side, and introduce a shielding gas. After the laser penetration backing welding is stable for 0.5 s, for the external weld with a groove depth of 6 mm - 10 mm after edge milling, use a SAW twin-wire submerged arc welding to start arc, fill, and cover the surface with 1 pass of welding. Finally, control the common movement of the laser head and the SAW twin-wire welding torch to complete the external weld welding process, and the welding speed is synchronized with the external weld welding speed at 1.6 ± 0.2 m / min.

2. The manufacturing method for super-large diameter spiral welded pipes according to claim 1, characterized in that, the height of the I-shaped root face is 8 mm - 16 mm.

3. The manufacturing method for super-large diameter spiral welded pipes according to claim 1, characterized in that, after the coil plate is jointed, the internal welding groove angle is 55° - 65°, and the internal welding groove height is 2 mm; the external welding groove angle is 55° - 65°, and the external welding groove height is 6 mm - 10 mm.

4. The manufacturing method for super-large diameter spiral welded pipes according to claim 1, characterized in that, after edge milling, a margin of about 1 mm is added to the calculated plate width to compensate for the shrinkage deformation of the thick-walled weld during laser welding.

5. The manufacturing method for super-large diameter spiral welded pipes according to claim 1, characterized in that, during large-angle forming, the aligner adopts a gantry frame type aligner, the width of the first section of the rear axle bridge body is expanded to 4600 mm, and a large forming angle of more than 80° is used to complete the low-stress forming of super-large diameter spiral welded pipes.

6. The manufacturing method for super-large diameter spiral welded pipes according to claim 1, characterized in that, In the laser welding + CMT internal welding and laser welding + SAW external welding, the laser power of the laser is 5 kW to 10 kW, the defocus amount is -1.5 mm to +1.5 mm. During the laser welding process, pure He gas with a flow rate of 5 L / min to 10 L / min needs to be introduced as the shielding gas, with the laser in the front and the He shielding gas in the rear.

7. A method for manufacturing an extra-large diameter spiral welded pipe according to claim 1, characterized in that, for the CMT internal welding, the CMT welding gun uses an isostrength welding wire with a diameter of 0.8 mm, the voltage is 20.5 ± 2 V, the current is 205 ± 20 A, and the CMT welding gun is shielded by He gas with a flow rate of 0.4 MPa to 0.6 MPa.

8. A method for manufacturing an extra-large diameter spiral welded pipe according to claim 1, characterized in that, for the SAW external welding, both of the two wires used are isostrength welding wires with a diameter of 4.0 mm. The first wire uses DC straight polarity, the current is 1300 ± 200 A, the voltage is 30 ± 4 V, the second wire uses DC reverse polarity, the current is 800 ± 150 A, and the voltage is 36 ± 2 V.

9. A method for manufacturing an extra-large diameter spiral welded pipe according to claim 1, characterized in that, the normalizing heat treatment of the weld is specifically implemented according to the following scheme: After the laser hybrid welding of the internal and external welds, the laser weld is subjected to normalizing heat treatment. A 1000 °C intermediate frequency inductor is used to heat the weld from the inner weld side for 2 s to 5 s, the weld temperature is 930 ± 20 °C, and the welded joint is naturally cooled in the air, turning the microstructure of the weld area after laser welding from a martensite-based microstructure into a fine-grained ferrite-based microstructure.

10. A large diameter spiral welded pipe manufactured by using the manufacturing method described in any one of claims 1 - 9 above, characterized in that, the nominal outer diameter of the large diameter spiral welded pipe is greater than 3000 mm, and the wall thickness is 16 mm to 25.4 mm.

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