A method for welding and installing a seismic isolation bearing for a steel bridge

Abstract

The present invention discloses a method for welding and installing a seismic isolation support for a steel bridge in an upward position, the method comprising the following steps: (1) grinding and cleaning the area to be welded; (2) lifting the seismic isolation support to be pressed against the main beam pad, then supporting and fixing the seismic isolation support on all sides, and adjusting the assembly gap at the same time; (3) preheating; (4) positioning welding; (5) bottom welding; (6) grinding the weld surface; (7) layer temperature control; (8) cover welding; (9) covering the joint area with insulation material for insulation, and slowly cooling to room temperature. The method for welding and installing a seismic isolation support for a steel bridge adopted by the present invention can effectively solve the problems of difficult control of the assembly accuracy of the seismic isolation support, high risk during the construction process, and poor quality of the upward position welding. The operation is simple, convenient, safe and reliable. The qualified rate of the seismic isolation support for one-time installation can reach more than 99.5%, the workload of rework is greatly reduced, and the production cycle of the project can be significantly shortened.

Description

Technical Field

[0001] The invention relates to a welding method, in particular to an upward position welding installation method for a seismic isolation support for a steel bridge. Background Art

[0002] In recent years, seismic isolation technology has been widely used in steel bridge structures. By installing seismic isolation bearings between steel main beams and piers, they can effectively dissipate or absorb seismic energy input, suppress the seismic response of the bridge's main structure, and significantly improve the bridge's seismic performance and service life. Seismic isolation bearings are typically welded to the main beam and bolted to the piers. However, the welding space between the main beam and the piers is narrow, making it impossible to weld the circumferential weld between the seismic isolation bearings and the main beam. Therefore, the seismic isolation bearings must first be welded to the main beam in an upright position and then hoisted and installed along with the main beam to the piers.

[0003] However, the overall cross-section and weight of the seismic isolation bearing are large, making it difficult to control the gap between the bearing and the main beam during upward installation. After tack welding, the bearing may suddenly fall off, making construction very dangerous. Furthermore, the bearing is mostly made of cast steel, a highly hardenable base material. This makes welding it to the low-alloy structural steel of the main beam very prone to longitudinal and transverse cracks, making weld quality difficult to guarantee. Therefore, improving the assembly accuracy of seismic isolation bearings, ensuring construction safety, and controlling the quality of their upward welding are major challenges that need to be addressed in the seismic isolation technology for steel bridge structures. Summary of the Invention

[0004] Purpose of the invention: The present invention aims to provide a method for welding and installing seismic isolation bearings for steel bridges with high assembly precision and good welding quality.

[0005] Technical solution: The method for welding and installing the seismic isolation bearing for a steel bridge according to the present invention comprises the following steps:

[0006] (1) Grind and clean the area to be welded: Grind and clean the area to be welded between the seismic isolation bearing and the main beam until the surface shows a metallic luster;

[0007] (2) Lift the seismic isolation support and place it close to the main beam pad, then support and fix the surrounding areas of the seismic isolation support, and adjust the assembly gap at the same time;

[0008] (3) Preheat the area around the weld between the seismic isolation support and the main beam;

[0009] (4) Positioning welding: Use solid wire CO2 gas shielded welding to perform positioning welding around the seismic isolation support;

[0010] (5) Bottom welding: Use solid wire argon-rich gas shielded welding to perform bottom welding around the isolation bearing in the upward position. After completion, grind the weld toe of the isolation bearing to achieve a smooth transition with the parent material. This can improve the stress distribution of the joint and reduce the tendency of thermal cracks.

[0011] (6) Grinding the weld surface: remove the welding spatter and slag near the weld area, and grind the base weld into a concave shape to avoid defects such as slag inclusion or lack of fusion;

[0012] (7) Layer temperature control: The temperature between weld layers is controlled at 80-110°C, and continuous temperature measurement points are set at 100-115mm from the joint during welding. The temperature of the temperature measurement points does not exceed 80°C to prevent damage to the non-metallic components of the support due to excessive temperature;

[0013] (8) Cover welding: Use solid wire argon-rich gas shielded welding to perform cover welding in the upward position;

[0014] (9) Use insulation material to cover the joint area for insulation, slowly cool it to room temperature, and reduce the cooling rate of the weld.

[0015] Furthermore, in step (1), the area to be welded is 25-30 mm around the weld.

[0016] Furthermore, in step (2), the seismic isolation bearing is lifted and pressed against the main beam pad by a forklift, and the support and fixation are carried out by a hydraulic jack. The assembly gap is checked with a feeler gauge to confirm that the circumferential assembly gap is controlled within 0.5 mm. If the gap exceeds 0.5 mm, the hydraulic jack under the seismic isolation bearing is further adjusted to make it fit tightly. When the assembly gap meets the requirements, the forklift is removed and the hydraulic jack limit valve is tightened.

[0017] Furthermore, in step (3), the preheating method is: flame heating, the preheating temperature is 80-100°C, and the preheating range is 50-60mm around the weld.

[0018] Furthermore, in step (4), the length of the positioning weld of the positioning welding is 90-110 mm, the weld spacing is 180-220 mm, and the weld leg size is 5-6 mm. Appropriately densifying and lengthening the positioning weld can significantly reduce the tendency of longitudinal cracks in the positioning weld during subsequent base layer welding; the solid welding wire used for positioning welding is G49A3C1S6 with a diameter of 1.0 mm. The raw materials of the solid welding wire include the following components by mass percentage: C 0.06-0.15%, S≤0.025%, Mn 1.4-1.85%, P≤0.025%, Si 0.8-0.15%, the rest is Fe, and solid wire argon-rich gas shielded welding is used for upward welding, which not only significantly improves the crack resistance of the weld joint, but also reduces welding spatter and improves the appearance quality of the weld formation; a solid wire with a diameter of 1.0 mm is used for positioning welding, which can ensure that the weld leg size of the positioning weld does not exceed one-half of the formal weld; the process parameters of the positioning welding are: shielding gas CO2 flow rate of 15-20 L / min, welding current of 190-200 A, arc voltage of 22-24 V, welding speed of 380-410 mm / min, DC reverse current, dry extension of 16-18 mm, and heat input of 7-8 KJ / cm.

[0019] Furthermore, in step (5), the process parameters of the base welding are: the shielding gas is 80% Ar and 20% CO2 by volume, the gas flow rate is 20-25 L / min, the welding current is 200-210 A, the arc voltage is 22-24 V, the welding speed is 330-360 mm / min, the power supply is reversed DC, the dry extension is 12-16 mm, and the heat input is 8-9 KJ / cm.

[0020] Furthermore, in step (5) and step (8), the solid welding wires used for the base welding and the cover welding are both G49A3C1S6 with a diameter of 1.2 mm. The raw materials of the solid welding wire include the following components by mass percentage: C 0.06-0.10%, S≤0.015%, Mn 1.4-1.85%, P≤0.015%, Si 0.8-0.15%, and the rest is Fe.

[0021] Furthermore, in step (8), the process parameters of the cap welding are: the shielding gas is 80% Ar and 20% CO2 by volume, the gas flow rate is 20-25 L / min, the welding current is 220-230 A, the arc voltage is 24-26 V, the welding speed is 400-430 mm / min, the power supply is reversely connected to DC, the dry extension is 12-16 mm, and the heat input is 7-9 KJ / cm; the cap welding adopts multi-pass welding, and the first weld of the cap layer is arranged at the weld toe position on the support side. The subsequent welds will play a post-weld heat treatment role on it, improve its microstructure, and eliminate internal stress.

[0022] Furthermore, the positioning welding, bottom welding and cover welding methods are: left welding, ensuring that the welding wire and the welding gun are moved from the right side to the left side of the joint, while the welding gun nozzle is facing the direction of the weld pool, and the inclination angle between the welding gun and the base material is 65-75°, which can reduce welding spatter and improve the appearance quality of the weld formation; the welding direction of the single-section weld is opposite to the overall growth direction of the weld, and the latter section of the weld is welded toward the arc starting position of the previous section of the weld.

[0023] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the upward welding installation method of the seismic isolation bearing for steel bridges adopted by the present invention can effectively solve the problems of difficult to control the assembly accuracy of the seismic isolation bearing, high risk in the construction process and poor quality of upward welding. The operation is simple and convenient, safe and reliable; and the qualified rate of the seismic isolation bearing for one installation can reach more than 99.5%, the workload of rework is greatly reduced, and the production cycle of the project can be significantly shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of the hydraulic jack supporting and fixing the seismic isolation bearing and the steel main beam in Example 1 of the present invention, where K is the welding size of the circumferential fillet weld;

[0025] Figure 2 Schematic diagram of the hydraulic jack supporting and fixing the seismic isolation bearing in step (2) of Example 1 of the present invention;

[0026] Figure 3 This is a schematic diagram of the positioning welding between the seismic isolation support and the steel main beam in Example 1 of the present invention, in which ①- It is the welding sequence number, and the arrow points to the single-pass welding direction;

[0027] Figure 4 This is a schematic diagram of welding the base layer and the cover layer between the seismic isolation support and the steel main beam in Example 1 of the present invention. In the figure, is the weld pass number, and the arrow points to the single-pass welding direction;

[0028] Figure 5 Schematic diagram of weld distribution of the weld between the seismic isolation support and the steel main beam in Example 1 of the present invention, in which ①-④ are weld pass numbers;

[0029] Figure 6 This is the weld diagram of Example 1 of the present invention;

[0030] Figure 7 This is the weld diagram of Example 2 of the present invention;

[0031] Figure 8 This is the weld diagram of Comparative Example 1 of the present invention;

[0032] Figure 9 This is the weld diagram of Comparative Example 2 of the present invention;

[0033] Figure 10 This is the weld diagram of Comparative Example 3 of the present invention;

[0034] In the figure: 1. Seismic isolation bearing, 2. Steel main beam, 3. Bearing upper plate, 4. Main beam pad, 5. Hydraulic jack, 6. Positioning weld, 7. Fillet weld. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be further described below in conjunction with the embodiments and drawings.

[0036] Example 1: The present invention takes the welding installation of the seismic isolation support of the steel-concrete composite beam of a Yangtze River Bridge as an example. Figure 1 As shown, the outline size of the seismic isolation bearing 1 is 780*820*160mm, the gross weight of the seismic isolation bearing 1 is 140kg, and its material is ZG270-500, that is, a medium-carbon low-alloy cast steel part, which needs to be welded in an upward position with the steel main beam 2 made of Q370qD. The cast steel part contains a large amount of impurity elements such as P and S, and is very likely to produce thermal cracks after welding with the low-alloy structural steel of the steel main beam 2, and the quality of the weld is difficult to guarantee. The upward welding installation method of the seismic isolation bearing of the present invention can effectively avoid the generation of welding cracks.

[0037] The above-mentioned method for welding and installing the seismic isolation bearing in an upright position comprises the following steps:

[0038] (1) Grinding and cleaning the area to be welded: Use a handheld grinding wheel grinder to grind away dirt, coatings, etc. in the 25mm area to be welded around the weld between the seismic isolation support 1 and the steel main beam 2, so that the surface shows a metallic luster;

[0039] (2) Use a forklift to lift the top plate 3 of the seismic isolation support and press it against the main beam pad 4. After tightening, use hydraulic jacks 5 to support and fix the seismic isolation support 1 around. Adjust the assembly gap while ensuring the safety of welding construction. Use a feeler gauge to check the assembly gap between the top plate 3 of the seismic isolation support and the main beam pad 4. Confirm whether the circumferential assembly gap is controlled within 0.5mm. If the gap is out of tolerance, continue to adjust the hydraulic jack 5 under the support to make it close. When the assembly gap meets the requirements, remove the forklift and tighten the limit valve of the hydraulic jack 5. Figure 2 As shown;

[0040] (3) Use flame heating to preheat the 60mm welding area around the weld between the seismic isolation support 1 and the steel main beam 2 to 95°C;

[0041] (4) Positioning welding: Use solid wire CO2 gas shielded welding to perform positioning welding around the vibration isolation support. The length of positioning weld 6 is 90 mm, the weld spacing is 210 mm, the weld leg size is 5 mm, the solid welding wire is G49A3C1S6, the diameter is 1.0 mm, the shielding gas CO2 flow rate is 16 L / min, the welding current is 190 A, the arc voltage is 22 V, the welding speed is 400 mm / min, the power supply is reversed DC, the dry extension is 18 mm, the heat input is 7 KJ / cm, and the sequence number and direction of positioning welding are as follows: Figure 3 As shown;

[0042] (5) Bottom welding: Use solid wire argon-rich gas shielded welding to perform bottom welding around the seismic isolation support. The solid wire is G49A3C1S6 with a diameter of 1.2 mm. The shielding gas is 80% Ar and 20% CO2 by volume. The gas flow rate is 22 L / min, the welding current is 200 A, the arc voltage is 24 V, the welding speed is 340 mm / min, the power supply is reversed DC, the dry extension is 14 mm, the heat input is 8 KJ / cm, and the welding sequence and weld direction of the bottom welding are as follows: Figure 4 As shown;

[0043] (6) Grinding the weld surface: Use an electric straight grinder to remove the welding spatter and slag near the weld area, and grind the base weld into a concave shape to avoid defects such as slag inclusion or lack of fusion;

[0044] (7) Layer temperature control: The temperature between weld layers is controlled at 95-110°C, and a continuous temperature measurement point is set at 115mm from the joint during welding. The temperature of the temperature measurement point does not exceed 80°C to prevent excessive temperature from damaging the non-metallic components of the support.

[0045] (8) Cover welding: Use solid wire argon-rich gas shielded welding for upward cover. Multi-pass welding is used for upward cover, and the first weld of the cover layer is arranged at the weld toe of the support side. The arrangement of the weld of the cover layer is shown in Figure 5 The solid welding wire is G49A3C1S6 with a diameter of 1.2mm. The shielding gas is 80% Ar and 20% CO2 by volume, the gas flow rate is 24L / min, the welding current is 220A, the arc voltage is 26V, the welding speed is 420mm / min, the power supply is reversed DC, the dry extension is 16mm, the heat input is 8KJ / cm, and the serial number and weld direction of the cap welding are also as follows: Figure 4 As shown;

[0046] (9) Use thermal insulation cotton to cover the joint area for insulation, slowly cool it to room temperature, and reduce the cooling rate of the weld;

[0047] The test results show that: 36 hours after welding, the weld seam of the seismic isolation support is visually inspected and tested by magnetic particle inspection. Figure 6As shown, no cracks or other defects were found. After removing the hydraulic jack below, the welding installation of the seismic isolation bearing 1 met the design and use requirements.

[0048] Example 2: The present invention takes the upward welding installation of the seismic isolation bearing of a highway bridge as an example. The outline size of the seismic isolation bearing is 1840*2070*345mm, the gross weight of the seismic isolation bearing is 460kg, and its material is ZG340-640, that is, a high-carbon low-alloy steel casting. It needs to be connected to the steel main beam made of Q420qD by upward welding. However, the seismic isolation bearing not only has poor weldability of the base material, but also has a large overall cross-section and weight. It is difficult to control the assembly gap with the main beam during upward installation, and it may suddenly fall off after positioning welding, which makes the construction risky. By adopting the upward welding installation method of the seismic isolation bearing of the present invention, the construction process is safe and reliable, the assembly accuracy is significantly improved, and the generation of welding cracks is effectively avoided.

[0049] The above-mentioned method for welding and installing the seismic isolation bearing in an upright position comprises the following steps:

[0050] (1) Grinding and cleaning the area to be welded: Use a handheld grinding wheel grinder to grind away dirt, coatings, etc. in the 25mm area to be welded around the weld between the seismic isolation support and the steel main beam, so that the surface shows a metallic luster;

[0051] (2) Use a forklift to lift the top plate of the seismic isolation bearing and press it against the main beam pad. After tightening, use a hydraulic jack to support and fix the four sides of the seismic isolation bearing. Adjust the assembly gap while ensuring the safety of the welding construction. Use a feeler gauge to check the assembly gap between the top plate of the seismic isolation bearing and the main beam pad. Confirm whether the circumferential assembly gap is controlled within 0.5mm. If the gap is out of tolerance, continue to adjust the hydraulic jack under the bearing to make it close. When the assembly gap meets the requirements, remove the forklift and tighten the hydraulic jack limit valve.

[0052] (3) Use flame heating to preheat the 60mm welding area around the weld between the seismic isolation support and the steel main beam to 95℃;

[0053] (4) Positioning welding: Solid wire CO2 gas shielded welding is used for positioning welding of the vibration isolation bearing ring. The length of the positioning weld is 100 mm, the weld spacing is 190 mm, the weld leg size is 6 mm, the solid welding wire is G49A3C1S6, the diameter is 1.0 mm, the shielding gas CO2 flow rate is 16 L / min, the welding current is 200 A, the arc voltage is 23 V, the welding speed is 410 mm / min, the power supply is reverse DC, the dry extension is 18 mm, and the heat input is 7 KJ / cm;

[0054] (5) Bottom welding: Use solid wire argon-rich gas shielded welding to perform bottom welding around the seismic isolation bearing in an upward position. During the welding process, the left welding operation technique is adopted. The solid wire is G49A3C1S6 with a diameter of 1.2 mm. The shielding gas is 80% Ar and 20% CO2 by volume. The gas flow rate is 25 L / min, the welding current is 210 A, the arc voltage is 24 V, the welding speed is 360 mm / min, the power supply is reversed DC, the dry extension is 16 mm, and the heat input is 8 KJ / cm;

[0055] (6) Grinding the weld surface: Use an electric straight grinder to remove the welding spatter and slag near the weld area, and grind the base weld into a concave shape to avoid defects such as slag inclusion or lack of fusion;

[0056] (7) Layer temperature control: The temperature between weld layers is controlled at 80-110°C, and a continuous temperature measurement point is set at 115mm from the joint during welding. The temperature of the temperature measurement point does not exceed 80°C to prevent excessive temperature from damaging the non-metallic components of the support.

[0057] (8) Cover welding: solid wire argon-rich gas shielded welding is used for upward cover. Multi-pass welding is used for upward cover, and the first weld pass of the cover layer is arranged at the weld toe of the support side. The solid wire is G49A3C1S6 with a diameter of 1.2 mm. The shielding gas is 80% Ar and 20% CO2 by volume. The gas flow rate is 25 L / min, the welding current is 230 A, the arc voltage is 26 V, the welding speed is 410 mm / min, the power supply is reversed DC, the dry extension is 16 mm, and the heat input is 9 KJ / cm.

[0058] (9) Use thermal insulation cotton to cover the joint area for insulation, slowly cool it to room temperature, and reduce the cooling rate of the weld;

[0059] The test results show that: 36 hours after welding, the welds around the seismic isolation bearings were visually inspected and magnetic particle tested. Figure 7 As shown, no cracks or other defects were found. After removing the hydraulic jack below, the welding installation of the seismic isolation bearing met the design and use requirements.

[0060] Comparative Example 1: The difference from Example 1 is that in step (2), a forklift is used to lift the top plate of the seismic isolation bearing close to the main beam pad, and no hydraulic jack is used to support and fix it. The assembly gap between the top plate of the seismic isolation bearing and the main beam pad is checked with a feeler gauge. The circumferential assembly gap can only be controlled within 2 mm.

[0061] Figure 8 The test results show that under the action of the deadweight of the seismic isolation bearing, the positioning welds are very likely to produce longitudinal and transverse cracks, and because the gap with the main beam assembly is difficult to adjust during the upward installation, the positioning welds may suddenly fall off after welding, which makes the construction very dangerous.

[0062] Comparative Example 2: The difference from Example 1 is that: in step (5), during the bottom welding, carbon steel flux-cored wire CO2 gas shielded welding is used to perform the bottom welding of the seismic isolation bearing in the upward position. The left welding operation method is adopted during the welding process. The carbon steel flux-cored wire is T494T1-1C1AUH5 with a diameter of 1.2 mm. The carbon steel flux-cored wire includes the following components in mass percentage: C: 0.03-0.10%, S≤0.03%, Mn≤1.75%, P≤0.03%, Si≤0.90%, and the rest is Fe; the shielding gas is CO2; in step (8), carbon steel flux-cored wire CO2 gas shielded welding is used to perform the upward covering. Multi-pass welding is used for the upward covering, and the first weld of the covering layer is arranged at the toe position of the support side. The carbon steel flux-cored wire is T494T1-1C1AUH5 with a diameter of 1.2 mm. The shielding gas is CO2.

[0063] The test results show that: 36 hours after welding, the welds around the seismic isolation bearings were visually inspected and magnetic particle tested. Figure 9 As shown in the figure, the total length of defects such as cracks is about 2.1m, and the pass rate of weld flaw detection in one time is only 34%, which is far from meeting the design and use requirements, and the workload of rework is extremely large.

[0064] Comparative Example 3: The difference from Example 2 is that: in step (5), stainless steel flux-cored wire CO2 gas shielded welding is used for the upward-position bottom welding of the seismic isolation bearing, and the left welding operation method is adopted during the welding process. The stainless steel flux-cored wire is E309LMOT-1 with a diameter of 1.2 mm. The stainless steel flux-cored wire includes the following components in mass percentage: C≤0.04%, S≤0.03%, Mn: 0.5-2.5%, P≤0.04%, Si≤1.0%, and the rest is Fe; the shielding gas is CO2; in step (8), cover welding: stainless steel flux-cored wire CO2 gas shielded welding is used for upward-position cover welding, the stainless steel flux-cored wire is E309LMOT-1 with a diameter of 1.2 mm, and the shielding gas is CO2.

[0065] The test results show that: 36 hours after welding, the welds around the seismic isolation bearings were visually inspected and magnetic particle tested. Figure 10 As shown, the total length of cracks and other defects is about 6.4m, and the pass rate of weld flaw detection in one time is only 18%, which is far from meeting the design and use requirements, and the workload of rework is extremely large.

Claims

1. A method for welding and installing a seismic isolation bearing for a steel bridge, characterized in that: The following steps are involved: (1) Grind and clean the area to be welded: Grind and clean the area to be welded between the seismic isolation bearing and the main beam until the surface shows a metallic luster; (2) Lift the seismic isolation bearing close to the main beam pad, then support and fix the surrounding of the seismic isolation bearing, and adjust the assembly gap at the same time; (3) Preheat the area around the weld between the seismic isolation support and the main beam; (4) Positioning welding: solid wire CO2 gas shielded welding is used for positioning welding of the vibration isolation support ring; the process parameters of the positioning welding are: protective gas CO2 flow rate of 15-20L / min, welding current of 190-200A, arc voltage of 22-24V, welding speed of 380-410mm / min, DC reverse current, dry extension length of 16-18mm, heat input of 7-8KJ / cm; the positioning weld length of the positioning welding is 90-110mm, the weld spacing is 180-220mm, and the weld leg size is 5-6mm; the solid welding wire used for positioning welding is G49A3C1S6 with a diameter of 1.0mm; (5) Bottom welding: Use solid wire argon-rich gas shielded welding to perform bottom welding around the seismic isolation support in an upward position. After completion, grind the weld toe of the seismic isolation support to achieve a smooth transition with the base material. The process parameters of the bottom welding are: shielding gas is 80% Ar and 20% CO2 by volume, gas flow rate is 20-25 L / min, welding current is 200-210 A, arc voltage is 22-24 V, welding speed is 330-360 mm / min, power supply is reversed DC, dry extension is 12-16 mm, heat input is 8-9 KJ / cm; (6) Grinding the weld surface: remove the welding spatter and slag near the weld area, and grind the base weld into a concave shape; (7) Layer temperature control: The temperature between weld layers is controlled at 80-110°C, and continuous temperature measurement points are set at 100-115mm from the joint during welding, and the temperature of the temperature measurement points does not exceed 80°C; (8) Cover welding: solid wire argon-rich gas shielded welding is used for upward cover welding; the process parameters of the cover welding are: shielding gas is 80% Ar and 20% CO2 by volume, gas flow rate is 20-25L / min, welding current is 220-230A, arc voltage is 24-26V, welding speed is 400-430mm / min, power supply is reverse DC, dry extension is 12-16mm, heat input is 7-9KJ / cm; cover welding is carried out by multi-pass welding, and the first weld pass of the cover layer is arranged at the weld toe of the support side; the solid welding wire used for the base welding and cover welding is G49A3C1S6 with a diameter of 1.2mm; (9) Use insulation material to cover the joint area for insulation and slowly cool it to room temperature; The positioning welding, bottom welding and cover welding methods are: left welding, the inclination angle between the welding gun and the base material is 65-75 degrees, the welding direction of the single section weld is opposite to the overall growth direction of the weld, and the latter section weld is welded towards the arc starting position of the previous section weld.

2. The method according to claim 1, characterized in that In step (1), the area to be welded is 25-30 mm around the weld.

3. The method according to claim 1, characterized in that In step (2), the support and fixation adopts a hydraulic jack, and the assembly clearance is within 0.5 mm.

4. The method according to claim 1, wherein In step (3), the preheating method is: flame heating, the preheating temperature is 80-100°C, and the preheating range is 50-60mm around the weld.

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