Supercritical phase carbon dioxide conveying X65 straight seam welding steel pipe and manufacturing method thereof

Abstract

The invention discloses a supercritical phase carbon dioxide conveying X65 straight seam welding steel pipe and a manufacturing method thereof. The base metal steel plate comprises, by mass, 0.03%-0.07% of C, 0.20%-0.40% of Si, 0.8%-1.5% of Mn, smaller than or equal to 0.010% of P, smaller than or equal to 0.002% of S, smaller than or equal to 0.050% of Nb, smaller than or equal to 0.05% of V, smaller than or equal to 0.04% of Ti, smaller than or equal to 0.25% of Cu, 0.30%-1.50% of Cr, 0-0.15% of Mo, 0.10%-0.30% of Ni, smaller than or equal to 0.0005% of B, smaller than or equal to 0.15% of Nb + V + Ti and the balance Fe. The method has the beneficial effects that the carbon dioxide corrosion resistance of the material is effectively improved by optimizing the microalloy content of the base material steel plate; welding parameters are reasonably optimized, chemical components of welding seams are adjusted, crystallization conditions of the welding seams and heat affected zones are improved, and low-temperature impact toughness of the welding seams is improved; the product meets the safe use requirement of the longitudinal submerged arc welded pipe for supercritical phase carbon dioxide conveying, safe operation of the pipeline is guaranteed, and the service life is prolonged.

Description

Technical Field

[0001] The invention relates to a straight seam welded steel pipe, in particular to an X65 straight seam welded steel pipe for transporting supercritical carbon dioxide and a manufacturing method thereof, belonging to the technical field of steel pipe forming and manufacturing. Background Art

[0002] The transported carbon dioxide mainly has four phases: gaseous, liquid, dense phase and supercritical. Among them, supercritical carbon dioxide has the characteristics of high density, low viscosity, low thermal conductivity, relatively small specific heat and compression coefficient, which is conducive to long-distance and large-volume transportation. Liquid free water is inevitably present in the medium for transporting carbon dioxide. Carbon dioxide reacts with liquid free water to generate carbonic acid, which will corrode the steel pipe. Therefore, the pipe body and welds are required to have sufficient resistance to carbon dioxide corrosion. When cracks occur in the pipeline, supercritical carbon dioxide, unlike natural gas, will produce decompression waves inside the pipeline, which is not conducive to crack prevention of the pipeline. When carbon dioxide leaks in the pipeline, extremely low temperatures will appear at the leak port, and the lowest temperature can reach -68°C. Therefore, the pipe body and welds of the pipeline for transporting supercritical carbon dioxide are required to have the ability to resist low-temperature toughness. Existing steel pipes cannot meet the requirements for long-distance and large-volume transportation of supercritical carbon dioxide. Summary of the invention

[0003] In order to overcome the deficiency that the existing steel pipes cannot meet the requirements of long-distance and large-volume supercritical carbon dioxide transportation, the present invention provides an X65 straight seam welded steel pipe for supercritical carbon dioxide transportation and a manufacturing method thereof.

[0004] The technical solution adopted by the present invention to solve the technical problem is: a supercritical phase carbon dioxide transport X65 straight seam welded steel pipe, the components and mass percentages of the parent steel plate are: C 0.03%-0.07%, Si 0.20%-0.40%, Mn0.8%-1.5%, P≤0.010%, S≤0.002%, Nb≤0.050%, V≤0.05%, Ti≤0.04%, Cu≤0.25%, Cr 0.30%-1.50%, Mo 0-0.15%, Ni 0.10%-0.30%, B≤0.0005%, Nb+V+Ti≤0.15%, and the rest is Fe; wherein CEpcm≤0.21; the ferrite content in the microstructure of the steel plate is greater than 95%.

[0005] Furthermore, the components and mass percentages of the parent steel plate are: C 0.04%-0.06%, Si 0.25%-0.35%, Mn 1.0%-1.3%, P≤0.010%, S≤0.002%, Nb≤0.050%, V≤0.05%, Ti≤0.04%, Cu≤0.25%, Cr 0.50%-1.30%, Mo 0.05%-0.10%, Ni 0.15%-0.25%, B≤0.0005%, Nb+V+Ti≤0.15%, and the rest is Fe.

[0006] The components and mass percentages of the steel pipe weld are: C 0.04%-0.08%, Si 0.20%-0.35%, Mn 1.0%-1.70%, P≤0.010%, S≤0.005%, Nb 0.03%-0.06%, V≤0.03%, Ti≤0.04%, Cu≤0.20%, Cr 0.30%-1.0%, Mo 0.10%-0.30%, Ni 0.10%-0.30%, B≤0.0010%, and the rest is Fe; wherein CEpcm≤0.22; the ferrite content in the weld microstructure is greater than 90%.

[0007] Furthermore, the components and mass percentages of the steel pipe weld are: C 0.05%-0.07%, Si 0.25%-0.30%, Mn 1.2%-1.50%, P≤0.010%, S≤0.005%, Nb 0.04%-0.05%, V≤0.03%, Ti≤0.04%, Cu≤0.20%, Cr 0.40%-0.8%, Mo 0.15%-0.25%, Ni0.15%-0.25%, B≤0.0010%, and the rest is Fe.

[0008] The upper bevel dimensions of the steel pipe weld are as follows: the upper bevel height is 13.5-14.5 mm, the upper bevel angle is 35°-45°, and the blunt edge thickness is 11.5-12.5 mm; the lower bevel dimensions of the steel pipe weld are as follows: the lower bevel height is 11.5-12.5 mm, and the lower bevel angle is 35°-45°.

[0009] The manufacturing method of the supercritical phase carbon dioxide transport X65 straight seam welded steel pipe adopts the following molding steps using a JCO molding machine:

[0010] Step 1: Use the JCO forming machine to bend the steel plate from one side to a predetermined curvature between the upper and lower dies of the forming machine, so that half of the steel plate is first formed into a "J" shape;

[0011] Step 2: Press and bend the steel plate into a predetermined curvature from the other side to form a "C"-shaped tube blank;

[0012] Step 3: Perform the final press bending in the middle to form the "C"-shaped tube into an "O"-shaped tube with a smaller opening;

[0013] Step 4, internal welding and external welding of the "O"-shaped tube blank;

[0014] Among them, in the pressing process of step 3, the total pressing passes are 19, and the pressing amount each time is 520-570 mm. After forming, the radial and axial misalignment amounts are both less than 1 mm.

[0015] Furthermore, during the press-forming process in step 3, the pressing amount each time is 535 to 555 mm.

[0016] The internal welding and external welding in step 4 are performed by four-wire submerged arc automatic welding, and the spacing between adjacent welding wires is 18 mm.

[0017] Furthermore, four welding wires are arranged in sequence along the weld. The first welding wire adopts backward tilt welding with a tilt angle of -10°±2°; the second welding wire adopts vertical welding with a tilt angle of 0°; the third welding wire adopts forward tilt welding with a tilt angle of 10°±2°; and the fourth welding wire adopts forward tilt welding with a tilt angle of 20°±2°.

[0018] The beneficial effects of the present invention are as follows: by optimizing the microalloy content of the base steel plate, the material's ability to resist carbon dioxide corrosion is effectively improved; the welding parameters are reasonably optimized, the chemical composition of the weld is adjusted, the crystallization conditions of the weld and the heat-affected zone are improved, and the low-temperature impact toughness of the weld is improved; the JCO forming process is optimized to ensure the forming quality of the steel pipe; the product meets the safety use requirements of the straight seam submerged arc welded pipe for supercritical phase carbon dioxide transportation, ensures the safe operation of the pipeline, and improves the service life.

[0019] Figure 1 It is a schematic diagram of the arrangement of the four-wire welding gun in the present invention.

[0020] In the figure: 1. weld, 2. base material, 3. first welding wire, 4. second welding wire, 5. third welding wire, 6. fourth welding wire. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. However, those skilled in the art should be aware that the present invention is not limited to the specific embodiments listed, and all embodiments should be included in the protection scope of the present invention as long as they conform to the spirit of the present invention.

[0022] The invention discloses an X65 straight seam welded steel pipe for conveying supercritical carbon dioxide and a manufacturing method thereof. The diameter of the X65 steel pipe is 610 mm and the wall thickness is 28.6-38 mm.

[0023] The components and mass percentages of the parent steel plate are: C 0.03%-0.07%, Si 0.20%-0.40%, Mn 0.8%-1.5%, P≤0.010%, S≤0.002%, Nb≤0.050%, V≤0.05%, Ti≤0.04%, Cu≤0.25%, Cr 0.30%-1.50%, Mo 0-0.15%, Ni 0.10%-0.30%, B≤0.0005%, Nb+V+Ti≤0.15%, and the rest is Fe; wherein CEpcm≤0.21; the microstructure of the steel plate is mainly ferrite, and preferably, the ferrite content in the microstructure of the steel plate is greater than 95%.

[0024] Furthermore, the components and mass percentages of the parent steel plate are: C 0.04%-0.06%, Si 0.25%-0.35%, Mn 1.0%-1.3%, P≤0.010%, S≤0.002%, Nb≤0.050%, V≤0.05%, Ti≤0.04%, Cu≤0.25%, Cr 0.50%-1.30%, Mo 0.05%-0.10%, Ni 0.15%-0.25%, B≤0.0005%, Nb+V+Ti≤0.15%, and the rest is Fe.

[0025] The present invention optimizes the microalloy content of the base steel plate, especially increases the content of Cr, improves the content of ferrite, and reduces pearlite and granular bainite with a high carbon content, thereby effectively improving the material's ability to resist carbon dioxide corrosion. At the same time, the steel plate has better low-temperature impact toughness and low-temperature DWTT performance, thereby ensuring the safe operation of the pipeline and increasing its service life.

[0026] The components and mass percentages of the steel pipe weld are: C 0.04%-0.08%, Si 0.20%-0.35%, Mn 1.0%-1.70%, P≤0.010%, S≤0.005%, Nb 0.03%-0.06%, V≤0.03%, Ti≤0.04%, Cu≤0.20%, Cr 0.30%-1.0%, Mo 0.10%-0.30%, Ni 0.10%-0.30%, B≤0.0010%, and the rest is Fe; wherein CEpcm≤0.22; the ferrite content in the weld microstructure is greater than 90%, and ferrite can effectively improve the low-temperature impact toughness of the weld.

[0027] Furthermore, the components and mass percentages of the steel pipe weld are: C 0.05%-0.07%, Si 0.25%-0.30%, Mn 1.2%-1.50%, P≤0.010%, S≤0.005%, Nb 0.04%-0.05%, V≤0.03%, Ti≤0.04%, Cu≤0.20%, Cr 0.40%-0.8%, Mo 0.15%-0.25%, Ni0.15%-0.25%, B≤0.0010%, and the rest is Fe.

[0028] The upper bevel size of the steel pipe weld is 13.5-14.5 mm in height, 35°-45° in angle, and 11.5-12.5 mm in blunt edge thickness; the lower bevel size of the steel pipe weld is 11.5-12.5 mm in height, 35°-45° in angle, and combined with the welding process, it can ensure complete penetration during the welding process, thereby ensuring the mechanical properties and good morphological characteristics of the weld.

[0029] The manufacturing method of the X65 straight seam welded steel pipe for conveying supercritical carbon dioxide comprises the processes of edge milling, pre-bending, JCO forming, internal welding, external welding, diameter expansion and the like for final forming.

[0030] The molding steps using the JCO molding machine are as follows:

[0031] Step 1: Use the JCO forming machine to bend the steel plate from one side to a predetermined curvature between the upper and lower dies of the forming machine, so that half of the steel plate is first formed into a "J" shape;

[0032] Step 2: Press and bend the steel plate into a predetermined curvature from the other side to form a "C"-shaped tube blank;

[0033] Step 3: Perform the final press bending in the middle to form the "C"-shaped tube into an "O"-shaped tube with a smaller opening;

[0034] Step 4, internal welding and external welding of the "O"-shaped tube blank;

[0035] Among them, in the pressing process of step 3, the total number of pressing passes is 19, and the pressing amount each time is 520-570 mm. After forming, the radial and axial misalignment amounts are both less than 1 mm, which ensures the forming quality of the steel pipe and is beneficial to the subsequent internal welding and external welding processes.

[0036] Furthermore, during the press-forming process in step 3, the pressing amount each time is 535 to 555 mm.

[0037] The internal welding and external welding in step 4 are performed by four-wire submerged arc automatic welding, and the spacing between adjacent welding wires is 18 mm.

[0038] See attached Figure 1Four welding wires are arranged in sequence along the weld 1. The first welding wire 3 adopts backward tilting welding with a tilt angle of -10°±2°; the second welding wire 4 adopts vertical welding with a tilt angle of 0°; the third welding wire 5 adopts forward tilting welding with a tilt angle of 10°±2°; the fourth welding wire 6 adopts forward tilting welding with a tilt angle of 20°±2°.

[0039] In order to ensure the safe use of X65 straight seam welded steel pipe for supercritical carbon dioxide transportation during operation, the DWTT test (drop weight tear test) temperature of the steel pipe is required to be -10°C, the average minimum requirement for shear area is 85%, and the single minimum requirement is 75%; the Charpy impact test is carried out on the parent material, weld and heat affected zone, and the average minimum requirement for the Charpy impact energy of the parent material (-10°C) is 390J, and the single minimum requirement is 290J; the average value of the Charpy impact energy of the parent material (-40°C) reaches 32 The average Charpy impact energy of the weld (-40℃) reached more than 120J, and the single values ​​were all above 80J; the average Charpy impact energy of the heat affected zone (-40℃) reached more than 220J, and the single values ​​were all above 160J; the average Charpy impact energy of the base material (-70℃) reached more than 120J, and the single values ​​were all above 100J; the average Charpy impact energy of the weld and heat affected zone (-70℃) reached more than 40J, and the single values ​​were all above 30J.

[0040] The DWTT performance, low-temperature crack initiation toughness requirement and low-temperature crack arrest toughness requirement of the pipe body, weld and hot zone of the X65 straight seam welded steel pipe manufactured by the present invention all meet the safe use requirements of straight seam submerged arc welded pipes for supercritical phase carbon dioxide transportation.

[0041] Embodiment 1

[0042] The thick-walled X65 straight seam submerged arc welded pipe for supercritical carbon dioxide transportation has a diameter of 610mm and a wall thickness of 38mm. The controlled rolled steel plate used is 1795mm wide and 38mm thick.

[0043] The composition and mass percentage of the base material 2 steel plate are as follows: C 0.05%, Si 0.30%, Mn 1.0%, P0.008%, S 0.001%, Nb 0.025%, V 0.025%, Ti 0.02%, Cu 0.15%, Cr 1.0%, Mo 0.10%, Ni0.20%, B 0.0003%, Nb+V+Ti=0.13%, and the rest is Fe; among which CEpcm=0.18.

[0044] The DWTT performance test was carried out on the above X65 controlled rolled steel plate, and the results are shown in Table 1.

[0045] Table 1 DWTT test results of X65 controlled rolled steel plate of Example 1

[0046]

[0047] As can be seen from Table 1, by optimizing the alloy composition and microstructure, the average shear area rate of the X65 controlled rolled steel plate used in the X65 straight seam submerged arc welded pipe of the present invention reaches more than 85%, and the shear area rate of each sample reaches more than 75%, which meets the requirements of the straight seam submerged arc welded pipe for supercritical phase carbon dioxide transportation for the parent material.

[0048] The CVN performance test of the above X65 controlled rolled steel plate was carried out, and the results are shown in Table 2.

[0049] Table 2 CVN test results of X65 controlled rolled steel plate of Example 1

[0050]

[0051] As can be seen from Table 2, by optimizing the alloy composition and microstructure, the average value of the Charpy impact energy (-10°C) of the X65 controlled rolled steel plate adopted by the X65 straight seam submerged arc welded pipe of the present invention reached more than 390J, the single values ​​were all above 290J, and the shear area rate was 100%; the average value of the Charpy impact energy (-40°C) reached more than 320J, and the single values ​​were all above 250J; the average value of the shear area rate was more than 85%, and the single values ​​were all above 75%, and the average value of the Charpy impact energy (-70°C) reached more than 150J, and the single values ​​were all above 130J; the average value of the shear area rate was more than 40%, and the single values ​​were all above 30%, which met the requirements of the supercritical phase carbon dioxide transportation straight seam submerged arc welded pipe for the parent material.

[0052] Embodiment 2

[0053] The thick-walled X65 straight seam submerged arc welded pipe for supercritical carbon dioxide transportation has a diameter of 610mm and a wall thickness of 38mm.

[0054] The components and mass percentages of the parent steel plate are: C 0.06%, Si 0.35%, Mn 1.3%, P0.006%, S 0.001%, Nb 0.040%, V 0.04%, Ti 0.03%, Cu 0.20%, Cr 1.40%, Mo0.14%, Ni 0.25%, B 0.0004%, Nb+V+Ti=0.14, and the rest is Fe; wherein CEpcm=0.20; and the ferrite content in the microstructure of the steel plate is 96%.

[0055] The straight seam submerged arc welded pipe of this embodiment is processed through plate probing, edge milling, pre-bending, JCO forming, pre-welding, internal welding, external welding, mechanical expansion of the entire pipe body, water pressure testing, UT testing, RT testing and other processes.

[0056] In the milling step, the upper and lower bevel angles are both 40°, the upper bevel height is 14.0 mm, the blunt edge thickness is 12.0 mm, and the lower bevel height is 12 mm.

[0057] In the JCO forming step: the JCO forming machine is used to bend the steel plate from one side (leaving the pre-bending area) between the upper and lower dies of the forming machine into a predetermined curvature, so that half of the steel plate first becomes a "J" shape, and then the steel plate is bent from the other side into a predetermined curvature to form a "C"-shaped tube blank, and finally the last bending is performed in the middle to form the "C"-shaped tube blank into an "O"-shaped tube blank with a smaller opening; in the pressing process, the total number of pressing passes is 19, and the pressing amount each time is 545mm.

[0058] In the internal and external welding steps: both internal and external welding adopt four-wire submerged arc automatic welding, and the spacing between adjacent welding wires is 18mm; the first welding wire 3 adopts backward tilt welding with a tilt angle of -11°; the second welding wire 4 adopts vertical welding with a tilt angle of 0°; the third welding wire 5 adopts forward tilt welding with a tilt angle of 11.5°; the fourth welding wire 6 adopts forward tilt welding with a tilt angle of 21°.

[0059] The components and mass percentages of the steel pipe weld are: C 0.06%, Si 0.28%, Mn 1.5%, P0.008%, S 0.004%, Nb 0.04%, V 0.02%, Ti 0.03%, Cu 0.15%, Cr 0.70%, Mo0.20%, Ni 0.22%, B 0.0008%, and the rest is Fe; wherein CEpcm=0.20; the ferrite content in the weld microstructure is 92%, and ferrite can effectively improve the low-temperature impact toughness of the weld.

[0060] By rationally optimizing the groove size and wire inclination, we can ensure complete penetration, adjust the chemical composition of the weld, improve the crystallization conditions of the weld and heat-affected zone, and improve the mechanical properties of the weld joint; increase the penetration depth and reduce the weld excess height, so that the weld has good morphological characteristics and a smooth transition with the parent material.

[0061] The Charpy impact properties of the steel pipe base material, weld and hot zone were tested, and the results are shown in Table 3.

[0062] Table 3 Charpy impact test results of steel pipe base material, weld and hot zone in Example 2

[0063]

[0064] The steel pipe base material and welded joints were subjected to tensile tests, and the results are shown in Table 4.

[0065] Table 4 Tensile test results of steel pipe parent material and welded joints in Example 2

[0066]

[0067] The DWTT properties of the steel pipe base material were tested, and the results are shown in Table 5.

[0068] Table 5 DWTT performance test results of steel pipe parent material of Example 2

[0069]

[0070] The hardness of the steel pipe welded joints was tested and the results are shown in Table 6.

[0071] Table 6 Steel pipe hardness test results of Example 2

[0072]

[0073] The steel pipe was subjected to a CO2 corrosion resistance test, the corrosive medium being 99% CO2, 0.04% water, and the remainder being N2; the test pressure was 10MPa, and the test temperature was 35°C; the carbon dioxide corrosion rate was 0.048mm / a.

[0074] It can be seen from the above test results that the mechanical properties and carbon dioxide corrosion resistance of the X65 straight seam submerged arc welded pipe manufactured by the technical solution of the present invention can meet the requirements of supercritical phase carbon dioxide transportation for steel pipes.

[0075] The X65 straight seam welded steel pipe for transporting supercritical carbon dioxide of the present invention and its manufacturing method, by optimizing the microalloy content of the base steel plate, effectively improves the material's ability to resist carbon dioxide corrosion, so that the steel plate has good low-temperature impact toughness and low-temperature DWTT performance, ensures the safe operation of the pipeline, and improves the service life; reasonably optimizes the groove size and welding wire inclination to ensure complete penetration, adjusts the chemical composition of the weld, improves the crystallization conditions of the weld and the heat-affected zone, and improves the low-temperature impact toughness of the weld; increases the penetration depth and reduces the weld excess height, so that the weld has good morphological characteristics and a smooth transition with the base material. In the JCO forming process, the total number of pressing passes and the amount of pressing are optimized to ensure the forming quality of the steel pipe. The pipe body, weld, DWTT performance of the hot zone, the low-temperature crack initiation toughness requirements, and the low-temperature crack arrest toughness requirements of the X65 straight seam welded steel pipe manufactured by the present invention all meet the safe use requirements of straight seam submerged arc welded pipes for transporting supercritical carbon dioxide.

[0076] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the claims of this patent.

Claims

1. A supercritical phase carbon dioxide transport X65 straight seam welded steel pipe, characterized by: The components and mass percentages of the parent steel plate are: C 0.03%-0.07%, Si 0.20%-0.40%, Mn 0.8%-1.5%, P≤0.010%, S≤0.002%, Nb≤0.050%, V≤0.05%, Ti≤0.04%, Cu≤0.25%, Cr0.30%-1.50%, Mo 0-0.15%, Ni 0.10%-0.30%, B≤0.0005%, Nb+V+Ti≤0.15%, and the rest is Fe; wherein CEpcm≤0.21; and the ferrite content in the microstructure of the steel plate is greater than 95%.

2. According to claim 1, the X65 straight seam welded steel pipe for transporting supercritical carbon dioxide is characterized by: The components and mass percentages of the parent steel plate are: C 0.04%-0.06%, Si 0.25%-0.35%, Mn 1.0%-1.3%, P≤0.010%, S≤0.002%, Nb≤0.050%, V≤0.05%, Ti≤0.04%, Cu≤0.25%, Cr 0.50%-1.30%, Mo 0.05%-0.10%, Ni 0.15%-0.25%, B≤0.0005%, Nb+V+Ti≤0.15%, and the rest is Fe.

3. According to claim 1, the X65 straight seam welded steel pipe for transporting supercritical carbon dioxide is characterized by: The components and mass percentages of the steel pipe weld are: C 0.04%-0.08%, Si 0.20%-0.35%, Mn 1.0%-1.70%, P≤0.010%, S≤0.005%, Nb 0.03%-0.06%, V≤0.03%, Ti≤0.04%, Cu≤0.20%, Cr0.30%-1.0%, Mo 0.10%-0.30%, Ni 0.10%-0.30%, B≤0.0010%, and the rest is Fe; wherein CEpcm≤0.22; the ferrite content in the weld microstructure is greater than 90%.

4. According to claim 3, the X65 straight seam welded steel pipe for transporting supercritical carbon dioxide is characterized in that: The components and mass percentages of the steel pipe weld are: C 0.05%-0.07%, Si 0.25%-0.30%, Mn 1.2%-1.50%, P≤0.010%, S≤0.005%, Nb 0.04%-0.05%, V≤0.03%, Ti≤0.04%, Cu≤0.20%, Cr0.40%-0.8%, Mo 0.15%-0.25%, Ni 0.15%-0.25%, B≤0.0010%, and the rest is Fe.

5. According to claim 3, the X65 straight seam welded steel pipe for transporting supercritical carbon dioxide is characterized by: The upper bevel dimensions of the steel pipe weld are as follows: the upper bevel height is 13.5-14.5 mm, the upper bevel angle is 35°-45°, and the blunt edge thickness is 11.5-12.5 mm; the lower bevel dimensions of the steel pipe weld are as follows: the lower bevel height is 11.5-12.5 mm, and the lower bevel angle is 35°-45°.

6. A method for manufacturing the X65 straight seam welded steel pipe according to claim 1, characterized in that: The molding steps using JCO molding machine are as follows: Step 1: Use the JCO forming machine to bend the steel plate from one side to a predetermined curvature between the upper and lower dies of the forming machine, so that half of the steel plate is first formed into a "J" shape; Step 2: Press and bend the steel plate into a predetermined curvature from the other side to form a "C"-shaped tube blank; Step 3: Perform the final press bending in the middle to transform the "C"-shaped tube into an "O"-shaped tube with a smaller opening; Step 4: Perform internal and external welding on the "O" shaped tube blank; Among them, in the pressing process of step 3, the total pressing passes are 19, and the pressing amount each time is 520-570 mm. After forming, the radial and axial misalignment amounts are both less than 1 mm.

7. The manufacturing method according to claim 6, characterized in that: During the pressing process in step 3, the pressing amount each time is 535 to 555 mm.

8. The manufacturing method according to claim 6, characterized in that: The internal welding and external welding in step 4 are performed by four-wire submerged arc automatic welding, and the spacing between adjacent welding wires is 18 mm.

9. The manufacturing method according to claim 8, characterized in that: Four welding wires are arranged in sequence along the weld. The first welding wire adopts backward tilt welding with a tilt angle of -10°±2°; the second welding wire adopts vertical welding with a tilt angle of 0°; the third welding wire adopts forward tilt welding with a tilt angle of 10°±2°; the fourth welding wire adopts forward tilt welding with a tilt angle of 20°±2°.

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