Precise positioning and mounting method for large full-capacity low-temperature storage tank wall lining plate

Abstract

The invention discloses a precise positioning and mounting method for a wall lining plate of a large full-capacity low-temperature storage tank, which innovatively divides the wall lining plate into an upper part and a lower part, optimizes the construction method, and improves the mounting precision of the wall lining plate of a 200,000-mLNG (Liquefied Natural Gas) low-temperature storage tank. The integral hoisting of the wall lining plates of more than five meters is realized through prefabrication and splicing, so that the overhead working amount is reduced, the mounting and positioning accuracy is improved, and the welding qualification rate of a welding seam assembly is improved to 99%; the wall lining plates are spliced and welded on the ground and are transported scientifically, so that the mounting quality is ensured; the number of hoisting points of the wall lining plate is four, the wall lining plate is hoisted through cooperation of an electric hoist and a chain block, meanwhile, an auxiliary clamp 7-shaped positioning block is used for limiting, the wall lining plate is kept in a natural vertical state in the hoisting process, friction between the wall lining plate and a wall is avoided, the lap joint amount between the wall lining plate and an embedded part can be accurately controlled, and the wall lining plate is prevented from being damaged. And the defect that the wall lining plate cannot be directly hoisted in place by the electric hoist due to insufficient tank top space is overcome, so that the normal installation of the wall lining plate is ensured, and the overall installation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of storage tank construction, and in particular relates to a method for accurately positioning and installing a wall lining of a large full-containment cryogenic storage tank. Background Art

[0002] Large full-capacity cryogenic storage tanks are mainly used for emergency reserves. When there is a gas outage or other accidents upstream, they can provide normal gas sources to the city gas pipeline network. They can also be used as peak-shaving facilities. After receiving LNG cargo, they are stored in supporting storage tanks and then transported to the market during the peak period of gas demand. Full-capacity storage tanks are generally composed of a prestressed concrete outer tank with stranded steel wire and a Ni9 steel inner tank, with a design temperature of -165°C. As part of the storage tank, the outer tank wall lining plays an important role in the storage of natural gas. However, the temperature of the gas in the liquid state is about -165°. In order to ensure its temperature, the storage tank is divided into four parts: outer tank concrete, outer tank wall lining, insulation layer, and inner tank. The outer tank wall lining is installed on the concrete wall as a link between the insulation layer and the concrete. On the one hand, it protects the insulation material from moisture, and on the other hand, it can prevent the vaporized natural gas from leaking out, ensuring the safe operation of the storage tank.

[0003] During the construction of storage tanks, the installation accuracy and quality of the outer tank wall lining directly affect the cold preservation effect of the storage tank, and then affect the operating performance. The wall lining is installed after the gas lifting of the arch is completed. Now three-stage wall lining installation is commonly used at home and abroad. The amount of high-altitude welding work is large, the amount of empty hanging basket used is also large, there are many cross-operations, the installation period is long and unsafe. Summary of the invention

[0004] In order to solve the above problems, the present invention discloses a method for accurately positioning and installing the wall lining of a large full-containment cryogenic storage tank. The wall lining is innovatively divided into an upper and a lower part, wherein the lower part is installed using a mobile scaffolding and an electric hoist; the upper part is first welded and assembled on the ground, hoisted by an electric hoist and adjusted into place using a fall chain, and then the operators ride in a hanging basket to weld and polish. This installation method greatly reduces the amount of high-altitude welding work on the outer tank wall lining of the LNG storage tank, reduces cross-operation, reduces the use of high-altitude hanging baskets, and shortens the installation period.

[0005] To achieve the above object, the technical solution of the present invention is as follows: The precise positioning and installation method of the wall lining of a large full-containment cryogenic storage tank includes the following steps: (1) Prefabricated tank wall lining, the tank wall lining is divided into upper wall lining and lower wall lining, where the upper wall lining is made of N sheets of plate spliced ​​vertically, where N>1; (2) Prefabricated corner panels; (3) Two upper and lower circumferential embedded parts and a number of vertical embedded parts are arranged on the outer wall of the outer tank; (4) Install the corner plate first, and overlap the corner plate with the lower circle of circumferential embedded parts and the edge bottom plate; (5) Weld the lower wall lining between the upper and lower annular embedded parts; (6) Lifting the upper wall lining: After the prefabrication and splicing of the upper wall lining is completed, four symmetrical lifting ears are welded and fixed on one end of the wall lining close to the wall. The upper two lifting ears are used to connect with the electric hoist, and the lower two lifting ears are used to connect with the fall chain after the lifting height of the wall lining reaches the lifting height limit of the electric hoist. The wall lining is continued to be pulled up to the designed height with the help of the fall chain, and the posture of the wall lining is adjusted by the fall chain. In order to prevent the upper end of the wall lining from colliding too much with the wall during the lifting process of the wall lining, the front two lifting ears are first connected to the hook of the electric hoist through a wire rope during lifting to prevent excessive bending of the upper part. When installing the two lower lifting ears, their installation position and angle should be coordinated with the electric hoist and the wire rope used for lifting. The installation position should fully consider the maximum lifting height that the electric hoist can provide and the bending deformation caused by the excessive length of the wall lining above the lifting ear and the friction and collision with the wall; the best position of the two lower lifting ears should be after the electric hoist reaches the maximum lifting limit, and the upper end of the wall lining is as close as possible to the overlap position of the pressure ring, so as to reduce the time of lifting with the fall chain and improve work efficiency; when installing the two lower lifting ears, the length of the wire rope and the angle formed between the two lifting ears during lifting should be fully considered, and the force of the installation lifting ears along the length of the weld and the direction after the wire rope is tightened should be kept in the same straight line as much as possible, so that the force state of the installation lifting ears is the most ideal, and a stable triangular structure is formed between the wire rope and the wire rope. When installing the lifting ears, the two lifting ears in the same row should be welded symmetrically along the central axis, so as to ensure that the wall lining is kept in a natural vertical state during the lifting process. After the lifting lugs are welded, all lifting lugs must undergo 100% PT testing and pass the test before lifting operations can be carried out. During operations, a warning area should be set up and dedicated safety protection personnel should be deployed to carry out on-site safety management.

[0006] After the upper wall lining reaches the designated position. Remove the ropes connecting the two lifting ears above the wall lining and the lower lifting ears, and use the hook of the fall chain to connect it instead. Install the hook on one side of the fall chain on the lifting ear welded in advance on the pressure ring, and connect the hook on the other side to the lifting ear above the wall panel. Adjust the length of the fall chain so that it is fully stressed. After completing the connection with the fall chain, loosen the connection between the electric hoist and the two lower lifting ears. Use the fall chain to adjust the horizontality and verticality of the wall lining, and place the adjusted bottom of the upper wall lining on the positioning block welded on the upper ring annular embedded parts, and align it with the three positioning blocks on the left vertical embedded parts. After it is in place, weld three positioning blocks on the right embedded parts to limit the wall lining to ensure the installation accuracy of the upper wall lining. After the position is adjusted, weld.

[0007] (7) Welding the upper wall lining.

[0008] As a supplement to the present invention, the length of the lower wall lining plate in step (1) = the height of the outer tank top - the height of the upper wall lining plate - the height of the corner plate.

[0009] As a supplement to the present invention, the corner plate described in step (2) is L-shaped, and its corner is arc-shaped.

[0010] As a supplement to the present invention, after the corner plate in step (4) is installed, the oblique support column is fixed by spot welding to control deformation during welding.

[0011] As a supplement to the present invention, before welding the lower wall lining plate in step (5), positioning blocks are respectively welded on the left vertical embedded parts and the lower annular embedded parts.

[0012] As a supplement to the present invention, the bottom of the upper wall lining plate in step (6) is placed on the positioning blocks of the upper circle of annular embedded parts and aligned with the three positioning blocks on the left vertical embedded parts. After being in place, three positioning blocks are welded on the right embedded parts to limit the upper wall lining plate.

[0013] As a supplement to the present invention, the positioning blocks in steps (5) and (6) are "7"-shaped positioning blocks.

[0014] As a supplement to the present invention, the inclination angle of the two lower lifting ears in step (6) is the same as the angle of the lifting rope.

[0015] As a supplement to the present invention, the welding method adopts manual arc welding.

[0016] The beneficial effects of the present invention are: (1) The wall lining is divided into upper and lower parts and installed separately, which optimizes the construction method. (2) The upper wall lining is installed with four lifting points, which are hoisted by electric hoist and fall chain, and limited by auxiliary clamp "7" shaped positioning block, which has the following functions: a: It can accurately control the overlap between the wall lining and the embedded parts. b: It overcomes the defect that the electric hoist cannot be directly lifted into place due to insufficient space on the tank top, ensuring normal installation; c: Keep the wall lining in a natural vertical state during the lifting process to avoid friction between the wall lining and the wall.

[0017] (3) The wall lining is welded on the ground, and round pipes are laid on the back for transportation, which reduces the technical difficulty of welding construction and ensures the welding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1It is the installation schematic diagram of the present invention.

[0019] Figure 2 It is a schematic diagram of the annular embedded parts and the vertical embedded parts on the inner wall of the storage tank according to the present invention.

[0020] Figure 3 It is a schematic diagram of the installation of the corner plate and the oblique support column described in the present invention.

[0021] Figure 4 Schematic diagram of the upper wall lining of the present invention Figure 5 This is a schematic diagram of the positioning block described in the present invention.

[0022] Figure 6 This is a schematic diagram of the installation of the upper wall lining plate described in the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0024] Taking a certain liquefied natural gas storage and transportation project in Jiangsu Province as an example, it is necessary to build a 20m³ large-scale full-containment concrete LNG storage tank with a height of 36 meters (excluding the height of the arch). The wall lining is installed after the gas lifting of the arch is completed. The material of the wall lining is 16MnDR steel plate with a thickness of 6mm. Two upper and lower circles of circumferential embedded parts 6 and 7 and several vertical embedded parts 8 are set on the outer wall of the outer tank; after the prefabrication and cutting, the wall lining is welded and fixed with the embedded parts installed on the concrete wall; each wall lining has a total of 720 pieces, which are arranged circumferentially along the inner wall of the concrete. The tank wall lining is divided into an upper wall lining 2 and a lower wall lining 3, among which the upper wall lining is vertically spliced ​​by 3 plates (three in one), and three whole plates are used for prefabrication and splicing. Through quality control and auxiliary facilities in the splicing process, it is ensured that the overall verticality of the upper wall lining after prefabrication and splicing can meet the design requirements. The welding quality of the wall lining plate and the embedded parts in the later stage is guaranteed by reserving appropriate welding joints at the overlapped cuts of the two plates. The lower wall lining plate 3 overlaps between the two circles of annular embedded parts 6 and 7 (the length of the lower wall lining plate = the height of the outer tank top - the height of the upper wall lining plate - the height of the corner plate). Below the lower wall lining plate is the corner plate 4, which overlaps with the lower circle of annular embedded parts 7 and the edge bottom plate.

[0025] The specific installation steps are as follows: (1) Prefabrication: There are 144 upper wall lining panels in total, each of which is made up of three 10-meter-long steel plates spliced ​​into a 30-meter-long lining panel. The lower corner panel is about 1 meter high, and the rest of the space is filled with lower wall lining panels; a: Corner plate 4 is cut and blanked by inverter air plasma cutting machine in the prefabrication yard. After blanking, the corner plate is rolled by three-axis plate rolling machine. The corner plate is L-shaped with arc-shaped corners. When rolling, the surfaces of several rollers should be smooth and there should be no foreign matter attached to the rolling rollers to prevent damage to the surface of the corner plate base material during the rolling process. In order to ensure the forming rate and quality of rolling, it is necessary to make corner plate samples according to the drawings so that they can be checked during and after the corner plate rolling process. The sample specifications should comply with SH / T3537-2009. Before rolling, a reserved right-angle edge of 260mm should be marked on the plate. During the rolling process, the sample should be used for timely verification to prevent excessive bending deformation.

[0026] b: The lower wall lining 3 is cut and cut using an inverter air plasma cutting machine in the prefabrication yard. The cutting line should be straight and the cutting surface should be free of defects such as cracks, slag inclusions, and scars. The wall linings that have been cut should be stored flat to prevent serious deformation of the wall linings.

[0027] c: The upper wall lining plates 2 are all made of whole sheets, so there is no need to cut and cut materials in the prefabrication yard. When splicing, the verticality of the three sheets is strictly controlled during the splicing process. According to the actual construction requirements on site, several angle lines are determined on the bottom lining plate by using a total station or by pulling wires, and the short side of the wall lining plate close to the wall and the long side of the upper wall lining plate are limited by welding angle steel 15 on the angle line. In this way, it can be ensured that the spliced ​​wall lining plates are kept on the same horizontal line and the overall verticality meets the design requirements. According to the actual situation on site, there are certain differences in the width and length of each wall lining plate, so special attention should be paid when splicing. If it is too wide or too long, it should be cut in time. When prefabricating and splicing three-joint one wall lining plates, in order to ensure the effective welding angle height of the overlap position of the two plates, it is necessary to make incisions on both sides of the edge of the upper overlapped plate, and the size of the incision should meet the design requirements.

[0028] The wall lining is welded on the ground, which reduces the technical difficulty of welding construction and ensures the welding quality.

[0029] (2) Install the corner plate, After the edge base plate is laid and welded, the corner plate can be installed. When installing the corner plate, start from the weld starting position required by the design drawing to avoid overlap between the corner plate weld and the edge plate weld joint and prevent the appearance of cross welds.

[0030] The corner plate is installed in a clockwise direction from 0°. During the installation process, a fall chain and a clamp are used for installation. During the installation process, the overlap between the two corner plates is strictly controlled to be 60mm, the overlap between the corner plate and the embedded part is 50mm, and the overlap between the corner plate and the edge plate is at least 60mm. During the installation, fixing and welding of the corner plate, in order to control the deformation of the corner plate, the oblique support column 9 (such as Figure 3 ), so that a stable triangular structure is formed between it and the edge plate of the bottom lining plate, ensuring that the deformation of its welding is controlled within the range of design requirements.

[0031] (3) Install the lower wall lining Before installing the lower wall lining, two lifting ears should be symmetrically welded on the upper side of the center line of its short side for cooperation with the fall chain during installation. During the installation process, the verticality of the lower wall lining should be measured at any time. If the posture of the lower wall lining changes, the horizontality and verticality should be adjusted in time with the fall chain to ensure the accuracy of the installation of the lower wall lining. Before installation, "7"-shaped positioning blocks 5 should be welded on the left vertical embedded parts and the first ring embedded parts to control the overlap size and verticality of the wall lining and the embedded parts. After hoisting the wall lining to the specified position, first contact the lower end face of the lower wall lining with the positioning blocks on the second ring embedded parts, and then adjust the lower wall lining to align with the left positioning blocks. After alignment, weld three positioning blocks on the right vertical embedded parts of the lower wall lining, and before welding the lower wall lining, the wall lining and the embedded parts are tightly fitted and fixed by cooperating with the wedges and positioning blocks to eliminate the gap between the lower wall lining and the embedded parts to ensure the welding quality.

[0032] (4) Install the upper wall lining After the upper wall lining is prefabricated and spliced, four symmetrical lifting ears 10 (such as Figure 4), wherein the two upper lifting ears 11 are used to connect with the electric hoist, and the two lower lifting ears 12 are used to connect with the fall chain after the lifting height of the wall lining reaches the lifting limit of the electric hoist, and the wall lining is continued to be pulled up to the designed height with the help of the fall chain, and the posture of the wall lining is adjusted by the fall chain. In order to prevent the upper end of the wall lining from colliding too much with the wall during the lifting process of the wall lining, the front two lifting ears are first connected to the hook of the electric hoist through the wire rope during the lifting to prevent the upper part from excessive bending. When installing the two lower lifting ears, their installation position and angle should be coordinated with the electric hoist and the wire rope used for lifting. The installation position should fully consider the maximum lifting height that the electric hoist can provide and the bending deformation caused by the excessive length of the wall lining above the lifting ear and the friction and collision with the wall. The best position of the two lower lifting ears should be when the electric hoist reaches the maximum lifting limit, and the upper end of the wall lining is as close as possible to the overlap position with the pressure ring, so as to reduce the time of lifting with the fall chain and improve work efficiency. When installing the two lower lifting ears, the length of the wire rope and the angle formed between the two lifting ears during lifting should be fully considered to ensure that the force of the installation lifting ears along the length direction of the weld and the direction of the tightened wire rope are kept in the same straight line (that is, the lower lifting ear 12 is tilted, such as Figure 6 As shown in the figure), the stress state of the installation eye is the most ideal, and a stable triangular structure is formed between the eye and the wire rope. When installing the eye, the two eyes in the same row should be welded symmetrically along the central axis, so that the wall lining can be kept in a natural vertical state as much as possible during the lifting process. After the eye welding is completed, all eyes should be tested 100% PT before the lifting operation can be carried out. During the operation, a warning area should be set up and special safety protection personnel should be equipped to carry out on-site safety management.

[0033] After the upper wall lining reaches the designated position, remove the ropes connecting the two lifting ears 11 above the wall lining and the lower lifting ears 12, and use the hook of the fall chain to connect them. Install the hook on one side of the fall chain on the lifting ear welded on the compression ring in advance, and connect the hook on the other side to the lifting ear on the wall panel. Adjust the length of the fall chain to make it fully stressed. After completing the connection with the fall chain, loosen the connection between the electric hoist and the two lower lifting ears. Use the fall chain to adjust the horizontality and verticality of the wall lining, and place the bottom of the adjusted upper wall lining on the positioning block welded on the upper ring embedded part ( Figure 6 ) and align them with the three positioning blocks on the left vertical embedded parts. After it is in place, three positioning blocks are welded on the right embedded parts to limit the wall lining to ensure the installation accuracy of the upper wall lining. After the position is adjusted, welding is carried out.

[0034] The precise positioning and installation method for the wall lining of a large full-volume cryogenic storage tank described in the present invention is aimed at the limitations of on-site construction operations in the tank and the characteristics of high-altitude operations in the tank. The method of ground assembly and overall hoisting is adopted to reduce the frequency of high-altitude operations and reduce the safety risks of high-altitude operations; the ground assembly reflects the advantages of the ideal welding position, ensures the welding quality of the weld, and improves the one-time welding pass rate. The coordinated hoisting of the electric hoist and the fall chain is adopted to reduce the safety risks of the previous single hoisting operations, and through the subtle adjustment of the fall chain and the "7"-shaped positioning block of the auxiliary fixture, the overlap amount between the wall lining and the embedded parts can be accurately controlled to ensure the working distance between the two wall linings during welding and improve the welding quality. By improving the construction process and method of the wall lining, the installation efficiency and welding quality are greatly improved, and the overall construction cost is also reduced to a certain extent.

[0035] The innovation of the present invention is achieved by optimizing the installation methods and construction processes of the upper and lower wall linings. Two sets of lifting lugs are added to the upper wall lining, and the mutual coordination of the fall chain and the electric hoist is improved; the "7"-shaped positioning block of the installation auxiliary tool is improved. The construction method is optimized to improve the installation accuracy of the wall lining of the 200,000 m³ LNG cryogenic storage tank; the installation positioning accuracy is high, and the welding qualification rate of the weld group is increased to 99%; the wall lining is welded on the ground, which reduces the technical difficulty of welding construction and ensures the welding quality; the wall lining is installed with 4 lifting points to ensure the installation accuracy of the wall lining and reduce the cumbersome procedures of the previous construction process, thereby improving the installation efficiency.

[0036] It should be noted that the above content only illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. The precise positioning and installation method of the lining plate of a large full-containment cryogenic storage tank is characterized by: The following steps are involved: (1) Prefabricated tank wall lining, the tank wall lining is divided into upper wall lining and lower wall lining, where the upper wall lining is made of N sheets of plate spliced ​​vertically, where N>1; (2) Prefabricated corner panels; (3) Two upper and lower circumferential embedded parts and a number of vertical embedded parts are arranged on the outer wall of the outer tank; (4) Install the corner plate first, and overlap the corner plate with the lower circle of circumferential embedded parts and the edge bottom plate; (5) Weld the lower wall lining between the upper and lower annular embedded parts; (6) Lifting the upper wall lining: After the upper wall lining is prefabricated and spliced, four symmetrical lifting ears are welded and fixed on the upper part of the wall lining, of which the upper two lifting ears are used to connect with the electric hoist, and the lower two lifting ears are used to connect with the fall chain after the lifting height of the wall lining reaches the lifting height limit of the electric hoist, and the wall lining is continuously pulled up to the designed height with the help of the fall chain, and the posture of the wall lining is adjusted by the fall chain; in order to prevent the upper end of the wall lining from colliding too much with the wall during the lifting process of the wall lining, the front two lifting ears are first connected to the hook of the electric hoist through the wire rope during the lifting to prevent the upper part from excessive bending; the lower two lifting ears are connected to the hook of the electric hoist through the wire rope to prevent the upper part from excessive bending; When installing the lifting lugs, their installation position and angle should be coordinated with the electric hoist and the wire rope used for lifting. The best position of the two lower lifting lugs is when the electric hoist reaches the maximum lifting limit, and the upper end of the wall lining is as close as possible to the overlap position with the pressure ring, so as to reduce the time of lifting with the fall chain; when installing the two lower lifting lugs, the force of the lifting lugs is kept in the same straight line along the length of the weld and the direction of the wire rope after tightening, forming a stable triangular structure with the wire rope; when installing the lifting lugs, the two lifting lugs in the same row are welded symmetrically along the central axis to ensure that the wall lining remains in a natural vertical state during the lifting process; Before hoisting the wall lining, measure the theoretical size of the wall lining required to overlap on the embedded parts, confirm the position of the wall lining, weld the "7" type positioning block, and after the upper wall lining reaches the specified position; remove the rope connecting the two lifting ears above the wall lining and the lower lifting ears, and use the hook of the fall chain to connect it, install the hook on one side of the fall chain on the lifting ear welded on the pressure ring in advance, and connect the hook on the other side to the lifting ear above the wall panel, and adjust the length of the fall chain to make it fully stressed; after completing the connection with the fall chain, loosen the connection between the electric hoist and the two lower lifting ears; use the fall chain to adjust the horizontality and verticality of the wall lining, and measure the verticality and horizontality of the wall lining with the theodolite, tape measure, etc. After confirmation, weld the "7" type positioning block on the embedded parts at the bottom of the wall lining to position it. After positioning, weld the upper part of the wall lining to the pressure ring to fix it, ensure that the wall lining does not deviate, and achieve the installation positioning accuracy of the wall lining; (7) Welding the upper wall lining.

2. According to claim 1, the precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank is characterized by: The length of the lower wall lining plate in step (1) = the outer tank top height - the upper wall lining plate height - the corner plate height.

3. The precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank according to claim 1 is characterized in that: The corner plate described in step (2) is L-shaped, and its corner is arc-shaped.

4. The precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank according to claim 1 is characterized in that: After the corner plate is installed in step (4), the oblique support column is fixed by spot welding to control deformation during welding.

5. The precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank according to claim 1 is characterized in that: Before welding the lower wall lining plate in step (5), positioning blocks are welded to the left vertical embedded parts and the lower annular embedded parts.

6. The precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank according to claim 1 is characterized in that: In step (6), the bottom of the upper wall lining is placed on the positioning blocks of the upper annular embedded parts and aligned with the three positioning blocks on the left vertical embedded parts. After it is in place, three positioning blocks are welded on the right embedded parts to limit the upper wall lining.

7. The precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank according to claim 5 or 6, characterized in that: The positioning block is a "7" shaped positioning block.

8. The precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank according to claim 1 is characterized by: The inclination angles of the two lower lifting ears in step (6) are the same as the angle of the lifting rope.

9. The precise positioning and installation method for the wall lining of a large full-containment cryogenic storage tank according to claim 1 is characterized in that: The welding method adopts manual arc welding.

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