Aerial assembly method for top grid structure of large-span meridian storage tank

Abstract

The invention discloses an aerial assembly method for a large-span meridian storage tank top grid structure. The method comprises the following steps: firstly, prefabricating a latticed shell and a latticed rod; after laying and welding of the bottom plate of the storage tank are completed, assembling and welding of the first to fourth circles of wall plates are completed through a forward assembling method; then assembling and welding the inner floating disc; after the inner floating disc is installed, assembling and welding of the fifth to eighth circles of wall plates are completed through a forward installation method; after the radian and butt weld of the net rod of the prefabricated net shell are detected to be qualified, longitudinal and transverse coordinate lofting is carried out on the floating roof in the storage tank, a single meridian net rod is hoisted in place, and the camber and load bearing are maintained through edge supporting rods, middle supporting rods and center supporting rods; carrying out lap joint full foot welding on the upper and lower net rods; laying a skin; and finally, filling water and lifting. According to the method, the installation cost of the storage tank can be reduced, and better economic benefits are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of building construction methods, and in particular relates to an aerial assembly method for a large-span meridian storage tank top grid structure. Background Art

[0002] The installation technology of large-span internal floating roof bidirectional meridian dome tank lattice shell is becoming more and more advanced, but the internal floating roof atmospheric pressure storage tank has always been restricted by the lattice shell installation technology. The traditional construction of large-span internal floating roof dome tank lattice shell has the problem of limited lattice shell installation, which requires a lot of scaffolding erection and dismantling costs and more high-altitude operations. The construction process is complicated and the cost is high. Summary of the invention

[0003] In order to solve the above problems, the present invention discloses an aerial assembly method for the top grid structure of a large-span meridian storage tank, which adopts a meridian grid shell structure. The grid shell grid rods are made of short-section grid rods prepared by a processing plant. The grid rods are assembled and welded into a whole on site. After being laid out, they are assembled and fixed on the floating plate using a jig. The floating plate and the grid shell are floated to the top of the tank and connected and fixed with the cone plate by a water filling test of the storage tank. A large amount of scaffolding erection and dismantling costs and more aerial operations are saved, and a variety of construction methods are integrated according to local conditions, and the upright installation method is combined with the inverted installation method to further reduce the installation cost of the storage tank and obtain better economic benefits.

[0004] When assembling the poles, two groups of meridian poles are overlapped, and the overlapped surface is welded with continuous full fillet welding; since a single meridian pole is butt-jointed, the method of first assembling and prefabrication is adopted, and the single pole is fully fused and welded on the ground. This process not only ensures the welding quality of the lattice shell and makes the overall structure more stable, but also reduces the time of high-altitude operations, making the installation of the overall structure safer and more efficient.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for assembling a large-span meridian tank top grid structure in the air, the method comprising the following steps:

[0007] (1) Prefabricated lattice shell and lattice poles;

[0008] (2) After the tank bottom plate is laid and welded, the first to fourth circle wall plates are assembled and welded by the positive installation method;

[0009] (3) Assembly welding of inner floating plate;

[0010] (4) After the inner floating plate is installed, the fifth to eighth circle wall panels are assembled and welded by the positive installation method;

[0011] (5) After the camber and butt weld of the prefabricated lattice shell in step (1) are inspected and found to be qualified, the longitudinal and transverse coordinates of the floating roof in the tank are set out, and a single meridian lattice pole is hoisted into place, and the camber and load-bearing capacity are maintained by edge support rods, intermediate support rods and center support rods;

[0012] (6) Full foot welding of upper and lower mesh rods;

[0013] (7) Skin laying;

[0014] (8) Filling with water and lifting the top. Before the water filling test, a temporary liquid level gauge shall be installed. All accessories and other components welded to the tank body shall be completed and inspected to be qualified. Before the water filling test, all welds related to the tightness test shall not be painted. Clean fresh water should be used for the water filling test, and the test water temperature should not be lower than 5°C. When the edge of the net rod contacts the cone plate, the buoyancy tank drives the net shell and part of the skin to float evenly along the guide pipe to the elevation position, stop the operation of the water pump, and weld and fix the net rod and cone plate. The water filling and lifting is completed.

[0015] (9) After the water filling and top raising are completed, personnel stand on the upper part of the buoyancy tank and begin to install the cone plate guardrail. When the welds between the cone plates are tested and qualified, the tank body, cone plates and net rods are connected together through rib plates to complete the installation of the main structure.

[0016] Furthermore, the specific method of prefabricating the lattice shell rods in step (1) is to make a number of prefabricated rod molds according to the needs of the construction site. The lattice shell rods are formed by butt-welding short-section rectangular tubes that are annealed and formed. Since the main rods are welded from 4 sections, the overall deformation of the lattice shell is controlled. The two main rods in the center are welded first, and then the secondary rods are welded. The secondary rods are selected according to the part number and welded after the positions are correct.

[0017] Furthermore, the specific method for detecting the arc butt weld of the lattice shell mesh rod prefabricated in step (1) described in step (5) is as follows: arc detection: after a single mesh rod is bent into shape and welded, an arc template is used to check the degree, the gap between which should not be greater than 5 mm, and the arc template should be placed on a platform to check its warping deformation, the deformation should not exceed 0.1% of the length of the component, and should not be greater than 6 mm; weld detection: the butt weld is detected by ultrasonic testing.

[0018] Furthermore, the specific method for laying out the longitudinal and transverse coordinates of the internal floating roof described in step (5) is to use a total station to determine the center of the intersection of the X-axis and the Z-axis before lifting the grid shell rods. Based on the center position, the length of the vertical line of each side node is made on the tank wall using the arc length values ​​of each segment known on the drawing, and then the horizontal reference plane of the X and Z axes is found to intersect with the equally divided vertical line to form a cross line, and the midpoint of the cross is the intersection position of the connecting piece.

[0019] Furthermore, the central support rod described in step (5) is specifically installed by fixing it at a known center position, aligning it with a theodolite or a plumb line in the vertical direction, and firmly supporting it with two diagonal rods in the 90° direction, i.e., the Z-axis direction. In order to ensure the installation and arch height of the lower mesh rod, before installing the lower mesh rod, a plurality of vertical support rods should be symmetrically temporarily arranged with the intersection of the X-axis and the Z-axis as the center, the bottom plate at the lower end of the support rod is firmly spot-welded to the bottom plate of the tank, and each column is provided with two diagonal braces to ensure the stability of the support system.

[0020] Furthermore, the upper and lower mesh rods are overlapped and fully welded in step (6). The specific method is that when welding, welding is carried out from the center top to the surroundings, the sections are overlapped and connected and fully welded according to the design requirements, the weld foot height is not less than 3mm, and there should be no sharp corners at the overlap. After welding is completed, the weld position is promptly polished for corrosion protection.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention adopts a water floating lifting method and utilizes a water filling test. As water is filled in, the floating cabin drives the arch along the two guide pipes of the storage tank and is evenly lifted to a specified elevation in the vertical direction. The connection between the grid shell and the tank body is completed on the floating cabin after the lifting, which reduces the difficulty of welding and assembly operations at high places, saves the cost of fully erected scaffolding, and also saves the cost of setting up a platform for completing the connection between the grid shell and the tank body.

[0023] 2. While installing the buoyancy tank, the present invention performs low-altitude assembly welding on the prepared short sections of the net rods and after passing the inspection, hoist the single meridian net rod to the upper part of the buoyancy tank in the tank for assembly, and uses a mobile scaffold for welding and fixing, thus reducing a large amount of high-altitude welding operations, ensuring the welding quality of the net shell net rods, and reducing the difficulty and cost of crane hoisting compared to overall hoisting.

[0024] 3. The present invention adopts a meridian lattice shell structure. The lattice shell mesh rods are made of short-section mesh rods that are baked in a processing plant. The mesh rods are assembled and welded into a whole rod on site. After layout, they are assembled and fixed on the floating plate using a jig. The floating plate and the lattice shell are floated to the tank top and connected and fixed to the cone plate using a water filling test of the storage tank. A large amount of scaffolding erection and dismantling costs and a large number of high-altitude operations are saved, and a variety of construction methods are integrated according to local conditions, combining the upright installation method with the inverted installation method to further reduce the installation cost of the storage tank and obtain better economic benefits. The construction sequence is improved, the tank bottom and tank wall are upright, and the buoyancy cabin and tank arch are inverted. That is, after the installation of the tank bottom is completed, when the tank wall is installed, the buoyancy cabin is prefabricated and hoisted synchronously, and then the lattice shell is prefabricated and hoisted synchronously. This can effectively improve construction efficiency and reduce installation period.

[0025] 4. When assembling the net poles, the two groups of meridian net poles are overlapped, and the overlapped surface is welded with continuous full fillet welding; since a single meridian net pole is butt-jointed, a method of first assembling and prefabrication is adopted, and the single net pole is fully fused and welded on the ground. This process not only ensures the welding quality of the net shell and makes the overall structure more stable, but also reduces the time of high-altitude operations, making the installation of the overall structure safer and more efficient. DETAILED DESCRIPTION

[0026] The installation of a 40,000 cubic meter storage tank is taken as an example. The 40,000 cubic meter storage tank is the largest internal floating roof atmospheric pressure storage tank in China. The tank body is made of Q345R steel, and the fixed roof and floating tank are uniformly made of Q235B steel. The tank diameter is 48m, the tank body height is 24m, and the arch height is 7.281m.

[0027] The main dimensions of the tank are shown in Table 1-1.

[0028] Table 1-1 Main structural dimensions of the tank

[0029] name Value / mm name Value / mm Tank inner diameter 48000 Dome ball radius 43448 Tank wall height 24000 Overall height of tank 31281 <![CDATA[Top ring tank wall thickness 注1 > 8.7 Height of lattice shell square beam 198 Tank wall height in the model 3000 Width of lattice shell beam 98 <![CDATA[Skin panel thickness 注1 > 3.7 <![CDATA[Thickness of the grid shell's square beam 注1 > 5 <![CDATA[Thickness of pressure ring 注1 > 26.7 Spacing of lattice beams (arc length) 2600 Width of pressure ring 650 Corrosion allowance 1

[0030] Note: 1 The table shows the dimensions of the finite element model, from which corrosion allowance, negative thickness deviation and forming thinning amount have been removed.

[0031] The project covers finished oil tank processing plant prefabrication, anti-corrosion, construction site assembly, leak test, water filling test and other engineering construction work. Due to limited production space, all storage tanks are manufactured in the processing plant and then transported to the installation site for installation.

[0032] This embodiment provides an aerial assembly method for a large-span meridian tank top grid structure, the method comprising the following steps:

[0033] (1) Prefabricated lattice shell and lattice poles: Several prefabricated lattice pole molds are made according to the needs of the construction site. The lattice shell and lattice poles are made by butt welding short-section rectangular tubes that are annealed and formed. Since the main lattice pole is welded from 4 sections, the overall deformation of the lattice shell is controlled. The two main lattice poles in the center are welded first, and then the secondary lattice poles are welded. The secondary lattice poles are selected according to the part number and welded after the position is correct.

[0034] 1.2 Process data

[0035] Table 1-2 shows the process load data of the lattice shell.

[0036] Table 1-2 Process load data of lattice shell

[0037] Process load data Numeric Tube data Numeric Design pressure / MPa 0 Vertical earthquake acceleration 0 Design temperature / ℃ 50 Platform inner diameter / mm 46520 Wind load / Pa 714 Platform outer diameter / mm 47820 Horizontal seismic acceleration 0.1g Platform pressure / Pa 1000

[0038] Note: 1g = 9.8m / s 2 .

[0039] 1.3 Material parameters

[0040] The performance parameters of the materials used for the lattice shell at the design temperature are shown in Table 1-3. The material parameters in this project are mainly taken from GB / T150-2011 "Pressure Vessels".

[0041] Table 1-3 Performance parameters of materials used for lattice shells at design temperature

[0042] name Q235B Q345R Q345R Material Specifications Square steel pipe Steel Plate Steel Plate Application area Grid Shell Skin, tank wall Pressure ring Corresponding temperature / ℃ 50 50 50 <![CDATA[Density / kg·m -3 > <![CDATA[7.85×10 3 ]]> <![CDATA[7.85×10 3 ]]> <![CDATA[7.85×10 3 ]]> <![CDATA[Elastic modulus 注1 / MPa]]> <![CDATA[2.03×10 5 ]]> <![CDATA[2.03×10 5 ]]> <![CDATA[2.03×10 5 ]]> Poisson's ratio 0.3 0.3 0.3 <![CDATA[Design stress intensity 注2 / MPa]]> 115 189 185 <![CDATA[Yield strength 注3 / MPa]]> 235 333 313

[0043] Note: 1 The elastic modulus is determined by linear interpolation based on Table B.13 in GB / T 150.2-2011 “Pressure Vessels”.

[0044] 2 The design stress intensity is determined by linear interpolation based on Tables 2 to 16 in GB / T 150.2-2011 “Pressure Vessels”.

[0045] 3 The yield strength is determined by linear interpolation based on Table B.1 to Table B.12 in GB / T 150.2-2011 "Pressure Vessels".

[0046] (2) After the tank bottom plate is laid and welded, the first to fourth circle wall plates are assembled and welded by the positive installation method;

[0047] (3) Assembly welding of inner floating plate;

[0048] (4) After the installation of the inner floating platform is completed, since the fixed roof of the storage tank is composed of a lattice shell and a skin, the maximum chord length of the lattice shell is 48m, the arc length is 50.853m, each meridian lattice rod is butt-welded in blocks using a jig, and the meridian lattice rod has a large span and deflection, and the total weight of the lattice shell is 42.2 tons. In order to ensure the arch requirements, after the installation of the inner floating roof is completed, a single meridian lattice rod is hoisted into place, and the arch and load-bearing capacity must be maintained through edge support, middle support and center support;

[0049] (5) Inspection of the curvature and butt weld of the prefabricated lattice shell rods in step (1), including curvature inspection: after a single lattice rod is bent and welded, an arc template is used to check the degree, the gap between them should not be greater than 5mm, and it should be placed on a platform to check its warping deformation, the deformation should not exceed 0.1% of the length of the component, and should not be greater than 6mm; weld inspection: since the lattice shell is the main load-bearing structure of the fixed roof, its welding quality is of vital importance. According to the drawings, the inspection of the butt weld is carried out by radiographic inspection, but radiographic inspection has strong radiation and the cost of radiographic inspection is relatively high. With the consent of the designer, ultrasonic inspection is used. After the welding of the butt weld is completed, a third-party inspection agency is contacted in time for flaw detection. If there is a problem, the on-site rectification is qualified, making the assembly and welding of the lattice shell rod more economical and efficient.

[0050] After the curvature and butt welds of the prefabricated lattice shell are tested and qualified, the longitudinal and transverse coordinates of the floating roof in the tank are laid out, and a single meridian lattice is hoisted into place, and the edge support rods, middle support rods and center support rods are used to maintain the curvature and load-bearing capacity.

[0051] Determination of vertical and horizontal coordinate points:

[0052] Before lifting the grid shell rods, use the total station to determine the center of the intersection of the X-axis and the Z-axis. Based on the center position and the known arc length values ​​of each segment on the drawing, make the vertical length of each side node on the tank wall, and then find the horizontal reference plane of the X and Z axes, and intersect the equally divided vertical lines to form a cross line. The midpoint of the cross is the intersection position of the connector.

[0053] Installation of the center support rod:

[0054] The center support rod is fixed at a known center position, aligned with a theodolite or plumb line in the vertical direction, and firmly supported by two diagonal rods in the 90° direction (Z direction). In order to ensure the installation and arch height of the lower mesh rod, before installing the lower mesh rod, multiple vertical support rods should be temporarily set symmetrically with the intersection of the X-axis and the Z-axis as the center. The bottom plate at the lower end of the support rod is spot welded firmly to the bottom plate of the tank, and each column is equipped with 2 diagonal braces to ensure the stability of the support system.

[0055] Installation of edge support rods:

[0056] Because the span of the lattice shell is about 48 meters long, the deflection is large, the number is large, and the weight is heavy, in order to reduce the deformation of the lattice shell, the arch and load-bearing are maintained through the central support and the temporary support added at the end of the lattice shell. The edge support points of the 40,000 cubic storage tank arch lattice are divided into 50 and the central support points are 25, which distributes the weight of the entire lattice shell to the inner floating plate, and makes the water filling and lifting after the fixed top is installed more reliable and safe.

[0057] In order to protect the finished parts and reduce the deformation of the floating plate, the support position corresponds to the pillar under the floating plate after the support between the floating plate and the bottom plate is installed, so that the weight of the lattice shell can be transferred to the bottom plate. Because the lattice shell is a spherical crown shape, the production length of each support column must be calculated according to the elevation calculated by the support layout diagram. When making the column, a certain length margin must be left or a length adjustment device must be added to overcome the deviation caused by welding deformation of the bottom plate and floating plate, component manufacturing error, position deviation, measurement error, etc.

[0058] (6) The upper and lower mesh rods are overlapped and fully welded; although the construction of the 40,000 cubic meter storage tank mesh shell does not require overall lifting, due to its large span, large deflection, heavy weight, and relatively compact tank spacing, it is necessary to calculate a crane that meets the requirements for lifting.

[0059] The arched bidirectional meridian lattice shell is composed of 38 lattice poles, 19 lattice poles in each of the upper and lower layers, with the longest arc length of a single pole being 50.853m and the chord length being 48m. The two poles with the longest arc length are hoisted first. The installation of lattice poles is carried out after the temporary support is installed. At this time, it is only necessary to hoist each lattice pole into place on the designated temporary support, and the maximum deviation of the welding nodes of the upper pole and the lower pole in the height direction must be controlled to be 25mm, and the maximum deviation of the node coordinates in the plane direction must be 10mm.

[0060] When splicing the first long net rod in the X direction, the excess height of the splicing weld on the upper surface of the net rod is ground flat, and then the second and third net rods in the X direction are installed on both sides symmetrically with the Z axis; then the first long net rod in the Z direction is installed, and the node 1 coincides with the node 1 of the long net rod in the X direction. The node positions must coincide and be spot welded in sequence, and the two end points are also spot welded to the edge node connectors. The same method is used to symmetrically install the spot welds on both sides with the X axis as the symmetry axis.

[0061] The upper and lower layers of lattice shell rods are overlapped, and the welding technology is strictly carried out in accordance with relevant requirements and regulations. When welding, welding is carried out from the center top to the surrounding areas. The sections are overlapped and fully welded according to the design requirements. The weld foot height is not less than 3mm, and there shall be no sharp corners at the overlap. After welding, the weld position shall be polished and anti-corrosion shall be carried out in time to prevent corrosion from being missed in some welds after the skin is hoisted.

[0062] (7) Skin laying;

[0063] (8) Fill with water and raise the roof.

[0064] After the storage tank body is completed, a water filling test is required to detect the reliability of the tank structure and the tightness of the tank body and the tank bottom. At the same time, in order to make more efficient use of water resources and not achieve the purpose of reducing costs and increasing efficiency, the water filling test is used to lift the fixed top.

[0065] 6.1 Calculate whether the buoyancy meets the requirements

[0066] The premise for taking the water filling test to lift the fixed roof is that there is sufficient buoyancy. The buoyancy calculation is used to determine whether the buoyancy compartment, the lattice shell and a certain amount of skin can be floated when filled with water.

[0067] According to the drawings, it is known that the materials of the buoyancy tank and the net pole are both Q235B, the mass of the buoyancy tank is M1=77645Kg, the mass of the net pole is M2=42600Kg, and the mass of the support pole is M3=81450Kg.

[0068] According to the Archimedean principle, an object immersed in a stationary fluid is subject to a buoyant force equal to the weight of the fluid displaced by the object.

[0069] The volume of the tank buoyancy tank is calculated as follows:

[0070]

[0071] V2=πR 2 H1=π23.8 2 0.85 = 1511.83 m 3

[0072] V3=πr 2 H2=π19.8 2 0.5 = 615.5 m 3

[0073] v=V2-V3-V1=447.39m 3

[0074] The maximum buoyancy provided by the buoyancy chamber H1 when it is completely submerged is:

[0075] F 浮max =p 水 V 排 =1000kg / m 3 9.8N / m 3 ·447.39m 3 =4384456.10N

[0076] G 总 =G 网壳 +G 蒙皮 +G 浮舱 =(m 网壳 +m 蒙皮 +m 浮舱 )

[0077] =(42600+81450+77645)kg×9.8N / kg

[0078] =1976611N

[0079] Since F floats max >G 总 Therefore, by using water filling test, the buoyancy tank, skin and lattice shell can float.

[0080] Prerequisites for water lifting

[0081] 1) Before the water filling test, a temporary liquid level gauge shall be set up, and all accessories and other components welded to the tank body shall be completed and inspected to be qualified; before the water filling test, all welds related to the tightness test shall not be painted; clean fresh water should be used for the water filling test, and the test water temperature should not be lower than 5°C; in special circumstances, when other liquids are used as the water filling test medium, it shall be approved by the relevant departments.

[0082] 2) All accessories on the floating roof (except the sealing device of rubber products) have been installed, and butter has been applied between the relative guide pipe parts.

[0083] 3) Check the single-plate pillars and cabin pillars one by one to confirm that each pillar is not spot-welded to the pad on the bottom plate of the oil tank.

[0084] 4) Thoroughly check the cabin bottom plate and the outer edge plate of the cabin to confirm that the positioning angle steels set on the tank wall plate and the tank bottom plate during the cabin installation have been completely cut off and there are no obstacles that affect the lifting and lowering of the floating roof.

[0085] 5) Confirm that all parts, brackets, etc. welded to the tank body have been installed.

[0086] 6) Confirm that all tank wall pipes including the pipe reinforcement rings have been assembled and welded, 100-200kpa compressed air has been introduced into the reinforcement plate through the signal hole, and there is no leakage in the welds. The floating tank side tank welds have passed the kerosene leak test, compressed air airtightness test, and vacuum box leak test.

[0087] 7) After the cleaning hole assembly welding is completed, stress relief heat treatment has been carried out and the weld PT flaw detection is qualified.

[0088] 8) The tank bottom vacuum box leak test is qualified, all wall panel welds are tested and heat treated.

[0089] 6.2 Water lifting process steps

[0090] When the water rises to the top and meets the conditions before the water filling test, the professional engineer reports to the project manager. After the project manager, supervisor and owner check and agree, two water pumps are prepared, one for use and one for backup. Start a single water pump, slowly open the water filling valve, and wait until the liquid level in the tank reaches the height of the float. Slow down the water filling speed. After the float and the fixed top float up, slowly adjust the water valve opening to make the grid shell continue to rise at a uniform speed. When the edge of the grid shell rises to a position close to the design elevation, stop filling with water, stabilize the height of the grid shell, and check and adjust the position of the fixed top.

[0091] Due to the calculated buoyancy, the buoyancy is much larger than the total gravity of the grid shell skin and the floating cabin. Therefore, when the floating cabin drives the grid shell skin to the designed elevation, personnel can carry out group welding operations on the upper part of the floating cabin, and carry out group welding of the cone plate around the storage tank and the tank top guardrail. After completion, water filling and lifting can be carried out. When the edge of the grid rod contacts the cone plate, the grid rod and the cone plate are welded and fixed, the water pump is stopped, and the water filling and lifting are completed.

[0092] 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. A method for assembling a large-span meridian tank top grid structure in the air, characterized in that: The method comprises the following steps: (1) Prefabricated lattice shell and lattice poles; (2) After the tank bottom plate is laid and welded, the first to fourth circle wall plates are assembled and welded by the positive installation method; (3) Assembly welding of inner floating plate; (4) After the inner floating plate is installed, the fifth to eighth circle wall panels are assembled and welded by the positive installation method; (5) After the camber and butt weld of the prefabricated lattice shell in step (1) are inspected and found to be qualified, the longitudinal and transverse coordinates of the floating roof in the tank are set out, and a single meridian lattice pole is hoisted into place, and the camber and load-bearing capacity are maintained by edge support rods, intermediate support rods and center support rods; (6) Full foot welding of upper and lower mesh rods; (7) Skin laying; (8) Filling with water and lifting the top. Before the water filling test, a temporary liquid level gauge shall be installed. All accessories and other components welded to the tank body shall be completed and inspected to be qualified. Before the water filling test, all welds related to the tightness test shall not be painted. Clean fresh water should be used for the water filling test, and the test water temperature should not be lower than 5°C. When the edge of the net rod contacts the cone plate, the buoyancy tank drives the net shell and part of the skin to float evenly along the guide pipe to the elevation position, stop the operation of the water pump, and weld and fix the net rod and cone plate. The water filling and lifting is completed. (9) After the water filling and top raising are completed, personnel stand on the upper part of the buoyancy tank and begin to install the cone plate guardrail. When the welds between the cone plates are tested and qualified, the tank body, cone plates and net rods are connected together through rib plates to complete the installation of the main structure.

2. The aerial assembly method of the large-span meridian tank top grid structure according to claim 1 is characterized in that: The specific method of prefabricating the lattice shell rods in step (1) is to make a number of prefabricated rod molds according to the needs of the construction site. The lattice shell rods are formed by butt-welding short-section rectangular tubes that are annealed and formed. Since the main rod is welded from four sections, the overall deformation of the lattice shell is controlled. The two main rods in the center are welded first, and then the secondary rods are welded. The secondary rods are selected according to the part number and welded after the position is correct.

3. The aerial assembly method of the large-span meridian tank top grid structure according to claim 1 is characterized in that: The specific method for detecting the arc butt weld of the lattice shell mesh rod prefabricated in step (1) described in step (5) is as follows: arc detection: after a single mesh rod is bent into shape and welded, an arc template is used to check the degree, the gap between which should not be greater than 5 mm, and the arc template should be placed on a platform to check its warping deformation, the deformation should not exceed 0.1% of the length of the component, and should not be greater than 6 mm; weld detection: ultrasonic testing is used to detect the butt weld.

4. The aerial assembly method of the large-span meridian tank top grid structure according to claim 1 is characterized in that: The specific method for setting out the longitudinal and transverse coordinates of the internal floating roof described in step (5) is to use a total station to determine the center of the intersection of the X-axis and the Z-axis before lifting the grid shell rods. Based on the center position, the length of the vertical line of each side node is made on the tank wall using the arc length values ​​of each segment known on the drawing, and then the horizontal reference plane of the X and Z axes is found to intersect with the equally divided vertical line to form a cross line, and the midpoint of the cross is the intersection position of the connecting piece.

5. The aerial assembly method of the large-span meridian tank top grid structure according to claim 1 is characterized in that: The central support rod described in step (5) is specifically installed by fixing it at a known center position, aligning it with a theodolite or a plumb line in the vertical direction, and firmly supporting it with two diagonal rods in the 90° direction, i.e., the Z-axis direction. In order to ensure the installation and arch height of the lower mesh rod, before installing the lower mesh rod, a plurality of vertical support rods should be symmetrically temporarily arranged with the intersection of the X-axis and the Z-axis as the center. The bottom plate at the lower end of the support rod is firmly spot-welded to the bottom plate of the tank, and each column is provided with two diagonal braces to ensure the stability of the support system.

6. The aerial assembly method of the large-span meridian tank top grid structure according to claim 1 is characterized in that: The specific method of the upper and lower mesh rods overlapped and fully welded in step (6) is as follows: when welding, welding is carried out from the center top to the surroundings, the sections are overlapped and fully welded according to the design requirements, the weld foot height is not less than 3mm, and there should be no sharp corners at the overlap. After welding is completed, the weld position is promptly polished for corrosion protection.