A design method for forged neck flange

Abstract

The present invention discloses a design method for a forged neck flange, including: determining the specifications and quantity of flange node connection bolts according to the tension exerted on the main pipe; determining the flange plate bolt inner margin and bolt outer margin according to the specifications of the connection bolts and the structural requirements; calculating the flange plate surface thickness according to the tension exerted on the bolts of each block; calculating the bending stress of the designed forged neck flange neck according to the main pipe force and structural requirements, adjusting the designed forged neck flange based on the calculation result, if the flange neck bending stress is greater than the steel design strength, the flange neck size needs to be further adjusted; otherwise, the flange neck size meets the design requirements. The present invention adopts the rigidity theory to design the forged neck flange, and the outer edge of the flange is disengaged when subjected to tension, and there is no influence of prying force, which truly reflects the axial tension stress mechanism of the forged neck flange.

Description

Technical Field

[0001] The invention relates to a design method for a forged neck flange and belongs to the technical field of power transmission towers. Background Art

[0002] With the planning and construction of UHV lines and the application of multi-circuit technology on the same tower, the external load of transmission towers has increased exponentially, and the tower structure has also tended to be large-scale. Steel tube towers have the advantages of simple structure, large overall stiffness, and good bearing capacity, and are suitable for use in towers with large loads. The promotion and application of steel tube towers in large-load towers can effectively reduce the weight of towers, reduce the root opening of poles and towers, compress line corridors, and reduce demolition and vegetation damage. Closed circular cross-section steel pipes have good air flow performance, isotropic force, good torsional resistance, high stable bearing capacity, large bending stiffness, better corrosion resistance than open cross-sections, and convenient processing and good visual effects. Steel tube components are widely used in power, metallurgy, petroleum, chemical industry, post and telecommunications and other industries, especially in radio and television systems. From quadrilaterals to octagons, 200m to 300m high radio and television towers, the application of steel tube structures has become quite common and has become the main structural form of TV towers.

[0003] From the design experience of foreign countries, most of the large-load towers in developed countries use steel tube tower structures. Since the 1990s, Japan has used steel tube tower structures in high-voltage and ultra-high voltage projects. All 1000kV ultra-high voltage lines and transmission towers have adopted this structural system, and carried out experimental research and theoretical analysis on the application of steel tube tower projects; South Korea has also adopted a large number of steel tube towers on 750kV transmission lines. The application of steel tube towers in my country's transmission towers started relatively late. Domestic steel tube tower structures are mostly used in large-span, 500kV double-circuit transmission towers and some substation structures. All 1000kV double-circuit ultra-high voltage transmission lines use steel tube tower structures.

[0004] The main material connection of the transmission steel pipe tower usually adopts flange nodes. The typical bolt-flange connection method consists of bolt assemblies, flange plates and gaskets. Common flange forms include rigid flanges, flexible flanges and forged neck flanges. Rigid flanges have good connection stiffness and bearing capacity characteristics, but their welding workload is large, and the welding of stiffening ribs is all manual welding, and there is a large welding residual stress in the node; the connection stiffness of the flexible flange plate is small, and the deformation of the plate surface is large. It is generally used as a minor rod node; the neck diameter and wall thickness of the connecting steel pipe of the forged neck flange are basically the same as those of the neck butt welding flange. Through the butt weld connection, the neck flange has a straight neck section and a variable slope section, which makes the flange force coordinated and the structure more reasonable, improves the force performance and connection stiffness of the non-stiffened flange, and if the design is reasonable, the connection stiffness of the neck flange is between the non-stiffened flange and the stiffened flange. Forged neck flange connection does not require welding stiffening ribs, and butt welds can be mechanically welded, which can solve the heavy work of manual welding of stiffening ribs of stiffened flanges and improve production efficiency and mechanization efficiency. The existing design method of forged neck flange is based on the design theory of flexible flange, that is, when the main pipe is pulled, there is a prying force between the outer edges of the flange. Due to the lever principle, the connecting bolts generate additional tension, which increases the bolt specifications and flange size, and has poor economic efficiency. Summary of the invention

[0005] In view of the shortcomings in the existing forged neck flange design technology, the present invention provides a forged neck flange design method, which does not consider the prying force on the outer edge of the disk when the flange is under tension, effectively reduces the tension on the bolts, thereby reducing the bolt specifications, reducing the flange disk size, reducing the flange mass, and effectively improving the economy and reliability of the flange node.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a forged neck flange design method, wherein the forged neck flange design includes designing the main pipe tension, the flange outer diameter and the flange thickness, and the design method includes:

[0008] The main pipe tension is calculated through the whole tower structure of the transmission steel pipe tower; the steel pipe specifications are calculated according to the main pipe tension, and the diameter and number of flange node connection bolts are calculated;

[0009] According to the specifications and quantity of the flange node connection bolts, the flange bolt inner margin and bolt outer margin are determined, and the flange surface size is determined based on this; the flange surface size includes the flange outer diameter;

[0010] Calculate the flange face thickness based on the flange face size and main pipe tension;

[0011] The bending stress of the neck of the designed forged neck flange is calculated, and the designed forged neck flange is adjusted based on the calculation results.

[0012] Furthermore, it also includes:

[0013] After determining the flange surface size, verify whether the flange bolt inner edge distance, bolt outer edge distance and bolt circumferential spacing meet the standard construction requirements. If not, redetermine the bolt specifications and quantity.

[0014] Further, the calculation of the flange surface thickness according to the flange surface size and the main pipe tension includes:

[0015] Calculate the arc length of each block of the flange as follows:

[0016]

[0017] Among them, S d represents the arc length of the block, d represents the outer diameter of the flange, θ represents the central angle corresponding to each block, and n represents the number of bolts;

[0018] The radial bending moment of each flange block is calculated based on the block balance equation as follows:

[0019]

[0020] Among them, T B0 Indicates the tension of each block bolt, T is the main tube tension, B is the bolt inner edge distance, M r represents the radial bending moment of the flange, and r represents the tangential bending moment coefficient of the flange surface;

[0021] Calculate the flange face thickness as follows:

[0022]

[0023] Where C represents the thickness of the flange surface, f y Indicates the design strength of steel.

[0024] Further, the calculation of the designed forged neck flange neck bending stress includes:

[0025] The cross section of the forged neck flange is divided into two equal parts along the diameter, and the flange isolation body bending moment is calculated based on the equilibrium equation corresponding to the flange isolation body;

[0026] Calculate the centroid of the forged flange section with neck, and calculate the flange section resistance moment based on the centroid of the forged flange section with neck;

[0027] The flange section bending stress is calculated based on the flange section resistance moment and the flange isolation body bending moment.

[0028] Furthermore, the balance equation corresponding to the flange isolation body is:

[0029] M0+0.5T(yt -y b )=0,

[0030]

[0031] Where M0 represents the flange isolation body bending moment, y t Indicates the distance from the main pipe wall to the center line, y b It represents the distance from the point where the resultant force of the bolt group acts to the center line, and K represents the flange bolt circle diameter.

[0032] Further, the calculation of the centroid of the forged neck flange section includes:

[0033] Divide the cross section of the forged neck flange into standard triangles and rectangles, and calculate the centroid of the cross section of the forged neck flange as follows:

[0034]

[0035] Among them, y O' It represents the distance between the center of gravity of the forged neck flange section and the X-axis. A1, A2, and A3 are the areas of the three regions divided by the flange section. These are the distances between the center of gravity of the three areas divided by the flange cross section and the X-axis.

[0036] Furthermore, the flange section bending stress is calculated as follows:

[0037]

[0038] Where M0 represents the flange isolation body bending moment, W y represents the flange section resistance moment, K represents the flange bolt circle diameter, H represents the flange section height, I y represents the flange section moment of inertia, y O' Indicates the distance between the center of gravity of the forged neck flange section and the X-axis.

[0039] Further, the adjustment of the designed forged neck flange based on the calculation results includes:

[0040] If the bending stress of the flange section is greater than the design strength of the steel, the flange neck width needs to be further adjusted; if the bending stress of the flange section is not greater than the design strength of the steel, the flange neck size meets the design requirements.

[0041] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0042] The method of the present invention adopts the rigidity theory to design the forged neck flange, that is, the outer edge of the flange is disengaged when under tension, and there is no influence of prying force, which effectively reduces the tension on the bolts, thereby reducing the bolt specifications, reducing the flange surface size, reducing the flange mass, and effectively improving the economy and reliability of the flange node. The ultimate bearing capacity of the forged neck flange of the same specification calculated by the present invention is slightly smaller than the test results and the numerical simulation results, and the two are in good agreement; while filling the gap in the regulations and specifications, the calculation method is reasonable, the calculation results are reliable, and it is conducive to guiding engineering design. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a design flow chart of a forged neck flange provided by the present invention;

[0044] Figure 2 It is a schematic diagram of the force on the flange of each block in the present invention;

[0045] Figure 3 It is a schematic diagram of the force on the flange cross section in the present invention;

[0046] Figure 4 It is a schematic diagram of the center of gravity position of the flange cross section in the present invention;

[0047] Figure 5 It is a cross-sectional dimension diagram of a design example of a forged neck flange in an embodiment of the present invention;

[0048] Figure 6 is a finite element simulation stress distribution diagram of a forged neck flange design example in an embodiment of the present invention;

[0049] Figure 7 It is a finite element simulation disk contact stress distribution diagram of a forged neck flange design example in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0051] An embodiment of the present invention provides a forged neck flange design method, such as Figure 1 As shown, the following steps are included:

[0052] Step 1: Calculate the pull-out force T of the steel pipe component through the whole tower structure of the transmission steel pipe tower, and use it as the external input condition of the steel pipe component and the corresponding flange node. Calculate the steel pipe specifications according to the pull-out force T and the equal strength principle, and calculate the diameter d0 and number n of the flange node connection bolts;

[0053] Step 2: Determine the flange surface size according to the specification d0 and quantity n of the flange node connection bolts, verify whether the flange bolt inner edge distance B, bolt outer edge distance A and bolt circumferential spacing meet the standard construction requirements. If not, adjust the corresponding flange surface size; and determine whether Nmax<Ntb is established. If so, the bolt configuration meets the requirements. If not, the bolt specifications need to be readjusted.

[0054] Step 3: According to the flange surface size determined in step 2 and the tensile force T of the bolts corresponding to each flange block B0 Calculate the flange surface thickness C, and the force diagram of each flange block is as follows: Figure 2 The specific calculation method is as follows:

[0055] Arc length of each flange block:

[0056]

[0057] Where: S d represents the arc length of the block, d represents the outer diameter of the main pipe, θ represents the central angle corresponding to each block; n is the number of bolts.

[0058] The equilibrium equation for each block is:

[0059] M r +2M t sin(θ / 2)=T B0 B,

[0060] Where: T B0 Indicates the tension on the bolts of each block, B represents the inner edge distance of the bolt, M r Indicates the radial bending moment of the flange, M t Indicates the flange tangential bending moment, M t = rM r , r represents the tangential bending moment coefficient of the flange surface.

[0061] Radial bending moment of flange in each block:

[0062]

[0063] Flange surface thickness:

[0064]

[0065] Where: C represents the thickness of the flange surface, f y Indicates the design strength of steel.

[0066] Step 4: Calculate the bending stress of the flange neck according to the tension on the main pipe and the structural requirements, and adjust the designed forged flange neck size.

[0067] Flange cross section force diagram Figure 3 The specific calculation method is as follows:

[0068] The cross section of the forged neck flange is divided into two equal parts along the diameter. Each part is subjected to the main pipe tension of T / 2, the bolt group tension of T / 2, and the bending moment of M0. The equilibrium equation corresponding to each isolator is:

[0069] M0+0.5T(y t -y b )=0,

[0070]

[0071] Where: y t Indicates the distance from the main pipe wall to the center line, y b It represents the distance from the point of action of the resultant force of the bolt group to the center line, M0 represents the bending moment borne by the flange isolation body, and K represents the flange bolt circle diameter.

[0072] like Figure 4 As shown in the figure, for the forged flange section with neck, the calculation process of the section center of gravity is as follows:

[0073]

[0074] Figure 4 In the figure, O1, O2, and O3 represent the centroid positions of the three regions divided by the dotted line on the flange section, and O' represents the centroid position of the flange section. A1, A2, and A3 represent the areas of the three regions divided by the dotted line on the flange section. Indicates the distance between the center of gravity of the three areas divided by the dotted line of the flange section and the X-axis.

[0075] Flange section bending stress σ f :

[0076]

[0077] Where: H represents the flange section height, I y Represents the flange section moment of inertia, W y Represents the flange section resistance moment.

[0078] If the flange section bending stress σ f Greater than the steel design strength f y , then it is necessary to further adjust the flange neck size, specifically the flange neck width; if the flange section bending stress σ f Not greater than the steel design strength f y , then the flange neck size meets the design requirements.

[0079] Example:

[0080] like Figure 5 As shown in the figure, the main pipe specification Φ356×8 corresponds to the forged neck flange node using 20M24 bolts, the bolt diameter d0=24mm, and the effective cross-sectional area of ​​the bolt is 353mm 2 , the central angle of adjacent bolts is 18°, 8.8 grade high-strength bolts are used, the tensile strength design value is 400MPa, and the tensile bearing capacity design value of a single bolt is 141.2kN. The main pipe material and flange material are Q420, and the main pipe design tension T = 2623kN. The outer diameter of the flange is 478mm, the bolt circle diameter is 430mm, the flange neck root diameter is 370mm, the outer diameter of the flange neck end is 370mm, the thickness of the flange neck end is 10mm, the inner diameter of the flange is 300mm, the flange thickness is 32mm, and the flange section height is 100mm. The verification process of the forged flange section is as follows:

[0081] Node bolt force:

[0082] Bolt outer distance:

[0083] Bolt inner edge distance:

[0084] Arc length of each flange block:

[0085] Radial bending moment of flange in each block:

[0086] Flange surface thickness:

[0087] Flange section bending moment stress:

[0088] like Figure 6-7 As shown, according to the above flange size, the main pipe design tension is used as the external input condition, and the flange plate thickness is used as the response index. It can be seen that under the same tension input condition calculated by the present invention, the maximum simulated stress of the flange section is basically consistent with the cross-section calculated stress, and there is no contact stress on the outer edge of the flange, indicating that the outer edge of the flange is disengaged, which is consistent with the rigidity theory adopted by the present invention. While filling the gap in regulations and specifications, the present invention has a reasonable calculation method and reliable calculation results, which is conducive to guiding actual engineering design and can be promoted and applied in actual engineering.

[0089] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for designing a forged neck flange, characterized in that: The forged neck flange design includes designing the main pipe tension, flange outer diameter and flange thickness, and the design method includes: The main pipe tension is calculated by calculating the entire tower structure of the transmission steel pipe tower; and the steel pipe specifications are calculated based on the main pipe tension, and the diameter and number of flange node connection bolts are calculated; According to the specifications and quantity of the flange node connection bolts, the flange bolt inner margin and bolt outer margin are determined, and the flange surface size is determined based on this; the flange surface size includes the flange outer diameter; Calculate the flange face thickness based on the flange face size and main pipe tension; The bending stress of the neck of the designed forged neck flange is calculated, and the designed forged neck flange is adjusted based on the calculation results.

2. A forged neck flange design method according to claim 1, characterized in that: Also includes: After determining the flange surface size, verify whether the flange bolt inner edge distance, bolt outer edge distance and bolt circumferential spacing meet the standard construction requirements. If not, redetermine the bolt specifications and quantity.

3. A forged neck flange design method according to claim 1, characterized in that: The calculation of flange surface thickness according to flange surface size and main pipe tension includes: Calculate the arc length of each block of the flange as follows: Among them, S d represents the arc length of the block, d represents the outer diameter of the flange, θ represents the central angle corresponding to each block, and n represents the number of bolts; The radial bending moment of each flange block is calculated based on the block balance equation as follows: Among them, T B0 Indicates the tension of each block bolt, T is the main tube tension, B is the bolt inner edge distance, M r represents the radial bending moment of the flange, and r represents the tangential bending moment coefficient of the flange surface; Calculate the flange face thickness as follows: Where C represents the thickness of the flange surface, f y Indicates the design strength of steel.

4. A forged neck flange design method according to claim 3, characterized in that: The calculation of the designed forged neck flange neck bending stress includes: The cross section of the forged neck flange is divided into two equal parts along the diameter, and the flange isolation body bending moment is calculated based on the equilibrium equation corresponding to the flange isolation body; Calculate the centroid of the forged flange section with neck, and calculate the flange section resistance moment based on the centroid of the forged flange section with neck; The flange section bending stress is calculated based on the flange section resistance moment and the flange isolation body bending moment.

5. A forged neck flange design method according to claim 4, characterized in that: The balance equation corresponding to the flange isolation body is: M0+0.5T(y t -y b )=0, Where M0 represents the flange isolation body bending moment, y t Indicates the distance from the main pipe wall to the center line, y b It represents the distance from the point where the resultant force of the bolt group acts to the center line, and K represents the flange bolt circle diameter.

6. A forged neck flange design method according to claim 4, characterized in that: The calculation of the centroid of the forged neck flange section includes: Divide the cross section of the forged neck flange into standard triangles and rectangles, and calculate the centroid of the cross section of the forged neck flange as follows: Among them, y O' It represents the distance between the center of gravity of the forged neck flange section and the X-axis. A1, A2, and A3 are the areas of the three regions divided by the flange section. These are the distances between the center of gravity of the three areas divided by the flange cross section and the X-axis.

7. A forged neck flange design method according to claim 4, characterized in that: The calculation of flange section bending stress is as follows: Where M0 represents the flange isolation body bending moment, W y represents the flange section resistance moment, K represents the flange bolt circle diameter, H represents the flange section height, I y represents the flange section moment of inertia, y O' Indicates the distance between the center of gravity of the forged neck flange section and the X-axis.

8. A forged neck flange design method according to claim 4, characterized in that: The adjustment of the designed forged neck flange based on the calculation results includes: If the bending stress of the flange section is greater than the design strength of the steel, the flange neck width needs to be further adjusted; if the bending stress of the flange section is not greater than the design strength of the steel, the flange neck size meets the design requirements.

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