A design method for the composite spigot thickness of a socket-and-spigot pipe

Abstract

The present invention discloses a design method for the composite spigot thickness of a socket-and-spigot pipe, comprising the steps of: S1: obtaining the radial deformation differential equation and the general solution of the ring according to the deflection curve differential equation and the moment balance equation of the ring; S2: calculating the calculation formula for the maximum radial deformation of the ring; step S3: obtaining the minimum spigot thickness of the base pipe that meets the deformation requirements; step S4: sleeve at least one layer of annular reinforcement ring in the spigot of the base pipe to form a composite spigot, if the reinforcement ring and the spigot are made of the same material, the thickness of the composite spigot is not less than the minimum thickness, if the reinforcement ring and the spigot are made of different materials, then go to step S5; S5: determine the minimum thickness of the reinforcement ring, the thickness of the reinforcement ring is not less than the minimum thickness. The present invention can obtain the minimum spigot thickness and the minimum thickness of the reinforcement ring that meet the deformation requirements of the socket-and-spigot pipes of different pipe diameters through theoretical analysis and calculation, with low cost and high efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of pipe design, and in particular relates to a design method for the composite spigot thickness of a socket-and-spigot type pipe. Background Art

[0002] Most of the water pipes in the water supply and drainage systems for life and production are socket-type pipes, with a socket at one end and a spigot at the other end. During installation, the spigot of one pipe is inserted into the socket of another pipe and sealed with a seal to achieve the connection of each pipe in the pipe network. For water supply pipes in normal use, they will be subjected to a large internal water supply pressure, which is a positive pressure, so the pipes must meet the specified strength requirements. Some existing standards (group standards and national standards) specify the nominal wall thickness under different pressure levels and different nominal diameters. Pipes that meet the standards can meet the strength requirements within the corresponding pressure level range. Therefore, the pipes produced by existing pipe manufacturers generally meet the requirements of the corresponding standards.

[0003] However, when a pipe network fails, for example, a pipe bursts in the pipe network, water in the pipe network will spray out from the burst pipe, and the pressure in the pipe network will drop rapidly, even forming negative pressure. In addition, the pipe will also be subject to some external pressure, for example, the pipe buried in the soil will be subject to the gravity of the soil above it. Under the above external pressure and internal negative pressure, the pipe will deform radially. If the deformation of the socket is too large, the socket will separate from the socket connected to it, causing leakage at the connection between the socket and the socket, causing the inside of the water pipe to be contaminated. Therefore, it is necessary to ensure that the deformation of the socket of the pipe does not exceed a certain range under the above circumstances. To this end, for the socket, the minimum socket thickness that meets the deformation requirements must be obtained. If the socket thickness of the selected pipe is less than the minimum socket thickness that meets the deformation requirements, measures need to be taken to make it meet the deformation requirements. For example, when the pipe is secondary processed or installed, at least one layer of annular reinforcement ring is sleeved on the socket to form a composite socket to enhance the ability to resist deformation. However, the material of the reinforcement ring is often different from that of the base pipe. The base pipe refers to the pipe in the factory setting, without the reinforcement ring installed and without secondary processing such as composite process. The base pipe includes the socket, pipe body and plug connected in sequence, and the outer diameter of the base pipe is the outer diameter of the pipe body. Because the reinforcement ring is in direct contact with the water in the pipe, it needs to be made of corrosion-resistant materials such as stainless steel, while the base pipe is generally made of relatively cheap materials such as ductile iron and Q235. Therefore, how to ensure that the above-mentioned composite plug meets the maximum deformation requirements becomes a problem to be solved. Summary of the invention

[0004] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a design method for the composite spigot thickness of a socket-and-spigot pipe. The minimum spigot thickness of the socket-and-spigot pipes of different pipe diameters that meets the deformation requirements can be obtained through theoretical analysis and calculation, providing a reference for secondary processing and installation. If the spigot thickness of the pipe that meets the strength requirements is less than the minimum thickness, the spigot thickness can be increased by installing a reinforcement ring on the spigot to make the spigot meet the deformation requirements, and the minimum thickness of the reinforcement ring can be calculated. When the thickness of the reinforcement ring is not less than the minimum thickness, the composite spigot formed by the spigot of the base pipe sleeved with the reinforcement ring can meet both the strength requirements and the deformation requirements; the pipes and pipe network systems installed in this way are more reliable to use, greatly reducing and avoiding the leakage and water supply pollution caused by the deformation and separation of the spigots and sockets of adjacent pipes when the pipe bursts, and saving costs for users. Users do not need to select pipes with strength values ​​far exceeding the requirements in order to meet the deformation requirements of the pipes. The design method is a theoretical calculation with low cost and high efficiency, providing strong support for experiments and pipe design.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for designing the composite spigot thickness of a socket-and-spigot pipe comprises the following steps:

[0007] Step S1: obtaining the differential equation of radial deformation of the ring and the general solution of the differential equation according to the deflection curve differential equation and the moment balance equation of the ring;

[0008] Step S2: Calculate and obtain a calculation formula for the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1;

[0009] Step S3: Calculating the minimum thickness of the base pipe that meets the deformation requirements according to the calculation formula of the maximum radial deformation obtained in step S2;

[0010] Step S4: for the base pipe whose socket thickness is less than the minimum thickness obtained in step S3, at least one layer of annular reinforcement ring is sleeved in the socket of the base pipe to form a composite socket. If the material of the reinforcement ring is the same as that of the socket of the base pipe, the thickness of the composite socket is not less than the minimum thickness obtained in step S3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step S5.

[0011] Step S5: Determine the minimum thickness of the reinforcement ring. If the thickness of the reinforcement ring is not less than the minimum thickness, the thickness of the composite socket is the minimum thickness that meets the deformation requirement.

[0012] As a further improvement of the above technical solution:

[0013] Preferably, in step S5, the minimum thickness of the reinforcement ring is obtained and determined by experiment, simulation or theoretical calculation.

[0014] More preferably, in step S5, the minimum thickness of the reinforcement ring is obtained based on the socket thickness of the base pipe and according to the calculation formula of the bending strength of the longitudinal composite beam.

[0015] The calculation formula for the maximum radial deformation of the annulus obtained in step S2 contains an unknown coefficient, which is introduced in consideration of the internal negative pressure that the pipe bears during testing and failure.

[0016] Step S2 includes the following steps:

[0017] Step S21: Assuming that the annular ring is subjected to at least two radial concentrated forces that are symmetrical relative to the center of the circle, based on the assumption, calculating the constant term in the general solution of the differential equation to obtain the first form of the differential equation;

[0018] Step S22: Based on the first form of the differential equation obtained in step S21, assuming that the annulus is subjected to only two radial concentrated forces that are symmetrical relative to the center of the circle, the first form of the differential equation is transformed into a second form of the differential equation;

[0019] Step S23: introducing the internal negative pressure of the annulus into the second form of the differential equation by introducing a coefficient, so as to obtain the third form of the differential equation;

[0020] Step S24: Obtain a calculation formula for the maximum change in the diameter of the ring with a coefficient according to the third form of the differential equation obtained in step S23.

[0021] In step S3, the minimum thickness of the socket that meets the deformation requirements is calculated based on the provisions of the allowable deformation of the pipe and the formula obtained in step S2.

[0022] Step S3 includes the following steps:

[0023] Step S31: Calculating parameters of a reference pipe according to an existing shear load formula, wherein the material and outer diameter of the reference pipe are respectively the same as the material and outer diameter of the base pipe;

[0024] Step S32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step S31;

[0025] Step S33: Substituting the maximum deformation of the socket obtained in step S32 into the calculation formula of step S2 to obtain the coefficient value in the calculation formula, thereby obtaining a calculation formula for the maximum radial deformation of the ring with a known coefficient;

[0026] Step S34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements according to the national standard allowable deformation regulations and the formula obtained in step S33.

[0027] In step S1, the radial deformation obtained is uThe differential equation is:

[0028] ,

[0029] The general solution is: ,

[0030] in, R is the average value of the outer circle radius and the inner circle radius of the ring; E is the elastic modulus of the pipe, Pa; I is the moment of inertia of the tube cross section, m 4 ; M is the bending moment borne by a certain section of the ring in the local area, in units of N*m; establish a two-dimensional coordinate system, The deformation is u The angle between the line connecting the point at and the origin of the coordinate system and the positive direction of the x-axis in the two-dimensional coordinate system, ; A1, A2, A3, B2, B3 are constants.

[0031] Assuming that the external force on the ring is symmetrical, the deflection curve equation is:

[0032] .

[0033] In step S2, it is assumed that the ring is subjected to at least two radial concentrated forces P that are symmetrical relative to the center of the circle, and the angle between two adjacent radial concentrated forces P is , the ring satisfies the following three boundary conditions:

[0034] (1) Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula:

[0035] ;

[0036] (2) Due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is, ;

[0037] (3) Cutting near point A, removing point A and the acting force P, it can be seen from the symmetry and equilibrium conditions that the shear force on the cross section of the circular cut is , that is: ;

[0038] Combining the above three formulas with the general solution of the differential equation, we get the first form of the differential equation:

[0039] ;

[0040] Assuming that the annulus is subjected to only two radial concentrated forces P which are symmetrical relative to the center of the circle, then: , we get the second form of the differential equation:

[0041] ;

[0042] Introducing the coefficient m, we get the third form of the differential equation:

[0043] ;

[0044] Point of application of force P The point is the point of maximum deformation, and the change in the diameter of the ring is:

[0045] .

[0046] The shear load formula used in step S31 is:

[0047] ,

[0048] in: W is the shear load, in Newton (N); F is the shear force acting on the interface, in Newton (N); M P is the weight of the test assembly pipe and the weight of the object in the pipe, in kilograms (kg); a The distance between the shear load application point and the end face of the socket inserted into the socket, in millimeters (mm); b The distance between the center of gravity of the spigot end pipe and the end face of the spigot inserted into the socket, in millimeters (mm); c It is the distance between the support point of the pad and the end face of the socket that has been inserted into the socket, in millimeters (mm).

[0049] In step S5, the calculation formula for the bending strength of the longitudinal composite beam is: ,in, C i The area is A i The distance from the centroid of the cross section to the bending center, I oi is the moment of inertia of the ith section about its own centroidal axis, E i is the elastic modulus of the corresponding material.

[0050] The beneficial effects of the present invention are as follows: the minimum thickness of the socket of the socket-type pipes of different diameters that meets the deformation requirements can be obtained through theoretical analysis and calculation, providing a reference for secondary processing and installation. If the thickness of the socket of the pipe that meets the strength requirements is less than the minimum thickness, the socket thickness can be increased by installing a reinforcement ring on the socket to make the socket meet the deformation requirements, and the minimum thickness of the reinforcement ring can be calculated. When the thickness of the reinforcement ring is not less than the minimum thickness, the composite socket formed by the socket of the base pipe and the reinforcement ring can meet both the strength requirements and the deformation requirements. The pipes and pipe network systems installed in this way are more reliable to use, greatly reducing the leakage and water supply pollution caused by the separation of the socket and the socket of the adjacent pipe due to excessive deformation of the socket when the pipe bursts, and saving costs for users. Users do not need to select pipes with strength values ​​far exceeding the requirements in order to meet the deformation requirements of the pipes. The design method is a theoretical calculation with low cost and high efficiency, providing strong support for experiments and pipe design. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the deformation of a circular ring before and after being subjected to a pair of radially symmetrical concentrated forces.

[0052] Figure 2 for Figure 1 Schematic diagram of local analysis.

[0053] Figure 3 Schematic diagram of a circular ring subjected to multiple uniformly arranged radial concentrated forces.

[0054] Figure 4 This is the stress analysis diagram of socket-type pipe.

[0055] Figure 5 It is a schematic diagram of a cross section of a composite socket per unit length in this embodiment. DETAILED DESCRIPTION

[0056] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0057] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0058] A method for designing the composite spigot thickness of a socket-and-spigot pipe comprises the following steps:

[0059] Step S1: According to the differential equation of the deflection curve of the circular ring and the moment balance equation, the differential equation of the radial deformation of the circular ring and the general solution of the differential equation are obtained; because the cross-sections of the pipe body and the socket of the pipe are circular rings, the deformation of the socket is analyzed by analyzing the radial deformation of the circular ring. In addition, a cylinder of unit length can be regarded as a circular ring.

[0060] Step S2: Calculate and obtain a calculation formula for the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1.

[0061] Step S3: The minimum thickness of the socket of the base pipe that meets the deformation requirements is obtained according to the calculation formula of the maximum radial deformation obtained in step S2.

[0062] Step S4: For a base pipe whose socket thickness is less than the minimum thickness obtained in step S3, at least one layer of annular reinforcement ring is sleeved in the socket of the base pipe to form a composite socket. If the material of the reinforcement ring is the same as that of the socket of the base pipe, the thickness of the composite socket is not less than the minimum thickness obtained in step S3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step S5.

[0063] Step S5: The material of the reinforcement ring is different from the material of the socket of the base pipe. The minimum thickness of the reinforcement ring is obtained based on the thickness of the socket of the base pipe and the calculation formula of the bending strength of the longitudinal composite beam. The thickness of the reinforcement ring is not less than the minimum thickness. Then, the thickness of the composite socket is the minimum thickness that meets the deformation requirement. In other words, the thickness of the composite socket of the pipe formed after the reinforcement ring is installed on the base pipe meets the deformation requirement and the strength requirement.

[0064] The following is a detailed introduction to each step.

[0065] In step S1, the radial deformation The differential equation is:

[0066] (1)

[0067] in ，R is half of the sum of the outer radius and the inner radius of the ring. In other words, R One quarter of the sum of the outer and inner diameters of the ring 。E is the elastic modulus of the pipe, Pa. I is the moment of inertia of the tube cross section, m 4 . M It is the bending moment borne by a certain section of the ring in the local area, in N*m. Establish a two-dimensional coordinate system, The deformation is u The angle between the line connecting the point at and the origin of the coordinate system and the positive direction of the x-axis in the two-dimensional coordinate system, In this embodiment, establish xy Coordinate system, point O is the coordinate origin and the center of the ring, such as Figure 1 Point m 1 The radial deformation at u， but om 1 and x The angle between the positive directions of the axes is 。

[0068] The above differential equation (1) is obtained as follows:

[0069] like Figure 1 and 2 As shown in the figure, the dotted line is the ring that has not been deformed by external force, and the solid line is the shape of the ring after being deformed by two symmetrical radial external forces P. The center point of the ring before and after deformation is O The position remains unchanged. Figure 1 midpoint O Too xy Vertex of the coordinate system ， point m and n are two points on the ring before deformation; m 1 and n 1 are two points on the deformed shape of the ring, and the points m 1 and n 1 Located on the line segment om and on superior, The deformation isu The line connecting the point at and point O is x The angle between the positive directions of the axes, om and on The angle between ， set up u Centripetal movement is positive. Figure 2 Middle, straight line m 1 t Passing point m 1 and perpendicular to the line segment om ,straight line m 1 t 1 For passing point m 1 A tangent line to n 1 t’ Passing point n 1 and perpendicular to on ,straight line n 1 t 1 ’ For passing point n 1 tangent.

[0070] Arc before deformation mn The arc length is ds , whose curvature is k 1 , arc after deformation m 1 n 1 The curvature is k 2 , du Yes m and Point n The difference in radial deformation is The arc before deformation mn exist m Tangent line of point and n The angle between the tangent lines of a point, The deformation amount is u The radius corresponding to the point at after deformation is Is an arc mn Deform to Arc m 1 n 1 back ds The increment of The arc after deformation m 1n 1 exist m 1 Tangent line of point and n 1 The angle between the tangent lines of the point is m 1 t 1 and The angle between , then:

[0071] (2)

[0072] (3)

[0073] (4)

[0074] (5)

[0075] m 1 t 1 and m 1 t The angle between , and The angle between .

[0076] m 1 section to n 1 The variable of the cross-section rotation is :

[0077] (6)

[0078] in, m The cross section is through om and perpendicular to the cross section of the ring, in other words, m The cross section is through the center axis and point of the corresponding pipe of the ring m The cross section of n The cross section is through on and perpendicular to the cross section of the ring, in other words, n The cross section is through the center axis and point of the corresponding pipe of the ring n cross section. m 1 t 1 and m 1 t The angle between m 1 The cross-sectional angle, and The angle between n 1 The corner of the cross section.

[0079] Substituting formula (5) and (6) into formula (4) yields:

[0080] (7)

[0081] By series expansion we have:

[0082] Ignoring the higher-order terms, substituting the series expansion into (7) yields: (8)

[0083] Substituting (2) into (8), we obtain:

[0084] (9)

[0085] Omitting the higher-order terms, we get: (10)

[0086] For a thin ring (i.e. a ring with a small difference between the outer diameter and the inner diameter relative to the diameter), we have: , by definition: ,therefore, , substituting into (10) we get, , combining formula (2) to obtain radial deformation The differential equation formula (1).

[0087] The general solution of the above differential equation (1) is:

[0088] (11)

[0089] Among them, A1, A2, A3, B2, and B3 are constants. If the external force is symmetrical, the odd function terms in the solution can be deleted, and the deflection curve equation is obtained as follows:

[0090] (12)

[0091] Step S2: Calculating and obtaining a calculation formula for the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1, comprising the following steps:

[0092] Step S21: Assume that the annulus is subjected to at least two radial concentrated forces P that are symmetrical relative to the center of the circle. Based on this assumption, calculate the constant term in the general solution of the differential equation to obtain the first form of the differential equation.

[0093] Step S22: Based on the first form of the differential equation obtained in step S21, assuming that the annulus is subjected to only two radial concentrated forces P that are symmetrical relative to the center of the circle, the first form of the differential equation is transformed into the second form of the differential equation.

[0094] Step S23: Introduce the internal negative pressure on the annulus into the second form of the differential equation by introducing coefficients to obtain the third form of the differential equation.

[0095] Step S24: Obtain a calculation formula for the maximum change in the diameter of the ring with a coefficient according to the third form of the differential equation obtained in step S23.

[0096] In step S21, it is assumed that the ring is subjected to at least two radial concentrated forces P symmetrically relative to the center of the ring, and the radial concentrated force P means that the direction of the force P is radial to the ring and points to the center of the ring, and the angle between two adjacent radial concentrated forces P is ,like Figure 3 shown. Figure 1 The circular ring shown in FIG. 1 is subjected to two radial concentrated forces P which are symmetrical relative to the center of the circle, and the two radial concentrated forces P are located on the y-axis.

[0097] The ring satisfies the following three boundary conditions:

[0098] (1) Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula:

[0099] (13)

[0100] (2) Due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is,

[0101] (14)

[0102] (3) Cutting near point A, removing point A and the acting force P, it can be seen from the symmetry and equilibrium conditions that the shear force on the cross section of the circular cut is , that is:

[0103] (15)

[0104] in, dM represents the differential with respect to M. It should be noted that point (3) is not a real cut of the ring, but an assumption.

[0105] Simultaneously formula (13), (14), (15), the solution is:

[0106] (16)

[0107] (17)

[0108] (18)

[0109] Substituting formulas (16), (17), and (18) into formula (12), we obtain:

[0110] (19)

[0111] Formula (19) is the first form of the differential equation obtained in step S21. is the radial deformation of the ring.

[0112] In step S22, if only one pair of radial forces P is applied to the ring, then , the deflection curve equation (19) becomes:

[0113] (20)

[0114] Formula (20) is the second form of the differential equation obtained in step S22.

[0115] In step S23, considering that the pipe generally needs to withstand an internal negative pressure of 0.1 MPa during testing, a coefficient m is introduced, that is,

[0116] (twenty one)

[0117] For water supply pipes, if a fault occurs during actual use, such as a burst pipe, a certain negative pressure will be formed inside the pipe. Therefore, when testing the pipe, a negative pressure will be created inside the pipe to ensure that the pipe performance meets the standards.

[0118] Formula (21) is the third form of the differential equation obtained in step S23.

[0119] In step S24, the maximum deformation is At the point where the force P acts, the change in the diameter of the ring is the maximum change in the diameter of the ring. u max :

[0120] (twenty two)

[0121] Formula (22) is the third form of the differential equation obtained in step S24.

[0122] Step S3: Calculate the minimum thickness of the base pipe that meets the deformation requirements based on the calculation formula of the maximum radial deformation obtained in step S2. It includes the following steps:

[0123] Step S31: Calculate the parameters of a reference pipe according to an existing shear load formula, wherein the material and outer diameter of the reference pipe are respectively the same as the material and outer diameter of the base pipe.

[0124] Step S32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step S31.

[0125] Step S33: Substitute the maximum deformation of the socket obtained in step S32 into the calculation formula of step S2 to obtain the coefficient value in the calculation formula, thereby obtaining the calculation formula for the maximum radial deformation of the ring with a known coefficient.

[0126] Step S34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements according to the national standard allowable deformation regulations and the formula obtained in step S33.

[0127] In step S31, the shear load formula used is derived from the group standard "Corrosion-resistant steel pipe with socket-type flexible joint for water supply and drainage" (T / CISA 108-2021), which is:

[0128] (twenty three)

[0129] like Figure 4 As shown, W is the shear load, in Newton (N); F is the shear force acting on the interface, in Newton (N); M P is the weight of the test assembly steel tube and the weight of the object in the steel tube, in kilograms (kg); a The distance between the shear load application point and the end face of the socket inserted into the socket, in millimeters (mm); b The distance between the center of gravity of the steel pipe at the spigot end and the end face of the spigot inserted into the socket, in millimeters (mm); c It is the distance between the support point of the pad and the end face of the socket that has been inserted into the socket, in millimeters (mm).

[0130] In this embodiment, the nominal diameter of the base pipe is DN=600mm, and the material is Q235. The nominal diameter of the reference pipe is DN=600mm, and the material is Q235. Its wall thickness is selected according to the provisions of the group standard, and the wall thickness when the nominal pressure is 3.0MPa, that is, the nominal wall thickness S=7mm. At this time, the outer diameter of the base pipe D0=630mm, R =312mm. In addition, the shear force F It should be no less than 30 times of the nominal diameter DN. In this embodiment, 30 times is taken, that is, F = DN × 30 = 600 × 30 = 18000 N. Take the pipe length as 1m, c = 800mm.

[0131] In this embodiment, the parameters in formula (23) are M P and W The calculation process is as follows:

[0132]

[0133]

[0134] in, is the density of water, is the density of steel. M P The diameter used in the calculation is the outer diameter D0 of the base pipe, and the calculation error is within the allowable range. In addition, in this embodiment, the material of the pipe socket is Q235, the elastic modulus of the steel pipe material is E=200GPa, and I=S 3 / 12. It should be noted that the calculation formula for the moment of inertia I of the circular tube section also needs to be multiplied by the length, but this solution considers a cylinder of unit length (i.e., the circular ring), so the length is 1.

[0135] Step S31 is thus completed.

[0136] In step S32, based on the parameters obtained by the above calculation, simulation software is used. In this embodiment, the maximum deformation of the socket of the reference pipe is simulated by finite element simulation. u max =12.19 mm. During simulation, the material parameter Poisson's ratio = 0.3. The simulation method is well known to those skilled in the art and will not be described in detail here.

[0137] In step S33, u max =12.19 Substituting into formula (22) we get m =1.18 (Note: When calculating, the length units are meters, and the unit of elastic modulus E is Pa), thus:

[0138] (twenty four)

[0139] From formula (24), we can see that u max The value is related to the pipe diameter and pipe thickness.

[0140] In this embodiment, in step S34, for a pipe with DN=600mm, the national standard stipulates that the allowable deformation must not be greater than 3.6% of the outer diameter of the socket DE=635mm, that is, u max =22.86 mm, and substituting it into formula (24), we can calculate that for a pipe with DN=600 mm, the minimum wall thickness of the socket is S=5.7 mm.

[0141] Table 1 Nominal wall thickness and absolute deformation of DN=600mm pipes at various nominal pressures

[0142]

[0143] In Table 1, each wall thickness is the nominal wall thickness under the corresponding nominal pressure specified in the industry standard, and the absolute deformation is calculated according to formula (24).

[0144] It can be seen from Table 1 that if the base tube purchased by the secondary processing enterprise or user is processed in accordance with the provisions of the industry standard, the base tubes with serial numbers 1, 2, and 3 in Table 1 have a socket thickness greater than 5.7 mm and an absolute deformation less than 22.86 mm, which meet the deformation requirements, while the base tubes with serial numbers 4, 5, and 6 have a socket thickness less than 5.7 mm and an absolute deformation greater than 22.86 mm, which do not meet the deformation requirements.

[0145] If the use requirement of the pipe in a certain occasion is to meet the nominal pressure within 2MPa, the general user will choose the pipe with serial number 4, and will not choose the pipe with serial number 1, 2 or 3 to meet the deformation requirement. Because if one of these three is selected, although it will meet both the strength requirements and the deformation requirements, their thickness is larger and the cost will be much greater than the pipe with serial number 4. If the pipe with serial number 4 is selected, its strength meets the use requirements. For the deformation requirement, some measures can be taken, such as sleeve-fitting an annular reinforcement ring in the socket to increase the thickness of the socket and improve its ability to resist deformation, and this measure is low in cost.

[0146] Step S4: For a base pipe whose socket thickness is less than the minimum thickness obtained in step S3, at least one layer of annular reinforcement ring is sleeved in the socket of the base pipe to form a composite socket. If the material of the reinforcement ring is the same as that of the socket of the base pipe, the thickness of the composite socket is not less than the minimum thickness obtained in step S3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step S5.

[0147] For example, in some occasions, the use requirement of the pipe is to meet the nominal pressure within 1.6MPa, and the selected base pipe is the pipe No. 5 in Table 1, with a wall thickness of 4mm. If the selected reinforcement ring and the base pipe are made of the same material, the thickness of the reinforcement ring is not less than 1.7mm to meet the deformation requirement, and the thickness of the composite socket is not less than 5.7mm.

[0148] Step S5: The material of the reinforcement ring is different from the material of the socket of the base pipe. The minimum thickness of the reinforcement ring is obtained based on the socket thickness of the base pipe and the bending strength calculation formula of the longitudinal composite beam. The thickness of the reinforcement ring is not less than the minimum thickness. Then, the thickness of the composite socket is the minimum thickness that meets the deformation requirements.

[0149] In this embodiment, the calculation formula for the bending strength of the longitudinal composite beam is as follows:

[0150] (25)

[0151] in, C iThe area is A i The distance from the centroid of the cross section to the bending center, I oi is the moment of inertia of the ith section about its own centroidal axis, E i is the elastic modulus of the corresponding part material. E is the elastic modulus of the base tube material, and I is the moment of inertia of the cross section corresponding to the minimum thickness obtained in step S3.

[0152] In this embodiment, the use requirement of the pipe in a certain occasion is to meet the nominal pressure within 1.6MPa. The selected base pipe is the pipe No. 5 in Table 1, and its wall thickness is 4mm. The composite spigot includes a base pipe spigot and a layer of annular reinforcement ring. The thickness of the reinforcement ring is x ,like Figure 5 The figure shows the cross section per unit length of the composite socket or composite beam, where the plane of the cross section passes through the central axis of the base pipe. The base pipe is made of Q235, and the reinforcing ring is made of 304 stainless steel. Figure 5 The distance from the center point of the cross section shown (the center of the composite beam) to the outer or inner surface of the composite socket is (4+ x ) / 2, for the base tube socket (original socket): A i =4, E i =200, C i = x / 2; For the reinforcement ring: A i = x , E i =193, C i =2, substituting into (25) we get:

[0153]

[0154] Find: x =1.73mm.

[0155] Therefore, the thickness of the reinforcement ring should not be less than 1.73 mm.

[0156] Finally, it is necessary to explain here that the above embodiments are only used to further illustrate the technical solution of the present invention in detail and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above content of the present invention all fall within the scope of protection of the present invention.

Claims

1. A method for designing the thickness of a composite spigot of a socket-and-spigot pipe, characterized in that: The steps include: Step S1: obtaining the differential equation of radial deformation of the ring and the general solution of the differential equation according to the deflection curve differential equation and the moment balance equation of the ring; Step S2: Calculate and obtain a calculation formula for the maximum radial deformation of the ring according to the general solution of the differential equation obtained in step S1; Step S3: Calculating the minimum thickness of the base pipe that meets the deformation requirements according to the calculation formula of the maximum radial deformation obtained in step S2; Step S4: for the base pipe whose socket thickness is less than the minimum thickness obtained in step S3, at least one layer of annular reinforcement ring is sleeved in the socket of the base pipe to form a composite socket. If the material of the reinforcement ring is the same as that of the socket of the base pipe, the thickness of the composite socket is not less than the minimum thickness obtained in step S3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step S5. Step S5: Determine the minimum thickness of the reinforcement ring. If the thickness of the reinforcement ring is not less than the minimum thickness, the thickness of the composite socket is the minimum thickness that meets the deformation requirement.

2. The design method according to claim 1, characterized in that: In step S5, the minimum thickness of the reinforcement ring is obtained and determined through experiments, simulations or theoretical calculations.

3. The design method according to claim 2, characterized in that: In step S5, the minimum thickness of the reinforcement ring is obtained based on the socket thickness of the base pipe and the calculation formula of the bending strength of the longitudinal composite beam.

4. The design method according to claim 1, characterized in that: The calculation formula for the maximum radial deformation of the annulus obtained in step S2 contains an unknown coefficient. Considering the internal negative pressure of the pipe during testing and failure, the coefficient is introduced. Step S2 includes the following steps: Step S21: Assuming that the annular ring is subjected to at least two radial concentrated forces that are symmetrical relative to the center of the circle, based on the assumption, calculating the constant term in the general solution of the differential equation to obtain the first form of the differential equation; Step S22: Based on the first form of the differential equation obtained in step S21, assuming that the annulus is subjected to only two radial concentrated forces that are symmetrical relative to the center of the circle, the first form of the differential equation is transformed into a second form of the differential equation; Step S23: introducing the internal negative pressure of the annulus into the second form of the differential equation by introducing a coefficient, so as to obtain the third form of the differential equation; Step S24: Obtain a calculation formula for the maximum change in the diameter of the ring with a coefficient according to the third form of the differential equation obtained in step S23.

5. The design method according to claim 1, characterized in that: Step S3 includes the following steps: Step S31: Calculating parameters of a reference pipe according to an existing shear load formula, wherein the material and outer diameter of the reference pipe are respectively the same as the material and outer diameter of the base pipe; Step S32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step S31; Step S33: Substituting the maximum deformation of the socket obtained in step S32 into the calculation formula of step S2 to obtain the coefficient value in the calculation formula, thereby obtaining a calculation formula for the maximum radial deformation of the ring with a known coefficient; Step S34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements according to the national standard allowable deformation regulations and the formula obtained in step S33.

6. The design method according to any one of claims 1 to 5, characterized in that: In step S1, the radial deformation obtained is u The differential equation is: , its general solution is: ， in, R is the average value of the outer circle radius and the inner circle radius of the ring; E is the elastic modulus of the pipe, Pa; I is the moment of inertia of the tube cross section, m 4 ; M is the bending moment borne by a certain section of the ring in the local area, in units of N*m; establish a two-dimensional coordinate system, The deformation is u The angle between the line connecting the point at and the origin of the coordinate system and the positive direction of the x-axis in the two-dimensional coordinate system, ; A1, A2, A3, B2, B3 are constants.

7. The design method according to claim 6, characterized in that: Assuming that the external force on the ring is symmetrical, the deflection curve equation is: 。 8. The design method according to claim 7, characterized in that: In step S2, it is assumed that the ring is subjected to at least two radial concentrated forces P that are symmetrical relative to the center of the circle, and the angle between two adjacent radial concentrated forces P is , the ring satisfies the following three boundary conditions: First, in Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula: ； Second, due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; That is: ； Third, cut near point A, remove point A and the force P, and from the symmetry and equilibrium conditions, we know that the shear force on the section at the circular cut is , that is: ; Combining the above three formulas with the general solution of the differential equation, we get the first form of the differential equation: ； Assuming that the annulus is subjected to only two radial concentrated forces P which are symmetrical relative to the center of the circle, then: , we get the second form of the differential equation: ； Introducing the coefficient m, we get the third form of the differential equation: ； Point of application of force P The point is the point of maximum deformation, and the change in the diameter of the ring is: 。 9. The design method according to claim 5, characterized in that: The shear load formula used in step S31 is: ， in: W is the shear load, in N; F is the shear force acting on the interface, in N; M P The weight of the test assembly pipe and the weight of the object in the pipe, in kg; a The distance between the shear load application point and the end face of the socket that has been inserted into the socket, in mm; b It is the distance between the center of gravity of the spigot end pipe and the spigot end face inserted into the socket, in mm; c It is the distance between the support point of the pad and the end face of the socket that has been inserted into the socket, in mm.

10. The design method according to claim 3, characterized in that: In step S5, the calculation formula for the bending strength of the longitudinal composite beam is: ,in, C i The area is A i The distance from the centroid of the cross section to the bending center, I oi is the moment of inertia of the ith section about its own centroidal axis, E i is the elastic modulus of the corresponding material.

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