A socket-and-spigot type multilayer pipe and a design method for the thickness of its socket and spigot

Abstract

The invention discloses a socket-and-spigot type multi-layer pipe and a design method for the thickness of its socket and the thickness of its spigot, belonging to the technical field of pipe design. The pipe comprises an inner pipe, an intermediate layer and an outer pipe which are sequentially sleeved from the inside to the outside. The outer pipe is made of metal, the intermediate layer is made of non-metal, the inner pipe is made of polyethylene, and the outer pipe comprises a socket, a pipe body and a spigot which are sequentially connected. Each end of the pipe is provided with a liner ring and a sealing gasket, the two liner rings respectively cover two sealing gaskets, the socket is a single-layer socket, and when the length of the liner ring extending into the inner pipe is less than the length of the spigot, it is a single-layer spigot. Otherwise, the spigot and the liner ring matched therewith form a composite spigot. The hot melt adhesive of the invention bonds the inner and outer layers together, and the liner ring and the rubber sealing gasket prevent the inner wall of the metal outer pipe from rusting and peeling off to cause water pollution. The spigot and the liner ring matched therewith form a composite spigot, and the minimum spigot thickness and the minimum socket thickness of the multi-layer pipe can be obtained through theoretical analysis and calculation.

Description

Technical Field

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

[0002] Composite pipes are widely used pipes, often used in liquid transportation pipe network systems. They are generally of a spigot-and-socket structure, including an outer metal pipe and an inner plastic pipe, that is, the plastic pipe is used as an inner liner, one end of the metal pipe is a spigot and the other end is a socket. During installation, multiple composite pipes are connected in sequence, and the spigot of a composite pipe is inserted into the socket of the adjacent composite pipe. However, liquids can easily penetrate from the pipe ends, causing the outer pipe to rust and contaminate the transported liquid, as well as causing the end faces of each layer to peel off and delaminate, and even wash away the inner layer under long-term scouring.

[0003] In addition, 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 corresponding standard requirements.

[0004] 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 end will separate from the socket end 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. For the socket, the existing standards do not give its wall thickness requirements, but generally it is necessary to ensure that its thickness is sufficient to meet the strength requirements. It is best to make the thickness of each part of the socket minimum or close to the minimum while meeting the use strength.

[0005] The metal tube of the outer layer is also the base tube, which refers to the tube in the factory setting, that is, the base tube has no reinforcement ring installed and has not undergone secondary processing such as composite process. The base tube includes a socket, a pipe body and a spigot connected in sequence. The pipe body can be divided into two parts, namely the main body and the transition part. The transition part is used for the transition connection between the main body and the socket, that is, the socket, the transition part, the main body and the spigot are connected in sequence. The inner wall surface of the pipe body is a cylindrical surface, that is, the inner diameter of the transition part is equal to the inner diameter of the main body. The main body is cylindrical, and the outer wall surface of the transition part is a conical surface. In other words, the thickness of the main body is basically uniform everywhere, and the thickness of the transition part gradually decreases along the direction from the socket to the spigot. The outer diameter of the pipe body refers to the outer diameter of the main body, and the thickness of the pipe body refers to the thickness of the main body. The outer diameter of the base tube is the outer diameter of the pipe body. Fig. 9 In the figure, X is the length of the chamfer at the end of the socket along the axial direction, Y is the height of the chamfer at the end of the socket (i.e. the radial dimension), DE is the outer diameter of the socket, and T6 is the length of the socket. Summary of the invention

[0006] 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 thickness of the socket and the thickness of the spigot and the socket of a multilayered socket-and-spigot type pipe and its socket. The middle layer is a hot melt adhesive, which bonds the inner and outer layers together to prevent the inner lining from being delaminated due to the negative pressure in the pipe. A corrosion-resistant metal liner ring and a rubber sealing gasket are arranged at the end of the pipe to prevent the ends of the bonding surfaces between the layers of materials from contacting with water and peeling off due to the tension of the water, and to prevent the inner wall of the metal outer pipe from rusting and peeling off to cause water pollution; the spigot and the liner ring matched therewith form a composite spigot, which is not easy to deform, and is convenient for the installation of the pipe, and improves the uniform sealing effect of the sealing gasket and the sealing ring at the connection between the two pipes, and reduces pipeline leakage. The minimum or near-minimum thickness of the composite spigot that meets the deformation requirements of the socket-and-spigot type pipes of different pipe diameters and the minimum or near-minimum thickness of the single-layer socket that meets the strength requirements can be obtained through theoretical analysis and calculation.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for designing the thickness of the socket and the thickness of the spigot of a socket-and-spigot type multilayer pipe, wherein the pipe comprises an inner pipe, an intermediate layer and an outer pipe which are sleeved in sequence from the inside to the outside, the outer pipe is made of metal, the intermediate layer is made of non-metal, the inner pipe is made of polyethylene, the outer pipe comprises a socket, a pipe body and a spigot which are connected in sequence, the end face of one end of the inner pipe, the end face of one end of the intermediate layer and the end face of the spigot are flush, the end face of the other end of the inner pipe, the end face of the other end of the intermediate layer and the end face of the pipe body are flush, and each end of the pipe is provided with a A liner ring and a sealing gasket, one sealing gasket covers the end face of the plug, the end face of one end of the middle layer, the end face of one end of the inner tube, and the inner wall of one end of the inner tube; the other sealing gasket covers the end face of the tube body, the end face of the other end of the middle layer, the end face of the other end of the inner tube, and the inner wall of the other end of the inner tube. The two liner rings cover the two sealing gaskets respectively, and the socket is a single-layer socket. When the length of the liner ring extending into the inner tube is less than the length of the socket, the socket is a single-layer socket. When the length of the liner ring extending into the inner tube is not less than the length of the socket, the socket and the liner ring matching it form a composite socket.

[0009] The design method of the composite socket thickness comprises the following steps:

[0010] Step a1: Obtain the differential equation of radial deformation of the ring and the general solution of the differential equation according to the differential equation of the deflection curve of the ring and the moment balance equation;

[0011] Step a2: 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 a1;

[0012] Step a3: Calculating the minimum thickness of the socket of the base pipe that meets the deformation requirements according to the calculation formula of the maximum radial deformation obtained in step a2;

[0013] Step a4: for a base pipe whose socket thickness is less than the minimum thickness obtained in step a3, 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 a3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step a5.

[0014] Step a5: 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.

[0015] The design method of the single-layer socket thickness comprises the following steps:

[0016] Step b1: Select multiple locations on the inner wall of the single-layer socket where stress is likely to be concentrated. The selection principle is: if the wall thickness of these locations meets the stress strength requirements, then the wall thickness of each location of the single-layer socket designed according to the outer wall design requirements meets the strength requirements;

[0017] Step b2: Determine the minimum wall thickness of each selected location in step b1, and obtain the outer wall of each selected location. The determination principle is: when the material of the single-layer socket and the material of the pipe body are the same, the stress at each selected location is not greater than the stress of the inner wall of the pipe body; when the material of the single-layer socket and the material of the pipe body are different, the ratio of the stress at each selected location to the yield strength of the single-layer socket material is not greater than the ratio of the stress of the inner wall of the pipe body to the yield strength of the pipe body material.

[0018] As a further improvement of the above technical solution:

[0019] The material of the middle layer is hot melt adhesive.

[0020] The sealing gasket includes a sealing gasket pressing edge and a sealing gasket flange. The sealing gasket pressing edge is cylindrical and the sealing gasket flange is annular. The lining ring includes a lining ring pressing edge and a lining ring flange. The lining ring pressing edge and the lining ring flange are an integral whole. The lining ring pressing edge is cylindrical and the lining ring flange is annular. The lining ring pressing edge presses the sealing gasket pressing edge tightly and the lining ring flange presses the sealing gasket flange tightly.

[0021] Step a2 includes the following steps:

[0022] Step a21: 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;

[0023] Step a22: Based on the first form of the differential equation obtained in step a21, 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;

[0024] Step a23: introducing the internal negative pressure of the ring into the second form of the differential equation by introducing a coefficient, so as to obtain the third form of the differential equation;

[0025] Step a24: Obtain a calculation formula for the maximum change in the diameter of the circular ring with coefficients according to the third form of the differential equation obtained in step a23.

[0026] Step a3 includes the following steps:

[0027] Step a31: 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;

[0028] Step a32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step a31;

[0029] Step a33: Substitute the maximum deformation of the socket obtained in step a32 into the calculation formula of step a2 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;

[0030] Step a34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements based on the allowable deformation regulations and the formula obtained in step a33.

[0031] In step a1, the radial deformation obtained is u The differential equation is:

[0032] ,

[0033] The general solution is: ,

[0034] 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, φ The deformation is u The line connecting the point at and the origin of the coordinate system is the same as the line connecting the point at and the origin of the coordinate system in the two-dimensional coordinate system. x The angle between the positive directions of the axes, ; A1, A2, A3, B2, B3 are constants.

[0035] In step a2, it is assumed that the ring is subjected to at least two radial concentrated forces P symmetrically 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:

[0036] First, in Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula: ;

[0037] Second, due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is, ;

[0038] 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: ;

[0039] Combining the above three formulas with the general solution of the differential equation, we get the first form of the differential equation:

[0040] ;

[0041] 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:

[0042] ;

[0043] Introducing the coefficient m, we get the third form of the differential equation:

[0044] ;

[0045] Point of application of force P The point is the point of maximum deformation, and the change in the diameter of the ring is:

[0046] , where I = S 3 / 12, S is the thickness of the tube body.

[0047] In step a5, the minimum thickness of the reinforcement ring is obtained and determined by experiment, simulation or theoretical calculation. When the minimum thickness of the reinforcement ring is obtained and determined by theoretical calculation, 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.

[0048] For the same base pipe, along the direction from the single-layer socket to the spigot, the inner wall of the single-layer socket includes a first step, a second step, a third step, a fourth step, and a fifth step arranged in sequence, one end of the inner wall of the pipe body is a sixth step, the chamfer at the connection between the fourth step and the fifth step is a first chamfer, the chamfer at the connection between the fifth step and the sixth step is a second chamfer, the chamfer at the connection between the second step and the third step is a third chamfer, the chamfer at the connection between the first step and the second step is a fourth chamfer, and the chamfer at the connection between the third step and the fourth step is a fifth chamfer.

[0049] In step b2, the minimum wall thickness of each selected point in step b1 is calculated by the stress calculation formula, and the single-layer socket is regarded as a pressure vessel including at least two coaxially connected pressure vessels with conical inner walls and at least one annular reinforcement ring installed on the inner wall of the pressure vessel. , ,in, is the hoop stress of the pipe body, is the hoop stress at the selected location, D0 is the outer diameter of the base pipe, D is the diameter of the selected location, p is the pressure of the fluid in the base pipe, S is the thickness of the base pipe, S0 is the wall thickness of the selected location, and α is the semi-cone angle of the cone at the selected location.

[0050] When the material of the single-layer socket is the same as that of the pipe body, the stress calculation formula is: .

[0051] When the material of the single-layer socket is different from that of the pipe body, the stress calculation formula is: , where Q0 is the yield strength of the pipe body material and Q1 is the yield strength of the material used for the single-layer socket.

[0052] When in use, the lining ring and the sealing gasket at one end of the plug form a full seal with the end face of the plug, and the lining ring and the sealing gasket at one end of the socket form a full seal with the end face of the pipe body.

[0053] The sealing gasket includes a sealing gasket pressing edge and a sealing gasket flange. The sealing gasket pressing edge is cylindrical and the sealing gasket flange is annular. The lining ring includes a lining ring pressing edge and a lining ring flange. The lining ring pressing edge and the lining ring flange are an integral whole. The lining ring pressing edge is cylindrical and the lining ring flange is annular. The lining ring pressing edge presses the sealing gasket pressing edge tightly and the lining ring flange presses the sealing gasket flange tightly.

[0054] The beneficial effects of the present invention are as follows: (1) The middle layer is a hot melt adhesive, which bonds the inner and outer layers together, thus preventing the inner lining from being delaminated due to negative pressure in the pipeline. (2) A corrosion-resistant metal liner ring and a rubber sealing gasket are arranged at the end of the pipe to prevent the bonding surface ends between the layers of material from contacting water and peeling off due to the tension of water, thereby preventing the inner wall of the metal outer pipe from rusting and peeling off, thus preventing water pollution; the liner ring and the sealing gasket fix the inner pipe, and in the case of seal failure and complete delamination of the inner lining, the lining can still be protected from being washed away by the scouring of water flow; the arrangement of the liner ring and the sealing gasket enhances the ring stiffness of the pipe port, and the socket can form a composite socket with the liner ring that matches it, which is not easy to deform, and is convenient for the installation of the pipe, thereby improving the uniform sealing effect of the sealing gasket and the sealing ring at the connection between the two pipes, and reducing pipeline leakage. (3) The minimum or near minimum thickness of the composite spigot or single-layer spigot that meets the deformation requirements of socket-and-spigot pipes of different diameters, as well as the minimum or near minimum thickness of the single-layer socket that meets the strength requirements, can be obtained through theoretical analysis and calculation, which saves materials and reduces the production, manufacturing and transportation costs of pipes. The method for designing the minimum wall thickness is theoretical calculation, which is low in cost and high in efficiency, and provides strong support for experiments and pipe design, and provides a reference for secondary processing and installation. After the thickness of the base pipe spigot is known, the minimum thickness of the reinforcement ring of the composite spigot that meets the deformation requirements can be calculated. The pipes and pipe network systems installed in this way are more reliable to use, and greatly reduce the leakage and water supply pollution caused by the separation of the spigot and the socket of the adjacent pipe due to excessive deformation of the spigot when the pipe bursts, as well as the cracking of the socket. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the pipe structure of the first embodiment of the present invention.

[0056] Figure 2 yes Figure 1 An enlarged schematic diagram of point A.

[0057] Figure 3It is a schematic diagram of the connection structure of two adjacent pipes in Example 1 of the present invention.

[0058] Figure 4 It is a schematic diagram of the cross-section deformation before and after the socket is subjected to a pair of radially symmetrical concentrated forces.

[0059] Figure 5 yes Figure 4 Schematic diagram of local analysis.

[0060] Figure 6 It is a schematic diagram of a circular ring subjected to multiple evenly arranged radial concentrated forces.

[0061] Figure 7 It is a force analysis diagram of socket-type pipe.

[0062] Figure 8 It is a schematic cross-sectional view of a composite socket per unit length according to an embodiment of the present invention.

[0063] Fig. 9 It is a schematic diagram of the socket and the spigot connection of the present invention.

[0064] Fig.10 It is a schematic diagram of the pipe structure of the second embodiment of the present invention. DETAILED DESCRIPTION

[0065] 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.

[0066] 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.

[0067] Embodiment 1

[0068] A socket-and-spigot type multilayer pipe, which is mainly used for passing water and corrosive liquids. Figure 1 and 2As shown, it includes an inner tube 2, a middle layer 3 and an outer tube 1 which are sequentially sleeved from the inside to the outside.

[0069] The outer tube 1 is made of metal, preferably ductile iron or carbon steel. The outer tube 1 includes a socket 11, a tube body 12 and a spigot 13 connected in sequence along its axial direction. The three are integrally cast, or the tube body 12 and the spigot 13 are integrally formed, and the tube body 12 and the socket 11 are welded together. The spigot 13 is cylindrical, and the spigot 13 is chamfered along the circumferential direction. The inner diameter, outer diameter and thickness of the tube body 12 are equal to or unequal to the inner diameter, outer diameter and thickness of the spigot 13.

[0070] The inner tube 2 is made of polyethylene and is cylindrical.

[0071] The material of the middle layer 3 is non-metal, preferably hot melt adhesive. Hot melt adhesive has bonding properties, and the inner tube 2 and the outer tube 1 are bonded together through the middle layer 3. Specifically, during production, the hot melt adhesive layer and the polyethylene layer are separately produced or heated and extruded by a co-extrusion pipe extruder, vacuum sizing, pulling, and cutting to form a two-layer plastic composite tube, the outer layer is a hot melt adhesive layer, and the inner layer is a polyethylene layer. Then, the outer tube 1 and the plastic composite tube are composited together through a composite process. During composite, the plastic composite tube is located inside the outer tube 1, first heated and then cooled, and the polyethylene is first melted and then solidified, and the outer tube 1 and the plastic composite tube are bonded together to form a three-layer composite tube.

[0072] The length of the inner tube 2 is equal to the length of the middle layer 3, which is equal to the sum of the lengths of the pipe body 12 and the socket 13. At the end of the socket 11, the ends of the inner tube 2, the middle layer 3 and the pipe body 12 are flush; at the end of the socket 13, the ends of the inner tube 2, the middle layer 3 and the socket 13 are flush.

[0073] The middle layer 3 is used as an adhesive layer. When the inner wall of the outer tube 1 is rough during compounding, the middle layer is heated and melted to fill the pits on the inner wall of the outer tube 1. If the thickness of the middle layer 3 is too small, poor adhesion is likely to occur in the area with large local roughness. When the thickness of the middle layer 3 reaches 0.2mm or more, a good peel strength can be stably obtained. The preferred thickness is 0.2mm-0.5mm.

[0074] A lining ring 5 and a sealing gasket 4 are provided at one end of the socket 13 of the pipe, and a lining ring 5 and a sealing gasket 4 are also provided at one end of the socket 11. The lining ring 5 is made of corrosion-resistant metal, preferably stainless steel, and the sealing gasket 4 is made of rubber. The sealing gasket 4 at one end of the socket 13 is used to cover and compress the end face and inner wall of the socket 13 of the pipe, and the lining ring 5 is pressed on the sealing gasket 4. The sealing gasket 4 at one end of the socket 11 is used to cover and compress the end face and inner wall of the pipe body 12 of the pipe near the socket 11, and the lining ring 5 is pressed on the sealing gasket 4.

[0075] like Figure 2 As shown, the sealing gasket 4 includes a sealing gasket pressing edge 41 and a sealing gasket flange 42, which are connected as one piece, and the sealing gasket pressing edge 41 can be regarded as a thin cylindrical shape, and the sealing gasket flange 42 is annular. The inner diameter of the sealing gasket flange 42 is equal to the inner diameter of the sealing gasket pressing edge 41, and the outer diameter of the sealing gasket flange 42 is greater than the outer diameter of the sealing gasket pressing edge 41. The sealing gasket pressing edge 41 and the sealing gasket flange 42 share a common center line.

[0076] The structure of the liner ring 5 is similar to that of the gasket 4. The liner ring 5 includes an integrally connected liner ring pressure edge 51 and a liner ring flange 52. The liner ring pressure edge 51 can be regarded as a thin cylindrical shape, and the liner ring flange 52 is annular. The inner diameter of the liner ring flange 52 is equal to the inner diameter of the liner ring pressure edge 51, and the outer diameter of the liner ring flange 52 is larger than the outer diameter of the liner ring pressure edge 51. The liner ring pressure edge 51 and the liner ring flange 52 share a common center line.

[0077] In this embodiment, the length of the liner ring pressure edge 51 at one end of the socket 13 is not less than the length of the socket 13. In other words, the length of the liner ring 5 extending into the tube is not less than the length of the socket 13, that is, the part of the liner ring 5 extending into the tube completely covers the inner wall of the socket 13, thereby ensuring that the socket 13 and the liner ring pressure edge 51 form a composite socket.

[0078] Figure 2 In the illustrated view, the upper end surface of the sealing gasket flange 42 does not extend beyond the upper end surface of the backing ring flange 52 .

[0079] At one end of the socket 11, the outer surface of the sealing gasket pressing edge 41 of the sealing gasket 4 fits the inner surface of the inner tube 2, and the inner surface of the sealing gasket pressing edge 41 fits the outer surface of the liner ring 5. One side of the sealing gasket flange 42 fits the end face of the inner tube 2, the end face of the intermediate layer 3 and the end face of the pipe body 12, and the other side of the sealing gasket flange 42 fits the liner ring 5. The liner ring pressing edge 51 of the liner ring 5 fits and compresses the sealing gasket pressing edge 41, and the liner ring flange 52 fits and compresses the sealing gasket flange 42.

[0080] At one end of the socket 13, the outer surface of the sealing gasket pressing edge 41 of the sealing gasket 4 fits the inner surface of the inner tube 2, and the inner surface of the sealing gasket pressing edge 41 fits the outer surface of the liner ring 5. One side of the sealing gasket flange 42 fits the end surface of the inner tube 2, the end surface of the intermediate layer 3 and the end surface of the socket 13, and the other side of the sealing gasket flange 42 fits the liner ring 5. The liner ring pressing edge 51 of the liner ring 5 fits and compresses the sealing gasket pressing edge 41, and the liner ring flange 52 fits and compresses the sealing gasket flange 42.

[0081] In this embodiment, the socket 11 of the outer tube is made of a single material and can be regarded as a single-layer socket. The entire inner wall of the socket 13 is covered by the lining ring 5. Therefore, the socket 13 of the outer tube and the lining ring 5 matched therewith can both improve the strength and deformation resistance of one end of the socket, and the socket formed by the two is a composite socket. Because the material of the middle layer 3 is hot melt adhesive and the material of the sealing gasket 4 is rubber, both of which are flexible materials, they have little effect on the strength and deformation resistance of the socket 13, so it does not belong to the category of composite sockets that can resist deformation.

[0082] Next, the thickness of the spigot end and the socket end of the composite pipe is optimized and designed.

[0083] The design method of the thickness of the composite socket includes the following steps:

[0084] Step a1: Obtain the radial deformation of the ring based on the differential equation of the deflection curve and the moment equilibrium equation of the ring The differential equation and the general solution of the differential equation; Because the cross-section of the pipe body and the socket is a circular ring, the deformation of the socket is analyzed by analyzing the radial deformation of the circular ring. In addition, the cylinder of unit length can be regarded as a circular ring.

[0085] Step a2: Calculate and obtain a calculation formula for the maximum radial deformation of the ring based on the general solution of the differential equation obtained in step a1.

[0086] Step a3: 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 a2.

[0087] Step a4: For a base pipe whose socket thickness is less than the minimum thickness obtained in step a3, 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 a3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step a5.

[0088] Step a5: The material of the reinforcement ring is different from that 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 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 requirements. 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 requirements and strength requirements.

[0089] The following is a detailed introduction to each step.

[0090] In step a1, the radial deformation obtained The differential equation is:

[0091] (1)

[0092] 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, φ The deformation is u The line connecting the point at and the origin of the coordinate system is the same as the line connecting the point at and the origin of the coordinate system in the two-dimensional coordinate system. x The angle between the positive directions of the axes, In this embodiment, establish xy Coordinate system, point O is the coordinate origin and the center of the ring, such as Figure 4 Point m 1 The radial deformation at u， but om 1 and x The angle between the positive directions of the axes is φ.

[0093] The above differential equation (1) is obtained as follows:

[0094] like Figure 4 and 5 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 4 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, φ The deformation is u 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 φ, set up u Centripetal movement is positive. Figure 5 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.

[0095] 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 1 n 1 exist m 1 Tangent line of point and n 1The angle between the tangent lines of the point is m 1 t 1 and The angle between , then:

[0096] (2)

[0097] (3)

[0098] (4)

[0099] (5)

[0100] m 1 t 1 and m 1 t The angle between , n 1 t 1 ’ and n 1 t’ The angle between .

[0101] m 1 section to n 1 The variable of the cross-section rotation is :

[0102] (6)

[0103] 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, n 1 t 1 ’ and n 1 t’The angle between n 1 The corner of the cross section.

[0104] Substituting formula (5) and (6) into formula (4) yields:

[0105] (7)

[0106] By series expansion we have:

[0107] Ignoring the higher-order terms, substituting the series expansion into (7) yields: (8)

[0108] Substituting (2) into (8), we obtain: (9)

[0109] Omitting the higher-order terms, we can get: (10)

[0110] For a thin ring (i.e. a ring with a small difference between the outer and inner diameters 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).

[0111] The general solution of the above differential equation (1) is:

[0112] (11)

[0113] Among them, A1, A2, A3, B2, 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:

[0114] (12)

[0115] Step a2: 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 a1, comprising the following steps:

[0116] Step a21: Assume that the circular ring 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.

[0117] Step a22: Based on the first form of the differential equation obtained in step a21, 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.

[0118] Step a23: 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.

[0119] Step a24: Obtain a calculation formula for the maximum change in the diameter of the circular ring with coefficients according to the third form of the differential equation obtained in step a23.

[0120] In step a21, it is assumed that the ring is subjected to at least two radial concentrated forces P symmetrically relative to the center of the ring. 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 6 shown. Figure 4 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.

[0121] The ring satisfies the following three boundary conditions:

[0122] First, in Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula:

[0123] (13)

[0124] Second, due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is,

[0125] (14)

[0126] 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:

[0127] (15)

[0128] in, dM represents the differential of M. It should be noted that the third point is not a real cut of the ring, but an assumption.

[0129] Simultaneously formula (13), (14), (15), the solution is:

[0130] (16)

[0131] (17)

[0132] (18)

[0133] Substituting formulas (16), (17), and (18) into formula (12), we obtain:

[0134] (19)

[0135] Formula (19) is the first form of the differential equation obtained in step a21. is the radial deformation of the ring.

[0136] In step a22, if only one pair of radial forces P is applied to the ring, then , the deflection curve equation (19) becomes:

[0137] (20)

[0138] Formula (20) is the second form of the differential equation obtained in step a22.

[0139] In step a23, considering that the pipe generally needs to withstand an internal negative pressure of 0.1 MPa during testing, the coefficient m is introduced, that is:

[0140] (twenty one)

[0141] 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.

[0142] Formula (21) is the third form of the differential equation obtained in step a23.

[0143] In step a24, 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 :

[0144] (twenty two)

[0145] Formula (22) is the third form of the differential equation obtained in step a24.

[0146] Step a3: 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 a2. It includes the following steps:

[0147] Step a31: Calculate the parameters of a reference pipe according to the existing shear load formula. The material and outer diameter of the reference pipe are respectively the same as the material and outer diameter of the base pipe.

[0148] Step a32: Obtain the maximum deformation of the reference pipe socket through simulation based on the parameters calculated in step a31.

[0149] Step a33: Substitute the maximum deformation of the socket obtained in step a32 into the calculation formula of step a2 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.

[0150] Step a34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements based on the national standard allowable deformation regulations and the formula obtained in step a33.

[0151] In step a31, 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:

[0152] (twenty three)

[0153] like Figure 7 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).

[0154] In this embodiment, the nominal diameter of the base pipe is DN=600mm, and the material is Q235 steel. 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.

[0155] In this embodiment, the parameters in formula (23) are M P and W The calculation process is as follows:

[0156]

[0157]

[0158] 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 steel, the elastic modulus of the steel pipe material is E=200GPa, 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.

[0159] Step a31 is thus completed.

[0160] In step a32, 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.

[0161] In step a33, 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:

[0162] (twenty four)

[0163] From formula (24), we can see that u max The value is related to the pipe diameter and pipe thickness.

[0164] In this embodiment, in step a34, 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.

[0165] Table 1 Nominal wall thickness and absolute deformation of DN=600mm pipes at various nominal pressures

[0166]

[0167] 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).

[0168] 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.

[0169] 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 in Table 1, 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 requirement and the deformation requirement, 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 requirement. 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.

[0170] Step a4: For a base pipe whose socket thickness is less than the minimum thickness obtained in step a3, 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 a3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step a5.

[0171] 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.

[0172] Step a5: The material of the reinforcement ring is different from that 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.

[0173] In this embodiment, the calculation formula for the bending strength of the longitudinal composite beam is as follows:

[0174] (25)

[0175] 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 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 a3.

[0176] For example, in some occasions, the use requirement of the pipe is to meet the nominal pressure within 1.6MPa. The selected base pipe is the pipe No. 5 in Table 1, with a wall thickness of 4mm. The composite spigot includes the base pipe spigot and a layer of annular reinforcement ring (i.e., liner ring pressure edge 51). The thickness of the reinforcement ring is x ,like Figure 8 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 8 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:

[0177]

[0178] Find: x =1.73mm.

[0179] Therefore, the thickness of the reinforcing ring only needs to be no less than 1.73 mm, that is, the thickness of the liner ring pressing edge 51 only needs to be no less than 1.73 mm.

[0180] For another example, if the thickness of the backing ring 5 is known due to process or other requirements, the required thickness of the original socket can be calculated using formula (25).

[0181] The above is the design method for the thickness of the composite socket.

[0182] The design method of the thickness of the single-layer socket is as follows:

[0183] The inner wall shape of the single-layer socket of the pipe material is in accordance with the inner wall shape specified in the group standard "Corrosion-resistant steel pipe with socket and spigot flexible joint for water supply and drainage" (T / CISA 108-2021) and GB / T 13295-2008, such as Fig. 9 As shown. The inner wall of the single-layer socket is stepped. For the same base pipe, along the direction from the single-layer socket to the spigot, the inner wall of the single-layer socket includes a first step 111, a second step 112, a third step 113, a fourth step 114, and a fifth step 115 arranged in sequence. One end of the inner wall of the pipe body is a sixth step 116, and the corresponding inner diameters are: D2, D1, (D3-2F0), D3, D4, (D0-2S), wherein the inner diameters of the sixth step 116, the first step 111, the fifth step 115, the third step 113, the fourth step 114, and the second step 112 increase in sequence, that is: (D0-2S) < D2 < D4 < (D3-2F0) < D3 < D1. The lengths of the first step 111, the second step 112, the third step 113, the fourth step 114, and the fifth step 115 are respectively: T3, T4, T5, (T2-T4-T5), (T1-T2-T3), that is, T1 is the sum of the lengths of the first step 111, the second step 112, the third step 113, the fourth step 114, and the fifth step 115, and T2 is the sum of the lengths of the second step 112, the third step 113, and the fourth step 114, and the lengths refer to the dimensions of the corresponding parts in the axial direction of the base pipe. S is the wall thickness of the pipe body, and F0 is the height of the third step 113 protruding from the fourth step 114, and F0 ≥ 0. The connection of each step is processed with chamfers, wherein the chamfer at the connection of the fourth step 114 and the fifth step 115 is the first chamfer R1, the chamfer at the connection of the fifth step 115 and the sixth step 116 is the second chamfer R2, the chamfer at the connection of the second step 112 and the third step 113 is the third chamfer R3, the chamfer at the connection of the first step 111 and the second step 112 is the fourth chamfer R4, and the chamfer at the connection of the third step 113 and the fourth step 114 is the fifth chamfer R5. Wherein, D0 is the outer diameter of the base pipe of the pipe.

[0184] Since the dimensions of the inner wall of the single-layer socket are fully given by the relevant standards, it is necessary to design some key dimensions of the outer wall on this basis, aiming to save material costs and meet strength requirements at the same time. In other words, the thickness of the single-layer socket is designed to be the minimum or close to the minimum while meeting the use strength requirements, so as to reduce the production, manufacturing and transportation costs of the pipe.

[0185] When two pipes are connected, the socket 13 of one pipe is inserted into the socket 11 of the adjacent pipe and sealed by the sealing ring z. Figure 3 As shown. In this embodiment, the inner wall of the fourth step 114 is a cylindrical wall. The inner wall of the fifth step 115 is the outer side surface of a truncated cone, that is, from the fourth step 114 toward the direction of the pipe body 12, the inner diameter of the fifth step 115 gradually increases, which is equivalent to a trumpet. Preferably, the maximum inner diameter of the fifth step 115 is smaller than the inner diameter of the fourth step 114. The minimum inner diameter of the fifth step 115 is larger than the inner diameter of the pipe body 12. In this way, the sixth step 116 is formed at one end of the pipe body 12 close to the fifth step 115. The inner wall trumpet of the fifth step 115 is set to provide a deflection angle for the adjacent pipe connected thereto, that is, to allow the center line of a pipe and the center line of the adjacent pipe connected thereto to be in an intersecting state rather than an overlapping state, which is to allow a certain installation angle deviation, facilitate actual operation, and allow the adjacent pipes to have a relative displacement of a certain angle when the soil moves naturally.

[0186] The design method of single-layer socket includes the following steps:

[0187] Step b1: Select multiple locations on the inner wall of the single-layer socket where stress is likely to concentrate. The selection principle is: if the wall thickness of these locations meets the stress strength requirements, then the wall thickness of each location of the single-layer socket meets the strength requirements.

[0188] Step b2: Determine the minimum wall thickness of each selected location in step b1, and obtain the outer wall of each selected location. The determination principle is: when the material of the single-layer socket and the material of the pipe body are the same, the stress at each selected location is not greater than the stress of the inner wall of the pipe body; when the material of the single-layer socket and the material of the pipe body are different, the ratio of the stress at each selected location to the yield strength of the single-layer socket material is not greater than the ratio of the stress of the inner wall of the pipe body to the yield strength of the pipe body material.

[0189] Step b3: Connect the outer walls of the selected locations in sequence to obtain the outer wall shape and thickness of the single-layer socket.

[0190] In step b1, based on material mechanics knowledge and experience, several locations on the inner wall of the single-layer socket where stress is most likely to be concentrated are selected, namely the first chamfer R1, the second chamfer R2, and the third chamfer R3. The analysis is as follows:

[0191] For the inner wall of the stepped single-layer socket, according to mechanical knowledge, the stress concentration point is located at the connection between adjacent steps, that is, at each chamfer. Since the single-layer socket is in a trumpet shape, the outer diameter of the single-layer socket decreases from the single-layer socket of the same base pipe to the spigot.

[0192] Based on the above premise, since the inner diameter at the fourth chamfer R4 is equal to the inner diameter at the third chamfer R3, both are equal to D1, the wall thickness at the fourth chamfer R4 must be greater than the wall thickness at the third chamfer R3 to meet the requirement that the single-layer socket is shaped like a trumpet. Therefore, it is equivalent to the wall thickness at the fourth chamfer R4 being greater than the third chamfer R3. At this time, as long as the wall thickness at the third chamfer R3 meets the stress strength requirement, the wall thickness at the fourth chamfer R4 must meet the strength requirement. Similarly, the inner diameter at the fifth chamfer R5 is equal to the inner diameter at the first chamfer R1, both are D3, so the wall thickness at the fifth chamfer R5 must be greater than the wall thickness at the first chamfer R1 to meet the requirement that the single-layer socket is shaped like a trumpet. Therefore, as long as the wall thickness at the first chamfer R1 meets the stress strength requirement, the wall thickness at the fifth chamfer R5 must meet the strength requirement. Therefore, the stress concentration points finally selected are the first chamfer R1, the second chamfer R2, and the third chamfer R3. In other words, the analysis area of ​​the single-layer socket is the area between the third chamfer R3 and the second chamfer R2.

[0193] In step b2, the minimum wall thickness of each location selected in step b1 is calculated by the stress calculation formula. The specific method is as follows: the analysis area of ​​the single-layer socket is regarded as consisting of at least two coaxial pressure vessels with conical inner walls connected end to end, plus several internal reinforcement rings, and the reinforcement rings are connected to the inner wall of the pressure vessel. In other words, the analysis area of ​​the single-layer socket is regarded as consisting of at least two conical pressure vessels plus several internal reinforcement rings. At this time, as long as the corresponding conical pressure vessel meets the strength requirements, the single-layer socket must meet the strength requirements. Fig. 9 shown.

[0194] For a thin-walled cylindrical pressure vessel, its wall thickness is S, its diameter is D0, and its internal pressure is p. From material mechanics, we can get the axial stress σ of the pressure vessel wall: 轴 and hoop stress σ 环 They are as follows:

[0195] (26)

[0196] (27)

[0197] The hoop stress σ 环 The diameter D0 is half of the sum of the outer diameter and the inner diameter of the cylinder, or the inner diameter of the cylinder, or the outer diameter of the cylinder.

[0198] Similarly, for a thin-walled conical pressure vessel, when the wall thickness is S, the internal pressure is p, and the diameter is D, the stress σ in the axial direction of the vessel wall is 轴 and hoop stress σ 环 They are:

[0199] (28)

[0200] (29)

[0201] in α It is the semi-cone angle of the conical pressure vessel, that is, half of the opening angle. In other words, in the section passing through the central axis of the cone, the angle between the cone wall and the central axis is the semi-cone angle. Wherein, the diameter D is half of the sum of the outer diameter and the inner diameter of the corresponding part of the cone, or the inner diameter of the corresponding part, or the outer diameter of the corresponding part.

[0202] From the above, in this embodiment, the analysis area of ​​the single-layer socket includes two coaxially connected conical pressure vessels plus several internal reinforcement rings. The two coaxially connected conical pressure vessels are respectively the first cone and the second cone, which share the same central axis with the single-layer socket, wherein the first chamfer R1 and the second chamfer R2 are located on the inner wall of the first cone, such as Fig. 9 The dotted line between the first chamfer R1 and the second chamfer R2 is the inner wall section of the first cone. The first chamfer R1 and the third chamfer R3 are located on the inner wall of the second cone. Fig. 9 The dotted line between the first chamfer R1 and the third chamfer R3 is the inner wall section of the second cone. For the area between the first chamfer R1 and the second chamfer R2, the portion between the inner wall of the first cone and the outer wall of the single-layer socket is the entire side wall of the first cone, and the portion between the inner wall of the first cone and the inner wall of the single-layer socket is an annular reinforcement ring. Similarly, for the area between the first chamfer R1 and the third chamfer R3, the portion between the inner wall of the second cone and the outer wall of the single-layer socket is the entire side wall of the second cone, and the portion between the inner wall of the second cone and the inner wall of the single-layer socket is another annular reinforcement ring.

[0203] exist Fig. 9 In the cross section shown, the angle between the straight line passing through the first chamfer R1 and the second chamfer R2 and the axis of the tube is the semi-cone angle of the first cone, set as α1. The angle between the straight line passing through the first chamfer R1 and the third chamfer R3 and the axis of the tube is the semi-cone angle of the second cone, set as α2.

[0204] but:

[0205] (30)

[0206] (31)

[0207] When the pipe body meets the strength requirements and the material of the single-layer socket is consistent with that of the pipe body, in order to make the single-layer socket meet the strength requirements, the hoop stress at the first chamfer R1 is Not greater than the hoop stress of the pipe body , hoop stress at the second chamfer R2 Not greater than the hoop stress of the pipe body , Hoop stress at the third chamfer R3 Not greater than the hoop stress of the pipe body , that is:

[0208] (32)

[0209] (33)

[0210] (34)

[0211] Then we have:

[0212] (35)

[0213] (36)

[0214] (37)

[0215] Among them, S1, S2, S 3 The wall thicknesses at the first chamfer R1, the second chamfer R2, and the third chamfer R3 are obtained:

[0216] (38)

[0217] (39)

[0218] (40)

[0219] Since there is a sealing ring z at the third chamfer R3, in order to achieve sealing, the pressure of the sealing ring z on the single-layer socket must be greater than the pressure p of the fluid in the pipe. According to existing research, the average pressure of the sealing ring z on the inner wall of the single-layer socket is generally 1.4 times the fluid pressure. It can be obtained from formulas (28) and (29) that the stress is proportional to the pressure and inversely proportional to the wall thickness. When the pressure increases to 1.4 times, in order to keep the stress unchanged, the wall thickness should be increased to 1.4 times at the same time. Then formula (40) is corrected to:

[0220] (41)

[0221] So we have:

[0222] (42)

[0223] (43)

[0224] (44)

[0225] Among them, S 1m , S 2m , S 3m They are the minimum wall thickness at the first chamfer R1, the second chamfer R2, and the third chamfer R3 respectively.

[0226] From above, Fig. 9 As shown, the minimum outer diameter at the second chamfer R2 d 1. Minimum outer diameter at the first chamfer R1 d 2 , the minimum outer diameter at the third chamfer R3 d 3 are as follows:

[0227] (45)

[0228] (46)

[0229] (47)

[0230] The following example is used to calculate the wall thickness parameters of a single-layer socket.

[0231] In this embodiment, the material of the pipe body and the single-layer socket is Q235.

[0232] Table 2 is the socket size parameter table for the nominal pipe diameters of 600mm and 1200mm at a pressure of 3MPa as specified in the relevant standards:

[0233] Table 2 Dimensional parameters of sockets with nominal pipe diameters of 600 mm and 1200 mm as specified in relevant standards

[0234]

[0235] Based on this scheme, the wall thickness dimensions of the two single-layer sockets in Table 2 are calculated and shown in Table 3.

[0236] Table 3 Wall thickness, outer diameter and semi-cone angle of two single-layer sockets

[0237]

[0238] In step b3, the outer diameter of the end face of the socket only needs to be larger than the outer diameter at the third chamfer R3, and the specific value can be flexibly selected.

[0239] When the pipe body meets the strength requirements and the material of the single-layer socket is inconsistent with the material of the pipe body, in order to make the single-layer socket meet the strength requirements, the stress at the first chamfer R1, the second chamfer R2, and the third chamfer R3 and the stress on the inner wall of the pipe body should meet the following conditions:

[0240] (48)

[0241] (49)

[0242] (50)

[0243] Among them, Q0 is the yield strength of the pipe body material, and Q1 is the yield strength of the material used for the single-layer socket.

[0244] Then we have:

[0245] (51)

[0246] (52)

[0247] (53)

[0248] Similarly, considering the influence of the sealing ring at the third chamfer R3, the wall thickness of each chamfer is:

[0249] (54)

[0250] (55)

[0251] (56)

[0252] Therefore, the minimum wall thickness at the first chamfer R1, the second chamfer R2, and the third chamfer R3 are as follows:

[0253] (57)

[0254] (58)

[0255] (59)

[0256] Based on the above, the design calculation of the minimum thickness of the single-layer socket is completed.

[0257] From the above, in this embodiment, the liner ring 5 at one end of the socket 13 can seal the end face of the pipe and stabilize the inner tube 2 of the pipe, and can also serve as a reinforcement ring and the socket 13 to form a composite socket, that is, the original socket 13 does not need to meet the strength requirements and deformation requirements, and the composite socket only needs to meet the strength and deformation requirements.

[0258] In addition, it should be noted that, in the present embodiment, the length of the liner ring 5 at one end of the pipe socket 11 can be smaller than the length of the liner ring 51 at one end of the plug 13, and the two do not need to be the same length. Generally, the length of the liner ring 51 at one end of the pipe socket 11 is not less than 20 mm.

[0259] Embodiment 2

[0260] Different from the first embodiment, in this embodiment, the length of the liner ring edge 51 at one end of the socket 13 is less than the length of the socket 13, that is, the portion of the liner ring 5 extending into the pipe cannot cover the entire inner wall of the socket 13, and the most vulnerable portion at one end of the pipe socket 13 is still only one layer of the original socket 13. At this time, the pipe socket is equivalent to a single-layer socket. Fig.10 shown.

[0261] In this embodiment, the length of the liner ring pressing edge 51 at one end of the socket 13 is not less than 20 mm and is less than the length of the socket 13 .

[0262] Therefore, in this embodiment, the liner ring 5 at one end of the socket 13 is only used to seal the end surface of the pipe and stabilize the inner tube 2 of the pipe, and does not serve as a reinforcement ring to form a composite socket with the socket 13.

[0263] In this embodiment, in order to make one end of the socket 13 of the pipe meet the strength requirements and deformation requirements, the thickness of the socket 13 needs to be no less than a certain value.

[0264] The thickness optimization design method of the single-layer socket only includes steps a1 to a3 of the thickness optimization design method of the composite socket of the first embodiment, without steps a4 and a5, which is equivalent to only needing to obtain formula (24) without formula (25). The specific process will not be repeated here.

[0265] 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 the socket and the thickness of the spigot-and-socket multilayer pipe, characterized in that: The pipe comprises an inner pipe (2), an intermediate layer (3) and an outer pipe (1) which are sleeved in sequence from the inside to the outside. The outer pipe (1) is made of metal, the intermediate layer (3) is made of non-metal, the inner pipe (2) is made of polyethylene, the outer pipe (1) comprises a socket (11), a pipe body (12) and a plug (13) which are connected in sequence, one end face of the inner pipe (2), one end face of the intermediate layer (3) and the end face of the plug (13) are flush, the other end face of the inner pipe (2), the other end face of the intermediate layer (3) and the end face of the pipe body (12) are flush, each end of the pipe is provided with a liner ring (5) and a sealing gasket (4), and a sealing gasket (4) covers the plug The end face of the mouth (13), the end face of one end of the intermediate layer (3), the end face of one end of the inner tube (2), and the inner wall of one end of the inner tube (2); another sealing gasket (4) covers the end face of the tube body (12), the end face of the other end of the intermediate layer (3), the end face of the other end of the inner tube (2), and the inner wall of the other end of the inner tube (2); two lining rings (5) respectively cover the two sealing gaskets (4); the socket (11) is a single-layer socket; when the length of the lining ring (5) extending into the inner tube (2) is less than the length of the plug (13), the plug (13) is a single-layer plug; when the length of the lining ring (5) extending into the inner tube (2) is not less than the length of the plug (13), the plug (13) and the lining ring (5) matched therewith form a composite plug; The design method of the single-layer socket thickness comprises the following steps: Step a1: Obtain the differential equation of radial deformation of the ring and the general solution of the differential equation according to the differential equation of the deflection curve of the ring and the moment balance equation; Step a2: 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 a1; Step a3: Calculating the minimum thickness of the socket of the base pipe that meets the deformation requirements according to the calculation formula of the maximum radial deformation obtained in step a2; The composite socket thickness design method further includes, based on the single-layer socket thickness design method: Step a4: for a base pipe whose socket thickness is less than the minimum thickness obtained in step a3, 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 a3. If the material of the reinforcement ring is different from that of the socket of the base pipe, go to step a5. Step a5: determining 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. The design method of the single-layer socket thickness comprises the following steps: Step b1: Select multiple locations on the inner wall of the single-layer socket where stress is likely to be concentrated. The selection principle is: if the wall thickness of these locations meets the stress strength requirements, then the wall thickness of each location of the single-layer socket meets the strength requirements; Step b2: Determine the minimum wall thickness of each selected location in step b1, and obtain the outer wall of each selected location. The determination principle is: when the material of the single-layer socket and the material of the pipe body are the same, the stress at each selected location is not greater than the stress of the inner wall of the pipe body; when the material of the single-layer socket and the material of the pipe body are different, the ratio of the stress at each selected location to the yield strength of the single-layer socket material is not greater than the ratio of the stress of the inner wall of the pipe body to the yield strength of the pipe body material.

2. The design method according to claim 1, characterized in that: The material of the middle layer (3) is hot melt adhesive.

3. The design method according to claim 1, characterized in that: The sealing gasket (4) comprises a sealing gasket pressing edge (41) and a sealing gasket flange (42), the sealing gasket pressing edge (41) is cylindrical, and the sealing gasket flange (42) is annular; the lining ring (5) comprises a lining ring pressing edge (51) and a lining ring flange (52), the lining ring pressing edge (51) and the lining ring flange (52) are an integral part, the lining ring pressing edge (51) is cylindrical, and the lining ring flange (52) is annular; the lining ring pressing edge (51) presses the sealing gasket pressing edge (41) tightly, and the lining ring flange (52) presses the sealing gasket flange (42) tightly.

4. The design method according to claim 1, characterized in that: Step a2 includes the following steps: Step a21: 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 a22: Based on the first form of the differential equation obtained in step a21, 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 a23: introducing the internal negative pressure of the ring into the second form of the differential equation by introducing a coefficient, so as to obtain the third form of the differential equation; Step a24: Obtain a calculation formula for the maximum change in the diameter of the circular ring with coefficients according to the third form of the differential equation obtained in step a23.

5. The design method according to claim 1, characterized in that: Step a3 includes the following steps: Step a31: 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; Step a32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step a31; Step a33: Substitute the maximum deformation of the socket obtained in step a32 into the calculation formula of step a2 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 a34: Calculate the minimum thickness of the base pipe socket that meets the deformation requirements based on the allowable deformation regulations and the formula obtained in step a33.

6. The design method according to claim 4 or 5, characterized in that: In step a1, the radial deformation obtained is u The differential equation is: , The 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, φ The deformation is u The line connecting the point at and the origin of the coordinate system is the same as the line connecting the point at and the origin of the coordinate system in the two-dimensional coordinate system. x The angle between the positive directions of the axes, ; A1, A2, A3, B2, B3 are constants.

7. The design method according to claim 6, characterized in that: In step a2, it is assumed that the ring is subjected to at least two radial concentrated forces P symmetrically 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: .

8. The design method according to claim 1, characterized in that: In step a5, the minimum thickness of the reinforcement ring is obtained and determined by experiment, simulation or theoretical calculation. When the minimum thickness of the reinforcement ring is obtained and determined by theoretical calculation, 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.

9. The design method according to claim 1, characterized in that: For the same base pipe, along the direction from the single-layer socket to the spigot, the inner wall of the single-layer socket includes a first step (111), a second step (112), a third step (113), a fourth step (114), and a fifth step (115) arranged in sequence, one end of the inner wall of the pipe body is a sixth step (116), the chamfer at the connection between the fourth step (114) and the fifth step (115) is a first chamfer (R1), the chamfer at the connection between the fifth step (115) and the sixth step (116) is a second chamfer (R2), the chamfer at the connection between the second step (112) and the third step (113) is a third chamfer (R3), the chamfer at the connection between the first step (111) and the second step (112) is a fourth chamfer (R4), and the chamfer at the connection between the third step (113) and the fourth step (114) is a fifth chamfer (R5).

10. The design method according to claim 9, characterized in that: In step b2, the minimum wall thickness of each selected point in step b1 is calculated by the stress calculation formula, and the single-layer socket is regarded as a pressure vessel including at least two coaxially connected pressure vessels with conical inner walls and at least one annular reinforcement ring installed on the inner wall of the pressure vessel. , ,in, is the hoop stress of the pipe body, is the hoop stress at the selected location, D0 is the outer diameter of the base pipe, D is the diameter of the selected location, p is the pressure of the fluid in the base pipe, S is the thickness of the base pipe, S0 is the wall thickness of the selected location, and α is the semi-cone angle of the cone at the selected location.

11. The design method according to claim 10, characterized in that: When the material of the single-layer socket is the same as that of the pipe body, the stress calculation formula is: .

12. The design method according to claim 10, characterized in that: When the material of the single-layer socket is different from that of the pipe body, the stress calculation formula is: , where Q0 is the yield strength of the pipe body material and Q1 is the yield strength of the material used for the single-layer socket.

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