A socket-and-spigot type multi-layer pipe with end edge and a manufacturing method thereof

Abstract

The present invention discloses a socket-and-spigot type multilayer pipe with an end hem and a manufacturing method thereof. The pipe comprises an inner pipe, an intermediate layer and an outer pipe. The intermediate layer is an insulating material. The inner pipe is made of a material with corrosion resistance. The outer pipe comprises a socket, a pipe body and a spigot connected in sequence. One end of the inner pipe covers the end face of the spigot, and the other end covers the end face of the pipe body. The inner pipe, the intermediate layer and the outer pipe are pressed tightly to form the pipe. The manufacturing method comprises the steps of treating the outer pipe, making the inner pipe and the intermediate layer; arranging the inner pipe, the intermediate layer and the outer pipe from the inside to the outside in sequence; pressing each layer; and arranging the hem. The corrosion-resistant inner pipe of the present invention prevents the outer pipe from rusting and polluting the water quality. The thickness of the inner lining is relatively small. The intermediate layer completely separates the inner pipe and the outer pipe. The hem and the inner sleeve are an integral whole to prevent the inner sleeve from electrochemical corrosion and being washed away by water flow. The hem has no steps, and the step water flow resistance is eliminated. The minimum thickness of the composite spigot and the minimum thickness of the single-layer socket can be obtained by theoretical calculation.

Description

Technical Field

[0001] The invention belongs to the technical field of pipe processing and manufacturing, and specifically relates to a socket-and-spigot type multi-layer pipe with an end edge and a manufacturing method thereof. Background Art

[0002] In the prior art, multi-layer pipes are generally composite pipes, which are widely used in liquid transportation pipe network systems. When in use, the parts of the pipes that are in contact with the liquid are required to have good corrosion resistance to prevent the pipes from rusting due to long-term contact with the liquid, which affects the quality of the transported liquid. Existing composite pipes generally have a metal pipe as the outer layer and a plastic pipe as the inner layer, that is, the plastic pipe is used as the inner lining, and the inner layer and the outer layer are composited by a composite process. The structure of the existing composite pipe is generally a socket-and-spigot structure, with one end of the metal pipe as a spigot and the other end as a bell. Lining rings are respectively provided at both ends of the composite pipe to tightly press the inner lining and the end face, and the lining rings at both ends are used to press the plastic pipes of the spigot and the bell onto the metal pipe and cover the end face, so as to prevent the end face of the composite pipe from being eroded for a long time during use and causing delamination. However, the liner ring and the inner liner are independent, and one end of the liner ring is pressed on the surface of the inner liner to form a step. Under the long-term scouring of the liquid, the liner ring is at risk of loosening or even falling off. The transported liquid may penetrate into the end face of the composite pipe through the loose liner ring, polluting the quality of the transported liquid. The inner diameter of the pipe at the liner ring is reduced, and the step formed by the liner ring and the inner liner increases the fluid resistance in the pipe and increases energy consumption. In addition, the thermal expansion coefficient of the plastic pipe liner is quite different from the expansion coefficient of the metal outer pipe. The inner and outer pipes will produce a certain amount of internal stress due to temperature changes, which will cause the inner liner to delaminate and fall off.

[0003] 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 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. Since 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 generally uses relatively cheap materials such as ductile iron and Q235. Therefore, how to ensure that the above-mentioned composite socket meets the maximum deformation requirements while the thickness is minimum or close to the minimum becomes a problem to be solved. The existing standards do not give the wall thickness requirements for the socket that is plugged into the composite socket, 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 base pipe refers to the pipe in the factory setting, that is, the base pipe has no reinforcement ring installed and no secondary processing such as composite process. The base pipe 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 pipe is the outer diameter of the pipe body. Fig.12 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 socket-type multilayer pipe with an end edge and a manufacturing method thereof. The inner pipe of corrosion-resistant material is used as an inner lining to completely isolate the outer pipe from the liquid flowing in the pipe, avoid the rust of the outer pipe to pollute the water quality, and improve the liquid transportation performance. The thickness of the inner lining is small, which improves the water transportation efficiency of the pipeline and reduces the operating energy consumption. The middle layer is made of plastic, which completely separates the inner pipe and the outer pipe to prevent the contact between the outer pipe and the inner pipe from causing electrochemical corrosion of the inner pipe. At the same time, it eliminates the uneven glue layer caused by the flow of ordinary liquid glue in the middle layer, and the electrochemical corrosion caused by direct contact between the inner lining and the outer metal pipe without bonding, and also overcomes the problems of easy aging and poor insulation of ordinary glue. Sealing pads and corrosion-resistant edge are provided at both ends of the middle layer. The sealing pads separate the edge and the metal outer pipe to prevent electrochemical corrosion of the edge after contact, and prevent water from penetrating into the inner wall of the outer pipe to pollute the water quality. The hemming and the inner sleeve are integrally formed or welded together to fix the inner sleeve, preventing the water flow from directly impacting the end of the inner sleeve and preventing the inner sleeve from being washed away by the water flow. The hemming has no hemming steps, eliminating the water flow resistance caused by the steps, making the pipe more efficient in conveying water and less energy-consuming in operation.

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

[0008] A socket-and-spigot type multi-layer pipe with an end edge, comprising an inner pipe, an intermediate layer and an outer pipe, wherein the intermediate layer is made of a material with an insulating function, the inner pipe is made of a material with a corrosion-resistant function, and the outer pipe comprises a socket, a pipe body and a spigot connected in sequence, one end of the inner pipe covers the end face of the spigot, and the other end covers the end face of the pipe body, and the inner pipe, the intermediate layer and the outer pipe are pressed tightly to form the pipe.

[0009] As a further improvement of the above technical solution:

[0010] Preferably, the inner tube comprises an inner sleeve and two edges, the inner sleeve and the two edges are an integral whole, and the inner sleeve, the middle layer and the outer tube are sequentially sleeved from the inside to the outside.

[0011] Preferably, the end face of the socket is covered by a sealing gasket, and the end face of the tube body is covered by another sealing gasket, and the sealing gasket is pressed against the edge.

[0012] More preferably, the sealing gasket at one end of the socket is pressed by one edge and the upper end surface of the sealing gasket does not exceed the upper end surface of the edge after coating, and the sealing gasket at one end of the tube body is pressed by another edge and the upper end surface of the sealing gasket does not exceed the upper end surface of the edge after coating.

[0013] More preferably, both ends of the inner tube are respectively flanged to form two edges at both ends, the inner sleeve covers the inner wall of the tube body and the inner wall of the socket, and the two edges respectively press the sealing gasket on the end face of the socket and the sealing gasket on the end face of the tube body.

[0014] Preferably, the length of the inner sleeve is less than the sum of the length of the tube body and the length of the socket, and the inner sleeve and the two hems are welded.

[0015] More preferably, the thickness of the edging is greater than the thickness of the inner sleeve.

[0016] Preferably, the edging includes an integrally connected edging press and an edging flange. At one end of the socket, the edging flange presses the sealing gasket on the end face of the socket, and the edging press is located on the inner wall of one end of the pipe socket, pressing the sealing gasket and / or the middle layer on the inner wall of the socket. At one end of the socket, the edging flange presses the sealing gasket on the end face of the tube body, and the edging press is located on the inner wall of one end of the tube body, pressing the sealing gasket and / or the middle layer on the inner wall of the tube body.

[0017] Preferably, the length of the hemming is not less than 20 mm.

[0018] Preferably, the material of the middle layer is plastic, and the material of the outer tube is metal.

[0019] More preferably, the outer tube is made of ductile iron or carbon steel.

[0020] Preferably, the thickness of the middle layer is not less than 0.2 mm, and the thickness of the inner sleeve 21 is not less than 0.1 mm.

[0021] The socket is a single-layer socket, and the spigot and the inner tube covering the inner wall of the spigot form a composite spigot.

[0022] The design method of the composite socket thickness includes the following steps:

[0023] 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;

[0024] 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;

[0025] 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;

[0026] 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.

[0027] 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.

[0028] The design method of single-layer socket thickness includes the following steps:

[0029] 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;

[0030] Step b2: Determine the minimum wall thickness of each selected location in step b1, and 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.

[0031] Step a2 includes the following steps:

[0032] 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;

[0033] 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;

[0034] 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;

[0035] 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.

[0036] Step a3 includes the following steps:

[0037] 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;

[0038] Step a32: obtaining the maximum deformation of the reference pipe socket through simulation according to the parameters calculated in step a31;

[0039] 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;

[0040] 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.

[0041] In step a1, the radial deformation obtained is u The differential equation is:

[0042] ,

[0043] The general solution is: ,

[0044] 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.

[0045] 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:

[0046] First, in Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula: ;

[0047] Second, due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is, ;

[0048] 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: ;

[0049] Combining the above three formulas with the general solution of the differential equation, we get the first form of the differential equation:

[0050] ;

[0051] 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:

[0052] ;

[0053] Introducing the coefficient m, we get the third form of the differential equation:

[0054] ;

[0055] Point of application of force P The point is the point of maximum deformation, and the change in the diameter of the ring is:

[0056] , where I = S 3 / 12, S is the wall thickness of the tube body.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] When the material of the single-layer socket is the same as that of the pipe body, the stress calculation formula is: .

[0061] 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.

[0062] A method for manufacturing a spigot-and-socket type multilayer pipe with an end-bagged edge, for manufacturing the multilayer pipe, comprises the following steps:

[0063] Step S1: processing the inner wall and outer wall of the outer tube, making the inner tube, and making the middle layer;

[0064] Step S2: Arrange the inner tube, the middle layer and the outer tube in sequence from inside to outside;

[0065] Step S3: Pressing the inner tube and the middle layer onto the outer tube;

[0066] Step S4: providing edging at both ends of the inner tube so that the edging covers the end surface of the socket end of the tube and the end surface of the tube body.

[0067] Preferably, in step S3, the inner tube is pressed tightly against the inner wall of the outer tube by spin forming or hydraulic forming.

[0068] Preferably, in step S1, the inner tube can be manufactured as a whole, and then in step S4, both ends of the inner tube are flanged to form a rim; or in step S1, the inner sleeve and the rim are manufactured separately, and then in step S4, the inner sleeve and the rim are welded together.

[0069] Preferably, when the inner sleeve and the edging are welded, the welding point is located on the inner wall of the tube.

[0070] The beneficial effects of the present invention are:

[0071] (1) The inner tube made of corrosion-resistant material is used as the inner lining to completely isolate the outer tube from the liquid flowing in the tube, effectively preventing the outer tube from rusting, playing a good anti-corrosion role, increasing the service life of the tube, avoiding the rust of the outer tube from polluting the water quality, and improving the liquid transportation performance.

[0072] (2) Compared with plastic pipe linings, the inner pipe made of corrosion-resistant material as the inner lining eliminates the inner surface wrinkles and uneven defects caused by the melting of the inner lining plastic during compounding, improves the flatness of the inner surface of the pipe, and has a smaller inner lining thickness, which improves the water delivery efficiency of the pipeline and reduces operating energy consumption.

[0073] (3) The inner pipe made of corrosion-resistant material is used as the inner lining. Compared with the plastic pipe lining, the pipe can be used to transport high-temperature liquid media.

[0074] (4) The middle layer is made of plastic, which completely separates the inner tube from the outer tube to prevent the outer tube from contacting the inner tube and causing electrochemical corrosion to the inner tube. At the same time, it eliminates the uneven glue layer caused by the flow of ordinary liquid glue in the middle layer, and the electrochemical corrosion caused by the direct contact between the inner lining and the outer metal tube without bonding. It also overcomes the problems of easy aging and poor insulation of ordinary glue.

[0075] (5) Sealing gaskets and corrosion-resistant edging are provided at both ends of the middle layer. The sealing gaskets separate the edging from the metal outer tube to prevent electrochemical corrosion of the edging after contact, and prevent water from penetrating into the inner wall of the outer tube and polluting the water quality. In addition, the edging is a part of the inner tube, and the edging and the inner sleeve are integrally formed or welded together to fix the inner sleeve, prevent the water flow from directly impacting the end of the inner sleeve, and prevent the inner sleeve from being washed away by the scouring effect of the water flow.

[0076] (6) In the case of welding the inner sleeve and the edging, since the two can be made separately, the thickness of the edging can be selected to be greater than that of the inner sleeve, which improves the rigidity of the edging, the sealing effect of the gasket and the fixing effect on the inner sleeve, reduces pipeline leakage, makes the edging less likely to deform, and does not need to increase the thickness of the inner sleeve, thereby reducing production costs and facilitating the installation of pipes.

[0077] (7) Compared with the process of installing lining rings on the inner lining at both ends of the pipe, the edge wrapping and inner pipe of this solution will not form steps, eliminating the water flow resistance caused by the steps, and the water conveying efficiency of the pipe is higher and the operating energy consumption is lower.

[0078] (8) The minimum or near minimum thickness of the composite spigot that meets the deformation requirements of socket-and-spigot pipes of different diameters and the minimum or near minimum thickness of the single-layer spigot 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. It 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, greatly reducing 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

[0079] Figure 1 It is a schematic diagram of the structure of the tube when the sealing gasket of the first embodiment of the present invention has no edge pressing.

[0080] Figure 2 It is a schematic diagram of the structure of the tube when the sealing gasket of the first embodiment of the present invention has a pressed edge and a flanging edge.

[0081] Figure 3 yes Figure 2An enlarged schematic diagram of point A.

[0082] Figure 4 It is a schematic diagram of the structure of the pipe when the sealing gasket of the second embodiment of the present invention has no edge pressing.

[0083] Figure 5 It is a schematic diagram of the structure of the pipe when the sealing gasket of the second embodiment of the present invention has a pressed edge and a flanging edge.

[0084] Figure 6 yes Figure 5 Enlarged schematic diagram of point C.

[0085] Figure 7 Schematic diagram of the cross-section deformation before and after the socket is subjected to a pair of radially symmetrical concentrated forces.

[0086] Figure 8 for Figure 7 Schematic diagram of local analysis.

[0087] Fig. 9 Schematic diagram of a circular ring subjected to multiple uniformly arranged radial concentrated forces.

[0088] Fig.10 This is the stress analysis diagram of socket-type pipe.

[0089] Fig.11 The figure is a schematic cross-sectional view of a composite socket per unit length according to an embodiment of the present invention.

[0090] Fig.12 It is a schematic diagram of the socket and spigot connection of the present invention. DETAILED DESCRIPTION

[0091] 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.

[0092] 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.

[0093] Embodiment 1

[0094] A socket-and-spigot type multilayer pipe with end flanges, such as Figure 1~Figure 3 As shown, it includes an inner tube 2, an intermediate layer 3 and an outer tube 1. The inner tube 2 includes an inner sleeve 21 and two edges 22. The inner sleeve 21 and the two edges 22 are a whole. The inner sleeve 21 is cylindrical. The inner sleeve 21, the intermediate layer 3 and the outer tube 1 are sequentially connected from the inside to the outside.

[0095] The outer tube 1 comprises a socket 11, a tube body 12 and a spigot 13 which are sequentially connected along the axial direction thereof, i.e., the socket 11, the tube body 12 and the spigot 13 share a central line. The spigot 13 is cylindrical, and a chamfer is provided along the circumferential direction at one end of the spigot 13 away from the tube body 12. The inner surface of the socket 11 is provided with steps and / or grooves, i.e., the socket 11 can be regarded as being formed by sequentially connecting a plurality of cylindrical structures with different inner diameters.

[0096] The outer tube 1 is made of metal, preferably ductile iron or carbon steel. Preferably, the socket 11, the tube body 12 and the spigot 13 are integrally cast, or the tube body 12 and the spigot 13 are integrally formed as a large tube body, and the large tube body and the socket 11 are manufactured separately and then welded together. The inner diameter, outer diameter and thickness of the spigot 13 may be substantially equal to or unequal to the inner diameter, outer diameter and thickness of the tube body 12.

[0097] The inner tube 2 is made of corrosion-resistant materials, including but not limited to stainless steel, titanium, and composite materials, preferably stainless steel. One end of the inner tube 2 covers the end face of the tube body 12 close to the socket 11, the middle of the inner tube 2 covers the inner wall of the tube body 12 and the inner wall of the socket 13, and the other end of the inner tube 2 covers the end face of the socket 13. Specifically, the inner sleeve 21 covers the inner wall of the tube body 12 and the inner wall of the socket 13, one edge 22 covers the end face of the socket 13, and the other edge 22 covers the end face of the tube body 12. As can be seen from the above, there are no holes on the inner tube 2, which is a continuous medium and can completely cover the end and inner wall of the tube body 12 and the inner wall and end face of the socket 13.

[0098] The middle layer 3 is made of a material having an insulating function, preferably plastic, and is located between the inner sleeve 21 and the outer tube 1 .

[0099] A sealing gasket 4 is arranged between the end surface of the socket 13 and one rim 22 , and a sealing gasket 4 is arranged between the end surface of the tube body 12 and the other rim 22 .

[0100] like Figures 1 to 3 As shown, the sealing gasket 4 includes an integrally connected pressing edge 41 and a flange 42. The pressing edge 41 can be regarded as a thin cylindrical shape, and the flange 42 is annular. The inner diameter of the flange 42 is equal to the inner diameter of the pressing edge 41, and the outer diameter of the flange 42 is greater than the outer diameter of the pressing edge 41. The pressing edge 41 and the flange 42 are coaxial. At one end of the socket 13, the pressing edge 41 is located between the inner wall of the socket 13 and the inner sleeve 21, and the flange 42 is located between the end face of the socket 13 and the edging 22 covering the end face. At one end of the socket 11, the pressing edge 41 is located between the inner wall of the pipe body 12 and the inner sleeve 21, and the flange 42 is located between the end face of the pipe body 12 and the edging 22 covering the end face.

[0101] It should be noted that the edge pressing 41 can be eliminated. Figure 1 As shown, the sum of the lengths of the tube body 12 and the socket 13, the length of the inner sleeve 21, and the length of the intermediate layer 3 are equal. One end face of the intermediate layer 3 is flush with the end face of the socket 13, and the other end face of the intermediate layer 3 is flush with the end face of the tube body 12. At this time, the sealing gasket 4 is equivalent to having only the flange 42 and no pressed edge 41. Figure 2 and 3 As shown, one end face of the middle layer 3 is not flush with the end face of the socket 13, and the end face of the socket 13 exceeds one end face of the middle layer 3. At this time, the sealing gasket 4 has both a flange 42 and a pressed edge 41. Similarly, the other end face of the middle layer 3 is not flush with the end face of the tube body 12.

[0102] The sealing gasket 4 is a rubber sealing gasket, which prevents the liquid in the pipeline from contacting the middle layer of the end face of the socket 13 or the end face of the tube body 12, and the liquid penetrates into the inner wall of the outer tube 1, causing the inner wall of the outer tube 1 to corrode and contaminate the transported liquid.

[0103] The inner wall of the socket 11 is provided with steps, wherein the inner wall of the step closest to the pipe body 12 is the outer side surface of a truncated cone, i.e., the inner diameter of the step gradually increases from the socket 11 toward the pipe body 12, which is equivalent to a trumpet. This setting is intended to provide a deflection angle for the adjacent multi-layer pipes connected thereto, i.e., to allow the center line of a multi-layer pipe to intersect with the center line of the adjacent multi-layer pipe connected thereto, rather than to overlap, in order to allow a certain installation angle deviation, facilitate actual operation, and allow adjacent pipes to have a relative displacement of a certain angle when the soil moves naturally.

[0104] The outer diameter of the inner sleeve 21 is slightly smaller than the inner diameter of the outer tube 1, and the thickness of the inner sleeve 21 is not less than 0.1 mm.

[0105] The main function of the inner sleeve 21 is corrosion protection, and its thickness should not be too large. A large number of welding tests have shown that under the conditions of the fiber laser welding process, a stainless steel plate with a minimum wall thickness of 0.1 mm can obtain a weld with high welding strength and small deformation.

[0106] The wall thickness of the intermediate layer 3 is not less than 0.2 mm. The intermediate layer 3 also serves as an insulating layer and needs a certain thickness to produce an insulating effect between the outer tube 1 and the inner sleeve 21. The electric spark test shows that when the thickness of the intermediate layer 3 is not less than 0.2 mm, a good insulation performance can be stably obtained.

[0107] The inner diameter of the middle layer 3 is slightly larger than the outer diameter of the inner tube 2 , and the outer diameter of the middle layer 3 is slightly smaller than the inner diameter of the outer tube 1 .

[0108] In this embodiment, the thickness of the inner sleeve 21 is equal to the thickness of the edge 22. The two ends of the inner sleeve 21 are respectively connected to the two edges 22 as a whole, and the two ends of the inner tube 2 are respectively flanged to form the two edges 22 at the two ends and the inner sleeve 21 in the middle.

[0109] A method for manufacturing a spigot-and-socket type multilayer pipe with an end-bagged edge, for manufacturing the pipe, comprises the following steps:

[0110] Step S1: processing the inner wall and the outer wall of the outer tube 1, manufacturing the inner tube 2, and manufacturing the intermediate layer 3.

[0111] In this step, the method for processing the inner wall and outer wall of the outer tube 1 is to first grind the inner wall of the outer tube 1, and then sandblast or shot blast the inner wall and outer wall. Use an internal grinder to grind the inner wall of the outer tube 1, grind the inner wall of the tube flat, and remove surface oxide scale, scum and rust. Alternatively, after the inner wall is polished flat, use a laser cleaning machine to clean the inner wall of the tube to deeply remove the oxide scale and rust on the inner wall of the tube. When sandblasting or shot blasting, remove dust, oxide scale, and rust on the inner and outer walls, and sandblast the inner and outer walls of the tube into a frosted surface.

[0112] Making the inner tube 2 comprises the following steps:

[0113] S11: Process the stainless steel sheet into a ring shape or a thin cylindrical shape, and complete the rolling. In this step, the rolling is performed by a rolling machine.

[0114] S12: Cut the rolled stainless steel sheet and weld it into a cylindrical shape. In this step, if a single roll is obtained in step S11 and its length is greater than the length of the inner tube 2, a straight seam welding is performed using a argon arc welder or a laser welder, and the weld extends from one end of the inner tube 2 to the other end. If multiple spirally connected rolls are obtained in step S11, a spiral seam welding machine is used to weld the multiple spirally connected rolls in sequence to form a thin cylinder.

[0115] Preferably, the length of the stainless steel round tube obtained in step S12 is not less than the length of the inner tube 2 of the pipe material that is finally processed. Specifically, the length of the stainless steel round tube obtained in step S12 is not less than the sum of the length of the tube body 12, the length of the socket 13, and the length of the two hems 22.

[0116] S13: Flanging one end of the stainless steel inner tube 2 to form a rim 22, and sleeve a sealing gasket 4 on the outer wall of the inner tube 2, with one end surface of the sealing gasket 4 contacting the rim 22. The sealing gasket 4 can be glued to the rim 22 according to the specific situation. In this step, the flanging operation is performed using an existing pipe flanging machine.

[0117] Step S2: Arrange the inner tube 2, the middle layer 3 and the outer tube 1 in sequence from the inside to the outside.

[0118] In this step, step S3 can be completed in the following three ways:

[0119] The first way is as follows:

[0120] First, the plastic is formed into a round tube by extrusion molding, vacuum sizing, traction, and cutting. Extrusion molding, vacuum sizing, traction, and cutting can be performed by an extruder, a vacuum box, a traction machine, and a cutting machine in the prior art. The extrusion molding is a prior art and will not be described in detail here.

[0121] Then, the obtained shaped intermediate layer 3 is sleeved on the outer wall of the inner tube 2. In this step, the sleeve can be made manually or by an existing sleeve machine.

[0122] Finally, the intermediate layer 3 and the inner tube 2 are inserted into the outer tube 1 as a whole. Similarly, in this step, the casing can be completed manually or by a pipe threading machine. The end of the inner tube 2 that has not been wrapped 22 is inserted into the outer tube 1 from one end of the socket 11 until the existing wrapped edge 22 presses the sealing gasket 4 against the end of the tube body 12 at one end of the socket 11.

[0123] The second way is as follows:

[0124] First, after the inner wall of the tube body 12 and the inner wall of the socket 13 are heated, a powdered plastic is rotationally molded or sprayed on the inner wall of the tube body 12 and the inner wall of the socket 13 by a roller coater or a plastic coating machine.

[0125] Then, the inner tube 2 is inserted into the outer tube 1 with the middle layer 3 on the inner wall.

[0126] It should be noted that when the sealing gasket 4 used includes a pressing edge 41 and a flange 42, during rotational molding or spray molding, a circle of the installation pressing edge 41 is covered with stainless steel to prevent the area where the pressing edge 41 is installed from being sprayed with plastic powder, affecting the subsequent installation of the pressing edge 41.

[0127] The third way is as follows:

[0128] First, after the outer wall of the inner tube 2 is heated, a powdered plastic is rotationally molded or sprayed onto the outer wall of the inner sleeve 21 of the inner tube 2 made of stainless steel by using a roller coater or a plastic coating machine.

[0129] Then, the inner tube 2 with the intermediate layer 3 on the outer wall is inserted into the outer tube 1.

[0130] Step S3: Press the inner tube 2 and the middle layer 3 onto the outer tube 1 .

[0131] This step can be completed by spin forming or hydraulic forming. In spin forming, the inner tube 2 is spun by a pipe spinning machine so that the inner sleeve 21 lined with stainless steel, the middle layer 3, and the outer tube 1 are closely attached in sequence. In hydraulic forming, the two ends of the inner tube 2 inserted into the outer tube 1 are sealed, and water is injected into the tube to pressurize it so that the inner sleeve 21, the middle layer 3, and the outer tube 1 are closely attached in sequence.

[0132] Step S4: flanging the two ends of the inner tube 2.

[0133] In this step, when the middle layer 3 is plastic, step S13 is performed, and at this time, only one end of the socket 13 of the inner tube 2 needs to be flanged and sealed. First, the sealing gasket 4 is put on the outer wall of the inner tube 2 beyond the end face of the socket 13 and the sealing gasket 4 is made close to the end face of the socket 13. Then, the inner tube 2 beyond the sealing gasket 4 is pressed by a crimping device, so that the part of the inner tube 2 beyond the sealing gasket 4 is flanged, that is, the original outer wall of the part of the inner tube 2 beyond the sealing gasket 4 is close to the sealing gasket 4, and the original inner wall becomes the end of the pipe, forming the stainless steel 22 at one end of the pipe socket 13.

[0134] Step S5: tighten the edge 22 and trim the edges.

[0135] In this step, the stainless steel flanges (i.e., the edge wrapping 22) at both ends of the pipe are tightened against the end faces of the socket 13 and the end faces of the pipe body 12 by a tightening device. The redundant sealing pads and stainless steel at both ends of the pipe are cleaned.

[0136] After completing the above steps, the outer wall of the pipe is sprayed with paint or plastic coated or other methods are used for external anti-corrosion treatment.

[0137] 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 inner tube 2. Therefore, the socket 13 of the outer tube and the portion of the inner tube 2 covering the socket 13 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. The middle part 3 is made of plastic, which is a flexible non-metallic material and has little effect on the strength and deformation resistance of the socket 13. Therefore, it does not belong to the category of a composite socket that can resist deformation.

[0138] Next, the thickness of the spigot end and the socket end of the composite pipe is optimized and designed.

[0139] The design method of the thickness of the composite socket includes the following steps:

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] The following is a detailed introduction to each step.

[0146] In step a1, the radial deformation obtained The differential equation is:

[0147] (1)

[0148] 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 7 Point m 1 The radial deformation at u， but om 1 and x The angle between the positive directions of the axes is φ.

[0149] The above differential equation (1) is obtained as follows:

[0150] like Figure 7 and 8 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 7 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 isx The angle between the positive directions of the axes, om and on The angle between φ, set up u Centripetal movement is positive. Figure 8 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.

[0151] 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 existm 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:

[0152] (2)

[0153] (3)

[0154] (4)

[0155] (5)

[0156] m 1 t 1 and m 1 t The angle between , n 1 t 1 ’ and n 1 t’ The angle between .

[0157] m 1 section to n 1 The variable of the cross-section rotation is :

[0158] (6)

[0159] 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.

[0160] Substituting formula (5) and (6) into formula (4) yields:

[0161] (7)

[0162] By series expansion we have:

[0163] Ignoring the higher-order terms, substituting the series expansion into (7) yields: (8)

[0164] Substituting (2) into (8), we obtain: (9)

[0165] Omitting the higher-order terms, we can get: (10)

[0166] 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).

[0167] The general solution of the above differential equation (1) is:

[0168] (11)

[0169] 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:

[0170] (12)

[0171] 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:

[0172] 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.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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 Fig. 9 shown. Figure 7 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.

[0177] The ring satisfies the following three boundary conditions:

[0178] First, in Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula:

[0179] (13)

[0180] Second, due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is,

[0181] (14)

[0182] 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:

[0183] (15)

[0184] 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.

[0185] By combining formulas (13), (14) and (15), we get:

[0186] (16)

[0187] (17)

[0188] (18)

[0189] Substituting formulas (16), (17), and (18) into formula (12), we obtain:

[0190] (19)

[0191] Formula (19) is the first form of the differential equation obtained in step a21. is the radial deformation of the ring.

[0192] In step a22, if only one pair of radial forces P is applied to the ring, then , the deflection curve equation (19) becomes:

[0193] (20)

[0194] Formula (20) is the second form of the differential equation obtained in step a22.

[0195] 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:

[0196] (twenty one)

[0197] 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.

[0198] Formula (21) is the third form of the differential equation obtained in step a23.

[0199] 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 :

[0200] (twenty two)

[0201] Formula (22) is the third form of the differential equation obtained in step a24.

[0202] 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:

[0203] 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.

[0204] Step a32: Obtain the maximum deformation of the reference pipe socket through simulation based on the parameters calculated in step a31.

[0205] 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.

[0206] 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.

[0207] 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:

[0208] (twenty three)

[0209] like Fig.10 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).

[0210] 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.

[0211] In this embodiment, the parameters in formula (23) are M P and W The calculation process is as follows:

[0212]

[0213]

[0214] 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.

[0215] Step a31 is thus completed.

[0216] 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.

[0217] 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:

[0218] (twenty four)

[0219] From formula (24), we can see that u max The value is related to the pipe diameter and pipe thickness.

[0220] 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.

[0221] Table 1 Nominal wall thickness and absolute deformation of DN=600mm pipes at various nominal pressures

[0222]

[0223] 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).

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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.

[0228] 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.

[0229] In this embodiment, the calculation formula for the bending strength of the longitudinal composite beam is as follows:

[0230] (25)

[0231] 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.

[0232] 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, whose wall thickness is 4mm. The composite spigot includes the base pipe spigot and a layer of annular reinforcement ring (i.e., the part of the inner sleeve 21 covering the spigot 13). The thickness of the reinforcement ring is x ,like Fig.11 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. Fig.11 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:

[0233]

[0234] Find: x=1.73mm.

[0235] Therefore, the thickness of the reinforcement ring should not be less than 1.73 mm.

[0236] For another example, if the thickness of the inner tube 2 is known due to process or other requirements, the required thickness of the original socket can be calculated using formula (25).

[0237] The above is the design method for the thickness of the composite socket.

[0238] The design method of the thickness of the single-layer socket is as follows:

[0239] 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.12 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 12 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.

[0240] 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.

[0241] The design method of single-layer socket includes the following steps:

[0242] 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.

[0243] 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.

[0244] 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.

[0245] 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:

[0246] 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.

[0247] 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.

[0248] 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.12 shown.

[0249] 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:

[0250] (26)

[0251] (27)

[0252] 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.

[0253] 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:

[0254] (28)

[0255] (29)

[0256] 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. 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.

[0257] 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.12 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.12 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.

[0258] exist Fig.12 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.

[0259] but:

[0260] (30)

[0261] (31)

[0262] 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:

[0263] (32)

[0264] (33)

[0265] (34)

[0266] Then we have:

[0267] (35)

[0268] (36)

[0269] (37)

[0270] Among them, S1, S2, S 3 are the wall thickness at the first chamfer R1, the second chamfer R2, and the third chamfer R3, respectively, and we get:

[0271] (38)

[0272] (39)

[0273] (40)

[0274] 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:

[0275] (41)

[0276] So we have:

[0277] (42)

[0278] (43)

[0279] (44)

[0280] Among them, S1m , 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.

[0281] From above, Fig.12 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:

[0282] (45)

[0283] (46)

[0284] (47)

[0285] The following example is used to calculate the wall thickness parameters of a single-layer socket.

[0286] In this embodiment, the material of the pipe body and the single-layer socket is Q235.

[0287] 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:

[0288] Table 2 Dimensional parameters of sockets with nominal pipe diameters of 600 mm and 1200 mm as specified in relevant standards

[0289]

[0290] Based on this scheme, the wall thickness dimensions of the two single-layer sockets in Table 2 are calculated and shown in Table 3.

[0291] Table 3 Wall thickness, outer diameter and semi-cone angle of two single-layer sockets

[0292]

[0293] 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.

[0294] 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:

[0295] (48)

[0296] (49)

[0297] (50)

[0298] 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.

[0299] Then we have:

[0300] (51)

[0301] (52)

[0302] (53)

[0303] Similarly, considering the influence of the sealing ring at the third chamfer R3, the wall thickness of each chamfer is:

[0304] (54)

[0305] (55)

[0306] (56)

[0307] Therefore, the minimum wall thickness at the first chamfer R1, the second chamfer R2, and the third chamfer R3 are as follows:

[0308] (57)

[0309] (58)

[0310] (59)

[0311] Based on the above, the design calculation of the minimum thickness of the single-layer socket is completed.

[0312] Embodiment 2

[0313] Different from the first embodiment, Figures 4 to 6 As shown, in this embodiment, the edge 22 is not formed by flanging the inner tube 2, but is made separately, and then welded with the inner sleeve 21 to form the inner tube 2, that is, the two ends of the inner sleeve 21 are respectively welded to the two edges 22. The edge 22 and the inner sleeve 21 are made of the same material, both of which are corrosion-resistant materials, preferably stainless steel.

[0314] In this embodiment, the length of the inner sleeve 21 is less than the sum of the length of the tube body 12 and the length of the socket 13 , and the welding points B (weld seams) between the two ends of the inner sleeve 21 and the two edges 22 are located on the inner wall of the tube.

[0315] like Figure 6 As shown, the edge 22 includes an edge pressing 221 and an edge flange 222 that are integrally connected. The edge pressing 221 can be regarded as a thin cylindrical shape, and the edge flange 222 is annular. The inner diameter of the edge flange 222 is equal to the inner diameter of the edge pressing 221, and the outer diameter of the edge flange 222 is greater than the outer diameter of the edge pressing 221. The edge pressing 221 and the edge flange 222 share a common center line. At one end of the socket 13, the edge flange 222 is located on the end surface of one end of the socket 13 and presses the sealing gasket 4 on the end surface of the socket 13, and the edge pressing 221 is located on the inner wall of one end of the pipe socket 13 and presses the sealing gasket 4 and / or the intermediate layer 3 on the inner wall of the socket 13. For one end of the socket 11, the edging flange 222 is located on the end surface of one end of the pipe body 12, pressing the sealing gasket 4 on the end surface of the pipe body 12, and the edging press 221 is located on the inner wall of one end of the pipe body 12, pressing the sealing gasket 4 and / or the middle layer 3 on the inner wall of the pipe body 12.

[0316] In this embodiment, the thickness of the edge 22 is greater than the thickness of the inner sleeve 21 .

[0317] In this embodiment, the length H of the hemming and pressing edge 221 is not less than 20 mm.

[0318] Based on the above structure, the manufacturing method of this embodiment is different from that of the first embodiment, and the manufacturing method includes the following steps.

[0319] Step S1: processing the inner wall and the outer wall of the outer tube 1, making the inner sleeve 21, making the edge 22, and making the intermediate layer 3.

[0320] The edge wrapping 22 is made by a rolling machine, and the edge wrapping 22 includes an edge wrapping pressing edge 221 and an edge wrapping flanging edge 222. The inner diameter of the edge wrapping 22 is substantially equal to the inner diameter of the inner sleeve 21, and the thickness of the edge wrapping 22 is greater than the thickness of the inner sleeve 21.

[0321] Step S2: Arrange the inner sleeve 21, the middle layer 3 and the outer tube 1 in sequence from the inside to the outside.

[0322] Step S3: Press the inner tube 2 and the middle layer 3 onto the outer tube 1 .

[0323] Step S4: insert the two edges 22 into one end of the socket 13 and one end of the pipe body 12 close to the socket 11 respectively, and weld the two ends of the inner sleeve 21 to the two edges 22 respectively.

[0324] In this embodiment, the calculation method of the thickness of the single-layer socket and the composite socket is the same as that of Embodiment 1. The thickness of the reinforcement ring of the composite socket obtained by calculation is the thickness of the inner sleeve 21.

[0325] 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 socket-and-spigot type multi-layer pipe with end-bagged edges, characterized in that: The pipe comprises an inner pipe (2), an intermediate layer (3) and an outer pipe (1); the intermediate layer (3) is made of a material having an insulating function; the inner pipe (2) is made of a material having a corrosion-resistant function; the outer pipe (1) comprises a socket (11), a pipe body (12) and a plug (13) which are connected in sequence; one end of the inner pipe (2) covers the end surface of the plug (13) and the other end covers the end surface of the pipe body (12); the inner pipe (2), the intermediate layer (3) and the outer pipe (1) are pressed together to form the pipe; The socket (11) is a single-layer socket, and the spigot (13) and the portion of the inner tube (2) covering the inner wall of the spigot (13) form a composite spigot. The design method of the composite socket thickness includes 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; 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 single-layer socket thickness includes 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 pipe according to claim 1, characterized in that: The inner tube (2) comprises an inner sleeve (21) and two edge covers (22), the inner sleeve (21) and the two edge covers (22) are an integral whole, and the inner sleeve (21), the middle layer (3) and the outer tube (1) are sleeved in sequence from the inside to the outside.

3. The pipe according to claim 2, characterized in that: The end surface of the plug (13) is covered by a sealing gasket (4), the end surface of the tube body (12) is covered by another sealing gasket (4), the edge (22) presses the sealing gasket (4), the sealing gasket (4) at one end of the plug (13) is pressed by one edge (22) and the upper end surface of the sealing gasket (4) does not exceed the upper end surface of the edge (22) after the cover, and the sealing gasket (4) at one end of the tube body (12) is pressed by another edge (22) and the upper end surface of the sealing gasket (4) does not exceed the upper end surface of the edge (22) after the cover.

4. The pipe according to claim 3, characterized in that: The two ends of the inner tube (2) are respectively flanged to form two edges (22) at the two ends, the inner sleeve (21) covers the inner wall of the tube body (12) and the inner wall of the plug (13), and the two edges (22) respectively press the sealing gasket (4) on the end surface of the plug (13) and the sealing gasket (4) on the end surface of the tube body (12); Alternatively, the length of the inner sleeve (21) is less than the sum of the length of the tube body (12) and the length of the socket (13), the inner sleeve (21) and the two edges (22) are welded, and the thickness of the edges (22) is greater than the thickness of the inner sleeve (21), in which case the edges (22) include an edge pressing edge (221) and an edge flange (222) that are integrally connected, and at one end of the socket (13), the edge flange (222) presses the sealing gasket (4) on the end surface of the socket (13), and the edge pressing edge (221) A sealing gasket (4) and / or an intermediate layer (3) is located on the inner wall of one end of the pipe socket (13) and is pressed against the inner wall of the socket (13); at one end of the socket (11), an edge wrapping flange (222) is pressed against the sealing gasket (4) on the end face of the pipe body (12); an edge wrapping flange (221) is located on the inner wall of one end of the pipe body (12) and is pressed against the sealing gasket (4) and / or the intermediate layer (3) on the inner wall of the pipe body (12); and the length of the edge wrapping flange (221) is not less than 20 mm.

5. The pipe according to claim 2, characterized in that: The material of the middle layer (3) is plastic, the material of the outer tube (1) is metal, the thickness of the middle layer (3) is not less than 0.2 mm, and the thickness of the inner sleeve (21) is not less than 0.1 mm.

6. The pipe 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.

7. The pipe 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.

8. The pipe according to claim 1, characterized in that: In step a1, 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, 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.

9. The pipe according to claim 8, 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: .

10. The pipe 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.

11. The pipe 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).

12. The pipe according to claim 11, 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.

13. The pipe according to claim 12, 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: .

14. The pipe according to claim 12, 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.

15. A method for manufacturing a multi-layered spigot-and-socket pipe with an end-bagged edge, used for manufacturing the multi-layered pipe according to any one of claims 2 to 5, characterized in that: The steps include: Step S1: processing the inner wall and the outer wall of the outer tube (1), manufacturing the inner tube (2), and manufacturing the intermediate layer (3); Step S2: arranging the inner tube (2), the middle layer (3) and the outer tube (1) in sequence from the inside to the outside; Step S3: pressing the inner tube (2) and the middle layer (3) onto the outer tube (1); Step S4: providing edging (22) at both ends of the inner tube (2) so that the edging (22) covers the end surface of one end of the socket (13) of the tube and the end surface of the tube body (12).

16. The manufacturing method according to claim 15, characterized in that: In step S3, the inner tube (2) is pressed tightly against the inner wall of the outer tube (1) by spin forming or hydraulic forming.

17. The manufacturing method according to claim 15, characterized in that: In step S1, the inner tube (2) can be manufactured as a whole, and then in step S4, both ends of the inner tube (2) are flanged to form the edging (22); or in step S1, the inner sleeve (21) and the edging (22) are manufactured separately, and then in step S4, the inner sleeve (21) and the edging (22) are welded together, and when the inner sleeve (21) and the edging (22) are welded, the welding point is located on the inner wall of the tube.

Images