A multi-layer composite pipe made of different materials and a manufacturing method thereof

Abstract

The present invention discloses a heterogeneous multilayer composite pipe and a manufacturing method thereof. The composite pipe comprises an inner pipe, a middle part and an outer pipe which are sleeved in sequence from the inside to the outside. The inner pipe is made of corrosion-resistant material. The middle part comprises a first adhesive layer, a transition layer and a second adhesive layer which are connected in sequence. The material of the first adhesive layer and the material of the second adhesive layer are hot melt adhesive. The manufacturing method comprises the following steps: S1: treating the inner wall and the outer wall of the outer pipe, making the inner pipe and the middle part; S2: arranging the inner pipe, the middle part and the outer pipe in sequence from the inside to the outside; S3: pressing the inner pipe and the middle part onto the outer pipe; S4: composite. The inner pipe of the present invention is lined with a corrosion-resistant material, which improves the internal corrosion resistance, sanitary performance, pipeline water delivery efficiency, and reduces the operating energy consumption. The middle part plays the role of insulation isolation and connection at the same time, preventing the outer pipe and the inner pipe from electrochemical corrosion and delamination. The minimum thickness of the composite socket of the socket-type pipe and the minimum thickness of the single-layer socket that meets the strength requirements can be obtained by theoretical calculation.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite pipes, and in particular relates to a heterogeneous material multilayer composite pipe and a manufacturing method thereof. Background Art

[0002] Composite pipe is a kind of pipe widely used in liquid transportation network system. When in use, the part of the pipe that contacts the liquid is required to have good corrosion resistance to prevent the pipe 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, or a metal pipe as the outer layer and a stainless steel pipe as the inner layer. When composite pipes with a plastic pipe as the inner layer are composited, the inner plastic pipe melts due to heat. When the temperature is too high, it is easy to produce an uneven inner surface or partial melting. The uneven inner surface will increase the resistance when transporting liquid. The partial melting of the inner plastic pipe will cause the product to be scrapped, and the production cost will increase. The inner plastic pipe has a large thermal expansion coefficient and shrinks greatly at low temperatures. The internal stress generated by mutual peeling with the outer metal pipe is large. There is a risk of lining delamination after long-term use. The composite pipe with a stainless steel pipe as the inner layer is prone to electrochemical corrosion due to the potential difference between the inner stainless steel pipe and the outer metal pipe, which affects the service life of the pipe. The inner lining stainless steel pipe and the outer metal pipe are not bonded, so the inner stainless steel pipe is prone to deformation and falling off under negative pressure, affecting the normal use of the pipe.

[0003] To solve the above problems, the current solution is to place glue or pure hot melt adhesive between the inner stainless steel tube and the outer metal tube. However, when glue is used as the middle part between the inner and outer layers, the glue is prone to aging. During bonding, due to the high fluidity of the glue, the inner stainless steel tube and the outer metal tube are easily in direct contact with each other, which cannot prevent electrochemical corrosion and negative pressure. If pure hot melt adhesive is used as the middle part, a certain thickness must be achieved to ensure the effect of preventing electrochemical corrosion. The hot melt adhesive in the middle part adopts the spraying / rotational molding technology solution, which has poor thickness uniformity and is difficult to guarantee quality. If the extrusion molding technology solution is used, the wall thickness is too thin and extrusion is difficult. If the thickness is too thick, the cost of hot melt adhesive materials is very high, resulting in high product production costs, which is not conducive to the market promotion of the product.

[0004] One end of the outer metal pipe is a spigot and the other end is a socket. During installation, multiple composite pipes are connected in sequence, and the spigot of one composite pipe is inserted into the socket of the adjacent composite pipe. 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 pipe must meet the specified strength requirements. Some existing standards (group standards and national standards) specify the nominal wall thickness under different pressure levels and different nominal diameters. Pipes that meet the standards can meet the strength requirements within the corresponding pressure level range. Therefore, the pipes produced by existing pipe manufacturers generally meet the requirements of the corresponding standards.

[0005] 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.

[0006] 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. Figure 8 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

[0007] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a heterogeneous multilayer composite pipe and a manufacturing method thereof, wherein the inner lining is an inner pipe made of corrosion-resistant metal material, which improves the internal corrosion resistance, sanitation, and water delivery efficiency of the pipe material, and reduces the operating energy consumption. The middle part is a composite layer formed by three layers, the transition layer is made of polyethylene, and the two sides are made of hot melt adhesive. Compared with the transition layer also using hot melt adhesive material, the production cost is reduced. The middle part also plays the role of insulation isolation and connection to prevent electrochemical corrosion of the outer pipe and the inner pipe. The middle part has a high bonding strength to prevent the inner pipe from being stratified and deformed under negative pressure. The middle part adheres the inner and outer layers together to prevent the stratification of the lining caused by negative pressure in the pipeline. The minimum or near minimum thickness of the composite socket that meets the deformation requirements of socket-type pipes of different pipe diameters and the minimum or near minimum thickness of the single-layer socket that meets the strength requirements can be obtained through theoretical analysis and calculation.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A multi-layer composite pipe of different materials comprises an inner pipe, a middle part and an outer pipe which are sleeved in sequence from the inside to the outside, the inner pipe and the outer pipe are connected through the middle part, the inner pipe is made of corrosion-resistant metal, and the middle part comprises a first bonding layer, a transition layer and a second bonding layer which are connected in sequence.

[0010] As a further improvement of the above technical solution:

[0011] Preferably, the material of the first adhesive layer and the material of the second adhesive layer are hot melt adhesives.

[0012] Preferably, the material of the transition layer is non-metal.

[0013] More preferably, the material of the transition layer is polyethylene.

[0014] Preferably, the outer tube is made of metal material.

[0015] More preferably, the outer tube is made of ductile iron or carbon steel.

[0016] Preferably, the outer tube comprises a socket, a tube body and a spigot which are integrally connected and coaxially arranged in sequence.

[0017] More preferably, the length of the middle portion is not less than the length of the tube body.

[0018] More preferably, the length of the inner tube is not less than the length of the tube body.

[0019] Preferably, the thickness of the inner tube is not less than 0.1 mm, the thickness of the first adhesive layer is not less than 0.1 mm, the thickness of the second adhesive layer is not less than 0.1 mm, and the total thickness of the middle portion is not less than 1.0 mm.

[0020] Preferably, the thickness of the first adhesive layer is 0.1 mm to 0.2 mm, and the thickness of the second adhesive layer is 0.1 mm to 0.5 mm.

[0021] A design method for the composite spigot and single-layer socket thickness of a socket-and-spigot type pipe is used to calculate the composite spigot thickness and / or single-layer socket thickness of the composite pipe. The socket is a single-layer socket, and the spigot and the portion of the inner pipe 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 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.

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

[0047] (2) Due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is,

[0048] ;

[0049] (3) Cutting near point A, removing point A and the acting force P, it can be seen from the symmetry and equilibrium conditions that the shear force on the cross section of the circular cut is , that is: ;

[0050] Combining the above three formulas with the general solution of the differential equation, we get the first form of the differential equation:

[0051] ;

[0052] 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:

[0053] ;

[0054] Introducing the coefficient m, we get the third form of the differential equation:

[0055] ;

[0056] Point of application of force P The point is the point of maximum deformation, and the change in the diameter of the ring is:

[0057] , where I = S 3 / 12, S is the wall thickness of the tube body.

[0058] 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.

[0059] 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.

[0060] 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 at the selected location, and α is the semi-cone angle of the cone at the selected location.

[0061] When the material of the single-layer socket is the same as that of the pipe body, the stress calculation formula is: .

[0062] 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.

[0063] A method for manufacturing a heterogeneous material multilayer composite pipe, used for manufacturing the composite pipe, comprises the following steps:

[0064] Step S1: processing the inner wall and the outer wall of the outer tube, making the inner tube, and making the middle part;

[0065] Step S2: Arrange the inner tube, the middle part and the outer tube in sequence from inside to outside;

[0066] Step S3: Press the inner tube and the middle part onto the outer tube;

[0067] Step S4: Compounding.

[0068] The beneficial effects of the present invention are:

[0069] (1) The inner lining is an inner pipe made of corrosion-resistant metal material. Compared with the plastic pipe lining, it improves the internal corrosion resistance and hygienic performance of the pipe, improves the flatness of the inner surface of the composite pipe, and has a small inner lining thickness, which can improve the water delivery efficiency of the pipeline and reduce operating energy consumption.

[0070] (2) The inner lining is made of corrosion-resistant metal. Compared with the plastic pipe lining, it greatly reduces the internal stress caused by the mutual peeling between the inner pipe and the outer pipe due to the inconsistency of the material expansion coefficient, and the inner lining is not prone to delamination and deformation.

[0071] (3) The inner tube made of corrosion-resistant metal is used as the inner lining. Compared with the plastic tube lining, the pipe can be used to transport high-temperature liquid media. When the pipe is affected by high temperature such as external fire, the inner lining will not be damaged.

[0072] (4) The middle part plays the role of insulation isolation and connection at the same time, preventing electrochemical corrosion of the outer pipe and the inner pipe. The middle part has a high bonding strength, preventing the inner pipe from delamination and deformation under negative pressure. The middle part bonds the inner and outer layers together, eliminating the delamination of the inner lining caused by negative pressure in the pipeline.

[0073] (5) The middle part is a composite layer formed by three layers, the transition layer is made of polyethylene, and the two sides are made of hot melt adhesive. Compared with the transition layer also using hot melt adhesive material, the production cost is reduced.

[0074] (6) The use of hot melt adhesive as the adhesive material overcomes the lining delamination phenomenon caused by the easy aging of ordinary glue and the uneven glue layer phenomenon caused by the high fluidity of ordinary liquid glue. It also solves the technical problems of low bonding strength, poor hygienic performance, poor insulation effect and uneven inner wall of the outer pipe resulting in the corrosion-resistant metal of the lining being suspended (i.e., there are areas in the inner pipe that are not connected to the outer pipe) caused by ordinary glue.

[0075] (7) 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

[0076] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0077] Figure 2 yes Figure 1 An enlarged schematic diagram of point A.

[0078] Figure 3 Schematic diagram of the cross-section deformation before and after the socket is subjected to a pair of radially symmetrical concentrated forces.

[0079] Figure 4 for Figure 3 Schematic diagram of local analysis.

[0080] Figure 5 Schematic diagram of a circular ring subjected to multiple uniformly arranged radial concentrated forces.

[0081] Figure 6 This is the stress analysis diagram of socket-type pipe.

[0082] Figure 7 The figure is a schematic cross-sectional view of a composite socket per unit length according to an embodiment of the present invention.

[0083] Figure 8 It is a schematic diagram of the socket and spigot connection of the present invention. DETAILED DESCRIPTION

[0084] 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.

[0085] 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.

[0086] A multi-layer composite pipe of different materials, such as Figure 1 and 2 As shown, it includes an inner tube 2, a middle part 3 and an outer tube 1 which are sleeved in sequence from the inside to the outside, and the inner tube 2 and the outer tube 1 are connected through the middle part 3.

[0087] The inner tube 2 is made of a corrosion-resistant material, including but not limited to stainless steel, titanium, and composite materials, preferably stainless steel. The outer tube 1 is made of metal, preferably ductile iron or carbon steel.

[0088] The middle part 3 comprises a first adhesive layer 31, a transition layer 32 and a second adhesive layer 33 which are connected in sequence. The first adhesive layer 31 and the second adhesive layer 33 are made of hot melt adhesive, and the transition layer 32 is made of non-metal, preferably polyethylene.

[0089] At least one group of intermediate parts 3 is provided. When one group of intermediate parts 3 is provided, the inner tube 2, the first adhesive layer 31, the transition layer 32, the second adhesive layer 33 and the outer tube 1 are sleeved in sequence from the inside to the outside. When more than one group of intermediate parts 3 is provided, the inner tube 2, each intermediate part 3 and the outer tube 1 are sleeved in sequence from the inside to the outside, and the first adhesive layer 31 of a group of intermediate parts 3 directly connected to the inner tube 2 contacts the outer wall of the inner tube 2, and the second adhesive layer 33 of a group of intermediate parts 3 directly connected to the outer tube 1 contacts the inner wall of the outer tube 1.

[0090] In this embodiment, the thickness of the inner tube 2 is not less than 0.1 mm, the thickness of the middle portion 3 is not less than 1 mm, and the thickness of the first adhesive layer 31 and the second adhesive layer 33 are not less than 0.1 mm respectively.

[0091] The main function of the inner tube 2 is corrosion resistance, so 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, when the inner tube 2 is made of stainless steel, a weld with high welding strength and small deformation can be obtained with a minimum wall thickness of 0.1mm. Taking into account the complexity and investment cost of the welding process equipment, as well as the fact that the middle part 3 shrinks at low temperatures due to its large thermal expansion coefficient, and generates internal stress that separates it from the outer tube 1, it is necessary to give full play to the supporting role of the inner tube 2 on the middle part 3 to offset the internal stress of the outer tube 1 and the middle part 3. The preferred thickness of the inner tube 2 is 0.1mm-2mm.

[0092] The middle part 3 is made by a three-layer co-extrusion molding process or three round tubes are made separately and then sleeved. When the tube is extruded, vacuum shaping is required. Since the temperature is high when the tube embryo enters the vacuum box after extrusion, the wall thickness of the tube is too small, and the vacuum easily sucks the tube wall apart. Only when the wall thickness reaches 1mm or more, stable production can be achieved. For the first adhesive layer 31 and the second adhesive layer 33, if the thickness is too small, poor adhesion is likely to occur in areas with large local roughness. The peel strength test shows that when the first adhesive layer 31 and the second adhesive layer 33 reach more than 0.1mm, a good peel strength can be stably obtained. Preferably, the thickness of the first adhesive layer 31 is 0.1mm-0.2mm, and the thickness of the second adhesive layer 33 is 0.1mm-0.5mm.

[0093] Compared with the thickness of the inner lining stainless steel required by the standard "Inner lining stainless steel composite steel pipe (CJ / T 192-2017)", when the middle part 3 uses hot melt adhesive, the inner lining stainless steel thickness is thinner and the cost is lower. When the inner diameter of the outer pipe 1 is the same, the inner diameter of the composite pipe is larger and the transportation efficiency is higher.

[0094] The conclusion of the lining peel strength test (this test uses an outer tube with an inner diameter of 100-300mm, an inner lining stainless steel thickness of 0.1mm-0.3mm, and only one group of middle part 3) is as follows:

[0095] When the rust removal level of the inner wall surface of the metal outer tube 1 reaches Sa2.5 and the surface roughness is Ra12.5~Ra25, and the thickness of the second adhesive layer 33 is not less than 0.1mm, the peel strength between the hot melt adhesive and the outer tube can stably reach more than 70N / cm; when the thickness of the first adhesive layer 31 is not less than 0.1mm, the peel strength between the hot melt adhesive and the inner lining can stably reach more than 150N / cm;

[0096] When the rust removal level of the inner wall surface of the metal outer tube 1 reaches Sa2.5 and the surface roughness is Ra25~Ra50, when the thickness of the second adhesive layer 33 is above 0.15mm, the peel strength between the hot melt adhesive and the outer tube can stably reach above 120N / cm; when the thickness of the first adhesive layer 31 is above 0.1mm, the peel strength between the hot melt adhesive and the inner lining can stably reach above 150N / cm;

[0097] When the rust removal level of the inner wall surface of the metal outer tube 1 reaches Sa2.5 and the surface roughness is greater than Ra50, and the thickness of the second adhesive layer 33 is above 0.2 mm, the peel strength between the hot melt adhesive and the outer tube can stably reach above 150 N / cm; when the thickness of the first adhesive layer 31 is above 0.1 mm, the peel strength between the hot melt adhesive and the inner lining can stably reach above 150 N / cm.

[0098] The peel strength between the hot melt adhesive and the lining of this solution can reach 150N / cm, and the corresponding bonding strength is 15MPa, that is, the lateral scouring force of liquid that the pipe of this solution can withstand is 15MPa, which is much greater than the maximum lateral scouring force of liquid in the existing pipe network system.

[0099] The thickness of the first adhesive layer 31 is preferably 0.1 mm to 0.2 mm, and the thickness of the second adhesive layer 33 is preferably 0.1 mm to 0.5 mm. When the thickness of the first adhesive layer 31 or the second adhesive layer 33 is greater than 0.5 mm, the peel strength remains substantially unchanged.

[0100] The outer tube 1 includes a socket 11, a tube body 12 and a spigot 13 which are integrally connected and coaxially arranged in sequence. The inner surface of the socket 11 is stepped, that is, the socket 11 can be regarded as a plurality of cylindrical structures with different inner diameters connected in sequence. The length of the middle part 3 is not less than the sum of the lengths of the tube body 12 and the spigot 13, so that the middle part 3 at least covers the inner walls of the tube body 12 and the spigot 13. The length of the inner tube 2 is also not less than the sum of the lengths of the tube body 12 and the spigot 13, so that the inner tube 2 at least covers the tube body 12 and the spigot 13.

[0101] The inner wall of the socket 11 can be coated with plastic and / or covered with stainless steel to isolate the socket 11 from the liquid in the pipe, and the stainless steel can be integrally connected to the inner pipe 2. Similarly, the end face of the pipe body 12 can be covered with stainless steel to isolate the end face of the outer pipe 1 from the liquid transported by the composite pipe.

[0102] The socket 11 is provided with a first step 111, a second step 112, a third step 113, a fourth step 114 and a fifth step 115 from the end away from the pipe body 12 to the end close to the pipe body 12. The inner diameter of the first step 111 is smaller than the inner diameter of the second step 112, the inner diameter of the third step 113 is larger than the inner diameter of the first step 111 and smaller than the inner diameter of the second step 112, and the inner diameter of the fourth step 114 is equal to or smaller than the inner diameter of the second step 112 and larger than the inner diameter of the third step 113. The inner wall of the fourth step 114 is the outer wall of a cylinder. The inner wall of the fifth step 115 is the outer side surface of a cylinder or a truncated cone. When it is the outer side surface of a truncated cone, the inner diameter of the fifth step 115 gradually increases from the fourth step 114 toward the pipe body 12, which is equivalent to a bell mouth. Preferably, the maximum inner diameter of the fifth step 115 is smaller than the inner diameter of the fourth step 114. The minimum inner diameter of the fifth step 115 is greater than the inner diameter of the tube body 12 . Thus, a sixth step 116 is formed at one end of the tube body 12 close to the fifth step 115 .

[0103] When two adjacent composite pipes are connected, the spigot 13 of one composite pipe is inserted into the adjacent socket 11, and a sealing ring is sleeved between the spigot 13 and the socket 11. The inner wall bell mouth of the fifth step 115 is set to provide a deflection angle for the adjacent composite pipe connected thereto, that is, to allow the center line of one composite pipe and the center line of the adjacent composite pipe connected thereto to be in an intersecting state, rather than a coincident state, in order to allow a certain installation angle deviation, to facilitate actual operation, and to allow a relative displacement of a certain angle of adjacent pipes when the soil moves naturally. There is a gap between the end face of one end of the spigot 13 of a composite pipe and the end face of the pipe body 12 of the adjacent composite pipe, and the existence of this gap is also to allow the existence of a deflection angle when two adjacent composite pipes are installed.

[0104] A method for manufacturing a heterogeneous material multilayer composite pipe, used for manufacturing the composite pipe, comprises the following steps:

[0105] Step S1: Process the inner wall and the outer wall of the outer tube 1, make the inner tube 2, and make the middle part 3.

[0106] 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 made of ductile iron, 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.

[0107] Making the inner tube 2 comprises the following steps:

[0108] 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.

[0109] 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.

[0110] When making the middle part 3, the hot melt adhesive and polyethylene are heated and extruded by a three-layer co-extrusion pipe extruder, vacuum sizing, pulling, and cutting to make a three-layer plastic composite pipe, wherein the three layers are a first adhesive layer 31 of hot melt adhesive material, a transition layer 32 of polyethylene material, and a second adhesive layer 33 of hot melt adhesive material. Furthermore, vacuum sizing, pulling, and cutting are achieved by a vacuum box, a pulling machine, and a cutting machine, respectively.

[0111] In this embodiment, the thickness of the middle portion 3 is not less than 1 mm, and the thickness of the first adhesive layer 31 and the second adhesive layer 33 is not less than 0.1 mm.

[0112] Obviously, the inner diameter of the middle portion 3 is slightly larger than the outer diameter of the inner tube 2 , and the outer diameter of the middle portion 3 is slightly smaller than the inner diameter of the outer tube 1 .

[0113] Step S2: Arrange the inner tube 2, the middle part 3 and the outer tube 1 in sequence from the inside to the outside.

[0114] In this step, the middle part 3 is first sleeved on the outer wall of the inner tube 2 by manual sleeve or sleeve machine, and then the sleeved middle part 3 and the inner tube 2 are sleeved into the outer tube 1 as a whole. In this step, the middle part 3 and the inner tube 2 can be sleeved as a whole by manual or sleeve machine.

[0115] Step S3: Press the inner tube 2 and the middle part 3 onto the outer tube 1 .

[0116] This step can be completed by spin forming or hydraulic forming. In spin forming, the inner tube 2 is spin formed by a pipe spinning machine, so that the inner tube 2, the middle part 3, and the outer tube 1 made of stainless steel are closely attached in sequence. In hydraulic forming, the two ends of the inner tube 2 made of stainless steel that penetrates the outer tube 1 are sealed, and water is injected into the tube to increase pressure, so that the inner tube 2, the middle part 3, and the outer tube 1 are closely attached in sequence.

[0117] Step S4: Compounding.

[0118] The pipe is heated by a medium frequency inductor or a heating furnace, the hot melt adhesive is melted, and after cooling, the outer pipe 1 and the inner pipe 2 are bonded together.

[0119] After compounding, the redundant parts at both ends of the inner tube 2 and the middle part 3 are removed by a trimming machine.

[0120] 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.

[0121] 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 hot melt adhesive, polyethylene, etc., which has little effect on the strength and deformation resistance of the socket 13, so it does not belong to the category of composite sockets that can resist deformation.

[0122] Next, the thickness of the spigot end and the socket end of the composite pipe is optimized and designed.

[0123] The design method of the thickness of the composite socket includes the following steps:

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] The following is a detailed introduction to each step.

[0130] In step a1, the radial deformation obtained The differential equation is:

[0131] (1)

[0132] in ，R is half of the sum of the outer radius and the inner radius of the ring. In other words, R One quarter of the sum of the outer and inner diameters of the ring 。E is the elastic modulus of the pipe, Pa. I is the moment of inertia of the tube cross section, m 4 . M It is the bending moment borne by a certain section of the ring in the local area, in N*m. Establish a two-dimensional coordinate system, The deformation is u The 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 3 Point m 1 The radial deformation at u， but om 1 and x The angle between the positive directions of the axes is 。

[0133] The above differential equation (1) is obtained as follows:

[0134] like Figure 3 and 4As 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 3 midpoint O Too xy Vertex of the coordinate system ， point m and n are two points on the ring before deformation; m 1 and n 1 are two points on the deformed shape of the ring, and the points m 1 and n 1 Located on the line segment om and on superior, The deformation is u The line connecting the point at and point O is x The angle between the positive directions of the axes, om and on The angle between ， set up u Centripetal movement is positive. Figure 4 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.

[0135] Arc before deformation mn The arc length is ds , whose curvature is k 1 , arc after deformation m 1n 1 The curvature is k 2 , du Yes m and Point n The difference in radial deformation is The arc before deformation mn exist m Tangent line of point and n The angle between the tangent lines of a point, The deformation amount is u The radius corresponding to the point at after deformation is, Is an arc mn Deform to Arc m 1 n 1 back ds The increment of The arc after deformation m 1 n 1 exist m 1 Tangent line of point and n 1 The angle between the tangent lines of the point is m 1 t 1 and The angle between , then:

[0136] (2)

[0137] (3)

[0138] (4)

[0139] (5)

[0140] m 1 t 1 and m 1 t The angle between , n 1 t 1 ’ and n 1 t’ The angle between .

[0141] m 1 section to n 1 The variable of the cross-section rotation is :

[0142] (6)

[0143] 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.

[0144] Substituting formula (5) and (6) into formula (4) yields:

[0145] (7)

[0146] By series expansion we have:

[0147] Ignoring the higher-order terms, substituting the series expansion into (7) yields: (8)

[0148] Substituting (2) into (8), we obtain: (9)

[0149] Omitting the higher-order terms, we can get: (10)

[0150] 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).

[0151] The general solution of the above differential equation (1) is:

[0152] (11)

[0153] 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:

[0154] (12)

[0155] 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:

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] In step a21, it is assumed that the ring is subjected to at least two radial concentrated forces P symmetrically relative to the center of the ring. The radial concentrated force P means that the direction of the force P is radial to the ring and points to the center of the ring, and the angle between two adjacent radial concentrated forces P is ,like Figure 5 shown. Figure 3 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.

[0161] The ring satisfies the following three boundary conditions:

[0162] (1) Because of symmetry, The rotation angle of the section at is 0, which satisfies the following formula:

[0163] (13)

[0164] (2) Due to symmetry, the total tangential displacement of the arc in each equally divided segment is 0; that is,

[0165] (14)

[0166] (3) Cutting near point A, removing point A and the acting force P, it can be seen from the symmetry and equilibrium conditions that the shear force on the cross section of the circular cut is , that is:

[0167] (15)

[0168] in, dM represents the differential with respect to M. It should be noted that point (3) is not a real cut of the ring, but an assumption.

[0169] Simultaneously formula (13), (14), (15), the solution is:

[0170] (16)

[0171] (17)

[0172] (18)

[0173] Substituting formulas (16), (17), and (18) into formula (12), we obtain:

[0174] (19)

[0175] Formula (19) is the first form of the differential equation obtained in step a21. is the radial deformation of the ring.

[0176] In step a22, if only one pair of radial forces P is applied to the ring, then , the deflection curve equation (19) becomes:

[0177] (20)

[0178] Formula (20) is the second form of the differential equation obtained in step a22.

[0179] 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:

[0180] (twenty one)

[0181] 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.

[0182] Formula (21) is the third form of the differential equation obtained in step a23.

[0183] 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 :

[0184] (twenty two)

[0185] Formula (22) is the third form of the differential equation obtained in step a24.

[0186] 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:

[0187] 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.

[0188] Step a32: Obtain the maximum deformation of the reference pipe socket through simulation based on the parameters calculated in step a31.

[0189] 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.

[0190] 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.

[0191] 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:

[0192] (twenty three)

[0193] like Figure 6 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); bThe 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).

[0194] 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.

[0195] In this embodiment, the parameters in formula (23) are M P and W The calculation process is as follows:

[0196]

[0197]

[0198] 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.

[0199] Step a31 is thus completed.

[0200] 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.

[0201] 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:

[0202] (twenty four)

[0203] From formula (24), we can see that u max The value is related to the pipe diameter and pipe thickness.

[0204] 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.

[0205] Table 1 Nominal wall thickness and absolute deformation of DN=600mm pipes at various nominal pressures.

[0206]

[0207] 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).

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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.

[0212] 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.

[0213] In this embodiment, the calculation formula for the bending strength of the longitudinal composite beam is as follows:

[0214] (25)

[0215] 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.

[0216] For example, in some occasions, the use requirement of the pipe is to meet the nominal pressure within 1.6MPa. The selected base pipe is the pipe No. 5 in Table 1, with a wall thickness of 4mm. The composite spigot includes the base pipe spigot and a layer of annular reinforcement ring (i.e., the part of the inner pipe 2 covering the spigot 13). The thickness of the reinforcement ring is x ,like Figure 7 The figure shows the cross section per unit length of the composite socket or composite beam, where the plane of the cross section passes through the central axis of the base pipe. The base pipe is made of Q235, and the reinforcing ring is made of 304 stainless steel. Figure 7 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): Ai =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:

[0217]

[0218] Find: x =1.73mm.

[0219] Therefore, the thickness of the reinforcing ring is not less than 1.73 mm. In this embodiment, the thickness of the inner tube 2 is 0.1 mm-2 mm, so the thickness of the reinforcing ring is 1.73-2 mm.

[0220] For another example, if the thickness of the inner tube 2 is known due to process or other requirements, the thickness of the original socket can be calculated using formula (25).

[0221] The above is the design method for the thickness of the composite socket.

[0222] The design method of the thickness of the single-layer socket is as follows:

[0223] 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 Figure 8As 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.

[0224] 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.

[0225] The design method of single-layer socket includes the following steps:

[0226] 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.

[0227] 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.

[0228] 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.

[0229] 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:

[0230] 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.

[0231] 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.

[0232] 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. Figure 8shown.

[0233] 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:

[0234] (26)

[0235] (27)

[0236] The hoop stress σ 环 That is, the circumferential stress, wherein 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.

[0237] 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:

[0238] (28)

[0239] (29)

[0240] in α It is the semi-cone angle of the conical pressure vessel, that is, half of the opening angle. In other words, in the section passing through the central axis of the cone, the angle between the cone wall and the central axis is the semi-cone angle. Wherein, the diameter D is half of the sum of the outer diameter and the inner diameter of the corresponding part of the cone, or the inner diameter of the corresponding part, or the outer diameter of the corresponding part.

[0241] 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 Figure 8 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. Figure 8The 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.

[0242] exist Figure 8 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.

[0243] but:

[0244] (30)

[0245] (31)

[0246] 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:

[0247] (32)

[0248] (33)

[0249] (34)

[0250] Then we have:

[0251] (35)

[0252] (36)

[0253] (37)

[0254] Among them, S1, S2, S3 are the wall thickness at the first chamfer R1, the second chamfer R2, and the third chamfer R3, respectively, and we get:

[0255] (38)

[0256] (39)

[0257] (40)

[0258] 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:

[0259] (41)

[0260] So we have:

[0261] (42)

[0262] (43)

[0263] (44)

[0264] Among them, S 1m , S 2m , S 3m They are the minimum wall thickness at the first chamfer R1, the second chamfer R2, and the third chamfer R3 respectively.

[0265] From above, Figure 8 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:

[0266] (45)

[0267] (46)

[0268] (47)

[0269] The following example is used to calculate the wall thickness parameters of a single-layer socket.

[0270] In this embodiment, the material of the pipe body and the single-layer socket is Q235.

[0271] 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:

[0272] Table 2 shows the socket size parameters for nominal pipe diameters of 600mm and 1200mm as specified in relevant standards.

[0273]

[0274] Based on this scheme, the wall thickness dimensions of the two single-layer sockets in Table 2 are calculated and shown in Table 3.

[0275] Table 3 Wall thickness, outer diameter and semi-cone angle dimensions of two single-layer sockets.

[0276]

[0277] 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.

[0278] 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:

[0279] (48)

[0280] (49)

[0281] (50)

[0282] 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.

[0283] Then we have:

[0284] (51)

[0285] (52)

[0286] (53)

[0287] Similarly, considering the influence of the sealing ring at the third chamfer R3, the wall thickness of each chamfer is:

[0288] (54)

[0289] (55)

[0290] (56)

[0291] Therefore, the minimum wall thickness at the first chamfer R1, the second chamfer R2, and the third chamfer R3 are as follows:

[0292] (57)

[0293] (58)

[0294] (59)

[0295] Based on the above, the design calculation of the minimum thickness of the single-layer socket is completed.

[0296] 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 multi-layer composite pipe made of different materials, characterized in that: The composite pipe comprises an inner pipe (2), an intermediate portion (3) and an outer pipe (1) which are sleeved in sequence from the inside to the outside, the inner pipe (2) and the outer pipe (1) being connected via the intermediate portion (3), the inner pipe (2) being made of corrosion-resistant metal, and the intermediate portion (3) comprising a first adhesive layer (31), a transition layer (32) and a second adhesive layer (33) which are connected in sequence; 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 composite pipe according to claim 1, characterized in that: The material of the first adhesive layer (31) and the material of the second adhesive layer (33) are hot melt adhesive.

3. The composite pipe according to claim 1, characterized in that: The material of the transition layer (32) is non-metallic, and the material of the outer tube (1) is metal.

4. The composite pipe according to claim 3, characterized in that: The material of the transition layer (32) is polyethylene, and the material of the outer tube (1) is ductile iron or carbon steel.

5. The composite pipe according to claim 1, characterized in that: The outer tube (1) comprises a socket (11), a tube body (12) and a spigot (13) which are integrally connected and coaxially arranged in sequence.

6. The composite pipe according to claim 5, characterized in that: The length of the middle portion (3) is not less than the sum of the lengths of the tube body (12) and the socket (13), and the length of the inner tube (2) is not less than the sum of the lengths of the tube body (12) and the socket (13).

7. The composite pipe according to any one of claims 2 to 4, characterized in that: The thickness of the inner tube (2) is not less than 0.1 mm, the thickness of the first adhesive layer (31) is not less than 0.1 mm, the thickness of the second adhesive layer (33) is not less than 0.1 mm, and the total thickness of the middle part (3) is not less than 1.0 mm.

8. The composite pipe according to claim 7, characterized in that: The thickness of the first adhesive layer (31) is 0.1 mm to 0.2 mm, and the thickness of the second adhesive layer (33) is 0.1 mm to 0.5 mm.

9. The composite 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.

10. The composite 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.

11. The composite pipe according to claim 9 or 10, characterized in that: In step a1, the radial deformation obtained is u The differential equation is: , The general solution is: , in, R is the average value of the outer circle radius and the inner circle radius of the ring; E is the elastic modulus of the pipe, Pa; I is the moment of inertia of the tube cross section, m 4 ; M is the bending moment borne by a certain section of the ring in the local area, in units of N*m; establish a two-dimensional coordinate system, φ The deformation is u The line connecting the point at and the origin of the coordinate system is the same as the line connecting the point at and the origin of the coordinate system in the two-dimensional coordinate system. x The angle between the positive directions of the axes, ; A1, A2, A3, B2, B3 are constants.

12. The composite pipe according to claim 11, 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: .

13. The composite 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.

14. The composite tube 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).

15. The composite pipe according to claim 14, 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 at the selected location, and α is the semi-cone angle of the cone at the selected location.

16. The composite pipe according to claim 15, 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: .

17. The composite tube according to claim 15, 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.

18. A method for manufacturing a multi-layer composite pipe of different materials, used for manufacturing the composite pipe according to any one of claims 1 to 6, 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 middle part (3); Step S2: arranging the inner tube (2), the middle part (3) and the outer tube (1) in sequence from the inside to the outside; Step S3: pressing the inner tube (2) and the middle part (3) onto the outer tube (1); Step S4: Compounding.

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