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

Abstract

The present invention discloses a design method for the thickness of a composite socket of a socket-and-spigot pipe. For the multilayer structure in the composite socket, the outermost layer of the composite socket is assumed to be a base layer, and the other layers are non-base layers. The design method includes the following steps: a1: based on the same strain of each layer of the composite socket, the calculation formula for the hoop stress of any non-base layer is obtained according to the equilibrium equation of non-single-layer materials; a2: determining the relationship between the thickness of any non-base layer and the thickness of the base layer, the principle being that the ratio of the stress of the non-base layer to the yield strength of the material of the layer is not greater than the ratio of the stress of the inner wall of the pipe body to the yield strength of the material of the pipe body; a3: calculating the thickness of the non-base layer and / or the base layer. The present invention can obtain the key dimensions of the multilayer structure part and the single-layer structure part of the composite socket respectively through theoretical analysis and calculation, thereby ensuring that the entire composite socket meets the strength requirements; the thickness of the processed composite socket is minimum or close to minimum, with low cost and high efficiency.

Description

Technical Field

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

[0002] Most of the water pipes in the water supply and drainage systems for life and production are socket-and-spigot pipes, with a socket at one end and a spigot at the other. During installation, the spigot of one pipe is inserted into the socket of another pipe and sealed with a seal, thus achieving the connection of each pipe in the pipe network. Figure 2 In the figure, M is the spigot and F is the socket. The socket F is shaped like a trumpet and has different outer diameters. In order to save materials and reduce the production, manufacturing and transportation costs of pipes, it is best to make the thickness of the socket F minimum or close to the minimum while meeting the use strength.

[0003] At present, the material of the socket F of the general base pipe is only one, such as ductile iron or Q235 steel, and this socket F is a single-layer socket. However, in order to improve the performance of the pipe, the socket F can be made into a composite socket, that is, a structure including at least two coaxial layers of different materials that are sequentially sleeved from the inside to the outside, such as an inner layer of stainless steel and an outer layer of Q235 steel, which can save costs and improve the corrosion resistance of the pipe. Similarly, if the composite socket can meet the strength requirements and the thickness is minimum or close to minimum, the cost can also be greatly reduced. For the composite socket, the inner wall of the base pipe socket F can be completely covered by the liner or not completely covered by the liner. When the inner wall of the base pipe socket F is not completely covered by the liner, the composite socket includes a single-layer structure and a multi-layer structure part, the single-layer structure is a part that is not covered by the liner, and has only one layer, that is, the outermost base pipe, and the multi-layer structure includes at least two layers, that is, the outermost base pipe and each liner sleeved in the base pipe.

[0004] In addition, for the single-layer socket F, in order to improve its corrosion resistance, the secondary processing manufacturer or user will generally insert a liner ring made of corrosion-resistant material into the socket F. Obviously, the liner ring can also be used as a reinforcement ring. At this time, the liner ring and the socket F of the base pipe form a composite socket.

[0005] In summary, it is necessary to design the minimum thickness of the composite socket. Summary of the invention

[0006] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a design method for the thickness of the composite socket of a socket-type pipe. The key dimensions of the multi-layer structure part and the single-layer structure part of the composite socket can be obtained respectively through theoretical analysis and calculation, thereby ensuring that the entire composite socket meets the strength requirements; the thickness of the processed composite socket is minimum or close to minimum, which saves materials and reduces the production, manufacturing and transportation costs of the pipe. The above-mentioned design method is a theoretical calculation with low cost and high efficiency, and provides strong support for experiments and pipe design.

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

[0008] A method for designing the thickness of a composite socket of a socket-and-spigot pipe, assuming that the outermost layer of the composite socket is a base layer and the other layers are non-base layers, for a multi-layer structure in the composite socket, the design method comprises the following steps:

[0009] Step a1: Based on the same strain of each layer of the composite socket, the calculation formula of the hoop stress of any non-base layer is obtained according to the non-single-layer material equilibrium equation;

[0010] Step a2: Determine the relationship between the thickness of any non-base layer and the thickness of the base layer, and the determination principle is: the ratio of the stress of the non-base layer to the yield strength of the material of the layer is not greater than the ratio of the stress of the inner wall of the pipe body to the yield strength of the material of the pipe body;

[0011] Step a3: Calculate the thickness of the non-base layer and / or base layer according to the relationship determined in step a2.

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

[0013] For the same base pipe, along the direction from the socket to the spigot, the inner wall of the 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.

[0014] In step a1, the multilayer structure is regarded as a structure including at least one pressure vessel with a conical inner wall and at least one annular reinforcement ring installed on the inner wall of the pressure vessel.

[0015] In step a1, the first cone is a pressure vessel whose inner wall is a conical surface, and the first chamfer and the second chamfer are located on the inner wall of the first cone.

[0016] In step a1, assuming that there are m layers of non-base layer and one base layer, the equilibrium equation of the multilayer structure is:

[0017] ;

[0018] in, p is the internal pressure of the conical container, D is the diameter of the conical container to be calculated, is the cone height, S1, S2, …, S m are the thickness of each non-base layer, S bis the thickness of the base layer, , , …, are the hoop stresses of each non-base layer, is the hoop stress of the base layer, α is the half cone angle of a conical container.

[0019] In step a1, the strain of the base layer and the strain of each non-base layer Same, satisfying: ,Right now , where E1, E2, …, E m are the elastic modulus of each non-base layer, E b is the elastic modulus of the base layer. Combined with the equilibrium equation, the calculation formula for the hoop stress of the nth non-base layer is: ,in, is the hoop stress of the nth non-base layer, n is 1~m, E n is the elastic modulus of the nth non-base layer.

[0020] In step a2, in order to make the composite socket meet the strength requirements, the internal stress of the nth non-base layer F and the inner wall stress of the pipe body meet the following conditions: , , where Q0, Q n are the yield strengths of the pipe body and the nth non-base layer material respectively; is the hoop stress of the pipe body, S is the thickness of the pipe body, D0 is the outer diameter of the pipe body, and p is the pressure given by the fluid in the pipe. The calculation formula for the hoop stress of the nth non-base layer is combined to obtain the relationship between the thickness of the nth non-base layer and the thickness of the base layer: .

[0021] When the thickness of the base layer corresponding to the maximum stress is known, the minimum thickness of the layer with the minimum yield stress is calculated based on the relationship between the thickness of the nth non-base layer and the thickness of the base layer. This layer is set as the minimum stress layer, and the thickness of other non-base layers is set to be no less than the minimum thickness of the minimum stress layer.

[0022] When the thickness of the non-base layer is known, first, select at least one point where the stress of the base layer is likely to concentrate. The selection principle is: after the strength of each selected point meets the requirements, the strength of other places of the base layer designed according to the outer wall design requirements also meets the requirements; then calculate the thickness of each selected point based on the relationship between the thickness of the nth layer of non-base layer and the thickness of the base layer.

[0023] For the single-layer structure part in the composite socket, the design method includes the following steps:

[0024] Step b1: selecting at least one location where stress of the single-layer structure is likely to be concentrated, and the selection principle is: if the wall thickness of each location selected meets the stress strength requirement, then the wall thickness of each location of the single-layer structure designed according to the outer wall design requirement meets the strength requirement;

[0025] Step b2: Determine the minimum wall thickness of each selected location in step b1, and the determination principle is: when the material of the single-layer structure 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 structure 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 structure 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.

[0026] In step b1, the socket is regarded as a structure including at least one pressure vessel with a conical inner wall and at least one annular reinforcement ring installed on the inner wall of the pressure vessel. The selected stress concentration point is located on the inner wall of the pressure vessel. In step b2, the minimum wall thickness of each selected point in step b1 is calculated using the annular stress calculation formula for a conical pressure vessel.

[0027] In step b1, the stress concentration point of the single-layer structure is the third chamfer. The second cone is taken for analysis. The first chamfer and the third chamfer are located on the inner wall of the second cone.

[0028] The beneficial effects of the present invention are:

[0029] (1) The key dimensions of the multi-layer structure and single-layer structure of the composite socket can be obtained through theoretical analysis and calculation, thereby ensuring that the entire composite socket meets the strength requirements;

[0030] (2) For the multi-layer structure of the composite socket, the relationship between the thickness of any non-base layer and the thickness of the base layer is obtained through theoretical analysis and calculation, and the thickness of the base layer and / or non-base layer is calculated based on this relationship. When the thickness of the base layer corresponding to the maximum stress point is known, the minimum thickness of the layer with the minimum yield stress is calculated based on the above thickness relationship, and this layer is set as the minimum stress layer. The thickness of other non-base layers is set to be not less than the minimum thickness of the minimum stress layer. The thickness of at least one other stress concentration point of the base layer can be calculated by giving or using the above thickness relationship. After the thickness of the key points of the base layer is determined, the entire thickness of the base layer can be determined. When the thickness of the non-base layer is known, first select at least one point where the stress of the base layer is likely to concentrate, and then calculate the thickness of the base layer at each selected point based on the above thickness relationship. After the thickness of the key points is determined, the thickness of the base layer at the designed location according to the pipe wall design requirements meets the strength requirements.

[0031] (3) For the single-layer structure of the composite socket, determine the minimum wall thickness at the point where stress is likely to concentrate. The thickness of other parts should not be less than this thickness to ensure that the single-layer structure meets the strength requirements;

[0032] (4) The thickness of the processed composite socket is the smallest or close to the smallest, which saves materials and reduces the production, manufacturing and transportation costs of pipes. The above design method is a theoretical calculation with low cost and high efficiency, which provides strong support for experiments and pipe design. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of a composite socket in which the inner wall of the base pipe socket is not completely covered by the liner of the present invention;

[0034] Figure 2 This is a schematic diagram of the socket and the spigot connection of the present invention;

[0035] Figure 3 It is a schematic diagram of a composite socket in which the inner wall of the base pipe socket is completely covered by the liner according to the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] A design method for the composite socket thickness of a socket-and-spigot pipe, wherein the inner wall shape of the pipe socket F is in accordance with the inner wall shape specified in the group standard "Socket-and-spigot Flexible Joint Anti-corrosion Steel Pipe for Water Supply and Drainage" (T / CISA 108-2021) and GB / T 13295-2008, such as Figure 2As shown. The inner wall of the socket F is stepped. For the same base pipe, along the direction from the socket F to the spigot M, the inner wall of the socket F includes the first step 1, the second step 2, the third step 3, the fourth step 4, and the fifth step 5 arranged in sequence. One end of the inner wall of the pipe body is the sixth step 6, and the corresponding inner diameters are: D2, D1, (D3-2F0), D3, D4, (D0-2S), among which the inner diameters of the sixth step 6, the first step 1, the fifth step 5, the third step 3, the fourth step 4, and the second step 2 increase in sequence, that is: (D0-2S) < D2 < D4 < (D3-2F0) < D3 < D1. The lengths of the first step 1, the second step 2, the third step 3, the fourth step 4, and the fifth step 5 are respectively: T3, T4, T5, (T2-T4-T5), (T1-T2-T3), that is, T1 is the sum of the lengths of the first step 1, the second step 2, the third step 3, the fourth step 4, and the fifth step 5, and T2 is the sum of the lengths of the second step 2, the third step 3, and the fourth step 4. 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 3 protruding from the fourth step 4, and F0 ≥ 0. The connection of each step is processed with chamfers, wherein the chamfer at the connection of the fourth step 4 and the fifth step 5 is the first chamfer R1, the chamfer at the connection of the fifth step 5 and the sixth step 6 is the second chamfer R2, the chamfer at the connection of the second step 2 and the third step 3 is the third chamfer R3, the chamfer at the connection of the first step 1 and the second step 2 is the fourth chamfer R4, and the chamfer at the connection of the third step 3 and the fourth step 4 is the fifth chamfer R5. Wherein, D0 is the outer diameter of the base pipe of the pipe. The base pipe refers to the pipe in the factory setting, and the base pipe is not installed with a reinforcement ring, and no secondary processing such as a composite process is performed. The base pipe includes a socket F, a pipe body and a socket M connected in sequence. The pipe body can be divided into two parts, namely a main body and a transition part, and the transition part is used for the transition connection between the main body and the socket F, that is, the socket F, the transition part, the main body and the socket M 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 of the transition part is a conical surface. In other words, the thickness of the main body is uniform or substantially uniform, and the thickness of the transition part gradually decreases along the direction from the socket F to the spigot M. The outer diameter of the pipe body refers to the outer diameter of the main body, the outer diameter of the base pipe is the outer diameter of the pipe body, and the thickness of the pipe body refers to the thickness of the main body. Figure 2 In the figure, X is the length of the end chamfer of the socket M along the axial direction, Y is the height of the end chamfer of the socket M (ie, the radial dimension), DE is the outer diameter of the socket M, and T6 is the length of the socket M.

[0039] The above inner wall shape and size are generally for single-layer socket. The size and shape of the inner wall of the composite socket can also be designed according to the above single-layer socket. In this solution, the size and shape of the inner wall of the composite socket are also designed according to the above single-layer socket.

[0040] Assume that the outermost layer of the composite socket is the base layer F1, and the other layers are the non-base layer F2. The thickness of the base layer F1 is uneven, and the thickness of the non-base layer F2 is uniform. In other words, the thickness of the base layer F1 is different or not completely the same at different places, and the thickness of the non-base layer F2 is the same at different places.

[0041] For the composite socket, since the dimensions of the inner wall are fully given by the relevant standards, it is necessary to design some key dimensions of the outer wall and the thickness of each non-base layer F2 on this basis, in order to save material costs and meet strength requirements. In other words, the purpose of this scheme is to design the thickness of the composite socket so that it is the minimum or close to the minimum thickness while meeting the use strength, so as to reduce the production, manufacturing and transportation costs of the pipe.

[0042] According to material mechanics knowledge and experience, the most likely places for stress concentration on the inner wall of the above-mentioned single-layer socket or composite socket are the first chamfer R1, the second chamfer R2 and the third chamfer R3. The analysis is as follows:

[0043] For the inner wall of the stepped socket F, according to mechanical knowledge, the stress concentration point is located at the connection between adjacent steps, that is, at each chamfer. Since the socket F is a trumpet-like shape, the outer diameter of the socket F tends to decrease from the socket F to the spigot M of the same base pipe.

[0044] Based on the above conditions, 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 socket F is shaped like a trumpet. Therefore, 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 socket F 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 places where stress is most likely to concentrate are the first chamfer R1, the second chamfer R2, and the third chamfer R3. Similarly, for the socket of a single-layer structure, as long as the thickness of the first chamfer R1, the second chamfer R2, and the third chamfer R3 meet the strength requirements, the base pipe socket manufactured according to the above requirements must also meet the strength requirements.

[0045] In the case where the inner wall of the base pipe socket F is not completely covered by the lining, since the third step 3 is the installation location of the sealing ring Z, the coverage range of the non-base layer F2 is generally from the fourth step 4 to the sixth step 6. Figure 1As shown. At this time, along the axial direction of the socket, one part is a single-layer structure, that is, there is no non-base layer F2 but only the base layer F1. In this solution, the first step 1, the second step 2, and the third step 3 are located in the single-layer structure part; the other part is a multi-layer structure, that is, there is a non-base layer F2 and a base layer F1. In this solution, the fourth step 4 and the fifth step 5 are located in the multi-layer structure part. At this time, if both the single-layer structure part and the multi-layer structure part meet the strength requirements, the entire composite socket meets the strength requirements.

[0046] For a single-layer structure, it is only necessary to ensure that the strength requirement is met at the point where the stress is maximum, and then the entire single-layer structure will meet the strength requirement.

[0047] For a single-layer structure of a composite socket, the design method comprises the following steps:

[0048] Step b1: Select at least one location where stress is likely to be concentrated in the single-layer structure. The selection principle is: if the wall thickness at each location meets the stress strength requirement, then the wall thickness at each location of the single-layer structure meets the strength requirement.

[0049] Step b2: Determine the minimum wall thickness of each selected location in step b1, and the determination principle is: when the material of the single-layer structure 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 structure 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 structure 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.

[0050] In step b1, it can be seen from the above that the stress of the single-layer structure is most concentrated at the third chamfer R3, and the socket F is a trumpet-shaped structure. As long as the thickness of the third chamfer R3 meets the strength requirement, the entire single-layer structure meets the strength requirement.

[0051] For a thin-walled cylindrical pressure vessel, when the wall thickness is S, the internal pressure is p, and the diameter is D (the diameter D can be 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), the hoop stress of the container wall is for:

[0052] (0)

[0053] For a thin-walled conical pressure vessel, when the wall thickness is S, the internal pressure is p, and the diameter is D (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), the hoop stress of the container wall is for:

[0054] (1)

[0055] in, αis the semi-cone angle of the conical shell, 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. In step b1, the base layer F1 is regarded as consisting of at least one pressure vessel with a conical inner wall plus several internal reinforcement rings j, and the reinforcement rings are connected to the inner wall of the pressure vessel. In other words, the base layer F1 is regarded as consisting of at least one conical pressure vessel plus several internal reinforcement rings j. At this time, as long as the corresponding conical pressure vessel meets the strength requirements, the base layer F1 will definitely meet the strength requirements. Therefore, it is sufficient to ensure that the conical pressure vessel meets the strength requirements.

[0056] In step b1, take the second cone and the reinforcement ring on the inner wall of the second cone, such as Figure 2 The dotted line between the first chamfer R1 and the third chamfer R3 is the inner wall section of the second cone. The first chamfer R1 and the third chamfer R3 are located on the inner wall of the second cone. 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 socket F 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 socket F is the annular reinforcement ring on the inner wall of the second cone.

[0057] exist Figure 2 In the cross section shown, 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 half cone angle of the second cone, which is set to α2.

[0058] but:

[0059] (2)

[0060] In step b2, if the material of the base layer F1 is consistent with the material of the pipe body, the pipe body meets the strength requirements. To make the single-layer structure meet the strength requirements, the hoop stress at the third chamfer R3 Not greater than the hoop stress of the pipe body , that is:

[0061] (3)

[0062] Then we have:

[0063] (4)

[0064] Among them, S b3 is the wall thickness of the base F1 at the third chamfer R3, S is the wall thickness of the tube body, and we get:

[0065] (5)

[0066] 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 socket F 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 socket F is generally 1.4 times the fluid pressure. From formula (1), it can be obtained 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 (5) is corrected to:

[0067] (6)

[0068] That is, the minimum wall thickness at the third chamfer R3 is: .

[0069] If the material of the base F1 is different from that of the pipe body, let the yield strength of the pipe body material be Q0, and the yield strength of the material used for the base F1 be Q1. Similarly, in order for the single-layer structure to meet the strength requirements, the stress at the third chamfer R3 and the stress on the inner wall of the pipe body should satisfy:

[0070] (7)

[0071] Then we have:

[0072] (8)

[0073] Considering the pressure of the sealing ring, the wall thickness at the third chamfer R3 is:

[0074] (9)

[0075] After the wall thickness at the third chamfer R3 is determined as above, the single-layer structure manufactured according to the above requirements meets the strength requirements.

[0076] For a multi-layer structure of a composite socket, the design method comprises the following steps:

[0077] Step a1: Based on the same strain of each layer of the composite socket and the non-single-layer material equilibrium equation, the calculation formula for the hoop stress of any non-base layer F2 is obtained.

[0078] Step a2: Determine the relationship between the thickness of any non-base layer F2 and the thickness of the base layer F1. The determination principle is that the ratio of the stress of the non-base layer F2 to the yield strength of the material of the layer 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.

[0079] Step a3: Calculate the thickness of the non-base layer and / or base layer according to the relationship determined in step a2.

[0080] In step a1, for the multilayer structure, the multilayer structure is regarded as being composed of at least one pressure vessel with a conical inner wall and several internal reinforcement rings j, and the reinforcement rings are connected to the inner wall of the pressure vessel. In other words, the multilayer structure is regarded as being composed of at least one conical pressure vessel and several internal reinforcement rings j. At this time, as long as the corresponding conical pressure vessel meets the strength requirements, the multilayer structure will definitely meet the strength requirements. Therefore, it is sufficient to ensure that the conical pressure vessel meets the strength requirements.

[0081] In this solution, for the multilayer structure, the two places where the stress is most concentrated are the first chamfer R1 and the second chamfer R2. Figure 1 As shown. Therefore, the selected analysis area includes a conical pressure vessel plus an internal reinforcement ring. The conical pressure vessel is the first cone, and the second cone and the first cone are two coaxially connected conical pressure vessels, which share the same central axis with the socket F. Figure 1 and 2 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 second chamfer R2 are located on the inner wall of the first cone, the portion between the inner wall of the first cone and the outer wall of the socket F 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 socket F (the innermost non-base layer F2) is an annular reinforcement ring j.

[0082] For the socket F, the maximum load it bears is the tensile stress in the circumferential direction. The annular equilibrium equation for the thin-walled internal pressure conical shell is as follows:

[0083] (10)

[0084] in, p is the internal pressure of the conical shell, D is the diameter of the conical shell to be calculated, is the cone height, S is the side wall thickness of the conical shell to be calculated, is the hoop stress of the conical shell, α is the semi-cone angle of the conical shell.

[0085] For a composite socket, assuming there are m layers of non-base layer F2 and one layer of base layer F1, then:

[0086] (11)

[0087] Among them, S1, S2, …, S m are the thickness of each non-base layer F2, S b is the thickness of the base layer F1, , , …, are the hoop stresses of each non-base layer, is the hoop stress of the base layer F1.

[0088] Since it is a thin-walled container, the hoop tensile stress of the composite socket can be regarded as the tensile stress of the composite beam, that is, the strain of the base F1 The strain is the same as that of each non-base layer F2, that is, it satisfies:

[0089] (12)

[0090] Right now:

[0091] (13)

[0092] Among them, E1, E2, …, E m are the elastic modulus of each non-base layer F2, E b is the elastic modulus of the base layer F1.

[0093] The stresses in formula (11) are To express, is the hoop stress of the nth non-base layer F2, where n is 1~m, then E n is the elastic modulus of the nth non-base layer F2, S n is the thickness of the nth non-base layer F2. Based on formula (13), (11) is rearranged to obtain:

[0094] (14)

[0095] Formula (14) can be rearranged to obtain the hoop stress of the nth non-base layer F2:

[0096] (15)

[0097] Step a1 is thus completed.

[0098] In step a2, in order to make the composite socket meet the strength requirements, the internal stress of the nth non-base layer F2 and the inner wall stress of the pipe body meet the following conditions:

[0099] (16)

[0100] (17)

[0101] Among them, Q0, Q n are the yield strengths of the pipe body and the nth non-base layer F2, respectively. The yield strength of the base layer F1 is Q b ;in is the hoop stress of the pipe body, S is the thickness of the pipe body, D0 is the outer diameter of the pipe body, and p is the pressure given by the fluid in the pipe.

[0102] Combining formulas (15), (16), and (17), we get:

[0103] (18)

[0104] Formula (18) is the relationship between the thickness of any non-base layer F2 and the thickness of the base layer F1.

[0105] Based on formula (18), the thickness of the non-base layer F2 can be calculated when the thickness of the base layer F1 is known, and the thickness of the base layer F1 can be calculated when the thickness of the non-base layer F2 is known. Two embodiments are used to illustrate this.

[0106] Embodiment 1

[0107] In this embodiment, there is no limit on the thickness of the non-base layer F2. For a multi-layer structure, it is only necessary to ensure that the layer with the smallest yield stress meets the strength requirement, and this layer is set as the minimum stress layer, and the thickness of other layers is not less than the thickness of the minimum stress layer, then the entire multi-layer structure meets the strength requirement.

[0108] The yield stress of the base layer F1 is generally greater than the yield stress of the non-base layer F2, so the layer with the weakest yield stress is the non-base layer. Assuming that the yield stress of the nth layer of non-base layer F2 is the weakest, if yielding occurs, the nth layer should yield first. Based on this, if the thickness of the nth layer of non-base layer F2 meets the strength requirements, the minimum thickness of the base layer F1 and the thickness of other non-base layers F2 are not less than the thickness of the nth layer of non-base layer F2, then the strength of the base layer F1 and other non-base layers F2 will also meet the requirements. In addition, the thickness of the base layer F1 is generally greater than the thickness of the non-base layer. Therefore, it is necessary to calculate the thickness of the nth layer of non-base layer F2. Formula (16) is rewritten as:

[0109] (19)

[0110] in, is the maximum stress inside the nth non-base layer F2, that is From formula (15), we can see that in the analysis area, i.e., the first cone, Take the maximum value, then D takes the maximum value, and the thickness of other non-base layers F2 takes the minimum value, that is, The maximum point is located at the first chamfer R1, the maximum value of D in the first cone is D3, the thickness of other non-base layers F2 is not less than the thickness of the nth non-base layer F2, that is, the thickness of the non-base layer F2 is Sn, and the half cone angle is α 1. In Figure 1 and 2 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 pipe is the semi-cone angle of the first conical pressure vessel, that is:

[0111] (20)

[0112] Substituting formula (17) and (20) into formula (19), we can obtain:

[0113] (twenty one)

[0114] From formula (21), we get:

[0115] (twenty two)

[0116] In this embodiment, S b Take the thickness of the base layer F1 at the first chamfer R1.

[0117] From the above, the number of layers m of the non-base layer F2 and the material of each layer are known, the material, thickness, diameter and other dimensions of the pipe body are also known, so the yield strength and elastic modulus of each layer are also known, and the internal shape and size of the socket F are in accordance with relevant standards. Therefore, the semi-cone angle α 1 is also known. In other words, in formula (22), only S n and S b Two unknowns. The thickness S of the base layer F1 at the first chamfer R1 is given according to experience or other requirements. b (i.e. S b1 ) can be obtained S n The minimum value of .

[0118] Therefore, according to formula (22), the minimum thickness of the non-base layer F2 with the smallest yield stress can be obtained, and the thickness of other non-base layers F2 should not be less than this value.

[0119] For the base layer F1, the thickness S of the base layer F1 at the first chamfer R1 is b1 It is given that the thickness S of the base layer F1 at the third chamfer R3 b3 It has also been calculated by formula (9), so we only need to give or calculate the thickness S of the base layer F1 at the second chamfer R2: b2 The thickness of the base layer F1 at each location can be determined to ensure that the multi-layer structure of the composite socket meets the strength requirements.

[0120] For the thickness S of the base layer F1 at the second chamfer R2 b2 , can be given directly, or can be set to the thickness S of the base layer F1 at the first chamfer R1 b1 Equal, can also be obtained by using formula (18), specifically, formula (18) is rewritten as:

[0121] (twenty three)

[0122] but:

[0123] (twenty four)

[0124] The thickness S of the nth non-base layer F2 has been calculated by formula (22): n , and the thickness of other non-base layers is not less than S n , then formula (24) becomes:

[0125] (25)

[0126] The thickness S of the base layer F1 at the second chamfer R2 is obtained by formula (25): b2 .

[0127] From the above, the thickness of each non-base layer and the thickness of the first chamfer R1, the second chamfer R2 and the third chamfer R3 of the base layer F1 are calculated. According to the requirement of the trumpet shape of the outer wall of the socket F, the outer walls corresponding to each chamfer are connected in sequence, and the thickness of each part of the base layer F1 and the thickness of each part of the composite socket are obtained. The outer diameter at the end face of the socket F can be greater than the outer diameter at the third chamfer R3, and the specific value can be flexibly selected.

[0128] When the non-base layer F2 has only one layer, that is, the conical shell is a double-layer material, then formula (11) is in the following form:

[0129] (26)

[0130] Formulas (12) and (13) can be organized into the following forms:

[0131] (27)

[0132] For double-layer sockets, the material of the non-base layer F2 (i.e., inner lining layer) is generally stainless steel, and the material of the base layer F1 (i.e., outer layer) is generally Q235 steel or ductile iron. The yield stress of the non-base layer F2 is generally smaller than that of the base layer F1, that is, if yielding occurs, the non-base layer F2 should yield first. Based on this, the stress in formula (26) should be To express, based on formula (27), rearranging formula (26) we can get:

[0133] (28)

[0134] Formula (28) can be rearranged to obtain the hoop stress of the non-base layer F2:

[0135] (29)

[0136] In step a2, in this embodiment, formula (21) is in the following form:

[0137] (30)

[0138] The thickness of the non-base layer F2 is:

[0139] (31)

[0140] That is, the minimum thickness of the non-base layer F2 is: .

[0141] At this time, formula (25) is: (32)

[0142] A specific example is shown below.

[0143] Assume the nominal diameter of the purchased base pipe is DN600 mm, E b =200GPa, E n =193GPa, the base F1 material and the pipe body material are both Q235 steel, and the yield strength of Q235 steel is 235MPa, that is, Q1=Q0=235MPa. The non-base F2 material is 304 stainless steel, with a yield strength of Qn=205MPa, S=7mm, D0=630 mm, D1=673.4 mm, D3=668 mm, D4=642.6 mm, =8.21 o , =5.82 o Assume that the thickness of the first chamfer R1 of the base layer F1 is Sb=6 mm.

[0144] The thickness S of the non-base layer F2 is calculated by formula (31): n ≥2.38 mm, and the thickness of other non-base layers shall not be less than 2.38 mm.

[0145] For the thickness S of the base layer F1 at the second chamfer R2 b2 It can be set equal to the thickness Sb=6 mm at the first chamfer R1, or calculated according to formula (32). When formula (32) is used, take Sn=2.38 mm, substitute each parameter into formula (32), and calculate S b2 ≥5.68 mm.

[0146] For the thickness S of the base layer F1 at the third chamfer R3 b3 , obtained by formula (6), substituting each parameter into formula (6), and obtaining S b3 ≥10.53 mm.

[0147] When the inner wall of the entire base pipe socket F is completely covered by the lining, it is equivalent to the entire composite socket being a multi-layer structure. At this time, the design method of the thickness of the base layer F1 and each non-base layer F2 is the same as the design method when the inner wall of the base pipe socket F is not completely covered by the lining. The difference is that the base layer thickness S corresponding to the third chamfer R3 is b3 At this time, the base thickness S corresponding to the third chamfer R3 b3 The method for calculating the thickness of the base layer F1 at the second chamfer R2 is the same as that for calculating the thickness of the base layer F1 at the second chamfer R2. It can be given directly, or it can be set equal to the thickness of the base layer F1 at the first chamfer R1. It can also be calculated using formula (18). Specifically, formula (23) gives:

[0148] (33)

[0149] In the case where the inner wall of the entire base pipe socket F is completely covered by the lining, there is generally no third step 3, or in other words, the inner diameter of the third step 3 is equal to the inner diameter of the fourth step 4, and the two are combined into a large step, such as Figure 3 shown.

[0150] Embodiment 2

[0151] In this embodiment, the thickness of the non-base layer F2 is limited. For example, in order to improve the corrosion resistance of the pipe, the secondary processing manufacturer or user sleeves a liner ring made of corrosion-resistant material in the socket F. The thickness of the liner ring is generally about 1 mm, which is equivalent to the known thickness of the non-base layer F2. In order to make the composite socket formed after the sleeve liner ring meets the strength requirements, it is necessary to calculate and design the thickness of the base layer F1 under this premise.

[0152] Based on this, formula (18) is rewritten as:

[0153] (34)

[0154] From the above analysis, it can be seen that in the multi-layer structure of the composite socket, the first chamfer R1 and the second chamfer R2 are the places where stress is most likely to concentrate, and the thickness of each non-base layer is uniform, that is, the thickness of each non-base layer is consistent. Therefore, it is only necessary to ensure that the thickness of the base layer F1 at the first chamfer R1 and the second chamfer R2 meets the strength requirements. The base layer F1 manufactured according to the above requirements and other parts of the multi-layer structure must also meet the strength requirements.

[0155] The thickness of the base layer F1 at the first chamfer R1 is S b1 , in formula (34), D is D3, and the half cone angle α for α 1, then formula (34) is:

[0156] (35)

[0157] The thickness of the base layer F1 at the second chamfer R2 is S b2 , in formula (34), D is D4, and the half cone angle α for α 1, then formula (34) is:

[0158] (36)

[0159] From the above, after knowing the thickness and material of the non-base layer F2, the minimum thickness of the base layer F1 at the first chamfer R1 and the second chamfer R2 can be calculated. If the outer wall of the composite socket is designed according to the above-mentioned trumpet-shaped requirement, the composite socket meets the strength requirement.

[0160] A specific example is shown below.

[0161] Assume a base pipe with a nominal diameter of DN600 mm, E b =200 GPa, the material of the tube body and the base tube F1 is the same, both are Q235 steel, yield strength Q1=Q0=235 MPa, S=7 mm, D0=630 mm, D1=673.4 mm, D3=668 mm, D4=642.6 mm, =8.21 o , =5.82 o A liner ring is sleeved inside, that is, there is a non-base layer F2, and the parameters of the liner ring are as follows: E n =193 GPa, 304 stainless steel yield strength Q n =205 MPa, Q1=Q0=235 MPa, Sn=1 mm. Then, we can calculate from equations (35), (36), and (9) respectively:

[0162] S b1 ≥7.33 mm, S b2 ≥7.01 mm, S b3 ≥10.53 mm.

[0163] When the thickness of the base pipe meets the above requirements, the composite socket formed by sleeve-fitting the liner ring inside meets the strength requirements.

[0164] When the inner wall of the entire base pipe socket F is completely covered by the lining, it is equivalent to the entire composite socket being a multi-layer structure. At this time, the design method of the thickness of the base layer F1 and each non-base layer F2 is the same as the design method when the inner wall of the base pipe socket F is not completely covered by the lining. The difference is that the base layer thickness S corresponding to the third chamfer R3 is b3 At this time, the thickness of the base layer F1 at the third chamfer R3 is S b3 , in formula (34), D is D1, and the half cone angleα for α 2, then formula (34) is:

[0165] (37)

[0166] Finally, it is necessary to explain here that the above embodiments are only used to further illustrate the technical solution of the present invention in detail and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above content of the present invention all fall within the scope of protection of the present invention.

Claims

1. A method for designing the composite socket thickness of a socket-and-spigot pipe, characterized in that: Assuming that the outermost layer of the composite socket is the base layer and the other layers are non-base layers, for the multi-layer structure in the composite socket, the design method includes the following steps: Step a1: Based on the same strain of each layer of the composite socket, the calculation formula of the hoop stress of any non-base layer is obtained according to the non-single-layer material equilibrium equation; Step a2: Determine the relationship between the thickness of any non-base layer and the thickness of the base layer, and the determination principle is: the ratio of the stress of the non-base layer to the yield strength of the material of the non-base layer is not greater than the ratio of the stress of the inner wall of the pipe body to the yield strength of the material of the pipe body; Step a3: Calculate the thickness of the non-base layer and / or base layer according to the relationship determined in step a2; Assume there are m non-base layers and one base layer, In step a1, the multilayer structure is regarded as a structure including at least one pressure vessel with a conical inner wall and at least one annular reinforcement ring installed on the inner wall of the pressure vessel; In step a2, in order to make the composite socket meet the strength requirements, the internal stress of the nth non-base layer and the inner wall stress of the pipe body meet the following conditions: , , combined with the calculation formula of the hoop stress of the nth non-base layer, the relationship between the thickness of the nth non-base layer and the thickness of the base layer is obtained: , where Q0, Q n are the yield strengths of the pipe body and the nth non-base layer material respectively; is the hoop stress of the pipe body, is the hoop stress of the nth non-base layer, S is the thickness of the pipe body, D0 is the outer diameter of the pipe body, p is the pressure given by the fluid in the pipe, E n is the elastic modulus of the nth non-base layer, E1, E2, ..., E m are the elastic modulus of each non-base layer, E b is the elastic modulus of the base layer, S1, S2, ..., S m are the thickness of each non-base layer, S b is the thickness of the base layer, D is the diameter of the pressure vessel with a conical inner wall, α is the semi-cone angle of the pressure vessel with a conical inner wall, and n ranges from 1 to m.

2. The design method according to claim 1, characterized in that: For the same base pipe, along the direction from the socket to the spigot, the inner wall of the socket includes a first step (1), a second step (2), a third step (3), a fourth step (4), and a fifth step (5) arranged in sequence, and one end of the inner wall of the pipe body is a sixth step (6). The corresponding inner diameters are: D2, D1, (D3-2F0), D3, D4, (D0-2S), respectively. The chamfer at the connection between the fourth step (4) and the fifth step (5) is the first chamfer (R1), and the fifth step (5) is the sixth step (6). The chamfer at the connection between the first step (1) and the sixth step (6) is the second chamfer (R2), the chamfer at the connection between the second step (2) and the third step (3) is the third chamfer (R3), the chamfer at the connection between the first step (1) and the second step (2) is the fourth chamfer (R4), and the chamfer at the connection between the third step (3) and the fourth step (4) is the fifth chamfer (R5), D0 is the outer diameter of the base pipe, S is the thickness of the pipe body, F0 is the height of the third step (3) protruding from the fourth step (4), and F0 ≥ 0.

3. The design method according to claim 2, characterized in that: In step a1, the first cone is a pressure vessel whose inner wall is a conical surface, and the first chamfer (R1) and the second chamfer (R2) are located on the inner wall of the first cone.

4. The design method according to claim 3, characterized in that: The equilibrium equation of the multilayer structure is: ； in, p is the internal pressure of the conical container, is the cone height, , , …, are the hoop stresses of each non-base layer, is the hoop stress of the base layer.

5. The design method according to claim 4, characterized in that: In step a1, the strain of the base layer The strain is the same as that of each non-base layer, satisfying: ,Right now , combined with the equilibrium equation, the calculation formula for the hoop stress of the nth non-base layer is: .

6. The design method according to claim 5, characterized in that: When the thickness of the base layer corresponding to the maximum stress is known, the minimum thickness of the layer with the minimum yield stress is calculated based on the relationship between the thickness of the nth non-base layer and the thickness of the base layer. This layer is set as the minimum stress layer, and the thickness of other non-base layers is set to be no less than the minimum thickness of the minimum stress layer.

7. The design method according to claim 5, characterized in that: When the thickness of the non-base layer is known, first, select at least one point where the stress of the base layer is likely to concentrate. The selection principle is: after the strength of each selected point meets the requirements, the strength of other places of the base layer designed according to the outer wall design requirements also meets the requirements; then calculate the thickness of each selected point based on the relationship between the thickness of the nth layer of non-base layer and the thickness of the base layer.

8. The design method according to claim 1 or 2, characterized in that: For the single-layer structure part in the composite socket, the design method includes the following steps: Step b1: selecting at least one location where stress of the single-layer structure is likely to be concentrated, and the selection principle is: if the wall thickness of each location selected meets the stress strength requirement, then the wall thickness of each location of the single-layer structure designed according to the outer wall design requirement meets the strength requirement; Step b2: Determine the minimum wall thickness of each selected location in step b1, and the determination principle is: when the material of the single-layer structure 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 structure 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 structure 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.

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