A plastic coated steel pipe bend joint suitable for low temperature working conditions
By introducing a corrugated compensator and a damping sliding pair structure into the bend joint of the plastic-coated steel pipe, combined with a polyurethane and polyethylene inner coating, the problems of loosening of the plastic-coated steel pipe connection and coating damage under low temperature conditions are solved, and a stable low temperature connection is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- 中电建路桥集团有限公司
- Filing Date
- 2025-08-15
- Publication Date
- 2026-06-02
AI Technical Summary
Existing plastic-coated steel pipe bends are susceptible to axial stress impact from freeze-thaw cycles under low-temperature conditions, leading to loose connections and coating damage.
The structure employs a corrugated compensator and a damping sliding pair to counteract the axial pressure generated by frost heave through elastic deformation and friction, while the inner coating of polyurethane and polyethylene enhances impact resistance and protection.
It effectively reduces the stress level in other parts of the pipeline, prevents coating cracking and pipeline deformation, and adapts to stable connection under low temperature conditions.
Smart Images
Figure CN224315752U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of pipe joint technology, and in particular to a plastic-coated steel pipe bend joint suitable for low-temperature working conditions. Background Technology
[0002] Plastic-coated steel pipe, also known as plastic-coated pipe or steel-plastic composite pipe, is a composite pipe material formed by fusing a polymer anti-corrosion coating onto the inner and outer surfaces of a steel pipe through electrostatic spraying, rotational molding, dip coating, or vacuum coating processes. Existing plastic-coated steel pipe bends primarily use conventional connection methods such as threaded connections, grooved connections, flange connections, and welding. These bend joint types can effectively secure the plastic-coated steel pipe and serve as transition joints. However, in low-temperature conditions, the pipeline experiences significant axial stress due to freeze-thaw cycles when transporting fluids. This stress impacts the bend's curvature, affecting the stability of the inner coating and the pipe itself, leading to loosening of the connection joints and even serious damage to the plastic coating.
[0003] Therefore, in view of the situation where axial stress causes impact damage when conventional elbows are used to connect the above-mentioned plastic-coated steel pipes, those skilled in the art have proposed a plastic-coated steel pipe elbow joint suitable for low-temperature conditions to offset part of the axial pressure caused by frost heave. Utility Model Content
[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a plastic-coated steel pipe bend joint suitable for low-temperature operating conditions.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] A plastic-coated steel pipe bend joint suitable for low-temperature operating conditions includes: a bend structure consisting of a bend and straight pipe sections welded to its two ends, and further includes:
[0007] The stress buffer device includes a corrugated compensator welded at the junction of the bend and the straight section, and a flow-slowing orifice plate connected to the other end face of the corrugated compensator.
[0008] The damping sliding pair includes a damping sliding tube fixed to the outer wall of the slow-flow orifice plate and a fixed damping kit fitted into the inner wall of the straight tube section.
[0009] The end face of the corrugated compensator connected to the flow-retardant orifice plate is a free end that slides axially along the straight pipe section, while the damping sliding tube and the fixed damping kit achieve a sliding seal through an elastic seal, and the outer peripheral surface of the damping sliding tube is tightly fitted with the inner wall of the fixed damping kit.
[0010] Preferably, a compressible gas medium is sealed and stored in the interlayer between the corrugated compensator and the straight pipe section.
[0011] Preferably, a raised flange is welded to the end face of the straight pipe section away from the bend section, which is connected to the external plastic-coated steel pipe, wherein the outer radius of the raised flange is the same as the inner diameter of the external plastic-coated steel pipe to which it is connected.
[0012] Preferably, the end face of the convex flange away from the bend is provided with a boss, and a fitting groove is provided at the connection between the boss and the convex flange, and an elastic sealing ring is nested in the fitting groove.
[0013] Preferably, the depth of the fitting groove is half the thickness of the boss.
[0014] Preferably, the outer diameter of the corrugated compensator is the same as the outer diameter of the flow-slowing orifice plate.
[0015] Preferably, the inner wall of the bend is coated with a polyurethane inner coating and a polyethylene inner coating in sequence from the outside to the inside.
[0016] This utility model has the following beneficial effects:
[0017] 1. In this utility model, the slow-flow orifice plate converts the impact kinetic energy into flow velocity energy, reduces pressure fluctuations, and reduces the direct impact on the bend.
[0018] 2. In this utility model, when the fluid inside the pipeline freezes and expands, the corrugated compensator is subjected to axial tensile force, and its corrugated structure can undergo elastic deformation. The entire corrugated pipe expands outward. In this process, the externally applied axial stress is converted into the elastic potential energy inside the corrugated pipe material. By absorbing and dispersing the axial stress, it effectively reduces the stress level borne by other parts of the pipeline and avoids the direct effect of stress concentration on the curved section of the pipe.
[0019] 3. In this utility model, the pressure caused by frost heave is offset by the sealing gas, the elastic material in the bellows compensator, and the friction generated by the relative sliding of the damping sliding tube and the fixed damping kit, making the joint fully adaptable to low-temperature working conditions.
[0020] 4. In this utility model, the bend section adopts a reset coating. The polyurethane coating slows down the freezing rate of the fluid and reduces the expansion rate through its low thermal conductivity. The polyethylene inner coating, due to its high molecular strength, is mainly located on the outermost layer of the inner wall, playing a protective role in impact resistance, waterproofing, and preventing peeling. Attached Figure Description
[0021] Figure 1 This is a perspective view of a plastic-coated steel pipe bend joint suitable for low-temperature working conditions proposed in this utility model.
[0022] Figure 2 An exploded view of a plastic-coated steel pipe bend joint suitable for low-temperature working conditions proposed in this utility model.
[0023] Figure 3 This is an isometric side sectional view of a plastic-coated steel pipe bend joint suitable for low-temperature working conditions proposed in this utility model.
[0024] Figure 4 for Figure 3 Enlarged diagram of point A in the middle.
[0025] Legend:
[0026] 1. Bend section; 2. Straight section; 3. Flow-retardant orifice plate; 4. Corrugated compensator; 5. Damping sliding tube; 6. Elastic sealing ring; 7. Fitting groove; 8. Raised face flange; 9. Fixed damping kit. Detailed Implementation
[0027] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0028] Reference Figures 1-2 This utility model provides an embodiment of a plastic-coated steel pipe bend joint suitable for low-temperature working conditions, comprising: a bend section 1 and straight pipe sections 2 welded to both ends of the bend section 1, forming a bend structure. The straight pipe section 2 can be made of Q235B carbon steel, with an inner diameter of 100mm and a length of 300mm. It also includes: a stress buffer device, comprising a corrugated compensator 4 welded at the junction of the bend section 1 and the straight pipe section 2, and a flow-retarding orifice plate 3 connected to the other end face of the corrugated compensator 4. The end face of the corrugated compensator 4 connected to the flow-retarding orifice plate 3 is a free end that slides axially along the straight pipe section 2. When fluid passes through the flow-retarding orifice plate 3, according to Bernoulli's equation, the orifice plate increases the flow velocity and decreases the static pressure, converting impact kinetic energy into flow velocity energy. An orifice plate with an opening ratio of 30% can reduce pressure fluctuations by more than 40%, reducing direct impact on the bend section. The bellows compensator 4 primarily absorbs energy through elastic deformation. When the low-temperature fluid inside the pipe freezes and expands or the pipe contracts, generating axial pressure, the pressure first acts on the stress buffer device, rather than directly on the bend. For example, when the low-temperature fluid inside the pipe freezes and expands, the bellows compensator 4 will be subjected to axial tensile force. Due to the elastic characteristics of the bellows, its corrugated structure can undergo elastic deformation, specifically, the distance between the corrugations increases, and the entire bellows expands outward. In this process, the externally applied axial stress is converted into the elastic potential energy inside the bellows material. By absorbing and dispersing axial stress, it effectively reduces the stress level borne by other parts of the pipe, avoiding the direct effect of stress concentration on the bend, thereby preventing problems such as coating cracking and pipe deformation. The bellows compensator 4 conforms to Hooke's Law. When axial force is applied, the corrugated structure undergoes elastic deformation (maximum displacement of 15mm in this embodiment), absorbing a maximum of energy. It can offset approximately 42J of energy generated by the freezing of a 1m long fluid within a 100mm diameter pipe.
[0029] Reference Figures 2-4 The damping sliding pair includes a damping sliding tube 5 fixed to the outer wall of the slow-flow orifice plate 3 and a fixed damping kit 9 fitted into the inner wall of the straight pipe section 2. The damping sliding tube 5 and the fixed damping kit 9 cooperate with each other. The damping sliding tube 5 and the fixed damping kit 9 achieve sliding sealing through an elastic seal. At the same time, the outer peripheral surface of the damping sliding tube 5 is in close contact with the inner wall of the fixed damping kit 9. The contact surface is made of a material with a high coefficient of friction. This ensures that when the damping sliding tube 5 and the fixed damping kit 9 slide relative to each other, that is, when freezing occurs in the pipe body and the bellows of the bellows compensator 4 moves axially along the straight pipe section 2, the damping sliding tube 5 and the fixed damping kit 9 offset part of the axial pressure generated by the friction.
[0030] Reference Figures 3-4 The corrugated compensator 4 and the straight pipe section 2 are sealed with a compressible gas medium. When the bellows of the corrugated compensator 4 moves axially along the straight pipe section 2, the outer wall of the bellows moves towards the inner wall of the straight pipe section 2 and tends to fit together. At this time, the gas medium stored in the gap between the two is compressed, its volume decreases and heat energy is generated, further offsetting the axial pressure generated by frost heave. It should be noted that under normal temperature conditions, the slow flow orifice plate 3 and the corrugated compensator 4, through their material strength, the limitation of the compressed gas between the bellows and the straight pipe section 2, and the high friction limit between the damping sliding pipe 5 and the fixed damping kit 9, enable the bellows to maintain its deformation within the elastic range under the impact of fluid, thereby continuously and effectively absorbing axial stress and avoiding stress concentration damage to the pipeline.
[0031] Reference Figures 2-3The straight pipe section 2 is welded with a raised flange 8 on the end face away from the bend section 1, which is connected to the external plastic-coated steel pipe. The outer radius of the raised flange 8 is the same as the inner diameter of the external plastic-coated steel pipe it is connected to. The end face of the raised flange 8 away from the bend section 1 is provided with a boss, and a fitting groove 7 is provided at the connection between the boss and the raised flange 8. An elastic sealing ring 6 is nested in the fitting groove 7. The depth of the fitting groove 7 is half the thickness of the boss. The outer diameter of the corrugated compensator 4 is the same as the outer diameter of the slow flow orifice plate 3, ensuring that the stress buffer device can play a normal buffering role. The sealing ring material is ethylene propylene diene monomer (EPDM) rubber, which has a low temperature resistance of -40℃, ensuring the stability of the sealing ring nesting. The upper part of the sealing ring can also play a good role in sealing the connection section and preventing leakage. The fitting groove 7 makes the sealing ring compression reach 50%, and the contact pressure ≥1.5MPa (greater than the frost heave pressure of 0.8MPa), preventing leakage from causing stress concentration.
[0032] Reference Figures 3-4 The inner wall of the bent section 1 is coated with a polyurethane inner coating and a polyethylene inner coating from the outside to the inside. The polyurethane coating slows down the freezing rate of the fluid and reduces the expansion rate due to its low thermal conductivity. The polyethylene inner coating, due to its high molecular strength, is mainly located on the outermost layer of the inner wall and plays a protective role in impact resistance, waterproofing, and preventing peeling. The polyethylene coating can withstand residual stress with its high tensile strength (≥20MPa) and avoid peeling.
[0033] Working Principle: This plastic-coated steel pipe bend joint utilizes a flow-slowing orifice plate 3 to convert impact kinetic energy into flow velocity energy. Simultaneously, it couples with a corrugated compensator 4. Under low-temperature conditions, when the fluid inside the pipe freezes and expands, the corrugated compensator 4 experiences axial tensile force, causing its corrugated structure to undergo elastic deformation. The entire corrugated pipe expands outward. During this process, the externally applied axial stress is converted into elastic potential energy within the corrugated pipe material. By absorbing and dispersing axial stress, it effectively reduces the stress level borne by other parts of the pipe, avoiding the direct effect of stress concentration on the bend's arc segment, thereby preventing problems such as coating cracking and pipe deformation. As the bellows compensator extends outward, the damping sliding tube 5 slides relative to the fixed damping kit 9. The damping generated by friction between the damping sliding tube 5 and the fixed damping kit 9 offsets part of the axial pressure caused by frost heave. Meanwhile, the outer wall of the bellows moves toward the inner wall of the straight pipe section 2 and tends to fit together. At this time, the gas medium stored in the gap between the two is compressed, its volume decreases and heat energy is generated, which further offsets the axial pressure caused by frost heave. The pressure caused by frost heave is offset by the sealing gas, the elastic material in the bellows compensator 4 and the friction generated by the relative sliding of the damping sliding tube 5 and the fixed damping kit 9, making the joint fully adaptable to low temperature conditions.
[0034] Finally, it should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.
Claims
1. A plastic-coated steel pipe elbow suitable for low-temperature operating conditions, comprising: The bent pipe structure, consisting of a bent pipe section (1) and straight pipe sections (2) welded to its two ends, is characterized by further comprising: The stress buffer device includes a corrugated compensator (4) welded at the junction of the bend (1) and the straight section (2) and a flow-slowing orifice plate (3) connected to the other end face of the corrugated compensator (4). The damping sliding pair includes a damping sliding tube (5) fixed to the outer wall of the slow flow orifice plate (3) and a fixed damping kit (9) fitted into the inner wall of the straight tube section (2). The end face of the corrugated compensator (4) connected to the slow flow orifice plate (3) is a free end that slides along the axial direction of the straight pipe section (2), while the damping sliding tube (5) and the fixed damping kit (9) achieve sliding sealing through an elastic seal, and the outer peripheral surface of the damping sliding tube (5) is tightly fitted with the inner wall of the fixed damping kit (9).
2. The plastic-coated steel pipe bend joint suitable for low-temperature working conditions according to claim 1, characterized in that: The corrugated compensator (4) and the straight pipe section (2) are sealed together to store a compressible gas medium.
3. A plastic-coated steel pipe bend joint suitable for low-temperature working conditions according to claim 1, characterized in that: The straight pipe section (2) is welded with a raised flange (8) on the end face away from the bend section (1) to be connected to the external plastic-coated steel pipe, wherein the outer radius of the raised flange (8) is the same as the inner diameter of the external plastic-coated steel pipe to which it is connected.
4. A plastic-coated steel pipe bend joint suitable for low-temperature working conditions according to claim 3, characterized in that: The convex flange (8) has a boss on the end face away from the bend (1), and a fitting groove (7) is provided at the connection between the boss and the convex flange (8). An elastic sealing ring (6) is nested in the fitting groove (7).
5. A plastic-coated steel pipe bend joint suitable for low-temperature working conditions according to claim 4, characterized in that: The depth of the fitting groove (7) is half the thickness of the boss.
6. A plastic-coated steel pipe bend joint suitable for low-temperature working conditions according to claim 1, characterized in that: The outer diameter of the corrugated compensator (4) is the same as the outer diameter of the slow-flow orifice plate (3).
7. A plastic-coated steel pipe bend joint suitable for low-temperature working conditions according to claim 1, characterized in that: The inner wall of the bent section (1) is coated with a polyurethane inner coating and a polyethylene inner coating from the outside to the inside.