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Comprehensive understanding of plastic corrugated pipes

corrugated pipe
The corrugated pipe refers to a tubular elastic sensitive element connected by a foldable wrinkle sheet along the direction of folding and expansion. corrugated pipe are widely used in instruments and meters, the main purpose is to be used as a measuring element of pressure measuring instruments to convert pressure into displacement or force. corrugated pipe have thinner walls and higher sensitivity, and the measuring range is from tens of MPa to tens of MPa. Its open end is fixed, the sealed end is in a free state, and the auxiliary coil spring or reed is used to increase the elasticity. When working, under the action of internal pressure, it is elongated along the length of the tube, so that the movable end produces a displacement that has a certain relationship with the pressure. The movable end can directly indicate the pressure by driving the pointer. corrugated pipe are often combined with displacement sensors to form pressure sensors with electrical output, and are sometimes used as isolation elements. Because the expansion of the corrugated pipe requires a large volume change, its response speed is lower than that of the Bourdon tube. corrugated pipe are suitable for measuring low pressure.
Chinese name corrugated pipe Foreign name Corrugated pipe Application instrumentation The main purpose of the instrument is used as the measuring element of the pressure measuring instrument. Scope of application Low-pressure types include metal corrugated pipe, corrugated expansion joints, corrugated heat exchange tubes, diaphragm membrane boxes and metal hoses
table of Contents
1 Types of corrugated pipe
2 Performance index
▪ Stiffness
▪ Sensitivity
▪ Effective area
▪ Service life
▪ tightness
▪ Natural frequency
▪ Operating temperature
3 Technical parameters
▪ Bearing load
▪ Displacement characteristics
▪ Elastic properties
▪ Residual deformation
4 Design
▪ Pressure resistance
▪ Stability
▪ Allowable displacement
▪ Life
5 Application
corrugated pipe type
corrugated pipe mainly include metal corrugated pipe, corrugated expansion joints, corrugated heat exchange tubes, diaphragm capsules and metal hoses. The metal corrugated pipe is mainly used to compensate the thermal deformation of the pipeline, shock absorption, absorption of settlement deformation of the pipeline, etc. It is widely used in petrochemical, instrumentation, aerospace, chemical, electric power, cement, metallurgy and other industries. Plastic and other corrugated pipes play an irreplaceable role in the fields of media transmission, power threading, machine tools, and home appliances.
corrugated pipe: A kind of pressure measuring elastic element in pressure measuring instruments. It is a cylindrical thin-walled wrinkled shell with multiple transverse corrugations. The corrugated pipe have elasticity and can produce displacement under the action of pressure, axial force, lateral force or bending moment. corrugated pipe are widely used in instruments and meters, the main purpose is to be used as a measuring element of pressure measuring instruments to convert pressure into displacement or force. corrugated pipe have thinner walls and higher sensitivity, and the measuring range is from tens of MPa to tens of MPa. In addition, the corrugated pipe can also be used as a sealing isolation element to separate the two media or prevent harmful fluids from entering the measurement part of the device. It can also be used as a compensation element, using its volume variability to compensate for the temperature error of the instrument. It is sometimes used as an elastic joint for two parts. Corrugated pipes can be divided into metal corrugated pipe and non-metallic corrugated pipe according to the constituent materials; they can be divided into single layer and multilayer according to the structure. Single-layer corrugated pipe are used in many applications. Multi-layer corrugated pipe have high strength, good durability and low stress, and are used in important measurements. The materials of corrugated pipe are generally bronze, brass, stainless steel, Monel and Inconel.
Performance
Stiffness
The load value required for the metal corrugated pipe or other elastic elements to produce unit displacement is called the stiffness of the element, which is generally expressed as "K". If the elastic properties of the element are non-linear, the stiffness is no longer constant, but changes with increasing load. For corrugated pipe type elastic elements used in general engineering, the rigidity tolerance can be limited to +/- 50%. The stiffness of the corrugated pipe is divided into axial stiffness, bending stiffness and torsional stiffness according to the load and displacement properties. In the application of corrugated pipe, most of the force is axial load, and the displacement method is linear displacement. The following are the main calculation methods for the design of axial stiffness of corrugated pipe:
1. Calculation of corrugated pipe Stiffness by Energy Method
2. Empirical formula to calculate the stiffness of corrugated pipe
3. Calculating the stiffness of corrugated pipe by numerical method
4. EJMA standard stiffness calculation method
5. Japan TOYO calculation stiffness method
6. American KELLOGG (new method) method of calculating stiffness
In addition to the above six methods for calculating stiffness, there are many other methods for calculating stiffness abroad, which will not be described here. Mechanics workers in China have done a lot of work in the theoretical research and experimental analysis of corrugated pipe, and have achieved fruitful research results. The main research methods are:
(1) Perturbation method
(2) Initial parameter method of numerical integration
(3) Integral equation method
(4) Perturbed finite element method
All of the above methods can calculate the corrugated pipe more accurately. However, due to the application of deeper theoretical and computational mathematics methods, engineering applications have certain difficulties and are difficult to master, and need to be further popularized.
Calculation of stiffness when metal corrugated pipe and helical spring are used together
In the process of use, when the rigidity is required to be large, and the rigidity of the metal corrugated pipe itself is small, it can be considered to configure a cylindrical coil spring inside or outside the corrugated pipe. This can not only improve the rigidity of the entire elastic system, but also greatly reduce the error caused by hysteresis. The elastic performance of this elastic system mainly depends on the characteristics of the spring and the stability of the effective area of the corrugated pipe.
corrugated pipe bending stiffness
corrugated pipe stress calculation
As an elastic sealing part, metal corrugated pipe must first meet the strength condition, that is, its maximum stress does not exceed the allowable stress under given conditions. The allowable stress can be obtained by dividing the ultimate stress by the safety factor. According to the working conditions of the corrugated pipe and the requirements for its use, the ultimate stress can be the yield strength, the critical stress when the corrugated pipe is unstable, or the fatigue strength. To calculate the maximum working stress of the corrugated pipe, the stress distribution in the corrugated pipe wall must be analyzed.
The stress on the corrugated pipe is caused by the pressure in the system and the deformation of the corrugated pipe. Pressure creates ring (circumferential) stresses on the corrugated pipe, while radial films and bending stresses are generated on the side walls, troughs, and crests of the waves. Thin shells that cannot resist bending are sometimes called thin films, and the stress calculated by ignoring bending is called thin film stress. When the corrugated pipe is deformed, radial film stress and bending stress are generated. When the corrugated pipe are working, some bear the internal pressure and some bear the external pressure. For example, the corrugated pipe of the corrugated pipe expansion joints and metal hoses bear the internal pressure in most cases, while the corrugated pipe used for valve stem sealing are generally Bearing external pressure Here we mainly analyze the stress when the corrugated pipe bear the internal pressure. The ability of the corrugated pipe to bear the external pressure is generally higher than the ability to withstand the internal pressure. With the wide application of corrugated pipe, a lot of analysis research and experimental verification work have been carried out on the stress of corrugated pipe, and many calculation formulas, calculation procedures and charts for engineering design have been proposed. However, some methods are inconvenient due to the complicated use of charts or programs, and some methods assume that the conditions are either too simplified or too ideal, and it is difficult to ensure the safety and reliability of use. Many methods have not been accepted by the engineering community. Therefore, there are few methods that truly meet practical requirements. There are two commonly used methods as follows:
1. Numerical method for calculating corrugated pipe stress
Assuming that all corrugations of the corrugated pipe are under the same condition, only a single half-wave of the corrugated corrugated pipe is studied in the calculation. In this way, the end ripple is not considered in the study, although the boundary condition of the end ripple is different from the middle ripple. The numerical method is based on E. Lesnell solves the nonlinear equations listed when the axially symmetrical deformation of a thin-walled rotating shell with variable wall thickness occurs. In derivation E. The general assumptions of the thin shell theory are applied to the Lesnell equation, including: the assumption that the thickness is small compared to the main radius of curvature of the ring shell; the assumption of uniformity and isotropy of the material. Using the above assumption will also bring some errors to the calculation. Because in the manufacture of corrugated pipes, the rolling of the billet, drawing and subsequent corrugated plastic forming will cause anisotropy and unevenness in the mechanical properties of the material.
2. American EJMA stress calculation method
Calculation of effective area of corrugated pipe
Effective area is one of the basic performance parameters of corrugated pipe. It characterizes the ability of corrugated pipe to convert pressure into concentrated force. When corrugated pipe are used to turn pressure into concentrated force output, effective area is an important parameter.
When the corrugated pipe is used in a force-balanced instrument, the stability of its effective area will directly affect the accuracy of the instrument. Therefore, in this case, not only the corrugated pipe are required to have a reasonable effective area, but also the effective area does not change with the working conditions during the working process.
1. The concept of effective area and the change of effective area
The effective area is an equivalent area, and pressure acting on this area will produce equal axial forces. In general, as the internal pressure increases, the effective area of the corrugated pipe becomes smaller, and as the external pressure increases, the effective area becomes larger.
2. corrugated pipe volume effective area
Under the action of external force or pressure difference, the ratio of the volume change of the corrugated pipe to the corresponding effective length change is called the volume effective area.
3. Calculation of effective area of corrugated pipe
The requirements and calculation methods for the effective area of the corrugated pipe depend on the use of the corrugated pipe. If the corrugated pipe are used as elastic seals or thermal compensation of the pipeline, the significance of the effective area is only used to calculate the axial force during the forming of the corrugated pipe and the thrust in the system. There is an urgent difference between the calculated value of the effective area of the corrugated pipe and the measured value. In general, the effective area of the corrugated pipe is calculated with a special formula, which can meet the needs.
When corrugated pipe are used in force balance instruments and field platforms that need to convert pressure into force, the effective area should be accurately determined, and measurements must be made one by one.
Sensitivity
The amount of metal corrugated pipe and other elastic components produced when the unit load is subjected to unit load is called the sensitivity of the component. Stiffness and sensitivity are the main functional parameters of corrugated pipe and other elastic elements, but they are two different ways of expressing the same usage characteristics. For different occasions, in order to facilitate the analysis of the problem, any of these parameters can be used.
Effective area
For the elastic element that realizes pressure-force or force-pressure conversion, there is another important functional index is the effective area. The effective area refers to the amount of elastic element that can be converted into concentrated force when its displacement is zero under the action of unit pressure.
Service life
There are two states when the elastic element is working; one is to work under a certain load and displacement, and keep the load and displacement constant or rarely change, which is called static work; the other is to use load and displacement Continuously changing back and forth alternately. The component is in a cyclic working state. Due to different working conditions, the mode of component damage or failure is also different. The elastic sensitive components of the instrument work in the elastic range, basically in a static working state, and the service life is very long, generally reaching tens of thousands to hundreds of thousands of times. The corrugated pipe components used in engineering sometimes work in the elastoplastic range or alternating stress state, and the service life is only hundreds of dry times. The components must be given the allowable working life, and the number of cycles, time and frequency must be specified when the components work in cycles.
The rated life of the elastic element is the expected service life determined during the design of the element. It is required that the element does not allow fatigue, damage or failure during this period.
Tightness
The tightness refers to the performance of the component to ensure no leakage under a certain internal and external pressure difference. When the corrugated pipe components work, the inner cavity is filled with gas or liquid medium, and there is a certain pressure, so it must be sealed. The test methods for air tightness include air pressure air tightness test, leakage test, liquid pressure test, and soapy water or helium mass spectrometer leak detector.
Natural frequency
The elastic components used in industry often have a certain degree of vibration in their working environment, and some components are used as vibration isolation components. It is itself under vibration. For elastic components applied under special conditions, the natural frequency (especially the fundamental frequency) of the component must be prevented from being close to the vibration frequency of any kind of vibration source in the system to avoid damage caused by resonance. corrugated pipe components have been widely used in various fields. In order to avoid damage to the resonance surface of the corrugated pipe, the natural frequency of the corrugated pipe should be lower than the system vibration frequency, or at least 50% higher than the system vibration frequency.
Operating temperature
The use temperature range of metal corrugated pipe components is very wide, generally given before the design and manufacture of elastic components. For some special-purpose corrugated pipe, the inner cavity passes liquid oxygen (-196 ℃) or lower temperature liquid nitrogen, and the pressure resistance is up to 25MPa. The large corrugated expansion joint (nominal diameter sometimes exceeds lm) used for the connection of the pipe network system requires a pressure of 4MPa, a temperature resistance of 400 ° C, and certain corrosion resistance stability. The temperature adaptability of the elastic element depends on the temperature resistance of the elastic material used. Therefore, according to the operating temperature range of the elastic element, the elastic material with suitable temperature performance parameters can be selected to process and manufacture qualified corrugated pipe components.
Technical parameter editing
Load
Various expected load values acting on metal corrugated pipe and other elastic elements, such as concentrated force F, pressure p and moment M, etc. When using metal corrugated pipe elastic elements, in addition to the given applied load value, the direction and position of the load must also be given. For the pressure load, it is also necessary to explain whether the elastic element is subjected to internal cavity pressure or external cavity pressure.
The maximum load value or full-scale value of metal corrugated pipe and other elastic elements allowed under normal working conditions. It is usually the expected design value, or a design value that has been revised after actual testing of the product prototype.
The specific elastic element products can withstand the rated load during the moment of operation or during the test without exceeding the load capacity without damage, failure or instability. For the elastic sensitive components of the instrument, the overload capacity is generally limited to 125% of the rated load. corrugated pipe components used in engineering are generally limited to 150% of the rated load. According to engineering requirements, when a large safety factor is required, the elastic element used does not allow any overload, so the load must be less than or equal to the rated load value.
Displacement characteristics
The position of a specific point (free end or center) in the metal corrugated pipe and elastic element changes. According to its trajectory, it can be divided into linear displacement and angular displacement. Under the action of external load, the metal corrugated pipe may produce axial displacement, angular displacement and lateral displacement.
The displacement value caused by the metal corrugated pipe and elastic elements under the rated load, that is, the working displacement allowed by them under normal use conditions.
Various types of elastic elements are allowed to exceed the rated displacement capacity during the working moment or during the test. When an overload displacement occurs, the elastic element should not be damaged, failed, or unstable. For the elastic sensitive components of the instrument, the overload displacement is generally limited to 125% of the rated displacement. The corrugated pipe components used in the project should be determined according to the engineering conditions and the degree of safety.
Elastic properties
The relationship between the displacement of the metal corrugated pipe and other elastic elements at a specified cooking temperature and the applied load is called the elastic characteristic, and both the displacement and the load should be stored in the elastic range of the element material. The elastic characteristics of the corrugated pipe-like components can be used as a function Expressions in equations, tables and graphs. Its elastic characteristics depend on the structure and loading method of various elastic elements. The elastic properties of the element can be linear or non-linear. Non-linearity can also be divided into two types: increasing characteristics and decreasing characteristics.
The elastic characteristic is a main performance index of corrugated pipe and other elastic components. The elastic elements used in instruments and measuring devices are always designed to make a linear relationship between the output of the element and the measured parameter (load). In this way, a simpler drive amplifying mechanism can be used to achieve the bisector scale of the instrument.
Residual deformation
The residual deformation of the metal corrugated pipe and other elastic elements refers to the displacement of the element after loading, and the elastic element still cannot return to its original position after a long period of time after unloading. Produce a permanently deformed residual value. elementThe residual deformation is related to the state of use. When the tensile (or compression) displacement gradually increases to a certain displacement value, the residual deformation will increase significantly.
Residual deformation is a parameter to determine the deformability of the elastic element. For elastic sensitive elements, if a large residual displacement occurs after reaching the rated displacement value, this will affect the measurement accuracy of the instrument. therefore. Generally, a certain limit value is given to the amount of residual deformation. corrugated pipe components (such as corrugated pipe expansion joints) used in engineering sometimes have large residual deformations in order to obtain larger displacements and make the components work in the elastoplastic zone. If it can meet a certain service life without failure. At this time, the amount of residual deformation is no longer considered.
Design editor
The theoretical basis of metal corrugated pipe design is plate and shell theory, material mechanics, and computational mathematics. There are many parameters for the design of corrugated pipe. Due to the different uses of corrugated pipe in the system, the focus of their design calculations is different. For example, corrugated pipe are used for force balance components, and the effective area of the corrugated pipe is required to be unchanged or small in the working range. For measuring components, the elastic properties of the corrugated pipe are linear; used for vacuum switch tubes as vacuum seals Requires the vacuum tightness, axial displacement and fatigue life of the corrugated pipe; used for valves as seals, the corrugated pipe should have certain pressure resistance, corrosion resistance, temperature resistance, working displacement and fatigue life. According to the structural characteristics of the corrugated pipe, the corrugated pipe can be used as a ring shell, flat cone shell or ring plate. Designing and calculating corrugated pipe means designing and calculating round shell, flat cone shell or ring plate.
The calculated parameters are stiffness, stress, effective area, instability, allowable displacement, pressure resistance and service life.
Withstand pressure
Pressure resistance is an important parameter of corrugated pipe performance. The maximum static pressure that the corrugated pipe can withstand without plastic deformation on the waveform at normal temperature is the maximum pressure resistance of the corrugated pipe. Under normal circumstances, the corrugated pipe work under a certain pressure (internal or external pressure) , So it must withstand this pressure during the entire work process without plastic deformation.
The pressure resistance of the corrugated pipe actually belongs to the strength category of the corrugated pipe. The key to the calculation is stress analysis, which means analyzing the stress on the corrugated pipe wall. As long as the stress at the maximum stress point on the corrugated pipe wall does not exceed the yield strength of the material, the pressure on the corrugated pipe will not reach its pressure resistance.
When the same corrugated pipe have the same other working conditions, the stability under external pressure is better than that under internal pressure. Therefore, the maximum withstand pressure under external pressure is higher than that under internal pressure.
When the two ends of the corrugated pipe are fixed, if sufficient pressure is applied to the inner cavity, the wave crest of the corrugated pipe may be blasted and damaged. When the corrugated pipe start to burst, the pressure value inside the corrugated pipe is called burst pressure. Burst pressure is a parameter that characterizes the maximum compressive strength of corrugated pipe. During the entire working process of the corrugated pipe, the working pressure is far less than the burst pressure, otherwise the corrugated pipe will be broken and damaged.
When the length of the corrugation is less than or equal to the outer diameter, the calculation result is very close to the actual burst pressure; the actual burst pressure of the elongated corrugated pipe is much lower. The bursting pressure is about 3 to 10 times the allowable working pressure.
stability
When both ends of the corrugated pipe are restricted, if the pressure in the corrugated pipe increases to a certain critical value, the corrugated pipe will be unstable.
Allow displacement
For a corrugated pipe working in a compressed state, its maximum compression displacement is: the maximum displacement value that the corrugated pipe can produce when the corrugated pipe are compressed to contact each other under pressure, also known as the maximum allowable displacement of the structure, which is equal to The difference between the free length of the corrugated pipe and the maximum compression length.
The maximum displacement that the corrugated pipe can obtain without plastic deformation is called the allowable displacement of the corrugated pipe.
The corrugated pipe will produce residual deformation during the actual work. The residual deformation is also called permanent deformation or plastic deformation. The corrugated pipe deforms under the action of force or pressure. When the force or pressure is removed, the phenomenon that the corrugated pipe does not return to its original state is called Residual deformation. Residual deformation is usually expressed by the amount that the corrugated pipe does not restore the original position, also known as zero offset.
The relationship between the displacement of the corrugated pipe and the zero offset, regardless of the tensile or compression displacement, at the beginning of the displacement of the corrugated pipe, its residual deformation is very small, generally less than the allowable zero position specified in the corrugated pipe standard Offset value. However, when the extension (or compression) displacement gradually increases to exceed a certain displacement value, it will cause a sudden increase in the zero offset value, which means that the corrugated pipe has a relatively large residual deformation, after this. If you increase the displacement a little more, the residual deformation will increase significantly. Therefore, the corrugated pipe should generally not exceed this amount of displacement, otherwise it will seriously reduce its accuracy, stability, reliability and service life.
The allowable compression displacement of the corrugated pipe when working in a compressed state is larger than the allowable tensile displacement when working in a stretched state, so when designing the corrugated pipe, the corrugated pipe should be operated in the compressed state as much as possible. Through experiments, it was found that, under normal circumstances, the corrugated pipe of the same material and the same specification, the allowable compression displacement is 1.5 times the allowable tensile displacement.
The allowable displacement is related to the geometrical parameters and material properties of the corrugated pipe. In general, the allowable displacement of the corrugated pipe is proportional to the yield strength of the material and the square of the outer diameter, and is inversely proportional to the elastic modulus of the material and the wall thickness of the corrugated pipe. At the same time, the relative wave depth and wave thickness also have a certain influence on it.
life
The life of the corrugated pipe is the shortest working period or the number of cycles that can ensure normal operation when used under working conditions. The elastic sealing system composed of corrugated pipe often works under the condition of withstanding a large number of cycles of variable load and large displacement, so it is of great significance to determine the service life of the corrugated pipe. Because the role of the corrugated pipe is different, the requirements on its service life are also different.
(1) When the corrugated pipe is used to compensate the position deviation caused by installation in the pipeline system, only a few times is required for its service life.
(2) corrugated pipe are used in thermostatic controllers with high switching frequency, and their service life must reach 10,000 times to meet the requirements of use.
(3) When the corrugated pipe is used as a vacuum switch as a vacuum seal, its service life must reach 30,000 times to ensure normal operation.
It can be seen from the above three usage examples that due to the different usage conditions, the required service life of the corrugated pipe varies greatly. The life of the corrugated pipe is related to the fatigue characteristics of the selected materials, but also depends on the residual stress of the formed corrugated pipe, the concentration of stress and the surface quality of the corrugated pipe. In addition, the service life is related to the working conditions of the corrugated pipe. For example: displacement, pressure, temperature, working medium, vibration conditions, frequency range, impact conditions, etc. of the corrugated pipe during operation.
The working life of the corrugated pipe depends on the maximum stress generated during the working process. In order to reduce stress, it is generally achieved by reducing the working displacement of the corrugated pipe and lowering the working pressure. In the general design, the working displacement of the corrugated pipe should be less than half of its allowable displacement, and its working pressure should be less than half of the pressure resistance of the corrugated pipe.
Tests on the produced corrugated pipe prove that if the corrugated pipe work according to the above specifications, its basic service life can reach about 50,000 times.
Depending on the nature of the working pressure, the allowable displacement of the corrugated pipe is also different. Generally, when the corrugated pipe only bears an axial load (tension or pressure), its allowable displacement can be selected from 10% to 40% of the effective length of the corrugated pipe When the corrugated pipe is subjected to lateral concentrated force, torsional moment or comprehensive force, the allowable displacement of the corrugated pipe should be appropriately reduced.
Application of multi-layer corrugated pipe can reduce the stress caused by rigidity and deformation, and thus can greatly improve the life of corrugated pipe.
When the corrugated pipe are operated under the same conditions but with different working pressure properties (constant or alternating load), their service life will be different. Obviously, when working under alternating loads, the life of the corrugated pipe is shorter than when working under constant loads.
Application Editor
The application of metal corrugated pipe [1] and finned corrugated pipe in the cooler of the internal combustion engine. Install 1 to 1000 metal corrugations with intermittent convex and concave in the cooler shell of the diesel engine or between the two tube sheets of the cooling core The tube is fixed on one end of the tube plate by means of the tube expansion method or the welding method to change the flow state of the cooling medium, so as to improve the heat transfer coefficient and increase the heat transfer efficiency. The invention has novel ideas, practical technology, low cost, reliable performance, high heat transfer efficiency, no scaling, long life and low thermal stress.
1. The pressure is based on the actual working pressure of the hose, and then query the nominal diameter and pressure gauge of the corrugation to decide whether to use the stainless steel mesh type.
2. The nominal diameter of the size hose, select the type of joint (mainly flange connection, thread connection, quick joint connection) and the size, length of the hose.
3. The state is according to the state of the hose at the time of use, referring to the correct use and installation method of the metal hose and the optimal length of the hose at the time of settlement compensation. The length of the hose in various motion states is calculated and the minimum bending number and minimum bending radius of the hose are factors. The parameters are correctly selected and installed correctly.
4. The working temperature and range of the medium in the temperature hose; the ambient temperature when the hose works. When the temperature is high, the temperature correction coefficient of the working pressure of the metal corrugated pipe at high temperature must be determined to determine the pressure after temperature correction to determine the correct pressure level.
5. The chemical properties of the media conveyed in the media hose determine the material of the hose parts according to the corrosion resistance parameter table of the hose material.
6. Vacuum hose is mainly used in the production of monocrystalline silicon to achieve negative vacuum
Mainly used in steel belt

Steel belt corrugated pipe, also called steel belt reinforced polyethylene spiral corrugated pipe, is a kind of winding structure wall tube which is made of high-density polyethylene (PE) as the matrix (inner and outer layers) and surface coated with adhesive resin steel belt. The pipe wall structure is composed of three layers: the inner layer is a continuous solid-wall PE inner layer tube, and the outer layer of the inner tube is wrapped with a ring-shaped corrugated steel strip reinforcement (formed into a "V" shape with a steel plate). The outer layer of polyethylene is compounded to form a spiral corrugated pipe. Its typical structure is shown in the figure. The modulus of elasticity of steel is nearly 200 times that of polyethylene (the modulus of elasticity of carbon steel [2] is around 190,000 MPa). The advantages of combining metals and plastics is obviously an ideal way to achieve high rigidity and low consumption High rigidity, high strength and the excellent characteristics of plastics such as corrosion resistance, wear resistance and flexibility are organically combined to take advantage of the two aspects, make up for the shortcomings of both aspects, and achieve the unification of high performance and low cost.

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