What is a corrugated pipe?
Corrugated pipe: It is a cylindrical thin-walled folded shell with multiple transverse corrugations. Bellows are elastic and can produce displacement under the action of pressure, axial force, transverse force or bending moment.Bellows are commonly called corrugated pipe or corrugated box in America and metallbulgen or metal bellows in Europe.
|Types||Material||Metal expansion joint|
|Non-metallic Expansion Joint||Metal hose||Metal bellows|
Types of Corrugated pipes
Corrugated pipes mainly include metal bellows, bellows expansion joints, corrugated heat exchanger tubes, diaphragm diaphragm boxes and metal hoses. Metal bellows are mainly used to compensate thermal deformation, shock absorption and settlement deformation of pipelines. They are widely used in petrochemical, instrumentation, aerospace, chemical, electric power, cement, metallurgy and other industries. The corrugated pipes made of plastic and other materials play an irreplaceable role in the fields of medium transmission, power threading, machine tools, household appliances and so on.
Bellows can be divided into metal bellows and non-metal bellows according to their composition materials, and can be divided into single-layer and multi-layer according to their structure. Single-layer bellows are widely used. Multilayer bellows have high strength, good durability and low stress, which are used in important measurement.
The materials of bellows are bronze, brass, stainless steel, Monel alloy and nickel alloy.
- 1. Super Austenitic Special Stainless Steel: 254SMO, 904L, AL6XN.
- 2. Duplex stainless steel: 2205 duplex steel (S31803).
- 3. Nickel-based alloy steel: INCOLOY800/800H/800HT/840/825, INCONEL600/601/690/625/X-750.
- Harrington alloy C-276/C-22/X, MONEL400/K500
- 4. Pure nickel: N4, N6 (Ni200, Ni201).
- 5. Stamping titanium plate: GR1, GR2, TA1, TA2.
- 6. Austenitic stainless steel: SUS304, SUS304L, SUS316, SUS316L, SUS310S, SUS321, SUS316Ti.
Expansion joints are also called compensators. The utility model is composed of a bellows (an elastic element) constituting the main body of the bellows and accessories such as an end pipe, a bracket, a flange, a conduit, etc. Expansion joint is a flexible structure installed on the shell or pipeline of container to compensate the additional stress caused by temperature difference and mechanical vibration. The effective expansion deformation of bellows is used to absorb the size changes of pipelines, conduits and containers caused by thermal expansion and cold contraction, or to compensate the axial, transverse and angular displacements of pipelines, conduits and containers. It can also be used in noise reduction, vibration reduction and heating. In order to prevent pipeline deformation or damage caused by thermal elongation or thermal stress during heating, compensators need to be installed on the pipeline to compensate the thermal elongation of the pipeline, so as to reduce the stress of the pipe wall and the force acting on the valve or support structure.
As an elastic compensating element with free expansion, expansion joint has been widely used in chemical industry, metallurgy, nuclear energy and other sectors due to its reliable operation, good performance and compact structure. There are many kinds of expansion joints used in containers. As far as the shape of corrugation is concerned, U-shaped expansion joints are the most widely used, followed by omega-shaped and C-shaped expansion joints. As far as structural compensation is concerned, the expansion joints used in pipelines can be divided into universal, pressure balanced, hinge and universal joints.
Metal expansion joint
(1) Bending expansion joint
Bend the pipe into a U-shaped or other shape (Fig. 1), also known as tension bending. It is an expansion joint compensated by the elastic deformation ability of the body. It has the advantages of good strength, long service life and can be manufactured on site. Its disadvantages are large space occupation, high consumption of steel and high friction resistance. This expansion joint is widely used in various steam pipes and long pipes.
Fig. 1 Bending expansion joint
(2) Bellows expansion joint
Bellows expansion joint is an expansion joint made of metal bellows. It can expand along the axis of the pipeline and allow a small amount of bending. Fig. 2 is a common axial bellows expansion joint, which is used to compensate the axial length of the pipeline. In order to prevent excessive compensation, a protective tie rod or a protective ring is arranged at both ends of the bellows, and a guide bracket is arranged on the two ends of the pipelines connected with the bellows. In addition, there are angular and transverse expansion joints, which can be used to compensate for the angular and transverse deformation of the pipeline. The advantages of this kind of expansion joint are space saving, material saving, easy standardization and batch production, but the disadvantage is short service life. Bellows expansion joints are generally used in pipes with low temperature and pressure and short length. With the improvement of bellows production technology, the application scope of this kind of expansion joint is expanding. Currently, bellows expansion joints can be used in piping systems with a maximum pressure of 6.0 MPa.
Fig. 2 bellows expansion joint
(3) Sleeve expansion joint
The casing expansion joint is composed of inner and outer casing which can move axially relative to each other. Packing box seal is used between inner and outer casing. When in use, keep both ends of the pipe moving on an axis. The product mainly consists of sleeve (core tube), shell, sealing material, etc. It is used to compensate the axial expansion of the pipeline and the axial rotation of any angle. It has the characteristics of small volume and large compensation. It is suitable for hot water, steam, grease and other media. It can compensate the thermal expansion of the outer sleeve by sliding sleeve.
The inner sleeve of sleeve compensator is connected with the pipeline. It adopts the principle and structure of high-performance self-pressure dynamic seal. It can slide freely in the outer shell with the expansion of the pipeline. It can meet the sealing requirements of any pipeline. A new type of synthetic material is used to seal the inner sleeve between the outer shell and the inner sleeve, which can resist high temperature, corrosion and aging. With temperature – 40 to 150, it can reach 350 under special circumstances. It can not only ensure the axial sliding, but also ensure that the medium inside the pipe does not leak.
Non-metallic Expansion Joint
(1) Rubber duct expansion joint
The air duct rubber compensator is divided into four types: FDZ, FVB, FUB and XB. It consists of rubber and rubber-fiber fabric composite material, steel flange, sleeve and heat insulation material. It is mainly used for flexible connection between various fans and air ducts. Its functions are shock absorption, noise reduction, sealing, medium resistance, easy displacement and installation, and it is a ring. In the field of environmental protection, it is an ideal accessory for shock absorption, noise reduction, smoke elimination and dust removal.
(2) Expansion joints of fibre fabrics
Fabric compensators are mainly made of high temperature resistant materials such as fibre fabrics, rubber and so on. It can compensate the vibration of fan and duct and the deformation of duct. Fibre fabric expansion joint can compensate for axial, transverse and angular products. It has the characteristics of no thrust, simplified support design, corrosion resistance, high temperature resistance, noise reduction and vibration reduction. It is especially suitable for hot air pipes and dust pipes in power plants. Fiber fabrics and insulating cotton body in non-metal compensators have sound absorption and vibration isolation functions, which can effectively reduce the noise and vibration of boilers, fans and other systems. The utility model has the advantages of simple structure, light weight and convenient maintenance.
Metal hose is an important component of connecting pipeline of modern industrial equipment.
Because the internal stress produced by bending at random and under the condition of rated bending radius is very small, it can bring great convenience to installation work, and also play a certain role in ensuring the safe operation of pipeline system. This is the main reason why metal hoses must be used in some pipeline systems. The good comprehensive performance of metal hose is fully embodied here. In the general industrial field, in addition to pressure and temperature, there are often some harsh conditions such as fatigue, corrosion, vibration, compression, impact and so on. Under such circumstances, it is most appropriate to compensate for the position movement of pipelines. Metal hose can absorb vibration. It can not only improve the ability of fatigue damage of pipeline system, but also reduce noise.
Metal hose is mainly composed of bellows, net sleeves and joints. Bellows are the body of metal hoses, playing a flexible role; net sleeves play a role of strengthening and shielding; joints play a role of connecting. For different use requirements, they are connected in different ways: bellows, mesh sleeves and joints are joined by welding, called welding; mechanical clamping, called mechanical clamping; in addition, there is a combination of the two methods, called hybrid.
Mesh sleeve: Mesh sleeve is made of several interlaced strands of wire or a number of cracked metal strips in a certain order. It is set on the outer surface of metal bellows at a specified angle and plays a role of strengthening and shielding. The mesh sleeve not only shares the static load of the metal hose in the axial and radial direction, but also ensures the safe and reliable operation of the metal hose under the condition that the fluid pulses along the pipeline. At the same time, it also ensures that the corrugated part of the hose is not directly subjected to mechanical damage such as relative friction and impact. The strength of the corrugated pipe with net sleeve can be increased by more than ten to dozens of times. The maximum shielding capacity can reach 99.95%. The material of the net sleeve is generally the same as that of the bellows. There are also two kinds of materials used in combination. Ordinary metal hoses only use one layer of mesh sleeve; in special occasions, there are also braided two or three layers. According to the size of bellows and different requirements for use, it is usually made of wire with a diameter of 0.3-0.8 mm or strip with a thickness of 0.2-0.5 mm. Wire rods are 4-15 per share and tapes are 1 per ingot. Most of the steel wire mesh sleeves produced are 24, 36, 48 and 64 strands. There are also 96 strands, 120 strands and 144 strands of corrugated pipes with extra large diameter. The main knitting parameters of mesh sleeve include not only the number of strands, wire diameter, ingot number and thickness, but also the covering area, knitting distance and knitting angle. They are the important basis for determining the performance of metal hoses.
Joint: The function of the joint is to connect the mesh sleeve with the bellows as a whole. At the same time, the joint is a part of the connection between the metal hose and the metal hose or other pipe fittings and equipment. It guarantees the medium to work normally in the pipeline system. Joint materials are usually the same as bellows and net sleeves, mostly stainless steel. In order to reduce production cost, some metal hoses with larger diameter can be made of carbon steel when conveying corrosive or non-corrosive medium. For the joint of metal hoses with corrosive medium, if appropriate measures are taken in design to avoid contact with medium, carbon steel can also be used. The structural forms of joints are generally divided into three categories: spiral, flange and fast.
1. Thread type: The joint of metal hose with diameter less than 50 mm is mainly threaded type under high working pressure. When the thread is tightened, the inner and outer taper surfaces of the two joints are closely matched to achieve sealing. Cone angle is generally 60 degrees, but also useful 74 degrees. The structure has good sealing performance, but the concentricity of the two butt parts must be ensured during installation. In order to solve the problems of repeated disassembly, assembly and concentricity which often occur in practical engineering, the joint can also be designed as the cooperation of conical surface and spherical head.
2. Flange type: The joint of metal hose with diameter over 25 mm is mainly flange type under general working pressure. It is sealed in the form of mortise and groove cooperation. The looper flange can rotate along the radial direction or slide along the axial direction to connect the two bodies under the action of the tension of the fastening bolt. The sealing performance of the structure is good, but the processing is difficult and the sealing surface is easy to be damaged. On special occasions requiring quick unloading, the holes through which the fastening bolt passes can be cut and made into fast unloading flange.
3. Fast type: The joints of all kinds of metal hoses whose diameter is less than 100 mm are usually fast type under the condition of fast loading and unloading. It is commonly used in fluoroplastics or special rubber made of “O” sealing ring. When the handle is moved at a certain angle, the claw finger equivalent to multi-thread is locked; the tighter the O-ring is pressed, the better its sealing performance. The structure is most suitable for fires, battlefields and other occasions where quick loading and unloading are necessary. In a few seconds, a set of connectors can be docked or disassembled without any special tools.
Because the main parts of the hose are made of austenitic stainless steel, the excellent temperature resistance and corrosion resistance of the hose are guaranteed. The working temperature range of the hose is very wide, ranging from – 196 to 600 C. The suitable stainless steel grade is selected for the hose according to the corrosiveness of the medium through which the hose is used, which can ensure the corrosion resistance of the hose.
- 1. Metal hose is made of 1Cr18Ni9Ti stainless steel with strong corrosion resistance.
- 2. The hose tube body is hydroforming of thin-walled stainless steel tube body, which has strong flexibility, flexibility, flexibility and anti-vibration ability. The braided mesh sleeve is strengthened to protect it and make it have higher bearing capacity.
- 3. The connection of both ends of hose can be made into other connection modes besides screw thread and flange standard, which is convenient for connection and use.
- 4. The product is not only suitable for matching with rotating joint, but also widely used for flexible connection of various fluid medium transportation.
Corrosion resistance, high temperature resistance, low temperature resistance (- 196 +420), light weight, small size, good flexibility. It is widely used in aviation, aerospace, petroleum, chemical industry, metallurgy, electric power, paper-making, wood, textile, construction, medicine, food, tobacco, transportation and other industries.
- 1. Flexible hose between pitches of metal hose with small bending radius.
- 2. Metal hose has good flexibility, no obstruction or rigidity.
- 3. Metal hose has light weight and good caliber consistency.
- 4. Metal hose has good flexibility, repeated flexibility and flexibility.
- 5. Metal hose has good corrosion resistance and high temperature resistance.
- 6. The metal hose has good anti-rat bite and wear resistance, and prevents the internal wires from being worn.
- 7. Metal hose has strong bending resistance, tensile resistance and lateral pressure resistance.
- 8. Metal hose is soft, smooth and easy to install and locate.
- 9. There are many hose joints with metal hoses, which are easy to connect with instruments and equipments.
Although the metal hose can be compressed and stretched, if it is not installed in the right place, it will break quickly and reduce its service life.
Hose can be installed horizontally, vertically or obliquely. Ideally, it should be installed vertically. At the same time, it should be avoided to be installed near the wheel, and baffles can be installed if necessary.
Generally, metal hoses can be divided into three lengths: the first is compression length, that is, the length when the hose is compressed to the limit position; the second is installation length, which is the length of the hose when it is in the middle position of half of the maximum displacement; the third is stretch length, the length when the hose is stretched to the maximum limit.
When the hose is installed, the hose should be placed in the middle position, that is, the so-called installation length. When installed in this position, the hose can move in two directions when it is subjected to axial load. Otherwise, if it can only move in one direction, it will affect the strength of the metal hose and reduce its service life.
In the actual installation process, considering that measuring the length of hose according to the calculation results may affect the production efficiency, some foreign manufacturers directly mount the ruler on the hose and cut the ruler off after installation.
- 1. When choosing the metal hose, in order to facilitate installation, please choose the metal hose with loose flange at one end as far as possible.
- 2. The surface of metal hose should be protected to prevent welding slag and arc ignition burn of metal hose during welding operation at construction site.
- 3. Strictly prohibit the twisted installation of metal hoses.
- 4. It should not bend along the root of the metal hose. There should be no dead bend.
- 5. The medium should not be corrosive to bellows. The chloride content in the medium should be less than 25PPM.
- 6. Strict installation diagram and correct installation method. (See Installation Guide)
- 7. Mechanical damage to flange sealing surface is strictly prohibited.
Metal bellows are a kind of regular corrugated pipe with regular appearance. Commonly used metal bellows are carbon steel, stainless steel, steel lined plastic, aluminium and so on. Mainly used for non-concentric axial transmission with very small bending radius, or irregular turning, expansion, or absorption of thermal deformation of pipeline, or for connection between pipeline and pipeline where fixed elbow installation is not convenient, or connection between pipeline and equipment.
Structure of Metal Bellows
Metal bellows are mainly composed of bellows and two end-to-end joint (one-time processing and forming). The structure sketch is shown in Fig. 3.
Fig. 3 Metal Bellows
In the working process of bellows, the life of bellows mainly depends on the maximum stress produced in the working process. In order to reduce stress, the working displacement and pressure of bellows are generally reduced. In general design, it is stipulated that the working displacement of bellows should be less than half of its allowable displacement and its working pressure should be less than half of the pressure resistance of bellows.
Tests on the produced bellows show that if the bellows work according to the above specifications, the service life of the bellows can reach about 50,000 times.
According to the nature of working pressure, the allowable displacement of bellows is also different from that of ordinary bellows, when they only bear axial load (tension or pressure), the allowable displacement of bellows can be selected between 10% and 40% of the effective length of bellows; while when bellows are subjected to transverse concentrated force, torsional moment or combined force, the allowable displacement of bellows is allowed. The displacement should be reduced appropriately.
The application of multi-layer bellows can reduce the stress caused by stiffness and deformation, and thus greatly improve the service life of bellows.
The service life of bellows will be different when they work under the same conditions and different working pressure properties (constant or alternating loads). Obviously, the service life of bellows under alternating load is shorter than that under constant load.
Source: China Corrugated Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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