How to get high quality bellow expansion joints?
What is an bellow expansion joints?
An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of construction materials, to absorb vibration, to hold parts together, or to allow movement due to ground settlement or earthquakes. They are commonly found between sections of buildings, bridges, sidewalks, railway tracks, piping systems, ships, and other structures.
An expansion joint consists of a bellows (a kind of elastic element), a bracket, a flange and connectors (stainless steel hoses) at both ends, which is also a kind of compensating component. An expansion joint uses effective deformation of its bellows to compensate expansion and contraction of a pipeline and a vessel caused by heat and cold due to temperature variation. An expansion joint can be used for compensating axial, lateral and angular displacement of a pipeline and a vessel, and it can also be used for reducing noise and vibration, which make an expansion joint widely used in modern industry. When temperature goes up in heat supply pipelines, the expansion joint should be installed on the pipeline in order to prevent the pipeline being deformed or destroyed due to expansion caused by heat or temperature stress.
The expansion joints can compensate expansion caused by heat so as to reduce stress of walls of pipes and acting force on valves and brackets. As an important part for pipework, the expansion joint plays an important role in ensuring the long-term normal operation of the pipeline.
Building faces, concrete slabs, and pipelines expand and contract due to warming and cooling from seasonal variation, or due to other heat sources. Before expansion joint gaps were built into these structures, they would crack under the stress induced.
What are metal bellows?
Metal bellows, as elastic sealing elements, are widely used in valve manufacturing, such as bellows gate valve and bellows, etc. The bellows structure converts the stem in the stuffing box to the static seal of the stem at the cover, making the valve seal more secure and reliable. However, due to metal bellows can only carry the tensile and compression, and can’t bear torque, therefore, the current application is limited to stem movement only axial lifting without radial rotating gate valve, globe valve and relief valve, etc.
Metal bellows are mainly divided into metal (stainless steel, alloy steel, carbon steel) bellows, plastic bellows. Metal corrugated pipe is mainly used in the thermal deformation compensation pipeline, shock absorption, absorption pipeline settlement deformation, and so on, are widely used in petrochemical, instrumentation, aerospace, chemical industry, electric power, cement, metallurgy, etc. Other materials such as new materials, such as dielectric conveying, power threading, machine tools, household appliances, etc. Are irreplaceable. Metal bellows are used for piping hot and cold ducts.
Betal bellows using range:
Applicable to the heat conduction oil, toxic, flammable, permeability is strong, pollution environment, fluid pipeline with radioactive as cut-off valve, can also be used to adjust, is to create quality products of the factory without leakage.
Advantages of metal bellows:
1. Double seal design (bellows + filler) if bellows fail, stem packing will also avoid leakage and comply with international seal standards.
2. Safe and environmental protection, no fluid loss, reduce energy loss, and improve plant equipment safety.
3. Long service life, reduce maintenance times and reduce operating costs.
4. Strong and durable bellows seal design to ensure zero leakage of stem and provide conditions without maintenance.
The main factors affecting the life of stainless steel bellows structure, geometry, pressure, temperature, materials, displacement, manufacturing processes and their work medium. Can use the finite element analysis of stainless steel bellows valve, you can more accurately analyze the fatigue life of the pipe, shorten the product development cycle, to improve the design of corrugated pipe.
Stainless steel bellows fatigue damage refers to the role of the bellows under cyclic load, after a period of time cracks, loss of sealing phenomenon. In the valve, the bellows not only need to withstand the working pressure of the fluid medium, but also need to withstand the valve opening and closing process tube tensile, compressive stress. These factors change cyclically over time, so fatigue damage is mostly multi-axis fatigue. Fatigue life is a very important performance parameter. With the development of computer technology and the maturity of finite element theory, it is possible to use the wired element to the bellows life expectancy.
Classification and application of metal bellows:
Metal hose is a kind of high quality flexible connecting pipe in modern industrial pipeline. It is mainly composed of metal bellows, metal mesh and various types of joints. Its inner tube is a spiral corrugated or circular corrugated stainless steel bellows. The outer sheath of the bellows is woven of stainless steel wire or stainless steel strip with certain parameters. The joints on both ends of the hose are prepared according to the connections of the user’s pipe or equipment.
What is a stainless steel hose?
A stainless steel hose is a flexible metal line element. There are two basic types of stainless steel hose that differ in their design and application: stripwound hoses and corrugated hoses. Stripwound hoses have a high mechanical strength (e.g. tensile strength and tear strength). Corrugated hoses can withstand high pressure and provide maximum leak tightness on account of their material. Corrugated hoses also exhibit corrosion resistance and pressure tightness under the most extreme conditions, such as in aggressive seawater or at extreme temperatures such as found in space or when transporting cooled liquid gas. They are particularly well suited for conveying hot and cold substances.
With a history of more than one hundred years, stainless steel hoses have given rise to other flexible line elements, including metal expansion joints, metal bellows and semi-flexible and flexible metal pipes. In Germany alone, there are about 3500 patents relating to stainless steel hoses.
Characteristics of stainless steel hose:
good softness, corrosion resistance, high temperature resistance, wear resistance, tensile, waterproof, and excellent electromagnetic shielding performance. Stainless steel hoses can freely bend into various angles and radius of curvature, and have the same softness and durability in all directions. Stainless steel corrugated hose has flexible and flexible joints, no obstruction and stiffness. The tension between the buckle of the stainless steel threaded hose has a certain tensile force, so as to prevent the damage of the hose from causing the exposed lines inside the hose to be exposed, and the axial pull force can withstand more than 6 times the nominal inner diameter.
In large water intake and drainage works, because of different gravity, the foundation of the pump house and the foundation of the flume will also produce different or unequal settlement. In order to solve this problem, the problem of displacement compensation should be considered in the design. As we all know, manufacturing 1m, 2m or larger caliber stainless steel stainless steel hose is not economical. Since the stainless steel hose has the same lateral displacement compensation function, the latter should be used. Many of the so-called flexible pipe joints, in fact, refers to the stainless steel hose.
In a drainage pipeline, a stainless steel hose with two opposite angles of angular displacement can be effectively compensated for lateral displacement. Because of their differences in natural conditions, their structural designs may be different. Some drainage pipes are arranged in a straight line. The drainage pipes are arranged in a “s” shape, which seems to bring some difficulties to conversion. In fact, no matter how they change, their design principles should be consistent: in order to facilitate the work of engineering designers, we first establish an accurate mathematical model.
There are two kinds of bellows used for stainless steel hose, one is spiral bellows, and the other is circular bellows.
(1) helix stainless steel hose is a tubular shell with spiral distribution. There is a spiral angle between adjacent two waves. All corrugation can be connected by a spiral line.
(2) the annular stainless steel hose is a tubular shell with a closed circular circular ring, which is formed in series between the wave and the wave. The annular stainless steel hose is formed by the seamless pipe or welded pipe. Compared with the spiral bellows, the length of the single tube is usually shorter than that of the spiral bellows. The advantages of the annular stainless steel hose are the good elasticity and the small stiffness.
Application areas of metal hoses
With its ability to meet high demands for conveying hot and cold substances, this modern technology has the following major areas of application:
- Electrical industry and mechanical engineering: as a protective hose for electrical cables or light conductors
- As a suction, conveying and coolant hose, e.g. when conveying and transporting liquid gas
- Automotive industry: as an exhaust gas hose that acts as a vibration decoupler in exhaust systems
- As a ventilation hose in technical building equipment
- Steel industry
- Measuring and control equipment
- Medical equipment
- Aviation and space travel
- Reactor technology
- Alternative energy (solar heat, wind turbines, etc.)
There are two basic variants of corrugated hoses that differ in their type of corrugation: annular corrugation and helical corrugation. In hoses with helical corrugation, usually a right-handed coil with a constant pitch that runs along the whole length of the hose. The annular corrugation, on the other hand, consists of a large number of equally-spaced parallel corrugations whose main plane is perpendicular to the hose axis. Hoses with annular corrugation have decided advantages over those with helical corrugation:
- When installed properly, they are free of damaging torsional strain during pressure surges.
- Because of the shape of their profile, they connect smoothly to connection fittings.
This increases process reliability during conduit assembly and use. For this reason, annular corrugated hoses are far more common, with only a few exceptions.
Manufacturing corrugated hoses
The first step in creating a corrugated hose is to shape the starting metal strip from the coil into a smooth, longitudinally welded tube. The strip is continuously welded using the highly precise shielding gas welding method. Then the tube is corrugated by one of the following procedures:
- The hydraulic corrugation method expands the tube from the inside to the outside. This method is used to create annular corrugated hoses.
- The mechanical corrugation method, on the other hand, is used to produce both annular and helical corrugated hoses. Usually, multiple profiled pressure rollers are positioned around the tube with an offset that enables them to roll the desired corrugation profile into the tube from the outside to the inside. Both corrugation methods cause material hardening and thus increase the pressure and fatigue resistance of the corrugated hoses.
In addition, corrugated hoses can be manufactured by a special method that is closely related to the manufacture of stripwound hoses. In this procedure, the starting strip is given a corrugated profile in a longitudinal direction. This profile strip is then wound helically and the overlapping coils are tightly welded along the helical seam. After corrugation, the hose may be equipped with a braided sheath (see below). In this case, the hose then passes through a braiding machine that has circumferential wire coil holders, or so-called bobbins.
The wire bundles are wrapped helically around the hose while also being alternately layered one over the other. This creates a tubular braid with the characteristic crisscross pattern. After the fittings are mounted, the hose line is complete. Production-related testing is an integral part of the manufacturing process. It encompasses incoming tests of the starting material as well as dimensional, leakage and pressure testing of the finished conduit.
The flexibility of the hose is achieved by means of the elastic behaviour of the corrugation profile. When the hose is bent, the outer corrugations separate while the inner corrugations are squeezed together. The flexibility, bending behaviour and pressure stability of corrugated hoses depend on the selected profile shape. While flexibility increases with an increase in profile height and a decrease in corrugation spacing, pressure resistance decreases. The frequently required semi-flexible bending behaviour is achieved by flat profiles. Depending on the use of the hose, special application-specific profile shapes can be implemented
Pressure resistance and flexibility can also be altered by varying the wall thickness. A reduction in the wall thickness increases the bending capacity but reduces the pressure resistance of the hose.
Tips for selecting expansion joints
Expansion joints have rectangular sections and waveform with similar shape. A single expansion joint in the pipe bears two-dimensional displacement. The pipeline comprising two expansion joints can bear three-dimensional displacement. Metal expansion joints could be classified into full-height expansion joints and half-height expansion joints.
1. After the user pick the appropriate expansion joint in accordance with the thermal displacement of the piping system, they have to provide details about the medium from the pipe, design pressure of the duct, the greatest temperature during operation, the general dimension of sections of the duct, the chosen waveform and the quantity of the waveform to be able to design and manufacture structure of expansion joints.
2. The maximum allowable expansion of each waveform
Full-height type: △α = ± 24 mm Half-height: △α = ± 12 mm.
3. The ash board: For pipes with less dust, the ash board doesn%u2019t need to be utilized for flue pipes with much dust, the ash board ought to be adopted.
4. In order to reduce the number of the waveform, we have to take into account the cold-drawn process for expansion joints.
5. Expansion joints are suitable for pipes whose cross-sectional areas are less than 4.6 square meters and one side of the overall dimension of the air and flue gas duct which is less than 1.5m but greater than 0.6 mm. Standard full-height expansion joints can be applied to all air and flue gas ducts.
Source: Network Arrangement – China expansion joints 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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