What is the Need of Expansion Joints and Bellows in Piping Systems?Expansion joint is a kind of flexible element which can effectively compensate axial deformation. For example, the expansion joint welded on the shell of the fixed tubesheet heat exchanger has large axial flexibility and is easy to deform, which can compensate the thermal expansion difference of the tube and shell due to the different wall temperature, reduce their axial load, thus reducing the temperature difference stress of the tube, tubesheet and shell, and avoid the damage of strength, instability and tube pull off. There are many kinds of expansion joints, commonly used are wave, ring plate welding and jacket type structures, among which wave expansion joint is the most widely used, ring plate welding expansion joint is only suitable for atmospheric or low pressure occasions.
What is the Need of Expansion Joints and Bellows in Piping Systems?As an important form of pipeline displacement compensation, expansion joint has been widely used in petroleum, chemical industry, metallurgy, electric power, cement, construction, urban district heating and other industries in recent years. However, in the actual use process, it is found that the failure of compensator and expansion joint is mostly corrosion failure, except for a small amount of fatigue failure and abnormal factor failure, and stress corrosion failure is the majority. Based on the analysis of corrosion failure expansion joints and bellows, it is found that corrosion failure usually consists of pitting corrosion and stress corrosion cracking, of which chloride stress corrosion cracking accounts for 95% of the total corrosion failure. Therefore, the safety and reliability of bellows compensator and expansion joint can be greatly improved by properly selecting the material and structure of bellows, reasonably designing the waveform parameters and fatigue life, and ensuring the installation quality.
There is hardly any manufacturing industry that does not have the use of piping. It is generally required to carry the fluids and gases, from one place to another. There are various conditions for which a piping system is designed. They can be required in high temperatures as well as low temperatures.
The Use of Expansion Joints and Bellows
Expansion joints and bellows are used in piping systems. They are made of accessories like flow liners, covers and tie rods. The metal bellows act like springs but they are restricted to contain the pressure of the fluid that flows through the expansion joint. A proper flow depends much on the movement of the connected piping.
If expansion joints are removed from the piping systems, high stresses would be created by the thermal expansion. This can cause huge pressure resulting in the crack of the welds and bending of the pipes.
More than a coil, also known as convolution or corrugation is used to make an expansion joint. The corrugations are designed in such a way that they can tolerate the huge pressure of the entire system. The assembly of the bellows is placed in such a way that it can flux under the thermal movement of the connected piping.
Types of Expansion Joints Required in Piping Systems
- 1. If the bellows expansion joint is classified according to the form of compensation displacement, it can be roughly divided into axial type, transverse type, angular type and pressure balanced type.
- 2. According to whether it can absorb the pressure thrust (blind plate force) generated by the medium pressure in the pipeline, it can be divided into unconstrained bellows expansion joint and constrained bellows expansion joint.
- 3. According to the waveform structure parameters of bellows, it can be divided into U-shaped, Ω shaped, S-shaped and V-shaped bellows expansion joints (at present, most of the expansion joints at home and abroad use U-shaped waveform structure).
Common Expansion Joints:
The common expansion joints made by the expansion bellows manufacturers are single expansion joints, required for undergoing a small amount of lateral and angular movements in the piping system. You can also have double expansion joints that are made of two or more bellows that are linked by common connectors.
Universal Expansion Joints:
These joints generally have two bellows linked with a center pipe and fitted with the tie rods. They are mainly required to absorb any of the three general movements, namely axial, lateral and angular in the piping system. What is beneficial in the universal expansion joints is that they are able to absorb a huge amount of lateral offset.
Hinged Expansion Joints:
Another much-required joint in the piping system is the hinged expansion joint. The main purpose of it is to absorb the angular rotation. The joint is made of two hinged plates that are linked to the end connection. The hinged hardware is meant for absorbing the pressure of the expansion joint assembly.
Axial Expansion Joints:
The axial expansion joints are mainly required for absorbing the angular movement in any place of the piping system. There are two sets of hinges linked with a floating ring that is responsible for absorbing the pressure of the expansion joint assembly.
Metallic expansion joints are able to withstand huge pressure. They are basically used in the extremely pressurised designs to ensure that the bellows is completely safe from by the outer pipe casing.
Rubber Expansion Joints:
Rubber Expansion Joints are a flexible connector fabricated from natural or synthetic elastomers and fabrics with metallic reinforcements designed to provide stress relief in piping systems due to thermal changes. When flexibility for this movement cannot be designed into the piping system itself, an expansion joint is the ideal solution. Rubber expansion joints compensate for lateral, torsional and angular movements preventing damage and undue downtime of plant operations.
The special construction of the rubber joints can solve problems like:
- Vibration, Noise, Shock, Corrosion, Abrasion
- Stresses, Load Stress, Equipment Movement
- Vibration, Pressure Pulsation and Movement in a Piping System
Structure and application of expansion joint
|Type||Tectonics||Actuating direction||Usage (fluid)|
|Single freedom type Expansion joint||axial Right angle direction||The most common type of general use. (exhaust gas, air, oil, cold, hot water and steam)|
|Non welding Expansion joint (type ENW)||axial Right angle direction Vibration||Absorption and pressure piping vibration and Engine exhaust. (exhaust)|
|Compound free form Expansion joint||axial In single form Absorptive displacement occasion||It can absorb a lot of axial expansion. (gas, air, oil, cold, hot water and steam)|
|Universal type Expansion joint||Right angle direction (axial)||Absorb the direct displacement of the axis. (gas, air, oil, cold, hot water and steam)|
|Hinge type Expansion joint||Angular displacement absorption||Individual components absorb the axial direction. Angular displacement|
|Balance ring type Expansion joint||Right angle direction angle||Absorb 3 dimensional angular displacement.|
|Outer cylinder type Expansion joint||axial (right angle)||Protection against external damage (gas, air, oil, cold, hot water and steam)|
|Square Shape Expansion joint (U font /V font)||axial||Balanced telescopic structure. With drainage function. (steam, drain)|
|Pressure balanced type Expansion joint||[curved tube] [straight tube]||axial Right angle direction||Balance thrust and reduce load.|
|Embedded type Expansion joint||axial Right angle direction||Buried in the ground. (use of tap water pipe)|
|Filled with hot material Expansion joint||axial (right angle)||Use of high temperature fluids to prevent liquids Intrusive deposits (Sisha A Govin air and combustion gas)|
|Insulating refractory type Expansion joint||axial (right angle)||Fire resistance is also very high. Adiabatic performance. (very high temperature moving air, Very high temperature combustion gas)|
In design, the stability of expansion joint should be considered to prevent the instability of bellows. The data shows that the compensation of bellows compensator and expansion joint depends on its fatigue life. The higher the fatigue life is, the smaller the single wave compensation of bellows is. In order to reduce the cost and increase the single wave compensation, the lower the allowable fatigue life is, the greater the radial bending stress caused by displacement is, and the higher the comprehensive stress is, which greatly reduces the stability of bellows and expansion joints. When the allowable service life of the bellows is low, not only the meridional comprehensive stress is high, but also the circumferential stress is high, which makes the bellows quickly enter into plastic deformation, leading to the failure of the bellows caused by instability.The analysis of the failure causes of bellows expansion joint shows that the main failure modes during operation are corrosion leakage and instability deformation, of which corrosion failure is the most. Based on the analysis of corrosion failure of corrugated expansion joints, it is found that corrosion failure usually consists of pitting corrosion and stress corrosion cracking, in which chloride ion stress corrosion cracking accounts for about 95% of the total corrosion failure. Therefore, the safety and reliability of the bellows can be greatly improved by properly selecting the material and structure, reasonably designing the wave parameters and fatigue life, and ensuring the installation quality. In design, the stability of expansion joint should be considered to prevent the instability of bellows. The data shows that the compensation of bellows depends on its fatigue life. The higher the fatigue life is, the smaller the single wave compensation of bellows is. When the allowable service life of the bellows is low, not only the meridional comprehensive stress is high, but also the circumferential stress is high, which makes the bellows quickly enter into plastic deformation, leading to the failure of the bellows caused by instability.
Besides the design, the material selection of bellows is also very important. For the material selection of bellows, in addition to the working medium, working temperature and external environment, the possibility of stress corrosion, the influence of water treatment agent and pipeline cleaning agent on the materials should also be considered. On this basis, combined with the welding, forming and performance price ratio of the bellows materials, the practical bellows materials that meet the working conditions should be selected. It is suggested that the material of bellows should meet the following conditions:
- (1) Good plasticity, convenient for the processing and forming of bellows, and sufficient hardness and strength can be obtained through subsequent processing (cold work hardening, heat treatment, etc.).
- (2) High elastic limit, tensile strength and fatigue strength to ensure the normal operation of bellows.
- (3) Good welding performance to meet the welding process requirements of bellows in the production process.
- (4) Good corrosion resistance to meet the working requirements of bellows in different environments.
At present, in addition to austenitic stainless steel (such as 304, 304L, 316, 316), 254SMO, 904L, AL6XN and other super austenitic stainless steel are also used as important materials by most manufacturers. For the thermal pipe network laid in the trench, when the terrain of the bellows compensator and expansion joint is low, the rainwater or accidental sewage will be soaked, and the materials with stronger corrosion resistance, such as high nickel alloy, iron nickel alloy, etc., such as Incoloy800, Incoloy825, Inconel625 and Hastelloy C-276, should be considered. Special materials for bellows compensator, expansion joint and expansion joint are as follows:
- 1. Super austenitic special stainless steel: 254SMO, 2507, AL6XN
- 2. Duplex stainless steel: 2205 duplex steel (S31803)
- 3. Nickel base alloy steel: Incoloy800 / 800H / 800ht / 840 / 825, inconel600 / 601 / 690 / 625 / X-750 / Hastelloy C-276 / C-22 / x, MONEL400 / K500
- 4. Pure nickel: N4, N6 (Ni200, ni201)
- 5. Titanium plate for stamping: GR1, Gr2, TA1, TA2
- 6. Austenitic stainless steel: SUS304, SUS, SUS316, SUS, SUS310S, SUS321, sus316ti (end)
Pressure test items and technical requirements of expansion joint
Expansion joint It is an elastic element bearing internal pressure and displacement load. It requires not only the functions required by the design, but also the safety of work. Obviously, this is very important. In order to assess the mechanical properties and safety. Must be right Expansion joint Perform relevant performance tests. Especially in the following circumstances, it is more necessary to carry out experiments: when new products are put into production, the products will be changed greatly due to their structure, material and technology after formal production. Expansion joint After the long term stop production, the labor department will make a series of performance tests if it requires quality certification by the manufacturing department or the quality supervision organization. The main items of the test are: withstand voltage test, air tightness test, stress measurement, stiffness measurement, stability test, fatigue test and blasting test. corrugated pipe Expansion joint All tests should follow the requirements of relevant standards and technical conditions of the state or industry, or refer to relevant foreign countries. Expansion joint Standards and technical conditions.
Expansion joint Withstand voltage testcorrugated pipe Expansion joint Products must be subjected to pressure test according to regulations before they leave factory. The purpose of the experiment is to test. Expansion joint The macroscopic strength of stainless steel under the condition of overload is checked. Expansion joint Whether it has the ability to operate safely under design load, and it can be tested at the same time. Expansion joint The compactness checks the possible problems in materials, structures and manufacturing processes. Pressure test, requirements Expansion joint The two ends are sealed with blind plates, and the two ends are fixed. Expansion joint It is not allowed to stretch. Under normal circumstances, the two ends are tightly strained by a strong pull rod. At the same time, we should measure the corrugation. Expansion joint The wave distances between the waves.
1) Expansion joint Hydraulic testExpansion joint During the hydraulic test, the test pressure is calculated according to the formula (68) and the formula (69), and the small values are obtained.
- PT=1.5P[sigma] / [Sigma]t (68)]
- PT=1.5PscE/Et (69)
- Medium: PT test pressure, Mpa;
- P (internal pressure or external pressure) design pressure, Mpa;
- The allowable stress of stainless steel metal bellows material under test temperature and design temperature is [Mpa] and t respectively.
- E and Et are the elastic modulus and MPa of stainless steel bellows under test and design respectively.
- Psc is Expansion joint The design limit of column instability is Mpa.
- Outside-in Expansion joint The test pressure is determined according to the formula.
2) Air pressure test of expansion jointWhen the structure of the expansion joint is complex, the hydraulic test is not enough to reflect the pressure test requirements of each point, or it is not suitable for hydraulic test for other reasons, the pneumatic test of the expansion joint can be considered. Reliable safety protection measures must be taken at the site when the expansion joint is subjected to air pressure test. The air pressure test medium is generally dry and clean air, or nitrogen or other inert gas. The test temperature also has certain requirements. When the connecting pipe is made of carbon steel and low alloy steel expansion joint, the test gas temperature shall not be lower than 15 ℃, for other materials, it shall be calculated according to the drawing. During the pressure test of the corrugated expansion joint, firstly increase the pressure slowly to 10% of the specified test pressure, maintain the pressure for 5-10 minutes, and carry out the initial inspection on all welds and connecting parts. If there is no leakage, continue to increase the pressure to 50% of the specified test pressure. If there is no abnormal situation, then increase the pressure step by step to the test pressure according to 10% of the specified test pressure of each level, maintain the pressure for 10 minutes, and maintain the pressure Remain unchanged. The pressure shall not be maintained by means of continuous pressurization. Do not tighten bolts under pressure. Leak detection by soap solution or other methods. If there is no air leakage, corresponding safety protection measures shall be taken during air tightness test, and it is qualified if there is no visible abnormal deformation.
Installation mode and precautions of expansion joint
The expansion joint belongs to a compensation element. The effective expansion and contraction deformation of the working main body bellows is used to absorb the size change caused by the thermal expansion and contraction of the pipeline, conduit and container, or to compensate the axial, lateral and angular displacement of the pipeline, conduit and container. It can also be used for noise reduction and vibration reduction. It is widely used in modern industry. In heat supply, in order to prevent the deformation or damage of the heating pipeline caused by thermal elongation or temperature stress when heating up, it is necessary to set compensators on the pipeline to compensate for 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.
- 1. Before installation, the model and specification of expansion joint of corrugated compensator and the support configuration of pipeline must meet the requirements of composite design.
- 2. For the expansion joint with inner liner, attention shall be paid to make the direction of inner liner consistent with the flow direction of medium (installed according to the flow direction sign of expansion joint). The hinge rotation screen of the plane angle expansion joint shall be consistent with the displacement plane.
- 3. For expansion joints that need to be “cold tight”, the auxiliary components used for pre deformation shall be removed after pre deformation of expansion joints.
- 4. After the installation of the pipe system, the auxiliary positioning mechanism and fasteners used for installation and transportation protection on the expansion joint shall be removed immediately, and the limit device shall be adjusted to the specified position according to the design requirements, so as to fully compensate the environmental conditions of the pipe system.
- 5. In addition to the pre deformation required by the design, it is strictly prohibited to use the bellows deformation method to adjust the installation deviation of the pipeline, so as not to affect the normal function of the expansion joint, otherwise the service life of the expansion joint will be reduced and the load of the pipeline system, equipment and supporting components will be increased.
- 6. All moving parts of the expansion joint shall not be blocked by external components or limit their normal operation.
- 7. During the installation process, it is not allowed to splash the welding slag on the surface of the group corrugated pipe and cause other mechanical damage to the corrugated pipe.
- 8. For the expansion joint and its connecting pipes used for gas medium, during the hydrostatic test, it is necessary to consider whether it is necessary to add temporary support to the connecting pipe of expansion joint to bear the load during water filling.
- 9. The water for hydrostatic test must be pure and non corrosive, and the content of chloride ion in the water shall not exceed 25ppm. After the hydrostatic test, the accumulated water in the bellows shall be drained as soon as possible, and the inner surface of the corrugated shell shall be dried quickly.
- 10. The pipeline shall be neutral. If there is no other method to ensure it, the method of cutting off the equal length pipeline and installing the expansion joint after laying the straight pipe can be used.
- 11. It should be noted that the expansion joint does not absorb torque, so when installing the expansion joint, it is not allowed to twist the expansion joint.
- 12. All moving parts of the expansion joint shall not be blocked by the external components or restrict the normal operation of their moving parts.
- 13. The insulation layer shall be made on the outer protective sleeve of the expansion joint and shall not be directly made on the bellows. Chlorine containing insulation materials shall not be used.
- 14. Welding slag splashing on the surface of bellows and other mechanical damage to bellows are not allowed during installation.
- 15. The support must meet the design requirements. It is strictly prohibited to test the pressure in the pipeline before the support is installed to avoid damaging the expansion joint.
- 16. The expansion joint is allowed not to exceed 1.5 times of the nominal system pressure test.
- 17. During the operation of the pipeline with expansion joint, the opening and closing of the valve shall be carried out gradually, so as to avoid the rapid change of temperature and pressure in the pipeline, resulting in the damage of the bracket or expansion joint.
If you own manufacturing machinery and want it always working properly, you need to install expansion joints and bellows of high quality. All you need to do before installing them is to know what type is suitable for your system. To have a proper knowledge about them, get in touch with the joints and bellows manufacturers.
Production quality control of corrugated expansion jointFirst of all, the raw material factory shall have the quality certificate with complete procedures to ensure that the quality of the materials used can meet the design requirements. After entering the factory, the materials shall be rechecked (including the chemical composition analysis and mechanical performance test of stainless steel plate, steel plate and other materials), and the unqualified materials shall be strictly prohibited. Secondly, in the production process, the quality of special process shall be strictly controlled, and the special process (such as welding, forming, NDT, test) must be strictly inspected with detailed inspection records and strict process supervision. There shall be obvious inspection and test status identification in production to ensure the reasonable and orderly production activities. Each process shall be handed over according to the inspection mark of the inspector. Parts without mark, wrong mark and unqualified parts shall not be transferred. The next process has the right to reject the products without conformity mark. The following items shall be inspected during assembly and welding of corrugated expansion joint:
- 1. The dimension public relations of inner and outer diameter of straight side section of corrugated pipe shall meet the requirements of class H12 in GB1804.
- 2. The size and technical requirements of the connecting flange and end pipe of the bellows expansion joint and pipeline (or equipment) shall meet the corresponding standards. When the end pipe is connected, the pipe orifices at both ends shall be beveled by 30 degrees ± 2.5 degrees.
- 3. When the end pipe of the bellows expansion joint is rolled steel welded pipe, the tolerance of the four perimeter and roundness of the external end of the end pipe shall conform to the tolerance table.
- 4. The circumferential weld between the bellows and the end pipe (or flange) shall be TIG welding or MFA welding. When the wall thickness of the bellows is more than 2mm, the arc welding can be used.
- 5. When assembling the bellows expansion joint, the bellows shall be protected to prevent the welding arc from burning through the bellows and welding slag splashing on the bellows. There shall be no crack, pore, slag inclusion and other defects in the weld of each part of expansion joint, and the undercut depth shall not be greater than 0.5mm
- 6. After the pressure weld of the corrugated expansion joint is welded, the pressure test shall be conducted on the pressure weld, and the test pressure shall be 1.5 times of the design pressure. According to the volume of the expansion joint, maintain the pressure for 10-30min, check whether there is leakage at each part of the expansion joint, and the ratio of the maximum wave distance and the wave distance before compression shall not exceed 1.15.
- 7. The appearance and geometric dimension of expansion joint shall be inspected after assembly and welding. Coaxiality tolerance of both ends of expansion joint: 5mm when the nominal diameter is less than or equal to 500mm; 1% and less than or equal to 10 mm when the nominal diameter is greater than 500mm. The perpendicularity tolerance between the two ends of expansion joint and the main axis is 1% of the nominal diameter and less than or equal to 3mm.
- (1) Stiffness test: the measurement methods and boundary conditions of axial type, transverse bending and bending stiffness are required, and the test times and data processing methods are given.
- (2) Fatigue test: fatigue test is carried out for the compensators of axial type, straight pipe pressure balance, hinge type, tension sensibility, flexible bar and other structural forms to simulate the actual deformation conditions, and the test method and judgment criteria are given.
- (3) Vibration test: the requirements of vibration mode, frequency range, vibration acceleration and scanning time of each frequency band are given.
- (4) Impact test: the impact acceleration, pulse duration, impact action times and the boundary conditions of impact test are specified.
- 1. To determine the pipe and expansion joint to grade, pressure determines the expansion joint of the corrugated part of the thickness.
- 2. Determine the type and quantity of expansion joints.
- 3. Determine the diameter of expansion joint, pressure level and compensation amount of expansion joint, and then the designer selects the model of expansion joint.
- 4. It is necessary to calculate the non property rights required by each section of the pipeline to determine the compensation amount of each expansion joint.
Source: China Expansion Joints Manufacturer – Yaang Pipe Industry (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.)
If you want to have more information about the article or you want to share your opinion with us, contact us at firstname.lastname@example.org Please notice that you might be interested in the other technical articles we’ve published:
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- Tips for selecting expansion joints
- What Is A Bellows Expansion Joint
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How Often Do You Need Expansion Joints?
Usually, expansion joints should be no farther apart than 2 to 3 times (in feet) the total width of the concrete (in inches). So for a 4 inch thick concrete slab, expansion joints should be no more than 8 to 12 feet apart.
How do expansion joints work?
An expansion joint or movement joint is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seismic activity.
Why use bellows in piping?
The effective expansion deformation of the bellows of the working main body of the expansion joint is used to absorb the size change caused by the thermal expansion and contraction of the pipeline, conduit and container, or to compensate the axial, transverse and angular displacement of the pipeline, conduit and container. It can also be used for noise reduction and vibration reduction. It is widely used in modern industry. In heat supply, in order to prevent the deformation or damage of the heating pipeline caused by thermal elongation or temperature stress when heating up, it is necessary to set compensators on the pipeline to compensate for 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.
Why do you need expansion joints in concrete?
The goal of the control joint is to allow the slab to crack, during expansion and contraction, in a known location and in a straight line. Expansion joints are put in place before the concrete is poured. Expansion joints are used to allow the slab to move and not put stress on whatever it abuts.