How to select expansion joint options?

Expansion joints are designed by taking into account factors such as the amount of deformation, design pressure, design temperature, and the layout of the pipeline system to be compensated. Depending on the type of compensation provided, these joints are generally classified into wave compensators, pressure-balanced wave compensators, hinge-type wave compensators, universal-joint type wave compensators, sleeve compensators, and spherical compensators. Currently, to reduce the thrust on fixed supports, straight-tube pressure balance compensators are commonly used for axial compensation.

Selection and Usage Guide for Expansion Joints – Selection of Bellows Expansion Joints 1. Method of Denoting Bellows Expansion Joint Models At present, there is no unified standard in China for denoting expansion joint models; various manufacturers tend to use their own methods for representation. However, the information indicated by the model is roughly the same, including the structural type, nominal diameter, operating pressure, compensation amount or wave number, and connection method. 2. Nominal pressure of bellows expansion joints: The nominal pressures listed in the product catalog are generally those at a design temperature of 300°C, and are available in several pressure grades such as 0.25 MPa, 0.6 MPa, 1.0 MPa, 1.6 MPa, 2.5 MPa, and 4.0 MPa. When the operating temperature is below or above 300°C, the pressure rating of the expansion joint must be appropriately adjusted. 3. Nominal diameter of bellows expansion joint: The nominal diameter of the bellows expansion joint is the same as that of the pipeline. 4. Compensation amount of corrugated expansion joints and number of cycles: There is a direct relationship between the number of cycles of a corrugated expansion joint and its compensation amount. Generally, the compensation amount specified in the product catalog corresponds to 1000 cycles. If the actual number of cycles is higher or lower than 1000, the compensation amount can be adjusted using the correction coefficient. 5. Material of bellows expansion joints: The bellows in bellows expansion joints are generally made of austenitic stainless steel (1Cr18Ni9Ti, SUS304, SUS316, SUS321, etc.). Carbon steel and composite layers can also be used depending on the operating conditions – in such cases, the inner and outer layers are made of stainless steel, while the middle layer is made of carbon steel with a higher elongation rate. Flanges, end tubes, and other accessories are made of carbon copper, while the welded parts are made of low-carbon steel. Stainless steel and low-alloy structural steel can also be used according to the user’s requirements and operating conditions. Procedure for selecting bellows expansion joints: The selection of bellows expansion joints follows this procedure: 1. Design the pipeline reasonably and divide it into sections, determining the type and quantity of bellows expansion joints to be used in each section. 2. Determine the operating pressure rating. 3. Calculate the amount of compensation required for each section of the pipeline, and determine the rated compensation capacity of each bellows expansion joint. 4. Select the appropriate model of bellows expansion joint based on the pipe diameter, pressure rating, and required compensation amount. The following explains this process: 1. Division of the pipeline into sections and determination of the type and quantity of bellows expansion joints. No matter how complex the pipeline is, it can be simplified into a certain number of relatively simple typical sections, such as straight sections, L-shaped sections, Z-shaped sections, etc., by using pipe supports. The displacement of these pipe sections can all be compensated for using different types of bellows expansion joints. Axial expansion joints are generally used for straight pipe sections ； L-shaped and Z-shaped pipe sections use transverse-type or compound hinge-type (or three-hinge system) expansion joints composed of angular types ； For the spatial Z-shaped pipe sections, expansion joints of the large tie rod type or the universal transverse type (or universal three-hinge system) composed of universal angular components are used. In urban pipeline networks, most pipe sections are straight. Therefore, axial expansion joints are widely used in urban pipeline networks. Axial bellows expansion joints are generally not suitable for compensating for lateral displacement, but they can be used for compensating for linear displacement in pipelines that have a slight degree of bending. In such cases, it is advisable to avoid placing the expansion joint at the bend; instead, fixed supports should be installed at that location. In pipe networks, if L-shaped and Z-shaped pipe sections are further broken down into several straight pipe sections, then only axial expansion joints need to be used. The entire pipeline is divided into straight sections; although this design can also address the issue of pipeline compensation and is not a wrong design, it is not the best or most appropriate design. To convert L-shaped and Z-shaped pipe sections into straight pipe sections, it is necessary to add support brackets to divide them into segments; each segment then requires an axial expansion joint for compensation. As a result, the number of brackets and expansion joints increases, leading to higher construction costs. Therefore, transverse expansion joints are widely used in L-shaped and Z-shaped pipe sections. Furthermore, due to the large compensation capacity of horizontal expansion joints, in pipelines with elbows (L-shaped and Z-shaped sections), one horizontal corrugated expansion joint is often used to replace multiple axial corrugated expansion joints. 2. Determining the working pressure rating: Generally, the nominal pressure of the expansion joint can be determined directly based on the design pressure of the pipeline. The nominal pressure class of the product is 0.1 ； 0.25 ； 0.6 ； 1.0 ； 1.6 ； 2.5 ； 4.0 (MPa). If necessary, the nominal pressure rating can be determined precisely; generally, the pressure ranges listed in the product catalogs correspond to values at a design temperature of 300 ℃. If the operating temperature of the pipe is not 300 °C, the nominal pressure class can be adjusted using a temperature correction factor. 3. Calculate the displacement of each pipe segment to determine the rated compensation amount of the expansion joint. The displacement of each pipe segment is determined based on the expansion and contraction that occur due to thermal expansion and contraction when the pipeline is at its highest and lowest temperatures. The rated compensation amount of the bellows expansion joint is determined based on the displacement of the pipe section. When making a determination, the displacement of the containers connected to the pipeline as well as the fixed supports must sometimes also be taken into account. The rated compensation amount of bellows expansion joints should be accurate, without considering an excessive safety factor. Otherwise, it will give the expansion joint great flexibility, reducing its stability. In practical applications, accidents caused by the instability of expansion joints far outnumber those resulting from fatigue failure. 4. Select bellows expansion joints based on the nominal diameter, nominal pressure, and rated compensation amount. The pipe support design involves using supports to hold the pipes in place, dividing the pipes into sections, and restricting the direction in which the pipes can move. Brackets are divided into fixed brackets, guiding brackets, and sliding brackets. The first two types of supports have a significant impact on the expansion joint. 1. Fixed supports: The function of fixed supports is to divide the pipeline into sections, provide fixing points, and ensure that expansion joints can operate properly within the pipe section between two fixed supports. Fixed brackets are further divided into primary fixed brackets and secondary fixed brackets. (1) The supports that bear the thrust exerted by the pressure in the pipeline due to the blind flange are primary fixed supports, and they are generally installed at the blind ends of pipelines, elbows, sections with changing cross-sections, as well as at the connections of valves and branch pipelines. (2) The secondary fixing bracket does not bear the blind plate force generated by the pressure inside the pipeline; it is generally installed on straight pipe sections between axial expansion joints to serve a fixing purpose. 2. Guiding brackets: Guiding brackets are used to ensure that the pipeline moves in a specific direction, preventing it from moving in other directions and thus ensuring the safe use of the expansion joint. Guiding brackets are divided into linear guiding brackets and planar guiding brackets. A linear guide bracket refers to a bracket that restricts the pipeline in two dimensions, allowing it to move only in one dimension (i.e., the axial direction). A planar guide bracket is a type of bracket that restricts a pipeline in one direction, allowing it to move and rotate within a plane. The use of various types of bellows expansion joints in typical pipe sections and the analysis of the forces acting on supports: Many fixed supports take into account only the force exerted on them by the typical pipe section, that is, they calculate only the force exerted by one side of the pipeline on the support. In actual design, however, it is necessary to consider the force from the other side as well, and then determine the vector sum of all forces acting on the support in order to find the total force it must withstand. Therefore, the primary and secondary fixing brackets take into account only the effect of the pipelines on one side; when the effect of the pipelines on the other side is considered, the roles of the primary and secondary fixing brackets may sometimes switch. Installation of corrugated expansion joints: 1. Only one expansion joint (or one set of angular expansion joints) can be installed between the two fixed pipe supports. 2. Compared with rigid pipes, corrugated expansion joints are much easier to install; some deviations in the pipes can be compensated for by the expansion joints. However, this does not mean that there are no requirements regarding pipe installation. Because if a large amount of displacement has already occurred during installation, its service life will be affected during operation. Therefore, in principle, it is not recommended to use expansion joints to compensate for installation errors. 3. Typically, the expansion joints of the basic type mentioned above do not absorb torque; therefore, it is not allowed for the expansion joint to be twisted during installation. 4. The fixed support must have sufficient strength to ensure that the expansion joint is not damaged. The guide bracket must have sufficient guiding capability; otherwise, it will affect the transmission of pipeline displacement. 5. Pre-tensioning or cold straining of expansion joints: To ensure that the corrugated expansion joints can provide compensation within the specified range of the structure and to reduce their deformation stiffness, the expansion joints in their supplied state should be pre-deformed according to the installation temperature at the site. 6. Installation precautions: (1) The pipes must be well aligned; when other methods cannot ensure proper alignment, the method of laying straight pipes first and then cutting off a section to install the expansion joint can be used to achieve this. (2) During installation, the bellows should be protected to prevent damage to it. (3) For expansion joints equipped with guide sleeves, the direction of guidance should be consistent with the flow direction of the medium. (4) After installation, the pre-tensioning rods and transportation fixing rods should be removed to allow the pipeline to expand and contract in response to changes in ambient temperature. (5) The supports must meet the design requirements; it is strictly prohibited to conduct pressure testing in the pipelines before the supports are properly installed, to avoid damaging the expansion joints. (6) The insulation layer should be applied to the outer protective cover of the expansion joint, and not directly to the bellows. Insulation materials containing chlorine shall not be used. (7) Expansion joints allow a system pressure test at a pressure not exceeding 1.5 times the nominal pressure. (8) When operating pipelines equipped with expansion joints, valves should be opened and closed gradually to prevent sudden changes in temperature and pressure within the pipeline, which could cause damage to the supports or expansion joints. (end)

Calculation and design of corrugated expansion joints, Classification and characteristics of expansion joints. The main component of a corrugated expansion joint is the bellows, which utilizes its ability to expand and contract easily to provide compensation. Based on the cross-section of the bellows, expansion joints can be classified into U-shaped, Ω-shaped, S-shaped, V-shaped, etc. U-shaped bellows have good processability and are easy to manufacture; they also exhibit good pressure resistance and compensation capabilities. Unreinforced U-shaped bellows are generally suitable for applications with pressures below 2.5 MPa. Currently, the vast majority of corrugated expansion joints use U-shaped bellows. The Ω-shaped bellows have average processability; reinforcement rings are used to strengthen the troughs, making them suitable for applications with high pressure and temperature, but their compensation capacity is relatively poor. The S-shaped bellows have poor workability and are complex to manufacture, but they do not tend to develop stress concentrations, resulting in a favorable stress condition within the bellows. When high pressure resistance and a large displacement are both required, an S-shaped bellows can be used. V-shaped bellows have strong compensatory capacity and can be used to absorb extremely large expansions, but they experience concentrated stress at the corners and have poor pressure resistance. Bellows expansion joints can be classified into single-layer and multi-layer types based on the number of bellows layers. A single-layer bellows consists of one layer of tube wall; it is easy to manufacture, but its compensation capacity is generally limited. A multi-layer bellows is composed of multiple layers of tube walls, resembling multiple thin sheet springs, and thus has low stiffness. Compared to single-layer bellows, under the same conditions of total wall thickness and wave pattern, multi-layer bellows are more prone to deformation and possess greater compensation capacity. The stress generated by deformation is low, resulting in a high fatigue life. Therefore, it can meet the requirements for large compensation amounts and high pressure shocks (a single-layer bellows requires a thin wall and deep corrugations) ； Multi-layer bellows require a thicker wall thickness and shallower corrugations; under certain operating conditions, namely specific pressures, compensation amounts, and fatigue life, multi-layer bellows have a smaller outer diameter and shorter length than single-layer bellows. This makes the multi-layer corrugated expansion joint compact, allowing for material savings and easier molding during production. Due to the low wave height, it is easy to install a protective outer sleeve, and it is convenient to set up supports and spacing. When bellows expansion joints are used in corrosive environments, the multi-layer bellows only need to have their inner and outer layers made of corrosion-resistant materials, thereby saving precious metals. Sometimes, for corrosion protection, the inner and outer layers can be made of materials with a greater thickness. Furthermore, if cracks appear in the inner layer of the pipe wall due to reasons such as corrosion, defects, fatigue, or improper installation, although leakage occurs in that inner layer, the other layers can still provide a sealing function. As a result, multi-layer bellows expansion joints are less prone to sudden failure, which helps to extend the maintenance interval. Due to the excellent performance of multi-layer corrugated expansion joints, they have seen significant development abroad. For example, countries such as the United States, Japan, Germany, the United Kingdom, and the former Soviet Union have all designed, manufactured, and used them. Multilayer corrugated expansion joint products manufactured abroad have a diameter of over 4 meters. The standards of the American Expansion Joint Manufacturers Association have included multi-layer corrugated expansion joints in their specifications. In our country, multi-layer corrugated expansion joints have also seen significant development, with most manufacturers adopting a multi-layer structure. Since the vast majority of bellows expansion joints produced and used in China today are of the U-shaped type, what is discussed below mainly refers to U-shaped bellows expansion joints. Several main calculation methods for expansion joints. The design and calculation of bellows represent a complex problem in elastic mechanics. As bellows expansion joints are increasingly used in pipelines, equipment, and installations, the deformation of these bellows is no longer limited to elastic deformation; significant plastic deformation also occurs. Relying solely on the theories of elastic mechanics leads to considerable errors in analysis. Since the bellows is a complex housing, its manufacturing process and operating conditions have a significant impact on its performance; therefore, it is not possible to develop an engineeringally practical calculation formula that can be applied under various conditions. In recent years, numerous analytical studies and experimental verifications have been conducted, and many calculation formulas and charts for use in engineering design have been proposed. However, some of these methods are inconvenient to use in engineering design due to the complexity of their formulas and charts ； Some of the assumptions are also overly simplified and idealized; they deviate significantly from real-world applications, making it difficult to ensure safety and reliability in engineering projects, and thus they have not been accepted by the engineering community. At present, there are not many calculation methods that can meet the practical requirements of engineering. The most commonly used methods include the following: 1. The standard calculation method of the American Expansion Joint Manufacturers Association (EJMA method); 2. The calculation method developed by Kellogg Company in the United States (KELLOGG method); 3. The calculation method of Toyo Company in Japan (TOYO method); 4. The calculation method proposed by Vehman and others in the former Soviet Union (Vehman method); 5. The calculation method specified in the AD code for pressure vessels in former West Germany (AD method); 6. The calculation method proposed by Hamada and Ichikakeen in Japan (Hamada-Ichikakeen method). The EJMA method has notable advantages in terms of calculation: it provides a comprehensive stress analysis of the bell-shaped shell, uses reasonable assumptions, and makes necessary adjustments to the formulas to account for actual conditions, thereby ensuring a certain degree of accuracy in the calculation results. At the same time, in terms of content, it not only provides corresponding formulas for the issues that must be considered in engineering design, such as strength, stiffness, displacement, fatigue, stability, and vibration, but is also applicable to various wave shells, whether multi-layer or single-layer, with or without reinforcing elements, thus meeting the practical requirements of engineering well. Especially as a standard specific to manufacturers of expansion joints, this standard not only has advantages in its calculation methods but also sets out regulations regarding the manufacturing, use, and even packaging and transportation of expansion joints; as a result, EJMA holds considerable influence. Currently, some foreign standards and regulations have gradually adopted the EJMA method, which can be recommended as a general calculation method in engineering design. In China’s standards such as **General Technical Requirements for Metal Expansion Joints (GB/T 12777), Steel Pressure Vessels (GB 15), and Steel Shell-and-Tube Heat Exchangers (GB 151), the calculations related to bellows utilize the EJMA calculation methods. At present, most of the manufacturers of bellows expansion joints in our country also use the EJMA method for product design. The KELLOGG method is the prescribed approach for engineering design by the American company Kellogg. It is simple and practical, and the evaluation criteria for various calculation aspects are based on practical experience; as a result, it is reliable and has been widely used abroad over the years. For example, the Japanese industrial standards JIS B 8243-1977 and JIS B 2352-1977 from 1977 still included the KELLOGG method. In recent years, Kellogg Company has further revised the calculation methods based on practical experience, resulting in more comprehensive content, significantly improved calculation accuracy and application scope, making them suitable for use and reference in engineering design. The TOYO method is capable of reflecting the characteristics of wave shells well due to its assumptions, resulting in fairly accurate calculations. Moreover, it features a simple algorithm and specific guidelines; in recent years, this method has also been applied in engineering design in China. However, compared to the above two methods, it falls short in terms of both the calculation content and the adjustment of relevant practical factors in the formulas, making it an unsuitable method for general-purpose calculations. The Wöhman method is also used in our country; the \"Design Code for Steel Pressure Vessels in the Petroleum and Chemical Industries (1977 edition)\” adopts this method. A major drawback of the Wihman method and the AD method is that they do not perform fatigue analysis; as a result, they are not very suitable for applications that require large amounts of compensation, experience significant load variations, or have complex waveforms, and thus they have considerable limitations. The Hamada Ichikaku-en method is rarely used in Japan due to its complex calculation charts. Structural design of expansion joints 1. Design of bellows connection types The connection types for bellows include welded pipe type and flange type. The welded pipe has good weldability, a simple structure, and low costs. The straight sections of externally welded bellows are subject to high stresses; reinforcement collars can be used based on calculations. Internally welded bellows are suitable for those with larger diameters, while they are not appropriate for bellows with smaller diameters due to limited space and difficulties in operation. The flanged welding process has good weldability, and its assembly is more convenient and easier than that of welded pipe types. The flange can serve as a support for tie rods or sleeves; it has a compact structure, but its cost is higher than that of welded tube types, and it is not suitable for large-diameter bellows. 2. Structural design: Bellows expansion joints can be classified by structure type into axial type, angular type (hinge type), transverse type, force-balanced type, etc. Because the axial stiffness of bellows expansion joints is very low, the axial force generated by the pressure inside the pipeline often affects the design and operation of the piping system. A bellows expansion joint in a piping system to which axial forces are transmitted without any restraint is called a free-type (unbalanced-type) bellows expansion joint ； Axial forces that are restrained by certain mechanisms or devices and cannot be transmitted to the bellows expansion joint are known as balanced bellows expansion joints. Among them, balanced bellows expansion joints are further divided into two types: damping type and absorption type. Those that use components such as tie rods and hinges to prevent the transmission of axial forces are of the damping type ； The bellows expansion joint that uses working pressure itself to achieve balance is of the absorptive type. Axial types (including the axial types of bending-resistant, directly-buried, externally-pressure-resistant, and one-time compensation types) and universal types are all free-type bellows expansion joints ； Hinged types (which can be divided into angular type, universal angular type, lateral type, and universal lateral type) and large tie rod types are damping-type balanced bellows expansion joints ； The straight-pipe force-balanced type and the elbow-pipe force-balanced type are absorption-type balanced bellows expansion joints. (end)

Types and structure of bellows expansion joints. Types of bellows expansion joints: Bellows, together with appropriate components, form bellows expansion joints that possess various compensation functions. Based on the form of compensation, they are classified into axial type, transverse type, angular type, and pressure-balanced type. Axial type: ordinary axial type, bending-resistant type, external pressure type, directly buried type, straight pipe force-balanced type, one-time directly buried type. Horizontal type: single-direction horizontal type, universal hinge horizontal type, large tie rod horizontal type, small tie rod horizontal type. Angular type: unidirectional angular type, omnidirectional angular type. The above are the basic categories, and each category has common functions. In some specific cases, special functions are also available, such as corrosion-resistant and high-temperature resistant types. Depending on the specific application, they are divided into those for catalytic cracking units and those for blast furnace flues. They are classified by the medium they are used for: for hot air, for flue gas, for steam, etc. Structure of corrugated expansion joints 1. Axial-type corrugated expansion joint – The ordinary suction-type is the most basic structure for axial expansion. Among them, the support nuts and pre-tensioning rods serve to support the expansion joint to reach its maximum rated tensile length and to adjust the installation length at the time of on-site installation (cold tightening). If the compensation amount is large, two or even three bellows can be used. When using multiple sections, guide limit rods to prevent instability should be added. Bending-resistant type: An external bending-resistant sleeve is added to endow the entire structure with bending resistance. In this way, it is not constrained by the requirement that the support setup must adhere to 4D and 14D rules; the support setup can treat this section as a rigid pipe. External pressure type: This structure subjects the outside of the bellows to pressure while allowing the inside to be in contact with atmospheric pressure. The enclosure must be a sealed container, characterized by the following: 1) The bellows does not suffer from column instability under external pressure, and multiple waves can be used to achieve a large degree of compensation. 2) The corrugations contain no impurities or water; when the steam supply is stopped, the condensate does not remain inside the corrugations and can be drained through the drain valve, so freezing is not a concern. 3) Slightly improved structure also possesses bending resistance. Direct-buried type: Its casing acts as a well, protecting the expansion joint. The sealing mechanism prevents soil and water from entering. The actual products are available in soil-proof types and soil-proof and water-proof types. A special requirement for expansion joints is that they must have the same service life as the pipeline. It is a disposable straight-type device. When installed on a pipeline, it heats the entire pipeline to an intermediate temperature within the pipeline’s designed temperature range; as a result, the pipeline expands, the bellows are compressed, the two sleeves slide closer to each other, and then they are welded together. Finally, pressure is applied through inspection ports to verify that there are no leaks in the welds. Its characteristics are: 1) Once welded, the bellows no longer functions, and its lifespan is sufficient for just one use. 2) The design pressure of the bellows is determined based on the heating pressure during construction. The material is ordinary carbon steel. 2. Transverse corrugated expansion joint, unidirectional transverse type: It can only bend and deform in a plane perpendicular to the hinge axis. Universal lateral type: It can compensate for deformation in all directions for spatial pipes that are not in the same plane. The large tie rod of the transverse type belongs to the universal transverse type; it can not only withstand significant lateral deformation but also absorb the thermal deformation of the long pipes in between. If there is no need to use tie rods to balance the thrust of internal pressure, it can also compensate for axial deformation from the pipeline, namely the so-called \"universal expansion joint\". Since bending and axial deformation occur simultaneously, and the axial deformation is shared by both bellows, it is necessary to limit their degrees of deformation within the expansion joint structure, so as to evenly distribute the deformation across the two bellows and prevent any of them from experiencing a deformation that exceeds the specified limit. The small tie rod of the transverse type can compensate for both lateral and its own thermal deformation when it is necessary to balance the internal pressure thrust with the help of tie rods. If there is no need for a tie rod to balance the internal pressure thrust, it can withstand axial compensation; this is also a type of universal expansion joint. Horizontal expansion joints have the following advantages: ① They can provide large displacement compensation. ② The axial force caused by internal pressure is balanced by the tie rods and hinges themselves, turning its support into a semi-fixed support and reducing the cost of the support. ③ The tie-rod transverse type also has the ability to absorb axial deformation, and can be useful in pipelines with complex deformations. ④ Its greater advantage is that the rotor is structurally protected by struts and hinges, making it less sensitive to installation errors or accidents in the pipes compared to axial expansion joints; sometimes, even in the event of a pipe accident, the expansion joint remains undamaged. In piping design, try to use horizontal expansion joints whenever possible. 3. Angular type bellows – unidirectional angular type: It can only bend and deform, resulting in angular displacement. The internal pressure thrust is borne by the hinge. Universal angular type: The universal angular type bellows expansion joint is characterized by the use of universal hinges, which allow it to bend in any plane passing through its axis. Angular types generally use two or three compensation wires in combination to address displacement. 4. Force-balanced bellows expansion joints: These types of expansion joints generate relatively high internal pressure forces, which can have an adverse effect on the connected equipment. A force-balancing expansion joint uses its own structure to balance the thrust generated by internal pressure, exerting little or no force on the connected equipment, while still maintaining its axial compensation function. Straight-tube force-balancing type: It consists of two working bellows, one balance bellows, as well as end plates and balance tie rods. The key here is that the effective area of the balancing bellows must be twice that of the working bellows. In this way, the axial thrust exerted outward due to the internal pressure in the working bellows is counteracted by the thrust in the opposite direction generated by the internal pressure in the balancing bellows, through the balancing rod; as a result, no axial thrust is produced, and the pipe or equipment is no longer under stress. During the normal compensation process, its own force balance remains unchanged. Force-balancing type for elbows: This is used at pipe bends to provide axial, lateral, or a combination of both types of compensation. It consists of a working bellows, a balancing bellows, as well as balancing rods and elbows. The effective area of the balancing bellows must be equal to that of the working bellows, so that the axial thrust caused by the internal pressure has an exact opposite direction and equal magnitude. It is canceled out by the tie rods. When the lateral displacement is large, two working bellows can be used; if both the lateral and axial displacements are small, one working bellows can be used. Other force-balancing types: To meet developmental needs, various force-balancing type bellows expansion joints suitable for use in different situations have been developed. They are generally designed according to the principle of self-balancing internal pressure, in line with specific requirements. Common types include: 1) Pressure-balanced expansion joints with straight pipes in series; 2) External-pressure floating-type expansion joints; 3) Internally connected pressure-balanced expansion joints with straight pipes; 4) Internal-pressure parallel-type expansion joints; 5) Expansion joints with bypass pipes for force balance. Pressure-balanced expansion joints are primarily used between equipment or in situations where it is not feasible to install fixed supports. It is not suitable for use in long pipelines that require many expansion joints. Its cost is very high, being more than four times that of ordinary axial expansion joints with the same operating parameters. Force-balancing expansion joints and ordinary axial expansion joints cannot be used in series on the same pipeline, otherwise the supports between them will become primary fixing supports, rendering force balancing meaningless. This point is emphasized because there have been cases of misunderstanding and incorrect use of force-balanced expansion joints. 5. Bellows expansion joints with special structures and insulation layers: An insulating material layer is added between the guide cylinder and the bellows. The gas between the insulating material and the corrugations is a dead zone, almost isolated from the high-temperature medium flowing inside the flow guide. The heat from the high-temperature medium can only be transferred to the bellows through the insulating layer, and heat conduction is slow. Outside the bellows is the atmospheric temperature; when the atmosphere is heated, convection occurs naturally, which serves to dissipate heat, and convection can also be enhanced artificially. By designing insulation layers of different thicknesses, the temperature of the bellows can be controlled so that it does not exceed the allowable operating temperature of the bellows material. Different types of insulating materials are selected based on the temperature of the medium. Insulating materials serve to provide thermal insulation; alternatively, steam or air at a pressure higher than that in the pipeline can be introduced from the outside. The clearance between the end of the guide cylinder and the end tube should be relatively small. Due to the continuous flow of gas, gas is continuously ejected into the pipeline from the gap between the end of the guide cylinder and the end tube, preventing the high-temperature medium from entering between the guide cylinder and the corrugated elements; as a result, the actual temperature of the corrugated elements does not exceed the temperature of the steam or gas. With a reinforcing ring: A circular ring with a rigid circular cross-section is added at the trough of the U-shaped corrugation, which enhances the resistance to column buckling and planar instability, thereby improving pressure resistance. When the working pressure is above 2.5 MPa, it is appropriate to use a reinforcement ring; the cross-section of this ring can be a solid circle or a hollow ring. If a stabilizing ring is used, its resistance to instability is greater. Welded structures: Bellows are formed by welding. Its characteristics are low stiffness, large compensation capacity, and small axial size. The disadvantage is its low voltage resistance. To improve voltage resistance, it can also be welded into multiple layers. Furthermore, it requires high technical skills and is costly; it is only suitable for use in special occasions. Rectangle: It is used for low-pressure, ventilated rectangular ducts. Its function is the same as that of a circular corrugated expansion joint, with axial, angular, lateral movements and combinations thereof. The wave shapes are generally U-shaped and V-shaped. There are three common types of corner structures for it, among which the arc-shaped corner has a better stress condition.

Functions and characteristics of expansion joints: An expansion joint is a device with compensatory functions, composed of a metal bellows and various components. It can compensate for the thermal and mechanical deformation of pipes, as well as absorb various mechanical vibrations, thereby reducing the deformation stress on the pipes and extending their service life. Due to its structural characteristics, expansion joints offer advantages such as smaller space requirements, simpler installation, lower construction costs, no risk of structural leakage, and the need for no maintenance. As a result, they are widely used and have seen rapid development compared to \"Π\"-type tension compensators, sleeve-type compensators, and spherical compensators, which also possess similar compensation capabilities. In the early 1970s, a range of products for corrugated expansion joints had already been developed abroad. Due to the needs of national economic development, our country began systematic development of expansion joints in the 1980s, and a range of products were quickly developed for widespread use in heating pipelines as well as in various industries such as chemicals, oil refining, and metallurgy. On the basis of overall development, a technical force has been established with colleges and universities, research institutions, and major manufacturers as its core; this force possesses strong capabilities in research, design, and manufacturing, as well as a robust quality assurance system, enabling it to supply various types of bellows expansion joints suitable for use under different conditions in the national economy. Performance of metal bellows expansion joints: There are two types of performance for expansion joints; one of them are the properties that must be ensured to meet operational requirements, such as pressure resistance, temperature resistance, fatigue resistance, and elastic compensation ； Another category includes parameters such as stiffness and effective area; although they are not required for use, they have a significant impact on the design of piping systems and the use of expansion joints, so it is necessary to have a thorough understanding of them. Pressure resistance: When working in pipelines, bellows expansion joints are subjected to certain pressures (internal or external), which requires them to have sufficient pressure resistance. It determines reasonable structural parameters through design and experimentation to ensure this. The pressure resistance capacity determined in the design is the design pressure. Since bellows expansion joints are a series of products, they are classified into series based on nominal diameter and nominal pressure. In most cases, its design pressure is classified into series corresponding to nominal pressures of 0.25, 0.6, 1.0, 2.5… (MPa). Only a few products are designed for required pressures outside the nominal pressure series. In piping design, the designer determines the maximum operating pressure of the pipes based on actual requirements, and then selects the nominal pressure of the required bellows expansion joints. Generally, the higher value is chosen to ensure greater safety. Compensation capacity: The compensation capacity of bellows expansion joints stems from the elastic deformation of the bellows, which includes tension, compression, bending, and combinations of these deformations. The magnitude of the compensation capacity is determined by the designer based on specific requirements; in the product, this is reflected as the specified rated compensation amount, which represents the maximum compensation capacity under certain conditions. Different types of bellows expansion joints offer various compensation methods, mainly axial, lateral, angular, and combinations of these. Temperature resistance: The temperature resistance of bellows expansion joints depends primarily on the temperature-resistant properties of the bellows material. The operating temperature range for expansion joints is from a minimum of -96°C to a maximum of 1000°C, or even higher. It requires various metal materials with temperature resistance to meet the usage requirements. However, the temperature resistance of materials is limited; it is impossible to address such a wide range of temperatures solely through the material itself. Other measures must be taken to increase the operating temperature of expansion joints. Most bellows expanders operate at temperatures below 400°C, and materials such as carbon structural steel, low-alloy structural steel, and austenitic stainless steel are suitable for this purpose. Service life: The service life is the number of fatigue cycles that a bellows expansion joint can withstand under given operating conditions, up to its maximum allowable displacement. Since there are many factors that affect lifespan, its determination must be carried out with great precision; in addition to using sufficient safety factors in the design calculations, it is also necessary to verify it through experiments. The rated life specified for expansion joints must be guaranteed to be 2 to 5 times the average experimental life. Stiffness: The stiffness of a corrugated expansion joint is the stiffness of the corrugated tube. Here, it is noted that the overall stiffness of expansion joints can be classified into axial stiffness, lateral stiffness, and angular stiffness according to the mode of deformation. The calculations related to stiffness in expansion joints include natural frequency, column stability, and elastic reactions in the piping system. Effective area: The effective area is of no use for bellows expansion joints and only causes problems. A large axial thrust is generated due to the internal pressure acting on the effective area. An expansion joint with a DN500 size and an internal pressure of 16 MP will generate an axial thrust of 37xl04 N. The thrust caused by the internal pressure of the axial expansion joint acts on the fixed support. The internal pressure thrust in transverse and angular expansion joints must be balanced by tie rods and hinges. Supply status: The so-called “supply status” refers only to the length of the product at the time of leaving the factory. Generally, there are two types of supply status: 1. Free state ； 2 Maximum rated tensile state. Different supply conditions will require different methods of \"cold tightening\", that is, the installation length is adjusted according to the temperature during installation, to ensure that the expansion mechanism operates within its rated tensile and compressive displacement ranges at all times. There is no over-stretching or over-compression. Design and manufacturing standards: Over the course of its long-term development, the expansion joint industry has, by drawing on advanced foreign technical expertise and through analysis, comprehension, assimilation, and further refinement, developed expansion joint standards suitable for various industries. These include GB12777-91, which specifies the technical requirements for metal bellows expansion joints ； JB/T6171-92 Metal Multi-layer Bellows Expansion Joints ； JB1121-83 Metal Wave Expansion Joint (for Pressure Vessels) ； GB12522-90 Stainless Steel Bellows Expansion Joint ； CB1153-95 Metal Bellows Expansion Joint (Marine) ； In addition, there are standards such as QJ811-83 (aerospace), HG526-90 (Ministry of Chemical Industry), and JB/YQ293-91. Referable foreign standards: American EJMA standard, Japanese JIS B2352-77 and JIS B8277-93. Among them, the EJMA standard has a significant impact in our country. GB12777-91 is widely adopted in China; it specifies the technical requirements for the design and manufacture of bellows expansion joints.

The manufacturing process of bellows expansion joints consists mainly of three parts: tube blank fabrication, bellows production, and assembly and welding of the expansion joint. Manufacturing process of bellows tubes: Bellows tubes can be made from either seamless or welded tube blanks. Seamless tube blanks are generally produced using pressure processing methods such as spinning, drawing, and rolling, and they are suitable for manufacturing tubes with smaller diameters ； Since bellows expansion joints have a larger diameter, welded pipe billets are mostly used. The welding of bellows tube blanks can be carried out using methods such as tungsten inert gas arc welding with direct current, pulsed tungsten inert gas arc welding, microbeam plasma welding, and gas tungsten arc welding. The appropriate welding method is selected based on the single-layer thickness of the tube blank; generally, for a single-layer thickness of 0.5–1 mm, tungsten inert gas arc welding can be used ； For thicknesses over 1 mm, gas metal arc welding can be used ； Manual arc welding can also be used for thicknesses over 2mm ； When the single-layer thickness is below 0.5 mm, pulsed tungsten arc welding and microbeam plasma welding can be used. Regardless of the welding method used, hard welding parameters (i.e., high current and high welding speed) should be employed to minimize the heat affect on the joint during welding, thereby improving the mechanical properties of the welded joint. For the tube blanks of multi-layer corrugated tubes, the thickness of each layer is generally less than 2 mm; in corrugated tubes with an inner diameter of less than 1 mm, tube blanks are often made from sheets with a thickness of 0.5 mm. Automatic welding is generally used during welding, as this helps to ensure the quality of pipe billet welding. In thin-walled welding, the welding defects are mainly external defects, such as burn-through, lack of penetration, over-heat, undercut, and weld depression. Therefore, welds are usually only inspected visually, without X-ray testing. It is not necessary to use X-ray inspection for the welds of tube blanks with a wall thickness of 0.5 mm, as defects (porosities, inclusions) larger than φ0.5 mm are unlikely to exist within the welds of such thin sheets; and even if such small defects do exist, it is difficult to detect them due to the sensitivity limitations of X-ray inspection. The material for bellows tubes is mostly SUS300 series stainless steel, which has good weldability. Additionally, thin-walled materials experience less constraint at the weld joint during welding, making cracks less likely to occur. For pipe billet welds with a wall thickness of 1–2 mm, if TIG welding or MIG welding is used in an automated manner, with a single-pass double-sided formation process and one welding layer, X-ray inspection may not be necessary. For pipe billet welds with a wall thickness greater than 2 mm, the supplier and the buyer may agree, based on the application requirements, whether to conduct X-ray inspection of the welds. The number of longitudinal weld seams on the tube blank should be kept as low as possible, and the distance between adjacent longitudinal weld seams should be greater than 250 mm. The tube blank manufacturing process is as follows: sheet cutting — winding onto a reel — pre-welding cleaning — welding of the tube blank — rounding of the tube blank — fitting of the tube blank onto the reel. Sheet cutting: According to the requirements of the process layout diagram and process cards, adjust the positioning guides of the cutting machine (or mark lines on the sheet), and then cut the sheet. After cutting the first sheet, a dimension check should be conducted; only if it passes can batch cutting proceed, with random inspections carried out every certain number of sheets (5–10 sheets). The inspection items include the circumferential expansion length and height, the straightness of the cut, and the perpendicularity between adjacent sides. Rolling: The cut sheets are rolled into cylinders using a rolling machine, depending on their diameter. For tube blanks with a high diameter-to-wall thickness ratio that can be freely bent into a cylinder, winding is not necessary. Pre-welding cleaning: To ensure welding quality, pre-welding cleaning is necessary; the welding joint must be free of oil and dust. The surface of the area to be welded can be cleaned using anhydrous ethanol or acetone, and welding should be carried out as soon as it has dried. Welders should not touch the surface of the area to be welded with their hands during the welding process. For tube blank welding, adjust the tube blank welding machine according to the welding parameters specified in the process sheet, clamp the tube blank in the welding fixture, and then proceed with welding. After welding, each piece is inspected; weld defects such as burn-through and incomplete penetration are not allowed. The weld depression (or excess height) and the misalignment between the joint surfaces should be less than 10% of the plate thickness. Billet rounding: The billet is rounded on a rolling mill. In the manufacturing of tube blank assemblies with multiple layers of corrugated tubes, the gap between adjacent layers should be less than or equal to the thickness of a single layer. When the nominal diameter is 1500 mm or less, the interlayer gap is 0.5 mm or less ； When the nominal diameter is greater than 1500 mm, the interlayer gap is less than or equal to 1 mm. Before assembling the tube blanks, the burrs on their ends should be removed to prevent scratching the surface of the tubes. The inner and outer surfaces of each layer of tube billet must be thoroughly cleaned, free from oil, water, and dust. When assembled, the longitudinal welds of the individual tube blanks should be evenly staggered with respect to one another. Bellows manufacturing process: Currently, the main methods for shaping bellows include hydroforming, mechanical expansion forming, and rolling forming. Hydroforming and rolling forming are relatively traditional methods for corrugated tube fabrication, and hydroforming is generally used for manufacturing corrugated tubes with small diameters ； For large-diameter bellows, rolling formation is generally used, but rolling formation can usually only be applied to single-layer bellows. Mechanical bulging is a more advanced forming method that has been developed in recent years. Compared with hydroforming, it increases production efficiency by more than 10 times (for bellows with larger diameters), and also significantly reduces labor intensity. When forming large-diameter multi-layer bellows, the ports do not need to be sealed in order to maintain cleanliness between the bellows layers. Moreover, the equipment is simple and the investment is low; mechanical expansion can be used for bellows with a diameter of 100 mm or more. A circular inner die is used for the mechanical bulging of bellows, and it consists of several die lobes. The manufacturing process for bellows is as follows: wave forming – welding of the bellows’ end edges – cutting of the bellows’ ports. 1. Wave forming (mechanical expansion method): The tube blank that has been fitted is placed outside the mechanical expansion die; the position of the first wave is determined. Then the hydraulic press is activated, and the die components move outward under the action of the hydraulic pressure (through the up-and-down movement of the die’s cones), thereby shaping the tube blank into waves. Once the wave shape meets the requirements specified in the drawings or process sheet, the limiting devices in the die prevent the die components from moving any further outward. At this point, the hydraulic press is moved in the retraction direction; under the action of the return spring, the cone and die petals in the mold gradually return to their original positions as the hydraulic press retracts. After full reset, move the tube blank a certain distance, then repeat the above steps to form a second ripple. This process is repeated until the desired number of corrugations is achieved. The positioning of the tube blank can be achieved by marking on the blank or by using external auxiliary positioning devices. The marking method involves making long marks along the axial direction of the tube blank at the points where the circumference is divided into three equal parts, in a single-wave pattern, to determine the positions for wave formation; the waves are then formed according to these marks ； The external auxiliary positioning device uses three brackets to support the tube blank (at equal intervals around its circumference), determines the position of the first corrugation using the port of the tube blank, and then uses the end face of the previous corrugation to determine the position of the corrugation to be formed. 2. Seaming welding of the bellows edges: Since multi-layer bellows are composed of multiple layers of thin-walled cylinders, in order to ensure the quality of welding between the bellows and the connecting elements (flanges or pipes), resistance seam welding should be used to fuse the edge layers into a single layer. This improves the weldability between the bellows and the connecting elements, results in reliable welding quality, and reduces the risk of leakage between layers. Position according to the length of the straight edge section specified in the process card, and select the welding parameters based on the wall thickness and number of layers for welding. Water cooling is generally used in resistance seam welding, but it is prohibited in the seam welding of bellows edges, as if cooling water enters the spaces between the layers of the bellows, those spaces become sealed after the ends are welded. During the operation of the bellows, if the operating temperature is high, the water remaining in those layers will vaporize rapidly, generating extremely high pressures due to this vaporization and leading to damage to the bellows. 3. Shearing of the bellows ports: The ports are sheared to the required length of straight edges as specified in the drawings or process cards. There are several methods for shearing: (1) Using manual or electric shears for port shearing – this method requires little investment and produces cuts of good quality, but it has low production efficiency, high labor intensity, and is not suitable for cutting thicker materials. (2) A dedicated roll shear is used; this method offers high production efficiency and good cut quality. However, this device is not a general-purpose device; it must be designed and manufactured by the manufacturer itself. (3) The air plasma cutting method is used; it is simple and easy to implement, the equipment is available in various models, its price is reasonable, and it offers high production efficiency. However, the quality of the cut edges is not as good as that obtained with the first two methods, and an oxide layer forms on the surface of the cut edges. Angular grinders are required for finishing the cuts, and the metal dust generated during cutting and grinding results in a poor working environment. 4. Inspection of bellows during manufacturing (1) Bellows may have slight stamping marks; however, there should be no scratches, pits, or unevenness that result in a negative deviation from the thickness of the steel plate. (2) The dimensional tolerances for the wave height, wave pitch, and total length of the bellows shall meet the requirements of grade Js18 as specified in GB 1804. (3) The coaxiality tolerance at both ends of the bellows is 5 mm when the nominal diameter is less than or equal to 500 mm ； When the nominal diameter is greater than 500 mm, it is 1% of the nominal diameter, and shall be less than or equal to 10 mm. (4) The planes at both ends of the bellows shall be perpendicular to the main axis; the deviation in perpendicularity shall be 1% of the nominal diameter, and shall be less than or equal to 3 mm. Assembly and welding of expansion joints: The welding procedures for corrugated expansion joints vary depending on the structure of the joint, but the main steps include: welding of the corrugated tube to the end tubes (or flanges) – welding of composite expansion joints (including accessories such as guide blocks or baffles) – pressure testing – installation or welding of other accessories (such as inner guides, outer shells, guide rods, pre-tensioning rods, etc.) – final assembly inspection. During the assembly and welding process of bellows expansion joints, the following items should be inspected: 1. The dimensional tolerances of the inner and outer diameters of the straight sections of the bellows shall meet the requirements of grade H12 (or h12) as specified in GB1804. 2. The dimensions and technical requirements of the connection flanges and end tubes of the corrugated expansion joint with the pipeline (or equipment) shall comply with the relevant standards. When connecting the end tubes, bevels of 30 degrees +/- 2.5 degrees shall be made at both tube ends. 3. When the end tubes of corrugated expansion joints are made by rolling steel plates into welded pipes, the perimeter tolerance and roundness tolerance of the external ports of these end tubes shall comply with relevant regulations. 4. The circumferential welds connecting the bellows to the end tubes (or flanges) shall be performed using tungsten inert gas welding or gas metal arc welding; arc welding may be used when the single-layer wall thickness of the bellows is greater than 2 mm. 5. When assembling the corrugated expansion joint, protective measures should be taken for the corrugated tube to prevent the welding arc from burning through it and spatter from reaching the tube. The welds in all parts of the expansion joint must be free from defects such as cracks, pores, and slag inclusions, and the root gap depth must not exceed 0.5 mm. 6. After welding the pressure-bearing weld of the corrugated expansion joint, a pressure test shall be conducted on this weld, with the test pressure being 1.5 times the design pressure. Depending on the volume of the expansion joint, maintain the pressure for 10 to 30 minutes and check for any leaks in various parts of the expansion joint; the ratio of the maximum wave length under pressure to the wave length before pressure application should not exceed 1.15. 7. After the expansion joint is welded, its appearance and geometric dimensions should be inspected. Tolerance for coaxiality of the two end surfaces of the expansion joint: 5 mm when the nominal diameter is less than or equal to 500 mm ； When the nominal diameter is greater than 500 mm, it is 1% of the nominal diameter, and shall be less than or equal to 10 mm. The tolerance for the perpendicularity of the two end surfaces of the expansion joint to the main axis is 1% of the nominal diameter, and shall be less than or equal to 3 mm. Expansion joints are pre-stretched before leaving the factory, and the tolerance for their length at the time of shipment after pre-stretching must also meet the specified requirements. Both the length of the expansion joint in its natural state and its length after pre-stretching are subject to inspection. The inspections carried out on expansion joints before leaving the factory mainly include the aforementioned visual inspection, geometric dimension inspection, and pressure test. For expansion joints with special requirements, other testing methods such as airtightness tests, leakage and coloring tests, as well as non-destructive testing, can be carried out in accordance with an agreement between the supplier and the buyer, based on the operating conditions and process requirements.

Applications of expansion joints: As a type of pipeline compensation component, bellows expansion joints are widely used in fields such as electricity, petrochemicals, heating, steel manufacturing, and urban construction. Its function is to act as a compensator in power or thermal piping systems, as well as in the connections between equipment and pipelines, and between different pieces of equipment. Bellows expansion joints compensate for the positional changes in piping systems or equipment caused by temperature differences (or mechanical movement) through axial expansion or angular deformation ； Eliminate vibration under startup, shutdown, or normal operating conditions of the equipment. The application of corrugated expansion joints in power or thermal piping networks: In the power piping networks of factories and the centralized heating networks in cities, significant thermal expansion occurs in the pipes due to the large temperature difference between when the pipes are in use and when they are not. Using bellows expansion joints to compensate for the thermal expansion of these pipelines offers significant advantages over traditional compensation methods such as Π-shaped tension devices and sleeve-type expanders. Bellows expansion joints take up less space, provide excellent sealing performance, are less prone to leakage, and have a high compensation capacity. As a result, they have been widely used in industrial power piping systems and urban central heating networks in recent years. Different types of bellows expansion joints can be used depending on the layout of the pipeline. Applications of bellows expansion joints in the connection between equipment and pipelines, as well as between different pieces of equipment. Bend-force-balanced bellows expansion joints are used for connecting equipment together; their function is to compensate for the thermal expansion of the pipelines between the devices, reducing the forces resulting from installation errors and facilitating installation. By using the force-balance principle of bent pipes in corrugated expansion joints, energy can be saved; this prevents the equipment from being subjected to the force generated by internal pressure due to blind flanges, improves the stress conditions on the equipment, and makes it easier to fix the equipment in place. Bellows expansion joints are used as flexible hoses for pumps, installed on the inlet and outlet pipelines of the pumps. Universal expansion joints, installed on the inlet and outlet pipelines of the pump, are used to compensate for the thermal expansion of the pipelines, reduce the thrust exerted by this thermal expansion on the pump, or absorb the vibrations generated during pump operation. Bellows expansion joints can be used for the flexible connection between storage tanks and pipelines. In recent years, storage tanks in oil fields, oil depots, and chemical plants have become increasingly large. Due to geological constraints, the foundation sinks naturally, causing changes in the position of the storage tanks as well as their inlet and outlet pipelines; this can lead to damage to the connecting pipelines and the tank walls. Therefore, wave expansion joints or metal hoses are installed in the inlet and outlet pipelines of the storage tanks to compensate for such displacement. A small tie-rod type (compound universal) bellows expansion joint is installed in the outlet pipeline of the storage tank. It not only absorbs the axial displacement caused by thermal expansion of the pipeline, but also compensates for the lateral displacement resulting from the settlement of the tank’s foundation, thereby preventing damage to the pipeline and the tank walls. Additionally, it provides some degree of shock and seismic protection. Bellows expansion joints are also widely used in the steel industry. In large blast furnaces and hot blast stoves, large-diameter corrugated expansion joints and rectangular corrugated expansion joints are primarily used. For example, in systems such as the pressure supply and discharge pipelines in blast furnace top equipment, the cooling pipelines of the blast furnace body, the air supply pipelines, the oxygen supply pipelines for large-scale converters, and the cooling water pipelines, different types of bellows expansion joints are used. A universal corrugated expansion joint was installed in the air supply branch pipe of the blast furnace body; it not only compensates for the displacement of the pipeline but also reduces installation stress. The application of corrugated expansion joints in shell-and-tube heat exchangers: In shell-and-tube heat exchangers, due to the temperature difference between the heat exchange tubes and the shell, there is a difference in their thermal expansion rates, which increases the stress on the tube sheet. Installing a corrugated expansion joint on the cylinder to absorb the difference in deformation between the heat exchange tubes and the cylinder will improve the stress conditions on the tube sheet and reduce its thickness.

I didn’t know anything about the selection of expansion joints before; now I have learned it! Thank you!

The introduction is extremely comprehensive; thank you so much!

I would like to know at what temperatures and to what extent of vibration expansion joints are necessary.