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Expansion joints

Expansion joints are devices containing a bellows membrane that are designed to absorb dimensional changes, such as those that occur due to thermal expansion or contraction of a pipeline, duct or vessel.


Expansion joints are designed to safely absorb the movement in pipework systems due to heat-induced expansion and contraction of pipework.

What are Expansion Joints

Expansion joints are devices containing a bellows membrane that are designed to absorb dimensional changes, such as those that occur due to thermal expansion or contraction of a pipeline, duct or vessel.

Expansion joints are devices containing a bellows membrane that are designed to absorb dimensional changes, such as those that occur due to thermal expansion or contraction of a pipeline, duct or vessel. The need to solve the problems of thermal expansion are not unique to anyone industry therefore expansion joints are used in a wide variety of market sectors specifically where there is a need to control the movement of pipelines due to changes in temperature. Thermal expansion problems can be solved where the natural flexing of the pipe is practical or where it is possible to install pipe loops however this is not always possible due to economic reasons or the design of modern structures are not capable of taking the loads of flexing pipework. In these situations the design engineer must seek an expansion joint solution.

Expansion joints come in two forms either restrained or unrestrained styles and although the bellows membrane incorporated in both styles look similar it is of great importance to recognize that they are used for entirely different applications.

Unrestrained expansion joints accommodate pipe movement by compressing and /or extending along their axis and hence they are also known as axial expansion joints. Axial expansion joints are very compact, adaptable and relatively inexpensive. Generally axial expansion joints are designed to accommodate movements between 25mm and 75mm however special bespoke expansion joints can be manufactured to suit specific site conditions. They must be suitably anchored and guided so as to prevent damage from the forces imposed on the pipework system. An installation with unrestrained expansion joints is called a non-pressure balanced solution

Restrained expansion joints are fitted with tie bars and / or hinges and therefore preventing the joint from moving axially. There are several expansion joint models that fall into the restrained group of expansion joints and are called Lateral, Fully Articulated, Hinged or Gimbal. The benefits of installing these types of expansion joints are that anchor forces are generally lower than installing unrestrained bellows and therefore savings can be made when selecting suitable anchors and guides. Restrained expansion joints are used in more complex pipe arrangements specifically on equipment where forces have to be kept to a minimum and, there is a requirement to take up large movements. Although retrained expansion joints are more expensive than unrestrained units significant cost savings on the total installation can be made due to reduced anchor and guide costs. An installation with restrained expansion joints is called a pressure balanced solution

The difference between metallic and rubber expansion joints

Metallic expansion joints prevent damage from thermal expansion, vibration and other movements such as building settlement. Metallic expansion joints are generally manufactured from stainless steels or for more demanding environments or extreme conditions can be produced in materials such as Inconel, Incoloy, Hasteloy and Monel.

Expansion joints can also be produced from a variety of synthetic rubber materials such as ethylene propylene diene monomer (EPDM), Nitrile, Hypalon and Viton materials. Rubber expansion joints are primarily used on pumps, chillers and other reciprocating machinery to reduce noise and vibration. Whilst rubber bellows have the capabilities of compensating small amounts of axial, lateral and angular pipe work movement Sunny Steel always recommend a specifically designed metallic expansion joint to accommodate pipe movements when solving thermal expansion problems.

Are expansion joints the same as movement joints?

Expansion joints – sometimes called expansion bellows, flexible joints, compensators or movement joints. The variety of terminology for the same piece of equipment can be misleading. However expansion joints are designed to safely absorb dimensional movement changes and therefore the different names given to this critical unit are all related to its ability to accommodate a variety of movements such as expansion & contraction due to temperature difference, vibration due to reciprocating machinery, installation misalignment or building settlement.

Complying with the highest standards

At Sunny Steel, we offer a vast selection of expansion joints to serve a variety of purposes and are always on hand to provide you with accurate, high-quality advice whenever you require it. Our range of expansion joints includes axial, lateral, angular and gimbal joints. Our expansion joints are designed and calculated to the latest prevailing standards and pressure directives and therefore where applicable conform to latest Expansion Joint Manufacturers Association (EJMA) calculations. We reserve the right to make changes in the technical calculations without notice. All products are supplied with detailed installation and maintenance instructions where applicable to ensure your pipework system is fully in accordance with recommended engineering practice.

Find the right expansion joints for your needs

We oversee a large amount of stock, which ensures we can minimise downtime and respond to your requests quickly. We can supply joints with a bespoke flexible lagging jacket if needed. Why not contact us today if you do have any queries about the products that we supply? More and more discerning clients are heading straight to Sunny Steel when they do require expansion joints of the highest quality. We are renowned for only supplying products of the highest quality that do the job to the best standard possible and are more than happy to talk you through the options available so you can easily come to an informed decision and invest in the products that are right for you.

What industries use expansion joints?

Expansion joints are used in all kinds of different sectors and in a huge range of different industrial contexts.

  • Expansion joints are particularly suited for aggressive chemicals and for abrasion resistance.
  • Sunny Steel Metal Expansion Joints can be custom-made from a range of carbon steels, austenitic stainless steels anc ceramic lined.
Stainless steel pipe expansion joint, with control rods

Essentially, wherever there is a need to control pipework movement expansion joints are required. They are used in factories and power plants wherever thermal expansion needs to be controlled, such as pipelines that connect with condensers or power turbines. They are used in oil and fuel gas applications.

Specific industries that use expansion joints include the Energy sector such as nuclear power plants and district heating schemes.

The Petrochemical industry on oil refineries, pumping stations and oil rigs.

Civil engineering, waste management, sewage treatment, recycling, water treatment, aerospace, aviation, defence, the automotive industry, agriculture, mining, metals manufacturing, food and dairy manufacturing and packaging, and so on.

Piping Expansion Joint Construction

Pipe expansion joints are also known as compensators, as they ‘compensate’ for the thermal movement.

Pipe expansion joints are necessary in systems that convey high temperature commodities such as steam or exhaust gases, or to absorb movement and vibration. A typical type of expansion joint for pipe systems is a bellows which can be manufactured from metal (most commonly stainless steel), plastic (such as PTFE), or an elastomer such as rubber.

A bellows is made up of a series of one or more convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept the axial, lateral, and/or angular deflections. Expansion joints are also designed for other criteria, such as noise absorption, anti-vibration, earthquake movement, and building settlement.

Tube – A protective, leak proof lining made of synthetic or natural rubber. The tubes primary function is to eliminate the possibility of materials being handled penetrating the carcass.

Carcass – The carcass or body of the expansion joint consists of fabric, and when necessary metal.

Cover – The exterior surface of the joint.

Fabric Reinforcement – The carcass fabric reinforcement is the flexibility and supporting member between the tube and cover.

Metal Reinforcement – Wire or solid steel rings imbedded in the carcass, often used for strengthening.

Retaining Ring – Used to compress the expansion joint flange to the mating flange to create a seal. Also called clamp bars or backing bars. Applies to most all expansion joints.

Mating Flange – Used to connect the pipe joint to the pipe in which it is being installed.

Control Rod – Used to limit the axial movements during operation, and prevent the joint from exceeding its movement capabilities. The rods attach the mating flange and expansion joint. Typically used on piping joints, but can be installed on most any joint when required.

Expansion joints are an assembly designed to safely absorb sound, expansion, con traction and vibration to ensure expansion jointsthat the application stays in fully working order.

When we apply this technique to pipe systems, we brand the term ‘pipe expansion joint’ or ‘bellows’.

These pieces of equipment are used in pipe work where movement, thermal expansion and much more could cause problems. The pipe expansion joints are made up from one or more convolutions, which are designed to move or expand to relieve the stress from the solid pipe. The amount of movement or expansion within the application will determine the number and shape of convolutions required. Expansion joints can be manufactured from a range of different materials, from stainless steel and PTFE, to rubber.

Pipe expansion joints are also designed for other criteria, such as noise absorption, anti vibration, earthquake movement and building settlement. Metal expansion joints have to be designed according to rules. Pipe expansion joints are used in a number of industries, including; oil, petrochemical and paper industries.

Pipe expansion joints are often manufactured to withstand temperatures from minus 300°F, up to 4000°F, as well as being able to resist at full vacuum or 2000 psig. Expansion joints can be manufactured from a range of different materials aforementioned. Before the introduction of pipe expansion joints, engineers were battling with the task of combating problems regarding thermal expansion, corrosion and abrasive factors that took effect on the functionality of various applications. Fabric joints can be used in a number of applications for turbines and pipelines, which can defend against resistance, heat and a range of other environmental factors.

Pipe expansion joints are crucial components in the pipe technology sector, which serve a huge number of industries. They are used to counterbalance length changes that generally occur in pipelines from temperature changes and can also absorb vibrations. It is a cost effective solution to increase the life span, reliability and costs of many applications through equipment and process management.

Expansion joint accessories

  1. Bellows
  2. Angle Flange
  3. Weld End
  4. Liner (Baffle)
  5. Cover
  6. Particulate
  7. Barrier/Insulation
  8. Liner Seal
  9. Purge
  1. Minimize the pressure drop through expansion joint.
  2. Prevent vibration of bellows induced by high velocity, turbulent flow.
  3. Prevent erosion of bellows in abrasive services.
  4. Internally insulate bellows in high temperature services.
  1. Divide piping into two separate segments insuring proper movement of each bellows in double type expansion joint.
  1. Protect bellows against mechanical damage during installation and in service.
  2. Protect personnel in hazardous services.
  3. Serve as support for external insulation.

Used in conjunction with internal sleeve to:

  1. Prevent packing, “coking”, of flue-solids between internal sleeve and bellows.
  2. Introduce coolant between bellows and internal sleeve in very high temperature service.
  1. Prevent application of pressure thrust to piping, or equipment when expansion joint is used for lateral deflection and/or angular rotation only.
  2. Used as limit rods on expansion joints for axial movement. Limit over-extension of joint and damage to piping or equipment if anchor fails.
  3. Used as control rods to limit and control movement of universal type expansion joints.
  1. Permit use of internal sleeve for joint moving laterally or angularly without reducing inside diameter.
  2. Used in conjunction with internal sleeve to reduce bellows temperature in very high temperature service.

Customer sketches Liners
Internal liners can be used to either protect the metallic bellows from erosion or reduce turbulence across the bellows. They must be used when purge connectors are included in the design. In order to provide enough clearance in the liner design, appropriate lateral and angular movements must be specified by the designer. When designing an expansion joint with combination ends, flow direction must be specified as well.

External covers should be used to protect the internal bellows from being damaged. They also serve a purpose as insulation of the bellows. Covers can either be designed as removable or permanent accessories.

Particulate barriers/purge connectors
In systems that have a media with significant particulate content (i.e. flash or catalyst), a barrier of ceramic fiber can be utilized to prevent corrosion and restricted bellows flexibility resulting from the accumulation of the particulate. Purge connectors may also be utilized to perform this same function. Internal liners must also be included in the design if the expansion joint includes purge connectors or particulate barriers.

Limit rods
Limit rods may be used in an expansion joint design to limit the axial compression or expansion. They allow the expansion joint to move over a range according to where the nut stops are placed along the rods. Limit rods are used to prevent bellows over-extension while restraining the full pressure thrust of the system.

Expansion Joints applications

An expansion joint is a useful component in an infinite number of applications.

Pipe expansion joints are necessary in systems that convey high temperature commodities such as steam or exhaust gases, or to absorb movement and vibration. A typical type of expansion joint for pipe systems is a bellows which can be manufactured from metal (most commonly stainless steel), plastic (such as PTFE), or an elastomer such as rubber.

A bellows is made up of a series of one or more convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept the axial, lateral, and/or angular deflections.

Expansion joints are also designed for other criteria, such as noise absorption, anti-vibration, earthquake movement, and building settlement.

Engineers and pipe designers routinely incorporate expansion joints into their pipe systems, as expansion joints add flexibility in to the design and reduce costs through removing the complexity of fix points, guides and reduces the overall space requirements for the pipe system.

Further, expansion joints are more effective than alternatives such as pipe bends and pipe loops due to their greater ability to conserve space, their economic efficiency and better performance in absorbing larger movements.

Where are expansion joints in use?

An expansion joint is a useful component in an infinite number of applications. Metal expansion joint assemblies are commonly used for all kinds of industries and applications including:

Metal Expansion Joints
Thick Wall Pipe Expansion Joint
  • Power Generation
  • Co-Generation, Petrochemical
  • Chemical Processing
  • Pulp Paper Manufacturing
  • Cryogenic Process
  • Pressure Vessel and heat Exchanger
  • Heat Steam recovery Generator
  • Architect Engineering
  • Construction Engineering
  • Mechanical contractor
  • Pharmaceutical manufacturing
  • Gas Turbine, Gas Transmission
  • Diesel Engine Mfg, Incineration
  • Waste Water Treatment

Expansion joints are often installed near boilers, heat exchangers, pumps, turbines, condensers, engines and in long pipe systems or pipe ducts.

What types of expansion joint types are available?

Expansion joints come in a wide variety of designs. Some of them are standard and some are customised as per client requirements.

Although their design may vary significantly, all expansion joints are nevertheless composed from some of the following components, all with one or more specific functionalities: bellows, welding ends, flanges, hinges, tie-rods, spherical washers, wire mesh, insulation, inner sleeve, external cover, elbow and/or ring reinforcement/equalizing rings.

In general, there are fabric, metallic, and rubber expansion joints.

  • Metallic Expansion Joints
    • Single Expansion Joints
    • Hinged Expansion Joints
    • Gimbal Expansion Joints
    • Universal Expansion Joints
    • Elbow Pressure Balanced Expansion Joints
    • In-line Pressure Balanced Expansion Joints
    • Externally Pressurized Expansion Joints
    • Toroidal Expansion Joints
    • Thick Wall Expansion Joints
    • Slip-type Expansion Joints
    • Rectangular Metallic Expansion Joints
    • Refractory Lined Expansion Joints
  • Fabric Expansion Joints
  • Rubber (Neoprene) Expansion Joints

In a piping system a Expansion joints alternately known as Bellows are like sealed springs. Sealed because it is required to contain the fluid pressure which is flowing through it and spring because it is required to respond to the movement of the connected piping without offering appreciable stiffness to the piping system.

Application of Expansion Bellows:

The Bellows are generally employed in a piping system in one of the following situations:

  • When the space constraints do not permit providing adequate flexibility by conventionalmethods (e. g. expansion loops etc.) for maintaining the system stresses withinacceptable limits.
  • When conventional solutions (e.g. expansion loops etc.) create unacceptable processconditions (e.g. excessive pressure drop).
    When it is not practical to limit the piping induced loads on the terminal nozzles of theconnected equipment within admissible limits by conventional methods.
  • When the equipment such as Compressors, Turbines, Pumps etc. necessitate isolatingthe mechanical vibrations from being transmitted to the connected piping.

These may be a cost-effective option for large-diameter piping systems which operate at low pressure. Metals can be selected to satisfy different temperature conditions. The distribution of axial, angular, and lateral forces will be different when thick-wall pipe expansion joints are used. We can provide your design engineers with the potential forces and movements for proper design of the structural members supporting the system. These joints have a long life which justifies the initial investment.

Thick-wall expansion joints are used primarily in heat exchangers and large diameter piping systems where thin-wall expansion joints would not be sufficient. The bellows are typically fabricated from A516 Grade 70 material, with the thickness ranging from 3/16″ to 1″. Other materials are available to meet different temperature requirements.

Thick Wall Expansion Joints are normally supplied without any end connections due to the fact that it is easier to weld the end fittings to them by a relatively less skilled welders. The heavy wall bellows are less susceptible to damage during installation and system start-up however these bellows possess high spring forces as a result of high convolution profile. The thickness of these thick wall bellows elements vary from 1 mm to 3 mm depending up on size and the height of convolution varies from 50 mm to 100 mm.

Thick Wall Expansion Joint (Bellows), has a very diverse methodology, which is explained in one of the articles below. The following calculations are supported:

  • Cylinder calculations
  • Differential axial thermal expansion
  • Axial rigidity
  • Radii requirements
  • Cylinder calculations
  • Cycle life
  • Minimum thickness based on material and service
Universal tied expansion joint

Universal tied expansion joints consist of two bellows with a central pipe and tie rods to withstand reaction forces produced by internal pressure.  The universal tied expansion joint allows large lateral movement in all planes, this movement can be increased by increasing the length of the central pipe. 

Universal tied expansion joint with flanges

The universal tied expansion joint can take greater axial, lateral and angular movements than a single tied expansion joint. If the universal tied expansion joint is designed with only two tie rods, equally spaced @ 180 degree, the expansion joint will take both lateral and angular movements. If more than two tie rods are used then this kind of expansion joint will only take lateral movement. Dome washers are also used depending upon the design requirement.

Universal tied expansion joint with pipe ends

Universal tied expansion joint, Universal expansion joint, Universal tied expansion joint with flanges, Universal tied expansion joint with pipe ends

Ducted Air Systems

Expansion joints are required in large ducted air systems to allow fixed pieces of piping to be largely free of stress as thermal expansion occurs.

Bends in elbows also can accommodate this.

Expansion joints also isolate pieces of equipment such as fans from the rigid ductwork thereby reducing vibration to the ductwork as well as allowing the fan to “grow” as it comes up to the operating air system temperature without putting stress on the fan or the fixed portions of ductwork.

An expansion joint is designed to allow deflection in the axial(compression) or laterally (shear) or angular (bending) deflections. Expansion joints can be non-metallic or metallic (often called bellows type). Non-metallic can be a single ply of rubberized material or a composite made of multiple layers of heat and erosion resistant flexible material.

Typical layers are: outer cover to act a gas seal, a corrosion resistant material such as Teflon, a layer of fiberglass to act as an insulator and to add durability, several layers of insulation to ensure that the heat transfer from the flue gas is reduced to the required temperature and an inside layer.

A bellows is made up of a series of one or more convolutions of metal to allow the axial, lateral or angular deflection required.

Bonding pipe joints

Bonding pipe joints, where two or more parts use a combination of welded joints, or refers to two or more parts connected by welding joints, including welds, fusion zone and heat affected zone.

Welded joints zone

After fitting the metal and filler metal melts faster speed Youyi formed after cooling and solidification. Weld from the cast structure of the liquid metal crystals, coarse grains, segregation, the organization is not dense. However, due to the small weld pool, fast cooling, strict control of the chemical composition, carbon, sulfur, phosphorus are low, but also by adjusting the chemical composition of the weld alloying, it contains a certain amount of alloying elements, so the performance of the weld metal not a big problem, meet the performance requirements, particularly strength easy reach.

Fusion zone

Melting zone and a transition portion between the non-melting zone. Chemical composition of fusion zone unevenly thick tissue is often coarse thick hardened tissue or overheating tissue. The performance of the welded joints are often the worst. Fusion zone and the heat affected zone of the overheated zone (or quench zone) is the worst of the mechanical properties of welded joints of the weak parts, will seriously affect the quality of welded joints.

Heat affected zone

Heated high-temperature weld zone microstructure and properties caused by changes in the region. Low-carbon steel heat-affected zone can be divided into overheated areas, and part of the phase transition region normalizing area.

  1. The maximum heating temperature superheat zone area above 1100 ℃, coarse grains, and even overheating tissue, called the superheat region. Ductility and toughness decreased significantly overheated zone, the heat affected zone is the worst part of the mechanical properties.
  2. The maximum heating temperature from normalizing zone area Ac3 to 1100 ℃, the air-cooled welding grains get smaller after normalizing organization called normalizing area. Better mechanical properties of the normalizing zone.
  3. Part of the maximum heating temperature phase transition region to region from Ac1 Ac3, only part of the organization phase transition, called partial phase transition area.

This area grain uneven performance is also poor. During the installation welding, welding welding method more often. The high temperature heat welded joint is locally heated matrix metal and the filler uniform body of molten metal while solidifying the molten form. Depending on the microstructure and properties of the various parts of welded joints can be divided into three parts.

Reliable research on Expansion joint

Compensator reliability is by the design, manufacture, installation and operation and management and other aspects of the composition. Reliability should also be considered from these aspects.

Material Selection For the selection of corrugated pipe for heating pipe network, in addition to considering the working medium, working temperature and the external environment, the possibility of stress corrosion should also be considered, the impact of water treatment agent and pipe cleaning agent on the material, etc.,

Based on this, the corrugated pipe material is welded and formed, and the cost performance of the material is optimized. The economical and practical corrugated pipe material is selected.

Under normal circumstances, the use of corrugated pipe material should meet the following conditions:

  1. high elastic limit, tensile strength and fatigue strength, to ensure the normal work bellows.
  2. good plasticity, easy corrugated pipe processing and shaping, and can be followed by the treatment process (cold hardening, heat treatment, etc.) to get enough hardness and strength.
  3. better corrosion resistance, to meet the bellows in different environments work requirements.
  4. good welding performance, to meet the bellows in the production process of the welding process requirements.

For the laying of the heat pipe network, when the compensator is located in the lower pipelines, rain or accidental sewage will soak corrugated pipe, should consider the use of more corrosion-resistant materials, such as iron-nickel alloy, high-nickel alloy. Due to the high price of such materials, it may be advisable to add a corrosion-resistant alloy only to the surface in contact with the corrosive medium when making the bellows.

What is the Function of Stainless Steel Bellows Expansion Joint?

Stainless steel bellows expansion joint mainly has three basic movement types: axial movement, lateral movement and angular movement. What’s the function of stainless steel bellows expansion joint? Generally speaking the functions are absorbing vibration, compensating movement and absorbing noise. Please check below detailed information.

Absorbing piping vibration

On one hand, stainless steel bellows expansion joint can enhance the fatigue rupture capacity, on the other hand, it has function of reducing piping noise.

Compensating piping movement

Take rubber hose as comparison, rubber hose has good flexibility and strong anti-fatigue ability, but it is inferior in temperature resistance, pressure bearing, aging resistance than stainless steel bellows expansion joint, it always needs to be changed after using a few months. While metal bellows owns comprehensive performances of out-standing corrosion resistance, temperature resistance, pressure resistance, fatigue resistance, in some complex environment, stainless steel bellows expansion joint is the most ideal element to compensate piping movements.

Piping installation stress

Typical installation problems always seen in some complex piping systems, the problems always caused by limitation of space and location. According to different pipeline diameter and working environment, the cold straightening value differs from several millimeters to dozens of millimeters, even hundreds of millimeters. Practise has proved that the larger of the cold straightening value, the higher of the internal stress, internal stress is a hidden danger to the pipeline system. Since stainless steel bellows expansion joint is able to bend freely and generate minimize internal stress in rated bending radius, thus, it is extremely convenient for installation, that’s the reason why stainless steel bellows expansion joint is the essential pipe fitting for some pipeline systems.

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