Expansion joints

Description

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.

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

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:

• 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.

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

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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.

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Pipe expansion joints

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.

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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

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

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.

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.

How do they work?

An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of construction materials, to absorb vibration, to hold parts together, or to allow movement due to ground settlement or earthquakes.

They are commonly found between sections of buildings, bridges, sidewalks, railway tracks, piping systems, ships, and other structures.

Expansion joints – sometimes called expansion bellows, flexible joints or Expansion joint – are devices that comprise of a flexible element known as the bellows membrane that is fitted to end connections that are best suited to the pipework they are to be installed in.

Most bellows membranes are manufactured from stainless steel and are made up of a series of convolutions manufactured to withstand the pressure of the system but also must be suitable to accept the movements for which they are designed. The bellows membrane comprises of a series of convolutions designed to withstand the internal pressures of the system, but at the same time flexible enough to accept axial, lateral and angular deflections.

The joint needs to be a highly resistant nature so it’s necessary to make sure that it’s far thicker than you’d expect. In turn, this slows down any effects of potential corrosion as although it may be affected by the elements over time, it will still retain its density.

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.

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What different varieties of expansion joints are there?

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.

An expansion joint/bellow element employed in a piping system is an assembly of generally more than one convolute in series. The convolutes are designed strong enough to withstand the internal pressure of the system, at the same time the typical contour of the convolute assembly allow sit to flex under thermal movement of the connected piping. As a result of this extreme flexibility the expansion joint / bellow as such is highly incapable of absorbing any longitudinal loads by its own,thereby requiring external attachments to transfer these longitudinal loads to its connected piping for maintaining the overall stability of the piping system under question.

Common types of expansion joints

• Simple Expansion Joint
• Universal Expansion Joint
• Pressure Balanced Expansion Joint
• Hinged Expansion Joint
• Gimbal Expansion Joint

However should site conditions demand a unique solution then end connections can be adapted to most applications.

What is the difference between a bellows and an expansion joint?

The terms can be confusing since there is no universally accepted meaning. We usually use the following definitions, but the terms “bellows” and “expansion joint” are generally considered interchangeable:

• Expansion joint: An expansion joint is a complete unit with metal, rubber or fabric bellows and end connections and accessories, as well as optionally, internal linings, outer covers, etc … Other terms used: compensator, flexible.
• Metal bellows: it is the flexible element of metal expansion joint.
• Rubber bellows: it is the flexible element of rubber expansion joint.
• Internal lining: the internal lining goes inside the expansion compensator, underneath the metal bellows or the rubber bellows to prevent the circulating fluid from falling directly on the bellows. This reduces flow disturbance and allows the bellows temperature to be controlled in the design.

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Expansion joint accessories

Accessories are added to an expansion joint installation to meet specific customer, application or code requirements. Some are used to control movement, others to protect the bellows in the event of pressure thrust, and still others to defend against corrosion caused by media inside or from the environment outside the bellows.

1. Bellows
2. Angle Flange
3. Weld End
4. Liner (Baffle)
5. Cover
6. Particulate Barrier/Insulation
7. Liner Seal
8. Purge

Internal sleeves

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.

Anchor base

Divide piping into two separate segments insuring proper movement of each bellows in double type expansion joint.

External cover

1. Protect bellows against mechanical damage during installation and in service.
2. Protect personnel in hazardous services.
3. Serve as support for external insulation.

Purge aeration connections
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.

Tie rods

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.

Oversized bellows

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.

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.

Covers

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.

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