Fabric Expansion Joints — The Expansion Joints Blog


Fabric Expansion Joints and Factors Influencing their Design

July 16th, 2012 Comments off

Fabric Expansion Joints and Factors Influencing their Design

Rectangular Fabric Expansion Joint with a Three Layer Fabric BeltFabric expansion joints perform a function of compensating for duct misalignment and duct thermal growth typical in power plants and other ducting systems. Proper design of these joints starts with asking the right questions about the application, providing the correct answers, and applying design rules to arrive at the appropriate solution.

The guiding principle for fabric joint design is to protect the fabric belt element so that it can absorb movement while retaining the media. The longevity of the belt life can be diminished by many factors. These factors include excessive temperature, harsh corrosives, exposure to abrasive particulate, excessive movements, fly ash weight against the belt, and high internal pressures. All of these problems can be solved if they are anticipated. The quality of the expansion joint design is only as good as the information provided up front. A realistic and accurate analysis of the system is step one. Assuming that is taken care of, these guidelines are a brief introduction to factors that influences the success of the expansion joint.


http://www.usbellows.com/images/literature/sample-multi-layered-fabric-ej.jpgFabric gas seal membranes have specific temperature capabilities. When necessary, the addition of insulating materials between the temperature source and the belt will extend the service life. The magnitude of the temperature will determine the thickness of the integral belt insulation and if a separate high density insulation pillow is required.

The belt attachment flanges should be outboard of the cavity and have sufficient standoff from the duct. Care should be taken to avoid external insulation or lagging outside of the belt which prevents proper heat dissipation.

Chemical Attack

Applications that do not have high temperatures sometimes have a different problem. Relatively low temperatures in flue gas ducting can lead to corrosive condensation. In these situations, a chemical barrier is required to protect the load bearing fiberglass carcass of the belt. External insulation over the joint in these locations can reduce condensation and heat loss.


High Temperature Round Fabric Expansion Joint Cross SectionGenerally, movements occur along the axis of the duct (usually compression but occasionally extension) or at right angles (lateral). The key to being able to handle these movements is having the proper width of belt installed in a sufficient span. For compression, a ratio of installed belt span to movement roughly at 4:1 is suggested. The lateral capability is influenced by the amount of belt slack available. Concurrent axial compression will provide the slack thus allowing more lateral. In certain situations, there is lateral offset in the cold installed condition. This may require “pre-compression” of the joint which is in essence just providing extra belt width.


In flue gas ducting with particulate, a liner should be used to protect the belt from direct exposure. If the pressure is negative, the belt stand-off from the gas stream should be increased to keep the belt from being pulled into the gas stream or against the liner. Belt clamping bar edges next to the fabric should be radiused. The belt attachment flange should also be smooth and free of rough surfaces.

Pressure Fluctuations

Fabric expansion joints exposed to sudden pressure fluctuations, such as near ID fans and dampers, may result in the belt “fluttering”. The fabric will fatigue over time resulting in tears. Using stiffer fabric material, installing a liner and increasing the standoff are steps to take to avoid flutter.


Each location throughout a ducting system can have different conditions that affect the design of expansion joints. As a result, there isn’t one design that can fit all applications. The goal of the expansion joint supplier is to work with engineers and end users to provide the optimum economical solutions.

View the full online Fabric Expansion Joint Catalog.

What is a fabric expansion joint, how do they work and what are the advantages of design integration?

July 2nd, 2012 Comments off

What is a Fabric Expansion Joint?

Diagram of fabric expansion joint in a power plantFabric expansion joints perform a function of compensating for duct misalignment and duct thermal growth typically in power plants and other ducting systems. Fabric expansion joints are found wherever there is a need to convey hot media in low pressure applications such as “in flowing air” and “out flowing gas” in large combustion processes.

Fabric expansion joints can absorb larger movements than metal expansion joints and do so without spring loads. This is critical to limiting thermally induced stresses in ducting, ducting supports, and related equipment.

How Does a Fabric Expansion Joint Work?

Frabic Expansion Joint Movement DiagramA fabric expansion joint is inserted into a gap in the ductwork where movement will occur. A fabric expansion joint has two main components — the fabric gas seal and the metal frames. The fabric gas seal is a closed loop, like a belt, with its two edges clamped all around to the metal frames that are in turn connected to the end of ducting. As the ducting moves the fabric belt deforms. The fabric material must do this without tearing or leaking while sometimes being exposed to high temperatures and/or corrosive media.

In some instances, additional components such as insulation pillows, accumulation barriers or flow liners are utilized to help protect the fabric material. The following section describes the basics of fabric expansion joint components and how they are designed.

Design Integration for Fabric Expansion Joints

Expansion Joint Assembly with Duct WorkIn addition to fabric expansion joints, U.S. Bellows is a major designer and fabricator of ducting. Design Integration is the design, manufacture and shipping of expansion joints integrated into the ducting as a complete unit directly from U.S. Bellows. This enables U.S. Bellows to offer optimum system design and the lowest installed cost.

Design Integration Advantages:

  1. Elimination of flanged connection gasketing and potential leaks.
  2. Elimination of the risk of installing sensitive assemblies at the job site.
  3. Fabric Expansion Joint Duct WorkSignificant costs savings of both manufacturing and installation labor.
  4. Delivery of the largest “shippable” duct and piping sections to the job site to eliminate as many filed connections as possible, further reducing installation labor.
  5. Minimize the number of flanged expansion joint connections.
  6. Allows integration of ducting to serve as expansion joint flow liner.
  7. Allows expansion joint frames to take the place of duct stiffeners.
  8. Elimination of labor to install flanged expansion joint assemblies at the job site.

Fabric Expansion Joint Style 100WU.S Bellows has considerable experience in design and fabrication of integrated ducting with metal and fabric expansion joints. U.S. Bellows is also very knowledgeable with transportation capabilities for wide and heavy loads and can make firm commitments “up-front” for the largest shippable size and heaviest weight.

The drawing below shows a cross section of an expansion joint designed to allow the ducting to serve as a flow liner. The joint frame takes the place of a stiffener flange. The complete duct/expansion joint ships as one factory assembled component.

Use Our Expansion Joint Catalog Online, Download a PDF Version or Request Your Own Copy

June 4th, 2012 Comments off

Access our full expansion joint catalog online, anytime. You can also download a PDF version from our site to use offline. If you would like your own copy, please fill out the Catalog Request Form. Our expanded catalog includes:

  • Expansion Joint Catalog CoverDetails about our bellows design
  • Bellows material characteristics and details
  • Types of deflection, including diagrams and examples
  • Cyclic deflections and cycle life
  • Types of metallic expansion joints (movements, principal advantages, limitations and uses)
  • Accessories, including liners, covers, purge connectors and limit rods
  • A full installation and maintenance guide, including the “Do’s and Dont’s” from EJMA
  • Inspection criteria and typical causes of expansion joint failure
  • Details on expansion joint design, pipe guide spacing, and flange data
  • Sample applications and examples
  • Glossary of terms
  • Safety recommendations
  • Equivalency charts
  • Terms of sale

Fabric Expansion JointsCheck out our new fabric expansion joint catalog online as well.

View the basics about fabric expansion joints, including how they work and some design integrations. Also learn about the factors that influence their design like: temperature, chemical attack, movements, abrasion, pressure fluctuations and summation. Read about fabric expansion joint applications, frame styles, materials, inspection and installation.

Neoprene Fabric Expansion Joints for a Ventilation Fan Intake Duct

May 21st, 2012 Comments off

Neoprene Fabric Expansion Joints for a Ventilation Fan Intake Duct

Neoprene fabric expansion joints were custom designed for a ventilation fan intake duct in a power plant. They are 42″ in diameter and are 65″ in overall length. They were designed for 1/4″ axial movement, 1/8″ lateral deflection and a 100″ water column at 200°F. The expansion joints are fabricated with a neoprene reinforced belt with stainless steel clamps, carbon steel spool pipe and angle flange ends. Each joint was dye penetrant examined prior to shipping.

View our past expansion joint and duct work projects in the Featured Product Archives

May 14th, 2012 Comments off

Check out some of our past projects in the Featured Product Archives section of our website.

  • View images of metallic and fabric expansion joints, duct work, and combination assemblies.
  • Also read the details on the project itself, including design specifications and testing requirements.
  • The projects are conveniently grouped by the type of expansion joint and then listed descending by the release date.

Here are a few examples:

36″ Tied Universal Expansion Joint for a Petrochemical Plant in Kuwait
36" Tied Universal Expansion Joint
U.S. Bellows Inc. designed and fabricated a 36″ tied universal expansion joint for a petrochemical plant in Kuwait. The expansion joint measures 36″ in diameter x 318″ from center of elbow to face of flange. It is fabricated from 316H stainless steel with Inconel® 800 bellows. The design pressure of the expansion joint is 65 PSIG, and the design temperature is 1076°F. It is designed for axial compression within the tie rods and lateral movement of 3.02″. Hydro-testing was performed at 98 PSIG to assure the integrity of the tie rods and also to assure quality. The pictures show the expansion joint leaving the shop on its way to the customer. The stainless steel flange faces are protected with 3/4″ plywood during delivery.
44″ Double Gimbal Universal Expansion Joint for an Oil Refinery in Wyoming
44" Double Gimbal Universal Expansion Joint
This gimbal expansion joint is designed for angular rotation in two planes of up to 4° in each plane. It has an overall length of 140″ with a total assembly weight of 11,000 lb. It is fabricated with 316 stainless steel bellows and carbon steel piping. This expansion joint was 100% dye-penetrant examined and hydro-tested prior to shipment. U.S. Bellows, Inc. and Piping Technology & Products, Inc. also furnished the spring supports and pipe attachments for this project.
128″ x 229″ Rectangular Fabric Expansion Joints for an Exhaust Duct
128" x 229" Rectangular Fabric Expansion Joints
The fabric expansion joints shown above are fabricated with a three layer fabric belt. The three layers consist of an inner layer of silica cloth, a middle layer of mineral wool and an outer layer of PTFE/coated fiber glass. The frame includes an insulation blanket of mineral wool and stainless steel wire mesh. The frame and liner are fabricated from 3/8″ thick 304 stainless steel and each expansion joint’s frame and liner welds were dye-penetrant tested before shipping. 

- Pressure: 1 PSIG
- Temperature: 1010°F

Design Movements:
- 2″ Axial Displacement
- 3/4″ Lateral Displacement

Fabric Expansion Joints Designed for a Lignite Coal Processing & Gasification Plant

April 23rd, 2012 Comments off

Fabric Expansion Joints Designed for a Lignite Coal Processing & Gasification Plant

Fabric Expansion Joints Designed for a Lignite Coal Processing & Gasification Plant

A total of thirty-six fabric expansion joints were custom designed for a lignite coal processing and gasification plant in Mississippi. They are 12″ diameter, 14″ overall length and designed for 1/4″ axial movement and .8″ lateral movement. The expansion joints are fabricated with carbon steel flange ends, stainless steel clamps and a PTFE coated fabric belt. They are designed for hot air circulation flow at 600°F and a pressure of 30″ water column.

Fabric Expansion Joints from High Temp. Furnace Bags to E.J. and Duct Work Assemblies

April 16th, 2012 Comments off

Fabric expansion joints are often used in ducts which carry hot gases at low pressures. The major design parameters are the temperatures and flow rates of the gases and the amount and abrasiveness of solids suspended in the gases. Layers of different fabrics insulation can be combined to accommodate the temperatures and pressure in the system. We specialize in all types of fabric expansion joints from high temperature furnace bags to fabric expansion joint and duct work assemblies.

View the Materials Comparison Chart to see the details behind each material used in fabric expansion joints.

Air Duct Fabric Expansion Joint 44" Diameter Fabric Expansion Joint 24" Diameter Fabric Expansion Joint
Air Duct Fabric
Expansion Joint
44″ Dia. Fabric
Expansion Joint
24″ Dia. Fabric
Expansion Joint

Get pricing now for your next fabric expansion joint project.

High Temperature Furnace Sealing Bags Designed to Prevent Heat Loss

April 2nd, 2012 Comments off

Furnace Sealing Bag, A High-Temperature fabric Expansion Joint

A special type of high-temperature fabric expansion joint developed by U.S. Bellows, Inc. is the furnace sealing bag. The objective of the bag is to seal the air inlet conduits’ penetrations into a furnace and thus prevent heat loss. Because of thermal expansion of both the conduits and the furnace, the bag must be able to expand and contract during normal cycles of operation.

Furnace Sealing Bag, A High-Temperature fabric Expansion Joint

The bag consists of a tapered sleeve formed from layers of flexible, flame and heat-resistant impervious fabric, which is connected at its upper end to another sleeve in the furnace floor. The lower end of the bag is connected to the air inlet

conduit (usually a pipe) so as to form an airtight seal. The connection to this pipe is made such that the fabric is collapsed when the furnace is cold and extended when the furnace is hot. When required, a tapered coil spring formed from suitable metal is installed around the conduit inside the bag. This prevents the fabric from collapsing inward during vacuum conditions inside the furnace. For most applications, band straps may be used to attach the bag at both ends.

Read more in this technical bulletin on High Temperature Furnace Seal Bags.

Browse Our Brand New Fabric Expansion Joint Catalog Online

March 26th, 2012 Comments off

U.S. Bellows is proud to release our online fabric expansion joint catalog!

Fabric expansion joints perform a function of compensating for duct misalignment and duct thermal growth typical in power plants and other ducting systems. Fabric expansion joints are found wherever there is a need to convey hot media in low pressure applications such as “in flowing air” and “out flowing gas” in large combustion processes.

Browse our fabric expansion Joint catalog!

  1. Learn About Fabric Expansion Joints
  2. Find the Right Fabric Expansion Joints by Applications & Conditions
  3. Fabric Expansion Joint Design Styles
  4. Fabric Expansion Joint Materials

Where Fabric Expansion Joints are Typically Used in a Fossil Fired Power Plant

March 2nd, 2012 Comments off

See an example of how fabric expansion joints are being used with ducting. The figure below represents a typical balanced draft system with a “cold” precipitator. The black components represent the locations of fabric expansion joints throughout the system.

Expansion Joints in a Typical Blanced Draft System with a Cold Precipitator

**The examples above are representative and should not be used for design. The user should obtain actual values for the particular system being considered

The main sections of the ducting are as follows:

  • FD Fan to Air Preheater
  • Air Preheater to Boiler
  • Air Preheater to Pulverizer
  • Air Preheater to Inlet from Boiler
  • Air Preheater to Precipitator or Bag house
  • Precipitator or Bag house to ID Fan
  • ID Fan to Scrubber
  • Scrubber to Stack



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