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Frame Designs for Fabric Expansion Joints

August 27th, 2012 Comments off

Fabric expansion joints consist of two major components, the fabric belt material and the metal frame. The frame can connect to the ducting by welding or bolting. Each U.S. Bellows frame style has features designed to minimize the detrimental effects of temperature, movements, pressure, media, and turbulence. The U.S. Bellows team is experienced in evaluating application conditions and implementing designs that lead to long term expansion joint service.

Design alterations can include the following:

  1. Adequate stand off height
  2. Adequate face to face dimension
  3. Inclusion of liner
  4. Frame material
  5. Belt material
  6. Inclusion of accumulation barrier
  7. Inclusion of insulation pillow
  8. Proper bolt hole spacing
  9. And more

Although U.S. Bellows can provide weld-in and bolt-in frame styles, wherever possible, it is strongly recommended that the expansion joint be welded in place.

Weld in Designs

Weld in design frame styles allow the expansion joint to weld directly to the duct or duct flanges. These frames styles are basic designs that can be augmented with optional components.

Benefits of weld in designs include:

  1. Weld in designs are less expensive to manufacture.
  2. Accurate field bolt hole dimensional data can be difficult to obtain and verify.
  3. Welded connections can accommodate “real world” field conditions and inaccuracies that occur during installation.


Style 100-W Style 200-W
Fabric Expansion Joint Movement Illustration Fabric Expansion Joint Movement Illustration

Bolt in Designs

Bolt in design frame styles allow the expansion joint to bolt directly to duct flanges or equipment flanges supplied by others. These bolt in designs are generally more expensive to manufacture and are potentially more difficult to install due to hole pattern irregularities and inaccuracies. These frame styles are basic designs that can be enhanced with the optional components.

Style 100-B Style 200-B
Fabric Expansion Joint Movement Illustration Fabric Expansion Joint Movement Illustration

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.

Temperature 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.

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.

New Equivalency Charts Online

November 14th, 2011 Comments off

We’ve added equivalency charts to our website so that you can easily find an ideal U.S. Bellows replacement for a similar expansion joint in your piping system. So far, the following charts are now live:

- Hyspan to U.S. Bellows Equivalency Chart
- Pathway to U.S. Bellows Equivalency Chart
- KE-Burgmann to U.S. Bellows Equivalency Chart

Looking for a product code not listed? Write us at or call us toll-free at 1-800-787-5914

Preview of the Hyspan to U.S. Bellows Equivalency Chart:

New Equivalency Charts Online

PDF Downloads Now Available in the Catalog

May 13th, 2011 Comments off

A convenient new feature has just been added to our online expansion joint catalog. On each and every data table,  right above the table,  you will now see a link to download the corresponding PDF file.

Now you can have a print-friendly copy of a catalog page  in your hands within minutes! Check out our various data tables to explore this feature a bit more!

Single Expansion Joints

Universal Expansion Joints

Externally Pressurized Expansion Joints


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