The Expansion Joints Blog

Install the FLEXXCEL HT belt material on the expansion joint frames per the BELT INSTALLATION INSTRUCTIONS. Leave section on top of duct “unbolted” at preferred splice area. Carefully trim FLEXXCEL HT belt material so the two ends “butt up” with each other.

Cut PFA film and 3″ wide FLEXXCEL material strip to equal the width of the installed belt. Staple the PFA film to the “gas side” of the FLEXXCEL material strip.

Slide the backer board under the splice area. Place the FLEXXCEL material strip over the “trimmed” HT material with the PFA film facing down. Place iron at edge of belt to begin splice. Apply pressure to iron handles during each splice. Each splice section should take approximately 5 minutes.

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U.S. Bellows manufactures high-performance fabric expansion joints for industrial applications. These expansion joints often require thermal-welding (heat seal splice) in field service. Cost effective and easy-to-use heat seal irons are available from U.S. Bellows for use with FLEXXCEL materials.

The main function of a heat seal iron is to introduce enough heat to allow a proper bond between PTFE surfaces of FLEXXCEL materials. The melting point of PTFE is around 621°F (327°C). However, the setting of a heat seal iron is determined by factors like ambient temperature, thickness of bonding materials, and the surface upon which you heat seal. Applying pressure can help facilitate a good bond, but in order to achieve a correct bond, the melting point of the U.S. Bellows FLEXXCEL materials must be achieved.

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1. Using the U.S. Bellows drawing, organize the parts per drawing information and “match markings” on parts.
2. Clean duct/flange surfaces and prepare for welding.
3. Tack weld frame segments into place. If the expansion joint has a liner, make certain that the flow arrow of the expansion joint/liner is in the proper system flow direction. If liner ships loose, install frames first to allow seal weld access.
4. Seal weld frames.
5. Install accumulation barrier/insulation pillow — if required.

View the Pre-Installation Check-list

Accumulation Barriers are typically designed to fill the entire cavity of the expansion joint. Wrap the accumulation barrier around the duct/expansion joint. Pack the accumulation barrier into the cavity of the expansion joint. The liner will prevent the barrier from falling into the duct. Use thread or wire to tie across the breach opening to support accumulation barrier during installation. Remove thread or wire prior to installing the fabric belt element.
Insulation pillows are typically designed to prevent high temperatures from contacting the fabric belt material; therefore it is critical to attach the pillow in place. There are multiple ways to attach the pillow. Follow U.S. Bellows drawing for details. Pinning the pillow to the liner (as shown) or the frame are common methods of attachment.

View the full installation instruction guide for unassembled fabric expansion joints. (Continues with instructions on gaskets for single ply belts or composite belts, and fabric belts with or without factory punched holes.)

Fabric expansion joints can be shipped in a variety of conditions to allow for the most economical installation. In certain instances, it is practical to ship joints fully assembled ready to drop into place. In other cases where access is limited or joint size exceeds normal shipping constraints, the joint can be broken down into small segments and then assembled in place at the job site.

U.S. Bellows will provide the appropriate detailed storage, handling, and installation instruction based on how the expansion joint is shipped.Please use these instructions for assembled fabric expansion joints in conjunction with the approved drawing provided by U.S. Bellows.

Pre-Installation Check-list:

1. Confirm dimensional data per U.S. Bellows’ approved drawing.
2. Confirm duct/duct flanges are in good condition.
3. Confirm duct/duct flanges are lined up correctly (ensure that lateral displacement and angular movement do not exceed agreed specifications)
4. Prior to installing the expansion joint frames, the opening into which the expansion joint will be installed must be inspected to verify that the opening is in accordance with design tolerances. The expansion joint is not designed to accommodate installation misalignment, unless clearly specified as a design requirement.
5. Make available the following tools/equipment to simplify the installation:- Suitable/safe scaffolding
   - Lifting equipment (fork lift, crane, hoist)
   - Drill
   - Come along
   - Rope
   - Pry Bar

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1. Compare the maximum continuous operating temperature of the application against the fabric temperature rating.

2. If the application has high fly ash or dust loading, select a material with high tensile strength.

3. If the application is near a fan or where flow turbulence is expected, select a material with high flutter resistance.

4. Elastomers vary in their chemical resistance. The selected Elastomer should be checked to insure that it is compatible with the particular media it will encounter.

* Not suitable for sustained service where oils, hydrocarbons or concentrated minerals acids are present.

Elastomers— A general name for the group of synthetic “rubber” materials that are characterized by their elastic property. These materials are also known by their commercial names as Viton®, Hypalon®, EPDM, and Chlorobutyl.

Before the development of Fluoroplastics, a group of synthetic “rubber” materials were commonly used in flue duct expansion joint applications. These materials, known as Elastomers, include Viton™, EPDM, Chlorobutyl, Hypalon™ and others.

Because of their elastic properties, the various Elastomers are built up into a multi-layered sheet reinforced with fiberglass or Aramid fabric. The finished product, 1/8″ to 1/4″ thick, is then used as a flat belt or as an integrally flanged U-shaped cross section that bolts directly to duct or equipment flanges. The inherent characteristics of flexibility, abrasion resistance, and flutter resistance translates to long service life when applied properly.

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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

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

Directional Movement for Fabric Expansion Joints

Fabric Expansion Joints and Factors Influencing their Design

Fabric 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

Fabric 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.

Movements

Generally, 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.

Abrasion

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.

Summation

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.