The Expansion Joints Blog

What is a Fabric Expansion Joint?

Fabric 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?

A 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

In 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:

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.

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 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″ Dia. Fabric Expansion Joint	24″ Dia. Fabric Expansion Joint

Get pricing now for your next fabric expansion joint project.

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.

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.

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

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.

**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

A total of three rectangular fabric expansion joints and six round fabric expansion joints were custom designed for an offshore oil extraction and natural gas project. The rectangular joints are 56″ x 81″ I.D. x 25″ O.A.L. and the round joints are 105″ dia. x 24″ O.A.L. 309 stainless steel was used for the duct, 310 for the liners, 316 for the covers, 321 for the studs, 309 for the flanges. The fabric belt was a three layer belt with an inner layer of glass cloth, a layer of KO wool and an outside layer of reinforced PTFE. The expansion joints were designed for 1 psig at a temperature of 1100°F. The rectangular joints were designed for 2″ axial compression, a 1″ extension, and a 1″ lateral offset. The round joints were designed for 4″ axial compression, a 1″ extension, and a 0.5″ lateral offset. All welds were dye penetrant examined.

U.S. Bellows 101: Expansion Joint  Basics Webinar

This Webinar is over… to view the recording, go to http://www.usbellows.com/news/webinar_index.html

* Live Webinars are approved for 1 PDH credit for TX P.E.’s

This presentation will briefly touch on the basics of fabric expansion joints; however, is mainly focused on the various designs, material details, and applications. Learn how fabric expansion joints are engineered and fabricated for various applications and the many factors that influence those designs. View the abundance of materials used, including Fluoroplastic and Fluoroelastomer, and their respective capabilities. Take a journey through a Fossil Fired Power Plant and see exactly where fabric expansion joints are required.

U.S. Bellows, Inc., a division of PT&P, has more than 50 years of experience designing and manufacturing expansion joints, along with replacement and repair services.

The two assemblies shown, a mitered elbow duct work and fabric expansion joint and duct work assembly, are designed for a sulfuric acid plant. Both assemblies are fabricated from 1/4" thick 304L stainless steel. They are designed for a 15" water column with a temperature of 180°F, axial compression of 3/4", and lateral movement of 3/4". A dye penetrant examination is performed on all welds prior to shipment.