These expansion joint components were fabricated for a pressure balanced expansion joint in a nuclear power facility in Pennsylvania. They are 46″ square, fabricated from carbon steel duct with Inconel 625 bellows, and 321 stainless steel liner. The design conditions were +/- 0.875″ axial compression, 1,346 lb./in. lateral spring rate and 15 psig at 250°F. All welds were 100% dye penetrant examined and a pneumatic pressure test at 15 psig was conducted prior to shipping.
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.
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.
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.
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.
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.
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.
This tied universal expansion joint with control rods was designed for an oil recovery plant in Canada. It is 48″ in diameter and 68″ in overall length. This expansion joint was designed for 1″ compression, 4″ lateral and 15 psig at 150°F. The pipe was fabricated from A-36 carbon steel material and the bellows were fabricated from 316L stainless steel. A dye penetrant exam, air and soap test, along with a vacuum test was conducted prior to shipping.
What is a fabric expansion joint, how do they work and what are the advantages of design integration?
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:
- Elimination of flanged connection gasketing and potential leaks.
- Elimination of the risk of installing sensitive assemblies at the job site.
- Significant costs savings of both manufacturing and installation labor.
- 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.
- Minimize the number of flanged expansion joint connections.
- Allows integration of ducting to serve as expansion joint flow liner.
- Allows expansion joint frames to take the place of duct stiffeners.
- Elimination of labor to install flanged expansion joint assemblies at the job site.
U.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.
U.S. Bellows provided the total engineering, design and fabrication package for this project that included: expansion joints, elbows, duct work, saddle supports, F-type variable spring supports, slide plates and pipe anchors.
A total of twelve, 119″ dia. double slotted hinged expansion joints, thirty-six, 72″ dia. elbows and twelve, 119″ dia., 55′ long header ducts were fabricated for a power plant in Mississippi. The expansion joint assemblies were designed for .5° angular movement, 3/8″ lateral, 1-1/2″ axial compression. The design conditions were 5 psig at 300°F. The duct work was fabricated from A-36 carbon steel material and the bellows were fabricated from 304 stainless steel. A dye penetrant exam, soap and air test and spot x-ray on all duct seam welds was performed prior to shipping.
We have an inventory of stock bellows for your quick-turn/emergency requirements. Contact us now if you need a replacement expansion joint. We can run it through our expedited manufacturing line using a prefabbed bellows and get it to you within 1-2 days in some cases.
Using our inventory, we can quickly assemble and ship a variety of expansion joints including single, single tied, universal, elbow pressure balanced and in-line pressure balanced expansion joints. Stock bellows are available from 2″ to 24″ diameter and in three pressure values: 85 psig, 150 psig and 300 psig.
Emergency Shutdown: Replacement of a Metallic Universal Expansion Joint for a Chemical Plant in Wisconsin
One of U.S. Bellows’ customer’s existing expansion joint failed and caused a plant shut down. They required an immediate replacement joint. This universal expansion joint order was placed, designed and fabricated in just one day. The order came in at 8:30 am on Saturday, Labor Day weekend and was shipped at 4:00 pm, which minimized the time of the plant shut down. This universal expansion joint is 96″ in overall length, 20″ inside diameter and can absorb 3.25″ lateral movement. A 100% dye-penetration test and a hydro-test were performed to ensure quality.
Three Day Emergency: 40″ Clam Shell Expansion Joint Fabricated for a Chemical Plant in Texas
Within a three day span, U.S. Bellows, Inc., fabricated a 40″ I.D., single coded, clam shell expansion joint for a chemical plant in Beaumont, Texas. The chemical company utilized U.S. Bellows’ 24 x 7 Quick Turn/Emergency service. After the representative from the chemical plant completed the online form, the U.S Bellows’ on-call team was immediately paged. Three days later the bellows had been successfully fabricated, welded to an A516-70 heat exchanger shell and shipped to the chemical plant to resume operation. The bellows was fabricated from A240 tp 321 SS and designed at 50 PSIG and 750°F. In order to detect any leaks in the weld, the bellow’s long seam weld was 100% x-rayed and its attachment weld was 100% dye-penetrant.
Various sizes of thick wall flanged and flued head expansion joints were custom designed for heat exchangers in California. Two are 30″ in diameter and two are 18″ in diameter. They were designed for 1″ axial extension and 14 psig at 300°F. All four expansion joints were fabricated from ASTM A-516 Gr. 70 carbon steel material. A dye penetrant exam was conducted prior to shipping.
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:
- Details 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
Check 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.
The pressure thrust produced by low pressures can be tremendous in large diameter systems, just as it can be at normal pressure ratings in small pipes. To avoid expensive anchors, to keep long pipe runs in tension, to prevent buckling, or reduce reaction forces on equipment, the pressure in the pipe can be used to generate balancing forces within the expansion joint. These combinations of bellows and thrust restraining structural components can accept almost any combination of movements, as shown in the following examples.
The pressure balanced elbow is ideal for absorbing the thermal expansion of equipment, such as turbines, pumps and compressors, which rely upon low reaction forces on their inlet and exhaust flanges. In this example, only an intermediate anchor is provided at the elbow, to isolate the equipment from any forces produced in the remaining piping.
The pressure thrust force produces tension on the equipment flange, but the only forces produced by the deflection, are the spring resistance of the bellows within the expansion joint. The spring rate of these units is the sum of the spring rates of the bellows on each side of the elbow, and care must be taken to provide a unit which produces spring forces low enough to satisfy the equipment maximums as stated by the equipment manufacturer. Bellows may also be cold sprung to reduce these forces even lower.
Example of how the flange is subjected to an axial force equal to the pressure thrust. In this example, which may be typical for a turbine exhaust application, the force on the machine’s flange is the spring reaction of the bellows in lateral deflection, as described in the above example. Again, the flange is also subjected to an axial force equal to the pressure thrust, as if it were capped, but the turbine’s mounts are not. The pipe guide between the expansion joint and the equipment flange absorbs the forces produced by the thermal expansion of the pipe, along its axis.
View all the examples in the full article on, Pressure Balancing Expansion Joints.
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.