July — 2012 — The Expansion Joints Blog

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Directional Movement for Fabric Expansion Joints

July 30th, 2012 Comments off

Directional Movement for Fabric Expansion Joints

Fabric Expansion Joint Diagram Showing Axial Compression

Axial Compression

The reduction in the breach opening along the axis of the duct. This is usually a result of thermal expansion of the ducting.

Fabric Expansion Joint Diagram Showing Axial Extension

Axial Extension

The increase in the breach opening along the axis of the duct. In certain configurations, the duct thermal expansion may result in extension at the expansion joint location.

Fabric Expansion Joint Diagram Showing Laterial Movement

Lateral Movement

The relative movement of the upstream and downstream faces in the direction perpendicular to the axis of the duct.

Fabric Expansion Joint Diagram Showing Torsional Rotation

Torsional Rotation

The twisting of one side of the duct about the longitudinal axis.

Fabric Expansion Joint Diagram Showing Angular Rotation

Angular Rotation

The twisting of one side of the duct about an axis perpendicular to the longitudinal axis.

View our online fabric catalog for more information on fabric expansion joint movement

Expansion Joint Components Fabricated for a Pressure Balanced Expansion Joint in a Nuclear Facility

July 23rd, 2012 Comments off

Expansion Joint Components Fabricated for a Pressure Balanced Expansion Joint in a Nuclear Facility

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

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

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.

Movements

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.

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.

Tied Universal EJ with Control Rods for an Oil Recovery Project

July 9th, 2012 Comments off

Tied Universal EJ with Control Rods for an Oil Recovery Project

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?

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.

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