UIP offers a complete line of non-metallic “fabric” duct expansion joints. Options include belt type, integrally flanged fully molded type, duct expansion joints for lower pressure gaseous service, as well as high temperature flue gas.
Fabric Expansion Joints are non-metallic, highly flexible connections that provide stress relief for piping and ducting systems by absorbing thermal growth and shock, isolating mechanical vibration, and allowing for misalignment. They provide significant flexibility when installed in large ducting and piping systems. Fabric joints can be manufactured from a variety of special woven, coated or laminated fabric materials. They offer extreme flexibility and can absorb movements simultaneously from several directions. Fabric joints are easily customized and require little space. They are also easy to transport and install. UIP fabric expansion joints offer excellent operational performance and reliability.
Our expansion joints are precision-engineered and specialized for your application, available in eight standard profiles from -110°F up to 2,000°F.
UIP Flue duct expansion joints are custom-engineered to handle low pressure (±3 psig) applications. Standard profiles include U-type, flat belt type, square, rectangular, and round.
Baffles are usually not necessary with elastomeric expansion joints due to the tube resistance to most abrasive particular matter. However, baffles must be used with fabric composite joints to protect the inner surface from particulates in the gas stream. UIP International, Inc. can supply baffles fabricated from carbon steel, stainless steel, or other materials as required.
Standard construction calls for 2″ wide, 3/8″ thick bars with slotted holes for easy installation. Retaining rings can be made from carbon or stainless steel.
Duct expansion joints can be found in a wide array of industries. Power plants, petrochemical plants, pulp and paper plants, and many other industries require fabric duct expansion joints due to their ability to add flexibility to industrial ducting systems. Their large movements in a given space, small spring rates, and wide temperature range allow for use in many instances where other joints will not work.
Industrial applications can be separated into general categories based on the media composition (air or gas) and temperature. This section is designed to aid in the selection of the appropriate expansion joint for the specific application range. All plants are unique; therefore, the service locations and temperatures may vary.
Ambient Air Services (-40°F to 400°F)
Ambient air temperature – clean air without particulate or chemicals to damage the flexible element. Expansion joint is used frequently for vibration and sound attenuation from fan equipment.
Locations for use:
• FD Fan intake/outlet
• Primary air fan to air heater
• Service air intakes
• Primary air to recovery boiler
A UIP integrally flanged elastomeric joint is suggested, using either the Therma Flex or Mighty-Span expansion joint styles. Neoprene, EPDM, or Viton® single layer belts are frequently used.
Hot Air Services (500°F to 800°F)
Clean air coming into contact with hot flue gases at the air pre-heater where temperatures are elevated with minimal particulate and or gas carry-over. Expansion joint will see thermal movements and vibration. Elevated temperatures require a composite flexible element and a flow liner.
Locations for use:
• Air heater/air outlet
• Over fire air fans
• Secondary air fan
• Mill air
A Therma Flex flat composite belt with a bolt-in or weld-in frame design and a flow liner is suggested.
Moderate Temperature Flue Gas Services (150°F to 600°F)
Flue gas which has passed through an air pre-heater and dust collector to reduce the temperature and particulate level. Flue gas may cycle near the dew point where condensation can occur, and chemicals are present. Expansion joint may see thermal movements, vibration, and chemical attack.
Locations for use:
• Precipitation outlet
• I.D. Fan inlet/outlet
• Scrubber inlet/outlet
• HRSG inlet/outlet
• Re-heater inlet/outlet
A single-layer belt with chemical barrier is suggested in either integrally flanged or flat belt type, such as the Therma-Flex weld in outboard angle frame design and PTFE coated single layer belt with gas film layer.
Hot Flue Gas Services (600°F to 1200°F)
Flue gas directly after combustion stage at elevated temperatures with possible particulate present. Expansion joint is used for large thermal movements at elevated temperatures.
Locations for use:
• Economizer outlet
• Cyclone inlet/outlet
• Precipitation inlet
• Recovery boiler outlet
• Air heater gas inlet/outlet
• Gas recirculation system
Therma Flex high-temperature composite flat belt style setback frames, cavity pillow, and flow liners are suggested.
A. Gas Seal Membrane
The gas seal membrane is designed to withstand system pressure and provide resistance to chemical attack from the interior and the exterior. The gas seal needs to have the flexibility to absorb thermal movements. Depending on system temperature, it may require additional thermal protection.
B. Insulating Layers
The insulating layers provide a thermal barrier to ensure that the inside surface temperature of the gas seal membrane does not exceed its maximum service temperature. The insulating layer can also reduce condensation that would be caused by the gas stream if it were to come in contact with the cool surface of an uninsulated gas seal membrane.
C. Insulating Retainer Layer
This layer keeps the insulating layers in place and maintains thermal integrity. The retaining layer must be able to withstand gas stream temperatures and must be chemically compatible with system media.
D. Back up Bars
Back up bars, positioned at the belt frame attachment, use clamping pressure to create the fabric-to-frame seal and restrain the fabric when it is subjected to the system pressure. The thickness and width of the back up bars should be sufficient to perform this function with the bolt spacing being used. The edges of the back up bars will have a radius to preclude cutting of the fabric.
E. Metal Liner or Baffle or Pillow
A liner is designed to protect the gas seal membrane and insulating layers of the flexible element from abrasive particles which may be present in the gas stream. A liner is also used to reduce flutter of the fabric element caused by turbulence, to help control the accumulation of dust or ash in the expansion joint cavity, and to reduce the temperature of the flexible element.
F. Expansion Joint Frame
An accumulation bag is intended to deter fly ash from building up in the expansion joint cavity. It is typically used, in conjunction with a liner, in duct runs from boilers to air clean-up equipment such as precipitators, scrubbers and bag houses, or whenever high amounts of dust or ash are present in the gas. A fly ash barrier must be capable of retaining its strength and flexibility while being exposed to maximum system temperatures and media.
G. Fabric Expansion Joint Frame
The expansion joint frame design controls the effectiveness of the connection of the flexible element to the ductwork. In some designs they can be attached directly to the duct work and thus eliminate the necessity for an adjoining duct flange. Frames can be designed with a “landing bar” duct attachment which allows some installation misalignment without affecting the flexible element. The frames establish the stand off height of the fabric, which is necessary to achieve thermal integrity during all movement conditions. The edges of the flanges in contact with the gas seal membrane should also have a radius to prevent damage.
H. Gasket
Single-ply fluoroplastic and fluoro-elastoplastic belt designs such as Ultrachem materials require flexible chemically inert gaskets. Cuff tape can also be applied in this area to protect the belt from conducted frame heat and movement abrasion.
A single-layer expansion joint is made of a single layer of material only. Depending upon the area of application, the layer is made from fabric, various (fluoro) elastomers or fluoropolymers accompanied by fabric reinforcement as composite materials. Single-layer expansion joints provide the tightness and chemical resistance necessary when exposed to heavy condensate.
Pre-Assembled Units
Usage of fabric expansion joints that are pre-assembled onto steel components offers a number of advantages:
The design of multi-layer expansion joints consists of four groups of materials. By combining different materials and considering their thermal, chemical, mechanical resistance, in addition to their fatigue properties, we can construct an expansion joint that provides the best solution in both technical and economical respects.
The four essential materials in the construction of fabric expansion joints include:
Important variables to consider when deciding the design and type of expansion joint needed:
Integrally Flanged “U” Type
The single layer belt can be provided either as a fully hand molded UIP International, Inc. “Mighty Span” Style 600 Elastomeric expansion joint or a continuous molded corner THERMA-FLEX Style Elastomeric or Fluoropolymer joint. Style 600 joints are available with or without various arch profiles molded into the body. The service temperature is limited by the material rating. U-type joints are used frequently in fan applications due to their minimal hardware requirements and vibration/sound attenuation.
Flat Belt Type
Available in single layer or composite belts mounted parallel to the duct on attachment frames. The frames may be either bolted to mating flanges or welded directly to the ductwork. See above for standard frame profiles. Flat belt types are commonly used in high temperature applications and where a setback is recommended or required or required. This configuration can be designed to readily accept various accessories such as telescoping or floating flow liners, cavity pillows and fly ash seals.