Mighty-Span Rubber Flue Duct Expansion Joints

“MIGHTY-SPAN” Style 600 Rubber Flue Duct Expansion Joints are designed to handle hot air or gasses in industrial duct work, as well as those generated by power plant and pollution control equipment. They are custom constructed of rubber and fabric to absorb thermal movements and vibration in duct work and to aid in the elimination of noises caused by scrubber equipment and mechanical dust collectors.

MIGHTY-SPAN is capable of handling any combination of large movements which might occur in a ducting system due to thermal expansion. MIGHTY-SPAN creates almost no load on damper and fan interfacing flanges, thus providing much needed protection in these critical areas.

A wide range of elastomers and fabric substrates are available to provide maximum resistance to corrosion and high temperature capabilities. Let UIP International, Inc. assist you in selecting the MIGHTY-SPAN product for your application.

Available in a wide choice of materials and Drill Patterns

square rubber flue duct

UIP International, Inc. style 600 joints may be constructed of *Nomex® (to 400°F), fiberglass or polyester cloth impregnated with one of the following:

  • Neoprene: Resistant to heat, adverse weather conditions, ozone and flue gases. Impervious to fats, oils, greases and other petroleum products. Recommended for use up to 250°F).
  • Chlorobutyl: An elastomer with all of the above advantages of neoprene with the exception of its inability to withstand oil. Designed for 300°F environments.
  • *Viton®**Fluorel®: In addition to providing all of the properties of Neoprene, Viton® is highly resistant to mineral acids and usable in 400°F applications
  • Silicone: A high-quality elastomer, recommended for all environments except those with sulphur gas (SO2 or SO3). Usable in -70 to 500°F applications.
  • EPDM: Excellent ozone, chemical, and aging resistance. Poor resistance to petroleum-based fluids. Temperatures up to 300°F; *not for steam service*
*E.I. duPont Trademark


Square, rectangular or round shapes can be produced in almost any size. Standard construction is “U” shape with a 9-inch face-to-face dimension, with a 3-inch flange (other face-to-face dimensions available). Arch shapes also available. Body thickness of this one-piece molded joint is a nominal 5/16 inch. Extra liners are usually not required, but may be ordered if necessary.

flue duct configurations

Typical Installation Arrangement

expansion joint installation
Environmental Conditions
Elastomer Usable to °F Recommended for Use In
Oils, Grease Ozone & Flue Gases
Neoprene 250 good good
Chlorobutyl 300 good
*Viton® 400 good good
Silicone 500 good
Recommended Service
Pressure to 3.0 PSIG, max.
Vacuum 6.12″ Hg, 83″ Hg
Compression* 2″
Extension* 1/2″
Transverse 1-1/2″
*U-Type compression and elongation formulas.
  1. Lateral Elongation= 2 lbs. per foot of perimeter per 1/16″ of movement. For example: 2′ x 2′ I.D.= 8′ perimeter deflection= 1″ = 16/16. 2 lbs. x 8″ x 16″=256 lbs.
  2. Axial Compression = 2.2 lbs. per foot of perimeter per 1/16″ of movement. For example: 2′ x 2′ I.D. = 8′ perimeter deflection = 1″ = 16/16. 2.2 lbs. x 8″ x 16″ = 282 lbs.