Polymeric, or “rubber”, expansion joint materials are the oldest and most widely used of any material available. These materials have excellent strength, flexibility, and have superior abrasion resistance to the attack of fly ash and other particulates. They are much lighter and easier to install than the older metal joints. They are also excellent for sound and vibration dampening. With proper set back from the gas flow, these products require no special baffles or flow liners.
Typically, this type joint is composed of a reinforced multi-ply construction similar to that of a conventional conveyor belt. Now, the reinforcements are usually fiberglass, Aramid/Glass combinations, stainless steel wire, or some combination. There are three polymers which have become the materials of choice: Fluoroelastomer, Chlorinated Isobutylene Isoprene, and Ethylene Propylene Dimonomer.
Fluoroelastomers (FKM) are manufactured in the U.S. by DuPont (Viton) and 3M (Fluorel). This elastomer has outstanding resistance to chemicals, oils, and heat when compared to any other rubber products. Specifically compounded terpolymers have been found to offer the best performance in a flue gas environment. This polymer will run at 400º F indefinitely, and will take short excursions to 700º F. Reinforced fluoroelastmers have been in use in power plants since 1971.
Chlorobutyl (CIIR) has outstanding resistance to ozone and oxidizing chemicals including some mineral acids and ketones. Chlorobutyl has good tensile strength, flexibility, and low gas permeability. This product has good temperature resistance with a maximum of 300º F continuous and excursions to 350º F. Chlorobutyl joints have been used in power plants since 1964.
Ethylene Propylene Dimonomer (EPDM) is a good, low-cost terpolymer with high tensile strength and flexibility. It has excellent resistance to oxygen and ozone. It has good flexing characteristics, low compression set, and good heat resistance up to 325º F continuous. It has excellent chemical and steam resistance. EPDM joints have been used in power plants since 1977.