Materials used in non metallic expansion joints

The performance of non-metallic expansion joints for various gas ducting systems is determined by the severity of the environment and by the selection of the materials for each component of the expansion joint.

Selection of materials must be based on functional requirements as well as temperature and chemical capability. A corrosive atmosphere that might not have a noticeable effect at low temperature could have a disastrous effect at higher temperatures still within the basic heat resistance capability of the material. Conversely, systems at or below the dow point can result in highly corrosive condensates.

The proper engineering of materials or material combinations can provide successful long-term performance of non-metallic expansion joints in even the most adverse ducting system environment. Elastomers and other coatings are specifically compounded for gas seals and barriers and for protection against mechanicial damage such as erosion or abrasion.

Fabrics are used for the reinforcement of elastomers and other coatings to yield the mechanical properties necessary to withstand the movements and pressures exerted upon the expansion joint by the ducting system. In addition, fabrics are used in inner and intermediate layers in composite style joints as thermal barriers and mechanical reinforcements. The selection of fabric is based upon compatibility with the specific thermal, chemical and mechanical requirements of the system.

Insulating materials are used to reduce interface temperatures to a level which permits satisfactory performance and life of the elastomeric and coated materials in the gas seal layer. Fiberglass blankets perform very well to 1000F and available ceramic blankets are rated above 1000F but do have mechanical and chemical limitations.

The information presented in this section is derived from published materials data and from testing results complied by member non-metallic expansion joint manufacturers. In some instances where published data is unavailable and testing is not feasible, the consensus of opinion of member manufacturers is presented.

Where specific data is not available to many variables that could affect the data, a word evaluation of the material is used to better describe the performance capability of the material.

Elastomers Commonly Used in Expansion Joints

Chloroprene (CR) Better known as neoprene is made from chlorine and butadiene. These rubbers are very resistant to oils, greases and many other petroleum products. Properly compounded chloroprenes have excellent resistance to abrasion, impact and damage from flexing and twisting. Reinforced chloroprene is used in air and gas ducting when system temperature ranges between 180F and 225 F. Expansio joints utilizing chloroprene have been used in generated stations and industrial plants since 1960.

Chlorosulfonated polyethylene(CSM)
More generally known by the trade name Hypalon (Dupont trade name), these rubbers have good tensile strength and elongation and excellent ozone resistance. The CSM rubbers are very resistant to oxidizing chemicals such as sulfuric acid and are sued in a sytem temperature range of 225F to 275F. Special compounding enhances heat resitace and provides excursion temperature capability. Expansion joints of reinforced CSM rubber have been utilized in power generating stations and industrial plants since 1976.

Etylene propylene (EPDM) These low cost terpolymers have high tesile strenth and elongation with excellent resistance to oxygen and ozone. They also have good flexing characteristics, low compression set and good heat resistance having a service range of 260F to 325F. Conventional compounding produces formulations with very good chemical resistance. Reinforced EPDM epansion joints have been used in power generating stations and industrialĀ  plants since 1977.