The Design of Fabric Expansion Joint Gas Seal Membranes

Fabric expansion joints are commonly used in round and rectangular ducting systems for accommodating differential thermal expansion and containing internal pressure. Fabric expansion joints are intended for sustained operation without significant leakage. Failure of fabric expansion joints can lead to plant shutdowns. The outer gas seal membrane is a structural material most commonly made from woven fabric with an elastomeric coating. The fibers in the fabric are comparatively strong and flexible but not chemically resistant. The coating protects the fibers from chemical attack and seals the woven fabric to minimize leakage through the material. The fabric material is typically clamped between metal frames attached to the ducting. The orientation of the fibers with respect to the frames is a critical design factor. Fabric expansion joints are normally designed in accordance with the guidelines of the Fluid Sealing Association Technical Handbook. The handbook gives helpful information but does not provide analytical methods for the mechanical design of gas seal membranes. The intent of this paper is to provide analytical methods for determining the movement capability and pressure capacity of gas seal membranes. Test results and non-linear finite element analysis are used to support the proposed methods.