News & Insights
Silicone Fabric for Expansion Joints: Weight, Coating Side and the SO2 Boundary
Non-metallic expansion joints need gas-tight, flex-fatigue fabric. Here is how VETEX specifies silicone coated fiberglass for compensators — and the media where silicone must not be used.
A non-metallic expansion joint (compensator) absorbs movement between duct sections while staying gas-tight. The fabric in its walls flexes with every thermal cycle, so specifying it is not the same as specifying a welding blanket. This guide covers the three decisions VETEX walks through with compensator buyers.
Quick Answer
For expansion joints we recommend heavier base fabric — 660, 840 or 1000 g/m² fiberglass — with double-side silicone coating for air-tightness. Then confirm the media: if the duct carries flue gas or steam containing SO2, silicone rubber is not the right coating, and we propose an alternative system.
Why Heavier Base Fabric
Compensator fabric is clamped into flanges and flexes continuously, so the base must carry clamping load and movement range without tearing. Moving from welding-blanket weights (430–840 g/m²) up to 660–1000 g/m² adds yarn where the movement concentrates. Tell us the media temperature and the axial/lateral movement range, and we size the ply count accordingly.
Why Double-Side Coating
Gas-tightness is the compensator’s core duty. Double-side silicone coating seals the base fabric from both the process side and the atmosphere side, and protects the yarn from media attack in both directions. Single-side coating is acceptable for fan flexible connections where leakage tolerance is higher, but compensators default to double-side.
The SO2 Boundary — Read This Before Ordering
Silicone rubber must not be used for pipeline compensators carrying flue gas or steam containing SO2. This is a material boundary, not a quality issue: the media attacks the polymer. If your gas analysis shows SO2, say so in the inquiry and we will move the specification to a different coating family on the same fiberglass base.
Related Constructions
The same silicone coated fabric family also serves fan flexible connections (softer finish, vibration damping) and fire soft joints between duct sections (specify your fire test standard). Each duty shifts the recommended weight and coating side — the ten-point confirmation list in our quotation guide applies here too.
Next Step
Send media composition (including SO2 yes/no), temperature, movement range and required dimensions. The VETEX team returns a recommended construction within one working day.