Insulation geometry – Fabric Expansion Joint

The geometry shown in Figure 1 is suitable both for ducts arranged with vertical axis and for ducts arranged with horizontal axis.

expansion joints with horizontal flanges

expansion joints with vertical flanges

The main requirements of shape and size can be summarized by the following recommendations: The metal flanges must be higher than the thickness of the insulation.

The metal flanges must be higher than the thickness of the insulation. Don’t cover more than 50% of the metal flange. When this is not possible, it is preferable to stop the insulation and smooth it directly up to the outer surface of the duct.

Leave at least 50 mm between the wing of the flange, which engages with the joint, and the beginning of the bevel of the insulation that must not have an inclination lower than 45°.

The geometry with vertical flanges is suitable both for ducts arranged with vertical axis and for ducts arranged with horizontal axis.
The main requirements of shape and size can be summarized in the following recommendations:

  • the insulation must only affect the duct and reach, at most, the base of the flange with the bevelled end of the coating (which must necessarily be clear);
  • the insulation edges depedends on the position of the bolt holes in any case it must not have an inclination that is lower than 45° with respect to the flange.

The types described above represent the common reference standards. Their correct application is a safe method to preserve the fabric expansion joint.

It is therefore necessary to make sure that, before starting the plant, all the insulation work close to the fabric expansion joints is completed or, alternatively, if this is not possible, it is important to verify that the insulating material is not positioned close to the flange, but is adequately set back from the flanges.