Project Description

Pressures and thermal stress for the fabric expansion joints


The effectiveness of an Isolmat bolster bag is also detectable in the case of operations under positive pressure. Its presence, in fact, it supports the multilayer fabric expansion joint thus preventing (when supporting metal structures are not present in the stratification) the possible separation of the layers caused by large movements and positive pressures.

Reduction of thermal stress

Provided that BBV Tech’s multilayer fabric expansion joints are always designed to resist the operational temperature regardless of the presence of the internal Isolmat bolster bag, the installation of an internal bolster bag, if attached, has the induced advantage of a lesser thermal stress of the expansion joint, which further prolong its lifetime.
In applications where the “dew point” occurs at low temperatures, the opportunity to install an internal Isolmat bolster bag protection must be evaluated in each individual case.


Multilayer fabric expansion joints must necessarily be able to dissipate external heat. It is therefore evident that any element that prevents or limits this phenomenon must be avoided. Insulation that is external to the joint is therefore not permitted, except for low temperature applications that get evaluated in specific cases.

The analysis, however, cannot be limited to this single evaluation: the geometry to be implemented in the vicinity of the joints needs to be further defined.
It must be also taken into account that the heat of the ducts, retained by external insulation, is transmitted by conduction to the flanges to which the joint is attached, thus causing a significant rise in temperature in those areas.

In those circumstances, the geometry of the external insulation in the flanging area of the joint assumes a relevant importance, which, to oppose the phenomena described above, must not limit the air circulation in anyway.
The substantial difference is related to the type of flanging.