what are the modalities for usage of fabric expansion joints ?
The said type of bellows follow ESA & FSA standards
FSA standards link is Piping Systems Non-Metallic Expansion Joint

I did not receive any reply so thought to elaborate the situation.
In one of projects the principal designer is planning to use Non Metallic type of expansion bellows made by manufactures such as KE-Burgmann which is insulated SS sandwiched fabric type bellows.The usage is in flue gas line. How to ensure that the Analysis will be correct and there will be not conflict of applicable Standards. I understand that Caesar internally uses only EJMA standards.

I suggest you contact the vendor and ask them how this type of joint should be modeled in a (beam element) piping program.

CAESAR II uses a 3D beam element formulation. This means that everything is modeled as an infinitely thin stick, with properties. Expansion joints fall into this category also. However, instead of the software determining the elemental stiffness properties, the user defines these values for the bellows element. EJMA rules and standards are only (optionally) employed at the back end, after the analysis, if the user desires to check/verify the expansion joint.