How can we model "Fabric Compensator" in CAESAR II
Pipe MOC - CS
ID - 2794 mm
Design temp = 450 deg C
Design Pressure = 14 Kpag
What are the other basic parameters required to model such component in Caesar II.

The flexibility of fabric bellows is not a big deal because pipe size is big but flexibility is very small. Normally it is ignored. You can model it as single element metal or rubber bellows but spring rate may be ignored or put arbitrary number.

Fabric bellows is used typically for flue gas of FCC, incinerator of sulfur plant, and power plant, and other industrial plants downstream of boiler or heat recovery systems. Major design factor is material selection of components against high temperature and abrasive fluid service such as refractory lining, packed design for temperature or erosion, etc. rather than flexibility.

The fabric joint provides virtually no resistance to displacemnt so whatever spring rate you use it should virtually near 0.0

I would just model the end coming into the joint as "free" and evaluate the displacements against the movement the fabric jint can take.