Pinoy,
Since you were decided to use EJ due to some reason, better refer to EJ catalog. Based upon the design temperature and pressure, EJ can be selected and the properties of that bellows are inserted into the piping model. IF the bellows reduces loads and stresses then the range of expansion movements on bellows must be checked. For each bellows, there is a limit to the cumulative axial, bending and lateral movement that can be absorbed by the joint without excessively deforming the convolutions.
After all movements are sets within the required allowable, then you are completed your EJ design.
Additional information, you can refer also to Technical reference manual of CAESAR II. There are some items that should be considered when dealing with EJ design.