can Caesar II input use 5" gaps on line stops. will the results be accurate.

You can input 5" in Caesar and the results are accurate provided that your assumptions are correct. But make sure you cover all possible operating scenarios.

Regards,

Yes you can input 5" displacement but it's too high. It will cause very large moments and stress in bends and other fittings. Also you should beware of low-cycle fatigue failure due to large deflection and rotation. Pipe clearances also should be checked during expansion against adjucent piping, equipments, structure, etc.

Please be aware that gap has a completely different approach in stress analysis than displacements.