Very true - I've found myself more sympathetic to the predicaments that FEED guys have to sort through like this...even if I do want to force choke them when I'm dealing with the results in detail design.
I agree, if the temperatures (if they are even known) allow you to meet the 16" allowables, then you will be in great shape.
If not, I would at least try to get the basic pump and piping layout such that it won't become physically impossible for the detail design guys to add flexibility if needed.
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Edward L. Klein
Pipe Stress Engineer
All the world is a Spring