Dear Silvano,
If I understand your question, you would like to use a half pipe jacket coil as a "line of support" for external pressure. My opinion is that this can be accomplished, but with some precautions. The half pipe jacket will essentially be performing double duty as both a stiffener and a transport conduit for a heating or cooling medium subject to internal pressure. If there is enough excess material left over after the half pipe jacket is designed, theoretically the excess can then be used as a stiffener. You will have to then decide on a length "L" and perform a manual calculation on the inertia available.
I would also strongly suggest that you seek the opinions of others experienced with this design concept and your notified body /inspector or inspection agency.
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Scott MayeuxCADWorx & Analysis Solutions
Intergraph Process, Power, & Marine