Dear Bill,

You are right that metallic bellow is designed for a limited fatigue cycle; not good for vibrating m/c.

But, here, we are mostly talking about non-metallic ambient temperature bellows.

Moreover, we, the stress engineers have not put the same in P&ID. If process engineers own this requirement, its safety will be be their headache, not ours. Also,in such duty the bellows will be changed regularly after a fixed time period as such items will not last the full plant life.

regards,
sam