We have vibration+noise problem in pipings. One dia 8" line operates at 280 C is joined by a branch (dia 3") which operates at 280 C (generally) & at approx 400 C under special circumstances. This 3" line is at slightly higher pressure.

Whenever the dia 3" line operates at 400 C, there is tremendous vibration at the branch joint.

As I don't have much grounding in fluid mechanics / flow induced vibration etc., any detailed answer/ reference to any internet link will be highly appreciated.