Dear all,

Our upstream relief line:
OD= 6" sch. 120
Pd= 92.7 barg
rho* V^2 = 63,869 kg/m/s^2

For relief line our client specification states:
rho* V^2 =< 50,000 kg/m/s^2 for P> 50 barg

For me it's simple, just raise the OD to 8" (raising of ID) which will reduce V so then reduce rho* V^2. But our client say that there is an optional vibration and pipe support study which may keep 6" line (not mentioned in their specification except for the downstream). I would like to thank to any suggestion and related reference. Thanks in advance.

It seems that you may be interested in acoustic fatigue. Look at Carrucci and Mueller's ASME paper 82-WA/PVP-8. Their work has been reproduced and extended by several operator companies.

When client standards get in the way of physics, physics wins. Note that sharp-edged orifices as in most relief valves cannot produce more than sonic flow for compressible fluids; this is physics. Also note that if the 6" line provides a restriction on the fluid flow entering or exiting the relief valve, then this must be considered in the sizing of the relief valve.

Possible solutions include using multiple relief valves, as is common in the US power industry, or re-sizing the relief line. See API PR 520, parts 1 and 2 for a full discussion of your options with refinery piping.