I am not a process expert but in the last few jobs I have done, the silencer was a welcome addition to the safety valve. During an event, there will be a pressure drop across the safety valve. In some cases the pressure drop and/or flow rate is too large so an orifice plate or some sort of flow restrictor is used. In my case, the silencer which has a pressure drop was used as the flow restrictor. I would also add that high pressure drops create extreme sound levels (up to 140 dBA) which are a danger to anybody in the area and thats why silencers are needed.
The only thing I know related to ASME would be the requirement that the silencer have ANSI flanges and the interior be treated as a pressure vessel(if it is a reactive silencer) re. welding due to the high pressures involved. C. Hugh (
There are backpressure restrictions in ASME Sec. VIII, Div. 1 for piping downstream of pressure relief valves. The maximum backpressure allowed for a standard (unbalanced) pressure relief valve is 10% of the set pressure. This is covered in section M-8 of Appendix M.
