Pressure reducing stations for process gases are used to reduce the line pressure based on the process requirement. This is achieved by, a valve. Sometime the pressure reduction is done in multiple stages through a series of pressure reducing valves.
Due to throttling the pressure from high pressure to low pressure, shock and turbulent wave emanated across the valve orifice releases a very high amount of acoustic energy which is transmitted as fluid borne acoustic energy in the downstream pipeline
This would result in very high vibration in the pipeline and may also lead to structural damage due to mechanical noise transmission through structures.

This can be solved by connecting an absorptive type silencer with properly designed diffusing arrangement and an expansive chamber immediately after the valve. When series of throttling valves are used for multiple stage pressure reduction it is advisable to fit a silencer for each stage. Alternatively, the throttle valves can be installed close to each other and the silencer can be installed in the last stage. However this arrangement requires proper acoustic treatment of all the valves and interconnecting pipe work.
The silencer vessel is normally designed as a pressure vessel as per ASME SEC VIII DIV I or as per customer requirement.