Dump Tubes or multi stage expansion stage orifices will be used where high pressure media must be expanded:

High pressure expansion stations (e.g. SHP steam to condenser)
Bypass stations from compressors
Dumps of pressure vessels

As described in chapter -Blow Off Silencers- during free venting or expansion of pressurised steam or gas kinetical energy in terms of waves with high pressure amplitudes will be released which leads to loud noise.
This effect causes already at an minor amounts of streaming media (500 – 1000 m³/h) and relatively low expansion pressures (1 – 2 bar) a quite high sound pressure level – depending on application – of 115 to 125 dB(A) in 1m distance from blow off opening (e.g. piping, etc.). At bigger blow off flow and higher expansion, e.g. blowing of safety valves, the sound pressure level SPL can increase up to 150 dB(A). This generating of noise can be reduced by using Dump Tubes /expansion orifices inside the piping system. At special design of the multi hole cylinders a noise reduction (sound transmission loss) of up to 30 dB(A) can be achieved.