Steam venting tank

Why do you think it would vibrate?

I assume the top is open to atmosphere and your diffuser is just stopping jets of steam coming out?

what does 400t/hr represent at atmospheric pressure in terms of volume flow?

what does your diffuser look like / what is the open hole surface area to inlet pipe cross section area ratio? 1.5? 2 or more?

How big is the hole in the orifice plate / pressure on the left hand side?

It's an atmospheric tank?

Most of your loads will be wind I would guess

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

if venting the steam to atmosphere, a steam silencer can be used at the steam outlet for venting.
Need the steam pressure and flow rate for the silencer sizing and installation.

Steam silencer sizing requires specifying the noise level.
The vendor will (or atleast did when we ordered one) size for flow at 1/2 psig at the inlet.

To achieve the quoted outlet dB, a length of inlet pipe same size as the silencer inlet flange is required. Pressure drop must be away from the inlet flange. If the pressure drop across your back pressure plates is calculated to result in 1/2 psig downstream at 400T/hr your design might achieve similar results.

With the pressure drop kept away from the silencer, the energy being dissipated inside the device is relatively low, stiffeners are required per - probably an industrial duct construction standard. If you are dropping significant pressure inside the device, the acoustic energy could be large, and might dominate.

Thanks for the input.

The diffuser pipe is the last in a number pressure drop devices taking the steam pressure down in ~50% steps. Pressure drop across the diffuser pipe is about 0.9 bar. holes are 50mm (hole area 83% of the diffuser X section area) . The other pressure drop devices (with smaller holes) are right on the silencer tank inlet flange. (we do usually locate these further upstream).

@FacEngrPE, Thanks for the point about pressure drop located away from the silencer. Will see if we can move pressure drop plates upstream.