RO Sizing

[Felicity900]

Hi

I would like to design an RO that limits the flow in a line to prevent AIV. I have calculated the allowable flow to avoid >155 db as per enegery institute guidelines. If my RO is sized to stay within that flow, can I just have a single stage RO? If audible noise is not an issue (a temporary solution with a short duration and other mitigations) can I just install a proper thickness single hole, single stage RO? Are there other factors to consider? What would drive me to multiple or multistage other than noise...

 

[Latexman]

If this is liquid flow, I couldn't tell, cavitation could force you into multiple RO's.

Good Luck,
Latexman

 

[LittleInch]

Gas?
Liquid?
Pressure drop?
Size of your RO?
Noise can travel a long way and emerge in places where it is a problem.

How is an RO solving an Acoustic Induced Vibration exactly?

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

 

[hacksaw]

Pipe size, flow rate, service application...

 

[Felicity900]

All thanks for the responses. Thanks little inch - I realise it is polite to respond - this is the soonest I was able to recheck this site and respond.
Some details:

1. It is a 3 inch natural gas line. (AIV not relevant in liquid lines I understand). This is a manually operated line which allows some flow from the process line to flare.
2. We have sized a 1 inch (approx) diameter RO. I am believing that an RO limiting the flow through this line (rather relying on operator controlling on the existing globe valve which if fully open will cause AIV due to large possible flow
3. Pressure drop of 60 bar

Appreciate any further thoughts

 

[Latexman]

AIV?

Good Luck,
Latexman

 

[georgeverghese]

For such purposes to avoid acoustic induced vibration, set up a single stage thick plate RO. A thin plate RO shows a discharge coeff exceeding 0.8. See design guidelines for setting up thick plate ROs' or talk to your field instrumentation engineer colleague. Obviously, you also want to keep line velocity <0.5Mach.

 

[Felicity900]

Thank you. Yes AIV = Acoustic Induced Vibration. Engineering contractors are telling me they need to approach the vendor for formal sizing and confirmation of number of holes and multistage requirements. I feel like it is possible to design and manufacture alone (single stage) if we can provide a strong enough plate (following guidelines for that) but wondering what problems this can cause, other than audible noise. ie - do I really need to go to the vendor? This is purely for limiting flow - not for measurement. This is a time critical issue.

 

[Snickster]

Never did something like that before - high differential orifice to flare - but have designed orifices that blowdown high pressure NG piplines to the atmosphere. I would make sure 1) a single orifice is thick enough to handle the differential pressure, 2) the exit pipe has straight length downstream so that the high velocity jet and critical flow pressure exiting the orifice has suficient length to achieve normal flow across the pipe crossection. I believe about 10 pipe diameters is sufficient but check. This is to avoid possible errosion and high vibration of the piping if it would hit an elbow immediately downstream, 3) and to design the pipe supports local to the orifice to handle the thrust force produced by the jet velocity exiting the orifice, and to support the downstream piping against vibration. Your orifice will have sonic critical flow at the vena contracta of course with a pressure of about 400 psig that immediately drops to flare header pressure on the downstrem side of the orifice, This in itself causes an extreme dissipation of energy all of a sudden downstrem of the orifice. You may be causing some of the same thing you trying to avoid.

 

[Snickster]

Also this appears to be a very high flow rate at 60 bar across a 1" orifice. What is the purpose of this? Is this continuous flow to flare from a pipeline? Why?

 

[georgeverghese]

If this is not a maintenance vent, but an operational vent line that may be running for some time to enable operational flexibility, then you may need a 2 stage RO to cut down on noise that may attract HSE concerns for operators, together with external sound insulation on the piping.
On second thought, if this is an operational vent or flare line, you ought to keep within 20m/sec without sound insulation, or 30m/sec with.

 

[shvet2008]

We have sized a 1 inch (approx) diameter RO

We used short distance piping segment for the same purpose and similar conditions. Depressurisation of hydrogen loop in hydrotreating processes.
Positive reports were obtained from operating team.
Be sure that this segment is designed to withstand choked flow and inspected properly after each relief.

Upgraded piping class is the option should be started with.

 

[pierreick]

Hi,
You may want to consult this company :

https://www.deltafluid.fr/en/produit/orifice-de-restriction-multi-etage

Pierre

 

[LittleInch]

Also check temperature and dew points.

Natural gas (I assume) from 60 bar to 1 is a drop of around 30 to 40 C.

So you could get freezing, hydrates and other things depending on what the composition of the "gas" actually is.

You can also either size the globe valve so that it only flows at the same flow when fully open or fit mechanical restrictors tot prevent opening beyond a certain precent.

You may need a cage type internal plug valve at that pressure drop instead of a simple globe or needle valve. Same thing applies.

The polite to respond bit is my strapline - you would be amazed at the number of people who never respond.....

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

 

[georgeverghese]

155db upper limit on noise sounds very high, and probably only meant for very short term emergency releases, such as emergency blowdown valves at peak initial rate, or safety relief valves where penultimate overpressure limiting devices are also enabled.

 

[casflo]

The attached paper helps to analyze the acoustically induced structural fatigue in pipes caused by throttling devices.