Noise Level Calculation 1

[wartono]

Dear friends,

Can anyone help me to calculate the noise level from a 2" pipe of Nitrogen gas at pressure of 6 barg, temp 40 oC and the flowrate is 80 NM3/hr

Thanks,
Joko

 

[hacksaw]

you can calculate the fluid velocity in the 2" pipe at 0 barg, that will give you an idea of what you are dealing with

 

[SooCS]

Assuming a sch 40 pipe and flowing temp of 60 oF, a quick check for straight pipe it is very closed to 85 dBa and for turns and manifold it exceeded 85 dBa. In other words, too noisy.

 

[mgp]

Some previous threads in other forums have referenced this guide which may be of help.

http://www.grc.nasa.gov/

http://WWW/AcousticalTest/PDF/REDUCED_NOISE.pdf

Regards
Mogens

 

[SooCS]

Sorry guys, missed out a conversion.

Based on the density of the gas of .45, to generate noise at 85 dBa, you will need a velocity greater than 70 ft/s. Based on your flowrate, the velocity is less than 35 ft/s. Your okay.

 

[vendora1]

Dear SooCS,
Could you please explain the formula which you obtain the velocity required for generating such noise level?
Thank you

 

[SooCS]

Setak

The noise level prediction equation that I use is the same equation as the NASA spec as mgp has indicated in this thread which is based on an article by Seebold in Hydro. Proc., Sept 1973.

Rather then calculated the exact noise level, I had developed a simplified chart to indicate a noise level of 85 dBa as a function of velocity and density, which are the basic parameters required except for the pipe thickness; I have used sch 40 pipe as a reference.
And for all practical purpose, we are just want to design the piping system, especially gas piping system not to exceed 85 dBa as most code allowed.

Let me know if you are interested in this chart. This chart is a very simple graph with two lines drawn across it but involved a very lengthy calculation to develop it many many years ago.

 

[Sandy01]

mgp
where do I get the Excel files referred to in the NASA guide.
Thanks Sandy01

 

[Flareman]

Wartono

Check out "Noise and Vibration Control" by Beranek; Published by McGraw-Hill.

Chapter 16 deals with the noise of gas flows and gives several graphs which can be used to deduce the total noise of the discharge as well as the shape of the frequency distribution. The whole chapter deals with this subject which is a combined function of mass flows, velocity, pressure drop and diameter so you should read the book.

As a very rough guide,
you first calculate the overall dB level of the noise based on mechanical stream power and the mechano/acoustic efficiency (from the curves)
Then, most noise is generated in a peak frequency which is a function of the velocity, diameter and Strouhal number which, in turn, depends on the pressure ratio Pr of the choked opening (upstream absolute pressure / downstream absolute pressure)
When you find the peak frequency, the spectrum shape is related to the total dB level and the peak frequency by another curve which gives you the output in the various frequency ranges, which you need to know in order to make an A scale compensation.
There are a number of other factors like directionality and distance which I am ignoring for this discussion but which will also have a bearing on your final result.

I suggest an afternoon in the engineering library.


David

 

[vendora1]

Dear SooCS,
I will be very appreciated if you drop me the chart at:
setak@parsiannet.com
Best Regards

 

[saxon]

WARTONO, Is this a new line yet to be installed or an existing line with a hydrodynamic noise problem? If it's the latter, take a noise dosimeter out to the field and collect some data. The EHS Group should have one.

As for caculating potential noise problems, all of the formulas will only give you ball park estimates. I've seen noise calculations that checked out ok, but after the pipe system was installed, they whistled and banged like a bad band out of tune. A lot of it has to do with high velocities and subsequent high reynolds numbers. All of these lead up to Hammer problems when valves are open and closed and high noise problems.

Hope this helps.
saxon

 

[SooCS]

setak,

I have problem with my scanner. As soon as I fix it I when scan a copy for you.

Best.

 

[ulama]

Dear SooCS...

would please to send me your chart on kusayang_kamu@lycos.com

thanks and regards

syam

 

[StressGuy]

Someone was asking about the spreadsheet refered to in the NASA document. It looks like this like will get you to it:

http://www.grc.nasa.gov/

http://WWW/AcousticalTest/HearingConservation/Software_For_EST.htm

Looks like a lot of information on noise and vibration at this site.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

 

[SooCS]

Hi sayang,

I guest you dont need my chart anymore when you can set the spreadsheet calculation.

Best Regards

 

[SooCS]

Hey Guys,

There seem to be an error in the Nasa spreadsheet.

The Cell "U55" of Flow Noise worksheet, should read

=-10*LOG(Q28/Q27*(1+6/(Q27/12))

This correction is necessary for consistant unit in "ft".


Gee! NASA does make mistake. No wonder they lost two space shutters.

 

[TD2K]

Don't forget the Mars lander they lost due to another unit conversion error (actually, lack of unit conversion).

 

[KylieS]

Hi,
In line with the previous questioning, I'm interested in determining the noise level from flow through a riser. The multi-phase well fluid rate is expected to be 400MMscfd, at 65C and 12200kPa. The riser is a 12inch duplex line.
So far, everything I've come across has to do with gases. If anyone has an equation they could pass on that would be great.
Thanks,
Kylie.

 

[SooCS]

Noise is seldom a problem in multiphase flow piping and is usually limited by erosional/corrosion velocity. Check it out in API RP 14E for erosional/corosion velocity guideline.

Best of luck.

 

[Instr13]

Hi Guys,
We have an air blower and are going to bleed partially through a control valve to the atmosphere. Inlet pressure to the control valve is 90 kPag, flow 1700 kg/hr at 105 deg C. Would you let me know if we require any silencer. The line size is supposed to be 3". The valve noise assuming full pressure drop is about 92 dBA and is going to be reduced by acoustic insulation.
If we should include silencer then what potion of pressure drop is required to get absorbed by the valve and silencer.
The pipe length is around 40 ft.