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Earlier post "Quick Estimation of Noise Level Across Pressure Reducing Device", discussion has been focused on estimation of Noise level across pressure reducing device i.e. control valve, pressure relief valve, restriction orifice, etc based on generated internal acoustic energy and transmission losses. The table presented in this post is typical wall thickness for Schedule STD. Increases in wall thickness (e) will results higher transmission loss and lower noise level is expected. Besides, magnitude of transmission loss is also depends to line diameter (D). How to relates transmission loss with wall thickness for different diameter ?



Noise Level Estimation

Noise level at 1 meter from a pressure reducing device can be estimated from Sound Power Level (PWL) as discussed in "Sound Power Level (PWL) Prediction from AIV Aspect". The Sound Power Level will be transmitted across the pipe wall and emitted to atmosphere. There will be noise correction when Sound power is transmitted across pipe wall (metal).

Noise level at 1 meter from a pressure reducing device,

L1m = PWL - LA

where
PWL = Sound Power Level (from Sound Power Level (PWL) Prediction)
LA = Noise correction (dB)

Noise Correction
The noise correction is subject to wall thickness and pipe size. Thicker wall will result higher noise correction. Following are sets of noise correction equation for different pipe size and wall thickness.

For Nominal Diameter equal to 750 (30 inches) and smaller,

LA = C3.e3 + C2.e2 + C1.e + C0 ......[1]

For Nominal Diameter 900 (36 inches) and above,

LA = C1.Ln (e) + C0 .....[2]

Where
e = Pipe wall thickness (mm)
C0, C1, C2, C3 = Parameters


Parameter for Noise Correction
Nom.Dia.
(Inch)
Eq.
C3C2
C1
C0
25
1
0.0580
-1.2556
11.6751
26.0942
50
1
0.0319
-0.8039
8.8155
25.7428
100
1
0.0070
-0.3107
5.6726
25.7582
150
1
0.0046
-0.2351
4.8724
24.2083
200
1
-0.0002
-0.0376
2.3897
31.0074
250
1
0.0023
-0.1395
3.1106
28.5213
300
1
0.0013
-0.0949
2.5482
29.9195
350
1
0.0012
-0.0858
2.4017
29.2649
450
1
0.0008
-0.0660
2.1185
30.5846
600
1
0.0003
-0.0371
1.5550
32.7016
750
1
0.0007
-0.0523
1.7118
31.1754
900
2
-
-
6.9521
27.3305
1050
2
-
-
10.4282
18.4957

Example
A pressure control valve (PV) passing 100,000 kg/h of gas with molecular weight (MW) of 22. The inlet condition is 87 barg and 50 degC and downstream pressure is about 7 barg. The pipe diameter is 18 inch with wall thickness of 9.53mm, estimate noise level at 1 m from PV.

PWL = 10 x Log [((87-7) / (87+1.01325))^3.6
x (100,000 / 3600)^2
x ((50+273.15)/22)^1.2]
+ 126.1

PWL = 167.5 dB

For 18 inches, equation [1] will be used.

LA = C3.e3 + C2.e2 + C1.e + C0
LA = 0.0008 x9.533 -0.0660x9.532 + 2.1185 x 9.53 + 30.5846
LA = 45.5 dB


Noise level at 1m,
L1m = PWL - LA
L1m = 167.5 - 45.5
L1m = 122 dBA

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posted by Webworm, 1:30 AM

5 Comments:

Anonymous Marine said...

Hello,
Your post is interesting.
Could you please provide the reference for the formula and the parameters ?
Thanks a lot

August 24, 2012 at 7:43 AM  
Blogger Webworm said...

Marine,

The equation is generated from a series of field data.
It is empirical information.

JoeWong

August 24, 2012 at 9:21 PM  
Anonymous Marine said...

Hello Joe,
Even if it is empirical information, do you know if it was published somewhere ?
Thanks,
Marine

October 4, 2012 at 1:58 AM  
Anonymous Marine said...

Hello,

Even if the information is empirical, do you know if it was published somewhere ?
Thanks,
Marine

October 19, 2012 at 1:33 AM  
Anonymous JoeWong said...

I did not publish these data.

November 16, 2012 at 9:56 PM  

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