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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
e = Pipe wall thickness (mm)
C0, C1, C2, C3 = Parameters
| Parameter for Noise Correction | |||||
| Nom.Dia. (Inch) | Eq. | C3 | C2 | 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
Related Topic
- Quick Estimation of Noise Level Across Pressure Reducing Device
- Assess AIV with "D/t-method"
- Extra Attention to Common Point and Similarity on AIV Failure
- Piping Excitation When Expose to Acoustic Energy
- Acoustic Induced Vibration (AIV) Fatigue
- Sound Power Level (PWL) Prediction from AIV Aspect
- Several Criteria and Constraints for Flare Network - Piping
- Flow Element (FE) Upstream or Downstream of Control Valve (CV) ?
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