<body><script type="text/javascript"> function setAttributeOnload(object, attribute, val) { if(window.addEventListener) { window.addEventListener('load', function(){ object[attribute] = val; }, false); } else { window.attachEvent('onload', function(){ object[attribute] = val; }); } } </script> <div id="navbar-iframe-container"></div> <script type="text/javascript" src="https://apis.google.com/js/plusone.js"></script> <script type="text/javascript"> gapi.load("gapi.iframes:gapi.iframes.style.bubble", function() { if (gapi.iframes && gapi.iframes.getContext) { gapi.iframes.getContext().openChild({ url: 'https://www.blogger.com/navbar.g?targetBlogID\x3d8968604820003269863\x26blogName\x3dChemical+%26+Process+Technology\x26publishMode\x3dPUBLISH_MODE_BLOGSPOT\x26navbarType\x3dBLUE\x26layoutType\x3dCLASSIC\x26searchRoot\x3dhttp://webwormcpt.blogspot.com/search\x26blogLocale\x3den\x26v\x3d2\x26homepageUrl\x3dhttp://webwormcpt.blogspot.com/\x26vt\x3d6402931565399164945', where: document.getElementById("navbar-iframe-container"), id: "navbar-iframe" }); } }); </script>

Chemical Process Technology

Continue to learn tips, knowledge and experience about Chemical Process Technology...

Enter your email address:


CLOSE WINDOW


 

Chemical & Process Technology

A place to share knowledge, lesson learnt...

Tuesday, May 26, 2009

Display problem ? Click HERE

Recommended :
- Tips on Succession in FREE Subscription
- Subscribes to FREE Hydrocarbon Processing

Pressure reducing device such as control valve, pressure relief valve, restriction orifice, etc, there will be pressure drop and mass passing through these device, internal acoustic energy is generated and transmitted to downstream piping and potentially lead to severe piping excitation, vibration and stresses on downstream piping and potentially lead to fatigue failure. Internal acoustic energy transmitted along the pipe may also transmitted to through the pipe and emitted as Noise.

One of the common safety requirement is limit the noise level to 85 dBA (Noise level with A-weighted) in continuous exposure and 115 dBA during intermittent exposure. In earlier conceptual or Front End Engineering Design (FEED) stage, the noise level across pressure reducing device may be estimated to determine overall noise control philosophy. The following will present a simple method to estimate noise level generated at 1 meter from a pressure reducing device.

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). The noise correction is subject to wall thickness. Thicker wall will result higher noise correction. Following are typical noise correction for pipe size and wall thickness.

Noise Correction
Nominal Dia.
(Inch)
Wall thickness
(mm)
Noise Correction
(dB)
25
3.38
54
50
3.91
50
100
6.02
50
150
7.12
49
200
8.18
48
250
9.3
47
300
9.53
47
350
9.53
46
450
9.53
46
600
9.53
45
750
9.53
43
900
9.53
43
1050
9.53
42

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 from above table

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

Noise level at 1m,
L1m = PWL - LA
L1m = 167.5 - 46
L1m = 121.5 dBA

As the noise level at 1m (normal trim) is 121.5 dBA, this is far too big from normal requirement. A low noise trim control valve may be considered and/or acoustic insulation to be provided.


Related Topic

Labels: , ,

posted by Webworm, 1:26 PM

3 Comments:

Anonymous Anonymous said...

Hi,

In the above link article to determine PWL, you showed an example of PWL calculation, which gives an answer in units of dB.

In the above table, the noise correction factor "LA" is in units of dB as well.

Therefore, should the above L1M anwer be in units of "dB" too, instead of "dBA"?

If this is so, how would you convert dB to dBA?

Thank you.

June 8, 2009 at 6:49 AM  
Blogger Webworm said...

The noise correction factor contain Sound Power Level (PWL) attenuation and correction from dB to dBA. Therefore the PWL generated at source minus the noise correction factor (attenuation plus correction) lead to noise level in dBA.

June 8, 2009 at 6:59 AM  
Blogger Renuga said...

hi thanks for the info. I find it really useful. Could you please provide me the reference for the attached noise correction table for the different pipe and wall thickness and the reference for the equation to determine noise correction.

January 13, 2010 at 7:19 PM  

Post a Comment

Let us know your opinion !!! You can use some HTML tags, such as  <b>, <i>, <a>

Subscribe to Post Comments [Atom]

Links to this post:

Create a Link

Home:

<< Home