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# Pressure Drop For Natural Gas

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6 replies to this topic
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### #1 aisah

aisah

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Posted 08 October 2007 - 02:28 AM

Dear,
What is the best formula to calculate pressure drop in natural gas pipelines? Is it Polyflo formula can be used?
Is there any range/limitation for linier velocity (v) in gas pipe lines? What is it?
Please help me to find the formula or article that have data about equivalent length for reducer (8 x 6"), reducer tee (8x8x4"), ball valve (8,4,3,2") and weld neck flange.

Thank you very much

### #2 Art Montemayor

Art Montemayor

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Posted 08 October 2007 - 08:59 AM

Aisah:

This query is posted in the Industrial Professional Forum so I assume that you are a practicing, professional engineer as me.

I don’t believe there is any such formula as the “Polyflo formula”. Could you please be more specific and detailed about the relationship you are describing?

The best formula to use in calculating the pressure drop in natural gas pipe lines depends on your application. It can be the Pan Handle Equation or the Darcy Equation. It depends on what you are trying to do and what your limitations are. You should refer to and have full understanding and knowledge of Crane’s Tech Paper #410, The GPSA Engineering Data Book, Cameron Hydraulic Data book, and various others. If you want to employ equivalent lengths in your calculations, be sure to read Phil Leckner’s excellent paper on that subject that you have available free, in this website. There is a lot of free information that you can download on the subject from the internet. You should construct your own spreadsheets and workbooks – like a lot of us have done so already and use those to do your calculations. A lot of the information you ask for exists on these forums. I have personally submitted workbooks on fluid flow and recommended velocities – including extensive data on fittings and valves. You should do a search on our forums and download all this information if you don’t already have it.

If you are specifically dealing with natural gas, say so. Don’t keep such information to yourself. If that is the case, you should obtain a copy of API RP 14E, “Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems”. In it you will find specific applications and equations for transporting natural gas.

I hope this helps.

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Posted 08 October 2007 - 09:18 AM

Thankfully im not the only person who'se never heard of the polyflo equation - is it maybe a CFD model???

You could try this link for an online natural gas calculator -

http://www.pipeflowc...algas/index.htm

Ive also added a pdf you might find useful.

btw - the 'Panhandle equation'??!!!??? please tell me this wasnt named after a guy called Panhandle.

### #4 fcontrer

fcontrer

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Posted 08 October 2007 - 03:32 PM

Aisah:

Check it:

http://www.aft.com/news/view.php?ID=97

Chemical Engineering - Gas Calculations: Don´t Choke
Posted: January 31st, 2000
As featured on the cover of Chemical Engineering magazine, 'Gas Calculations: Don't Choke' by Applied Flow Technology's Trey Walters discusses in depth the important factors related to compressible flow calculations and the limitations of widely accepted, but incorrect, assumptions"

Its Free.

Frank.

### #5 aisah

aisah

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Posted 09 October 2007 - 02:50 AM

Thank you very much for your extraordinary answer. Actually I'm confuse when choose between industrial professional and Student. Firstly I would like to choose Student Forum because I am a beginner but it looks I click the wrong forum and enter in industrial professional. Sorry for this mistake.
I have just accepted in Natural Gas Distribution Company. And I have assignment to calculate pressure drop in gas pipelines.
I have article that mentioned about Polyflo equation

Q = ((6.44(pi2-po2)D^4.848)/(S^0.848*L*T))^0.541

Thank you again for your information, I will try to learn it first.

### #6 ashetty

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Posted 14 October 2007 - 11:26 PM

aisahm,

I`ve never heard of the Polyflo equation.Im not sure if you should be using the same for your calcs.
Please read pg 6 of attached article and pg 10 onwards for solved problems.If possible read the entire article.useful.
For long gas transmission lines the panhandle equation is normally used. If mixed phase flow is invoved i think you better use some other equation.Also use your engineering judgement at times, for example take into account the expected liquid hold up in the lines (when velocites are low & flow is mixed).This will increase the DP across the lines.
Regards.

### #7 fcontrer

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Posted 25 October 2007 - 08:13 AM

The Beggs and Brill correlation is able to predict the liquid holdup and pressure drop that occur during two-phase flow in pipes at all angles and at several flow conditions. For more information please refer to the classical paper by Beggs and Brill: "Journal of Petroleum Technology", May 1973, P607-617.
I am not sure if is the best correlation for GN pipelines or only is "Adequate"