Estimation of Pressure Drop in Gas Pipelines 1

[pyMorty]

Hi Everyone,

This is my first post in the forum, I´m Industrial Engineer, from Mexico. I work as a Project Engineer for a natural gas compression company. I´m now more often involved in compression infraestructures, I use to select the pipe diameters, valves, fittings and instrumentation required, but when it comes to pressure drop calculation along the pipeline I frequently come across with troubles to calculate it and resort to some basic software for this porpouse. The thing is that I'd like to know how to calculate it by myself, at least a rough estimate, since my position doesn´t require me to make detailed calculation and I only have the most basic inputs to it, i.e. inlet pressure, distance, pipe diameter, temperature, gas density, elevations, assumption of Z value, gas velocity (this one just if calculate the outlet pressure, in which case I wouldn´t need to recalculate the pressure drop). So, basically, the question is whether, with the mentioned inputs I can estimate the pressure drop. I want to get involved in fluids mechanics from now on, but I have to start from the basics, so I hope you can help me developing these skills.

Thank you guys in advance.

 

[pyMorty]

I´d like to clarify, I´ve read some topics about this issue, but as I told before, I´m not very familiar with this and I´m just starting, so, I´d appreciate you to tackle this as a sort of "formulas for dummies".

 

[MortenA]

There are thousands of textbook on this subject. If you have a basic understanding on the subject try API 14E (ISO 1373). Its not for pipelines but piping but the principles are the same.

 

[PEDARRIN2]

It would be very difficult to give a quick and easy explanation of calculating pressure drop for compressible fluids.

I could tell you to use Darcy's formula and use the Moody Friction Factor Diagram, but then you might ask what those are, and if you know, you would be asking how to apply it.

The resource that I have found most helpful explaining all this is Crane Technical Paper No. 410. It is actually a booklet, but has explained (and shows examples) of how to solve about every fluid flow problem there is.

Get this resource and study it. It will be invaluable.

 

[pyMorty]

Thank you both guys.

I'll check both API14E and Crane. Definitely I need to study more on this subject before trying to do anything.

 

[BigInch]

Weymouth Formula
Panhandle A and B equations
AGA Gas Flow Equation
can all be used to calculate pressure losses in natural gas pipelines (within their certain limitations), including allowance for the compressibile fluid that it is.

download this and scroll towards the end of the slides. You will see most of those formulas there.

https://www.google.co.uk/url?q=http...kQFjAD&usg=AFQjCNFSNICRBFG0pJTEwGhP7utBNRd41Q

I hate Windowz 8!!!!

 

[pyMorty]

Thanks BigInch,

Now that you mention it, I´ve used the Weymouth to calculate both the flow and diameter, since among the inputs of that formula it is the outlet pressure what I have to do is to solve for outlet pressure.

 

[LittleInch]

The issue with most of the relatively simple equations is how many sections or change in pressure the equation is reasonably accurate for. I've heard before somewhere that once you change the pressure by more than 10-15% the accuracy of the equations starts to grow and become increasingly invalid. Therefore you may need to break your line into a number of sections and solve for each of those using the output from the previous stage.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

The above equations have some compressibility effect considered, so that 10% maximum pressure drop limit is for equations that have no built-in correlation at all. The above will do better, but how much better depends on how well you stay within the envelope of validity of the formulas. Use them for long pipelines that are between 100 and 1000 psig, preferably above 6" diameter and running at normal temperatures. Weymouth was developed using a 20" pipeline as it's central case.

Diego, The standard form of the equations are usually to calculate the outlet pressure. If not, you can do some algebra and reverse the equation to solve directly for outlet pressure, or do some iterative calculations.

I hate Windowz 8!!!!

 

[pyMorty]

Thank you Little and BigInch ()

I'll try some examples with Weymouth, reversing the equation, and then with Pipesim and see how close the results are.

 

[katmar]

A good starting point is the article "A Tutorial on Pipe Flow Equations" by Donald Schroeder. This is available at

http://www.ewp.rpi.edu/hartford/~er...udents/Douglas/PipeFlowTutorial-Schroeder.pdf

This, and other conference articles, used to be freely available from the Pipeline Simulation Interest Group but I see that they have given the job of handling all their artilces to OnePetro who now charge a small fee for any downloads.

https://www.onepetro.org/

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"