How to calculate pressure in pipeline

[galata]

Hi all,

Could you please help me. How to calculate pressure in closed pipeline.
I have 8 km, 1" line fill with hydraulic oil. The pipe will be laid at 40m depth in the sea. I can calculate volume of Oil in the pipe, but how to calculate, how many liters of oil will need to increase pressure to for example 100 bar.
I need formula to show the connection between Volume and Pressure.

Thanks in advance
Regards

 

[zdas04]

What you are really talking about is the compressibility of your hydraulic oil and to a lesser extent the elastisity of the pipe. Mostly hydraulic oil is around 0.004 L/L per 1000 psi and reasonably linear so to increase pressure 1450 psi would require adding 0.0058 L/L. Your system holds 4176 L so if you disregard pipe stretch (which might be a reasonable approximation for a 1-inch under 40m of water) then you would have to add 24L to get to pressure.

You should be able to work out a formula from the above.

David

 

[galata]

Thank you very much David

You mean that, I need to know hydraulic oil compressibility. Probably the vendor can give me this info.
If I know how many liters I need, then I can calculate how many minutes my pump will running.

Regards
Dian

 

[BigInch]

You seem surprized. Of course you need to know the compressibility of the oil to develop a volume and pressure relationship. The volume relationship alone is [π] * r^2 * L, but David assumed you know that. As David said, there are two other factors, compressibility of the oil and expansion of the pipe. Expansion of the pipe is neglected, because it isn't that much in such a small diameter line. If you want to include that, its probably about 2 more liters or so.

Just to insure that we have the correct understanding of your problem, David and I too assume that your question was regarding only to do a pressure test on that pipeline and it was not at all related to finding any necessary pressure to flow some quantity of oil in that pipeline. Correct?

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[ione]

galata,

If you want to check longitudinal elongation due to pressure and evaluate extra-amount of oil to compensate it (very low in this specific case, but sometimes not trivial) you can use the formula below:

Epsilon = [(P*D)/(4*t*E)]* (1-2*Poisson)

Where :

Epsilon = longitudinal strain
P =applied pressure
D= pipe mean diameter
t = pipe thickness
E = Pipe Young Modulus
Poisson = Pipe Poisson’s ratio

 

[galata]

Thank you very much everyone.