Volume from pressure drop during hydrotest 1

[snyper]

Hello

Wondering if there is a quick formula to calculate volume of water lost from a pipeline under hydrostatic test, given a known drop in pressure and total volume in system. Test medium is water.

Thanks

 

[israelkk]

You can if you know the water compressibilty factor. However, are you sure there is absolutly no air inside?

 

[snyper]

Where do I get the compressibility factor?
I know that if the line has air in it the calculation will be out, but I am only after a rough estimate, so will assume the line contains only water.
Thanks

 

[jte]

snyper-

See also

http://slc.ca.gov/Division_pages/MF...Terminal Engineering Issues/Pringee paper.pdf

and

http://www.slc.ca.gov/Division_Pages/MFD/MFD_Home.htm.

Towards the bottom of the Marine Facilities Division home page you'll see a paragraph about the Static Liquid Pressure Test and a contact to get their spreadsheet.

jt

 

[25362]

Isothermal compressibility of water at 20^oC,

[κ] = -(1/V)([∂] V/[∂] P)_T= 4.59 [×] 10^-4/MPa​

At 30^oC, [κ] = 4.48 [×] 10^-4/MPa

 

[Zapster]

k = (Bulk Modulus)^-1

 

[DMcGrath]

You didn't specify, but all the computations above seem to assume steel pipe. When hydrostatic testing plastic pipe (HDPE), there is a volume allowance for the pipe to "stretch" that shows up as a pressure drop. Once the test pressure is restored by adding more water, then the actual leak test begins. Look at "Plastic Pipe Institute" on the web and then their guidelines for testing.

 

[athomas236]

the question is "is there is a quick formula to calculate volume of water lost from a pipeline under hydrostatic test"

according to my understanding there should be no water lost during hydro test

 

[Montemayor]

athomas236:

Kudos for your accurate analysis of the basic, original question and the correct response. No hydrotest is valid or acceptable if it has to withstand water leaks.

Agreeably, the original question probably isn't worded or written correctly but, until it is, the answer is just as athomas has replied.

 

[snyper]

Who said anything about this hydrotest being valid or acceptable? In the real world, tests do sometimes fail. The formula I was chasing was to give a basic understanding of the severity of the failure.
Cheers for all your replies guys.

 

[zdas04]

The fun thing about a test with water is that any leak will take the pressure to zero very quickly. I did a test once that dropped two miles of 10-inch pipe from 900 psig to zero in 15 minutes through a reasonably small packing leak in a 1-inch gate valve.

I was hoping that someone would be able to provide you with a way that I could estimate how much volume that would be, but the number is vanishingly small.

David

 

[Zapster]

Ref:
“Pipe Line Rules of Thumb Handbook” E.W. McAllister, Editor, 4th edition
Gulf Publishing Company, Houston, Texas

Appendix A, Page 127 & 128, Volume of Water Required to Fill Test Section

Equation and Sample Calculation are given in the Appendix.

Equation:

Vtp = V * Fwp * Fpp * Fpwt

Vtp = Gallons in section at test pressure

Fwp = Factor to correct for compressibility of water from 0 to test pressure

Fpp = Factor to correct for volume change in pipe from 0 to test pressure

Fpwt = Factor to correct for the change in water volume and pipe volume due to change in temperature from 60 to pipe and water temp.

This reference list out the equations for V, Fwp, Fpp, and Fpwt so it should answer your question.

 

[hydrodude]

I have some formulas that take into account the size and wall thickness of the pipe, the temperature of the underground and above ground piping and the length of the pipe. But the easiest way is to drain a known amount of water out of the line and see how much your pressure drops and calculate from that. Remember though that temperature change will make a huge difference in pressure, always let your water stabilize to the ground temp around the pipe for at least 24 hours. I was involved in a test last year that was on 30 inch pipe 20 miles long with water being put in from a river at 85 degrees and it took over a week for the pressure to stop dropping from temp change. Once the temp stabilized it held a perfect test.

 

[dougg33]

My local standards provide for allowable leakage in gallons per length per time per pipe size (for water systems). The only way I can think of to accurately quantify leakage for the test is to refill the system at the end of the test and measure (with a flowmeter or other device) the volume required to get back to starting pressure.
Any other thoughts on this?

Thanks!

 

[Rsz131079]

I ASKED IF I CAN GET PDF FILE FOR THE HYDROSTATIC TEST PROCEDURE AND STANDERDS

Ramy El-zeiny
process Eng.
gulf of suez pet. co.
Egypt