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Hydrostatic Testing of Gas Pipelines

02/18/2009 6:59 AM

Hi to all,

I have open this discussion about hydrostatic tests of pipelines, fittings, traps, etc. Now I have a task to calculate testing pressure for hydrostatic test for GAS pipeline on field.

Parameters: D=6.625in; WT=0.5in; Material- X60, Design P=4118 PSIG and T=110C.

I have API 5L, ASME B31.3 and ASME 31.5 standards. But in these standards I received a different values.

As per API5L (I take analogy with pipe) Ptest=6790 PSIG. As per ASME 31.5 - 130% from Pdesign. May be I'm wrong, than you can correct me.

And other question - how can I choose test time? >10 seconds or >10 minute or ......

If somebody have experience to design or inspecting pipelines, or you have good tip - I'm waiting your suggestions. Also for me interesting any information about testing.

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#1

Re: Hydrostatic Testing of Gas Pipelines

02/18/2009 1:46 PM

You need to test it as per the code that the piping system was designed to.

I am not going to detail all the stipulations

ASME B31.3 - Please review Chapter IV

ASME B31.5 - Refrigeration piping - NOT APPLICABLE

ASME B31.4 - Please review Section 437

The minimum hydro test times are stipulated in the codes. (HINT: B31.3 - not less than 10 minutes; B31.4 - depends on design stress levels: maybe 1 hour, maybe 4 hours)

Basics of hydro testing include:

  • Remove all air
  • Keep everyone out of the area
  • Watch for pressure increases due to thermal expansion
  • Avoid pneumatic testing

Please, also see API 1110, and this paper: http://www.hse.gov.uk/research/crr_pdf/1998/crr98168.pdf

And last, but not least, REVIEW THE APPLICABLE DESIGN CODE

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#2

Re: Hydrostatic Testing of Gas Pipelines

02/19/2009 10:55 AM

Good morning ANDREI. In another life I worked for a gas distribution co. Thru the cobwebs of time, I remember for Design Pressure we used DP = (2St/D)FET, where S was the yield strength of the steel, t the wall thickness, D the OD, F a factor based on location, E a factor based on pipe construction, and T a derating factor for temperature. Assuming the location was away from sensitive public areas, F=1. Assuming the pipe was modern Electric Resistance Welded, E=1. And of course, temperature was not elevated, so T=1. This gives a DP of 9,057psi in your case. We always tested at 1.5 x MAOP (Maximum Allowable Operating Pressure), so TP would be 1.5 x your 4118psi, or 6177psi. Assuming constant weather parameters, we always tested for 24 hours, so the plot of pressure always came back to the same pressure, after decreasing for night temperatures. I am curious as to the value of T for your temperature of 110ºC (230ºF). Inasmuch as they want $350 to download ASME B31.3, I do not have access to this info.

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#3
In reply to #2

Re: Hydrostatic Testing of Gas Pipelines

02/22/2009 2:42 AM

Thanks flyinghigh for answer.

As per your information : "..Pressure we used DP = (2St/D)FET, where S was the yield strength of the steel, t the wall thickness, D the OD, F a factor based on location, E a factor based on pipe construction, and T a derating factor for temperature. Assuming the location was away from sensitive public areas, F=1. Assuming the pipe was modern Electric Resistance Welded, E=1. And of course, temperature was not elevated, so T=1."'

I saw the same formula for TESTED PRESSURE in API 5L is present - you can find, that for X60 Steel

--> P = (2St/D) (for Imperial System) or P = (2000St/D) (for SI).

And for my case (WT=0.5in, 6", X60, P= 4118psi) P=(2*0.75*60000*0.5)/6.626; P=6790psig (or standard limited = 3000psig).

So, which is the kind of this pressure in formula?

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#4
In reply to #3

Re: Hydrostatic Testing of Gas Pipelines

02/22/2009 10:02 AM

Good morning ANDREI. I wonder what the 0.75 is in your formula? Also, you are not considering temperature; why?

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#5
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Re: Hydrostatic Testing of Gas Pipelines

02/23/2009 2:11 AM

Hi,

in formula 0.75 - is a percentage for SMYS (in i.9.4.3 API 5L) for material X42-X60 and pipe Diameter 5"-8".

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#6
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Re: Hydrostatic Testing of Gas Pipelines

02/23/2009 3:23 AM

If you are testing a piping system that has been fabricated/installed - don't worry about the original piping specification, API 5L; you must test to the design/fabrication code whether it is ASME B31.3, B31.4, B31.8, or .........

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