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roadbikeruler (Petroleum) (OP)
30 Nov 08 3:15

Need some advice about hydro testing in cold weather with glycol.
-Understand when pipe temp rises the pressure goes up.
-When pipe temp is dropping the pressure will drop.
-How much would you compensate for pressure drop?
-If glycol  in the storage tank &  the pipe temp are within 2-3 degree difference.
Should the pressure drop be minimum like a 1 to 5 pound drop.
When I walk the line for leaks find no traces of a leak (only within the test limits)
The PTR & specs for Company X say to Hold test for 10 minutes
Look on internet not much help.
Would you know if there is some type of chart for pressure lost at minus temperatures
 
BigInch (Petroleum)
30 Nov 08 6:51
Pipe expansion, Pressure decreases with temperature increase
Fluid expansion, pressure increases with temperature increase, for most fluids, but some (yes water is one) depend on the temperature and the temperature range during the test. The resulting pressure varies with temperature depending on the temperature expansion coefficients of one in relation to the other.

For a 10 minute test, I doubt that temperature will stabilize enough to get much of a test, or really be a factor worth considering, as there shouldn't be much temperature change in 10 minutes, other than to determine if there is tightness or not.  That would hardly be enough time for the pipe temperature and fluid temperature to equalize.

Therefore, if its just a short time tightness test, I wouldn't worry much about temperature at all.  If you get any effect, what you're measuring would not give an accurate indication of leaks anyway.

**********************
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic  (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/

zdas04 (Mechanical)
30 Nov 08 14:54
Why in the world are you doing a glycol test?  Disposal of glycol is very difficult and expensive and after picking up pipe scale and welding slag it will not be reusable.  I'm sure there is a reason, but I'd sure ask the question about what the cost/benefit of glycol vs water or a glycol/water mix (which has a lower freezing point than pure glycol if that is your concern in a cold weather test).

I don't know what the coefficient of thermal expansion of glycol is, but with water it works out to about 100 psi pressure change (from elevated pressure) for every degree F of temp change, so your 2-3 F temp change could be 200-300 psi pressure change.  I'd find out what the number is for glycol before starting a glycol test.  

In a 10 minute test, nothing will reach an equilibrium temp so your question doesn't feel right to me, it feels like there is something missing.  

I've got a document under "samples" on my web page that might help you answer some of your questions.

 

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.

"Everyone is entitled to their own opinion, but not their own facts"  Patrick Moynihan

BigInch (Petroleum)
30 Nov 08 15:37
I thought it was a glycol line in a dehy system or something.

**********************
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic  (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/

Bribyk (Mechanical)
3 Dec 08 0:37
"Glycol" likely means a 50/50 mix with water.  It's commonly used to test drilling rig equipment in cold climates where it ends up mixed with the toxic drilling fluid which have to be disposed of anyway.  It's also usually fluorescent green which makes it easier to spot leaks around oily/muddy/snowy equipment.

50/50 glycol is a very leak-prone substance (NFPA 37 recommends welded over threaded fittings for it).  If you can't see a leak and there's no where for it to leak internally (i.e. past a valve into a vessel) it's probably a temperature issue.

How much is your test pressure dropping?
belowzero (Mechanical)
3 Dec 08 16:09
roadbikeruler (Petroleum) says

Quote:

If glycol  in the storage tank
so I pressume he does mean 100% Glycol. Surely this is quite a difficult test, much like Helium against Nitrogen when doing gas tests, as the Glycol has a very small molecule and is known to be very 'searching'. This would surely find leaks that would not normally be detected if using water or water/Glycol.
B
Bribyk (Mechanical)
3 Dec 08 19:22
You could be right, belowzero.  It's half the cost though to cut it with water though.
davefitz (Mechanical)
4 Dec 08 12:42
you may need to confirm the metal temp is above the ductile britel transition temp, or the metal has adequate notch toughness, prior to hydrotest at low ambient temp.

As I recall ASME I requires a min metal temp above 60 F for hydrotest, based on alloys weldments, and heat treatments permitted in that code.

Most of the catastrophic failures of presure vessels that I can recall during hydrotesting were related to failure to ensure adequate metal temperture to avoid brittle fracture.
metengr (Materials)
4 Dec 08 14:25
The minimum temperature for the water is 70 deg F for ASME B&PV Code activities. The NBIC provides guidance for metal temperature at 60 deg F.
BigInch (Petroleum)
4 Dec 08 16:53

Quote:


-Understand when pipe temp rises the pressure goes up.
-When pipe temp is dropping the pressure will drop.
...
-If glycol  in the storage tank &  the pipe temp are within 2-3 degree difference.
...
When I walk the line for leaks find no traces of a leak (only within the test limits)

Testing pipe.  

**********************
"Pumping systems account for nearly 20% of the world's energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic  (Note: Make that 99.99% for pipeline companies) http://virtualpipeline.spaces.live.com/

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