Q: 16" buried pipeline hydrotest
Q: 16" buried pipeline hydrotest
(OP)
Good day all,
We are hydrotesting a 16" CS buried pipeline with a crude oil service.
This will be done by 2 stages:
stage 1: 2 hrs strength test at nearly 1126 psi.
stage 2: 24 hrs tightness test at nearly 1070 psi.
At the end of stage 2, when we are reviewing the pressure and temperature charts, there was a 150 psi drop against a 3 degrees C drop only.
I couldn't find an acceptance criteria for such a case, but normally we estimate it. Like if there's 20 or 30 psi drop; we accept that. But 150 it quite a pressure drop.
Appreciating your inputs.
We are hydrotesting a 16" CS buried pipeline with a crude oil service.
This will be done by 2 stages:
stage 1: 2 hrs strength test at nearly 1126 psi.
stage 2: 24 hrs tightness test at nearly 1070 psi.
At the end of stage 2, when we are reviewing the pressure and temperature charts, there was a 150 psi drop against a 3 degrees C drop only.
I couldn't find an acceptance criteria for such a case, but normally we estimate it. Like if there's 20 or 30 psi drop; we accept that. But 150 it quite a pressure drop.
Appreciating your inputs.





RE: Q: 16" buried pipeline hydrotest
Off hand I'd say you did well.
What would you be doing, if you knew that you could not fail?
RE: Q: 16" buried pipeline hydrotest
It has been a really long time since I did a 24 hour test (they were often required in the 70's, but by 1990 they had become rare), but the last one I did caused me to develop acceptance criteria as part of all of my test procedures. Typically I define "success" as any test that ends up with pressure at the test point higher than MAWP (the procedures do not allow adding water after the test starts, but you can bleed pressure off if necessary). It is pretty arbitrary, but I've never had an auditor take exception to it.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Q: 16" buried pipeline hydrotest
What would you be doing, if you knew that you could not fail?
RE: Q: 16" buried pipeline hydrotest
BigInch: I believe it's worth.
Mohammed Diab.
Inspection Supervisor - Saudi Aramco.
RE: Q: 16" buried pipeline hydrotest
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Q: 16" buried pipeline hydrotest
Do you have a thermal lag rate (varying temperature (of the soil -> of the pipe & fluid)) vs soil depth, soil temperature for that spreadsheet?
Seems that, over a long period of 4-12 hours of the test, as the air temperature, sun's exposure, and soil temperature are going to vary, the internal pipe temperature is going to vary as well. But the pipe temp's are going to be slower, since the deeper you go, the less the soil temp will change.
So, whatever the temperature of the fluid is as it first goes in, over a period of time, it will (almost) assume the soil temperature around it, but will always lag the soil temperature, which is lagging the top few inches of soil temperature and air temperature.
My hydrostatic tests have always been in steam, oil, and water pipes out of the ground, so I don't have any experience to compare with your oil field/oil pipeline knowledge, but if 0.5 to 1 degree matters in correcting for temperature in a long pipe.... Topside, outside of the ground in power plants, the thermal lag is 100% in that "little bit of metal" around a large mass of water, so it was only pressure changes we monitored.
RE: Q: 16" buried pipeline hydrotest
What would you be doing, if you knew that you could not fail?
RE: Q: 16" buried pipeline hydrotest
After filling the water, we are giving 24 hrs for thermal stabilization between the water and the pipe.
There are no vents nor drains installed. Rather, for venting, we are running a foam pig forward ahead of the water being filled, and for draining, we are running the pig backwards.
There are 2 small portions of the pipe, at the start and at the end of the pipe section, above-ground to allow the installation of 2 temporary test headers for launching and receiving the pig.
Indeed, the manifold and pressure gauges are installed above ground, and are being affected by a higher temperature specially during the day. While the probe of the temperature recorder is dipped in the soil trying to read the temperature of the largest segment of pipe which is buried.
Thus, the pressure of the buried section cannot be actually measured. And we don't have a record of the above-ground temperature.
It would've been easier to re-test, but when this problem reached me, I found them already de-watered and the system is under positive pressure lay-up. Which leaves re-testing as an impractical solution at this stage, specially that it's a 30 kilometer pipeline section.
Mohammed Diab.
Inspection Supervisor - Saudi Aramco.
RE: Q: 16" buried pipeline hydrotest
The 24 hour soak is a good thing, but it is useful both for equilibrating temperature as well as for allowing the dissolved gases that will evolve out to do so. If you don't vent the gases off, the soak probably did more harm than good.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Q: 16" buried pipeline hydrotest
I also like to have large capacity pumps and to fill the section as quickly as possible to cleanly push the air ahead of the water and without any pigs, given my choice. They can give you trouble in hilly terrain, but I suspect you have a flat profile and there are no pig run-away problems, so a pig might be working to your advantage in keeping water on one side and air on the other.
It is important to meter water pumped in and equate that to pipe volume of the test segment to get an idea of how much air might still be in there. Air in the line is the most problematic, since volume change of air pockets with both temperature and pressure, can make for very erratic readings. In any case Mohd you have apparently made a successful test. IMO the 24 hour stabilization time was the most important factor. No worries.
What diameter and length of test segment was involved?
What would you be doing, if you knew that you could not fail?
RE: Q: 16" buried pipeline hydrotest
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Q: 16" buried pipeline hydrotest
David
RE: Q: 16" buried pipeline hydrotest
So you did.
What would you be doing, if you knew that you could not fail?