Thermal pressure cycling in buried pipe

[TMEldridge]

Does anyone have experience with pressure dips in buried pipe - we are looking into the possibility it is based on 'cold' ground and pipe. The fluid is moved from aoveground tanks thru buried piping to remote stations, and occasionally it is held below grade (such as shutdown overnight). When it is held, the pressure drops considerably. It appears this is the fluid cooling. Has anyone seen this happen before?

 

[robsalv]

I don't see pressure as the problem. If the line is thermally cycling, then it is growing and contracting which could lead to all sorts of other issues depending on the design and layout.

Amongst other things, coatings don't tend to hang on if the buried pipe is moving relative to the earth... corrosion wont be far behind when the coating goes.

Cheers

Rob

 

[TMEldridge]

I probably did not use the right terminology to describe. As it seems to be working, the fluid is at ambient (70-80degF) in the aboveground tanks. If the process is stopped, this 70-80 degF fluid stops in the buried pipe, which is at 50-55degF, and the fluid cools to "below-grade ambient". As the fluid cools, the pressure drops (closed volume, temp change, etc). Does this sound plausible? We aer trying to determine why the pressure is dropping while the system stops.

 

[stanier]

Yes this is plausible. Try it in reverse. Enclose a liquid in a pipe and allow it to warm up. Thats why they invented thermal relief valves.

 

[sailoday28]

Is the fluid in the buried piping closed off by isolation valves?

 

[StoneCold]

eldridge9
What makes you think that there is not a leak in the pipe underground?

StoneCold

 

[TMEldridge]

sailoday28, buried pipe is closed off by isolation (gate)valves. we've isolated the line and drained the non-isolated connecting pipe to see if it is leakage, and it is not.

StoneCold, leak is the concern. However, we believe there is no leak as (1) the recent pipe pressure test was successful (2) the pressure rises in the morning as (we assume) the ground heats back up.

I've been trying to figure out how to estimate if this heat loss is corrolated to the pressure drop, but unknowns like air entrapment make it difficult. Is there a rule of thumb anywhere? This is a kerosene-based fluid.

 

[CRG]

The best technical paper, that I have read, which discusses your question is, “Vista Research Technical Note No. TN97-06, “HYDROSTATIC PRESSURE TESTING OF BULK FUEL PIPING SYSTEMS,” by Joseph W. Maresca, Jr. & Michael R. Fierro.

Vista Research, Inc.
755 North Mary Avenue
Sunnyvale, California 94085

I took a look on their website where I downloaded the document years ago and I could not see where they have it posted. You could contact these folks and see if they will email you a copy.