Thermal Relief Valve Issue

[processfm]

In that moment I am doing the evaluation to include a thermal relief valve in a diluent pipeline of 25 Km (82000 ft) of length when the fluid is trapped. Only 200 m (656 ft) of this one is expose to the sun and the rest of it is underground.
According to the heat balance calculation on the pipe expose to the sun, the thermal relief valve is required.
But I do not know the effect of the thermal expansion on the total pipeline, may be the thermal relief valve is not required.

I would appreciate your help on this issue.

Sincerely
processfm

 

[sailoday28]

If one can assume that the buried piping has negligible temperature increase, AND const volume system then
DP/DT approx = -dp/dv (isothermal)*dv/dt (const pressure)
Having the DT, allows computation of the pressure rise.
This question has RECENTLY been answered on the forum, but I can't locate the thread.

 

[BenThayer]

easy enough to calculate. do the thermal expansion for the length of pipe and calculat the volume increase and then compare to the thermal expansion of the liquid for the two temperatures.

you have the s.g. of the liquid for the two temperatures, correct?

 

[pandora]

processfm,

Don't forget to cover the case where the pipe is blocked in for a whole day for calculating the heat input. Thermal expansion of liquids can produce "unexpected" pressures, but the relief valves also tend to be very small.

pandora

 

[CHD01]

Your making the problem harder than it needs to be. To determine the maximum rate just size it conservatively on the heat input and thermal expansion rate required for the exposed pipe and don't worry about the difference in liquid expansion coefficients, specific gravity, etc for the buried pipe with its cooler liquid. The end result is that the relief valve selected will be much larger than required in all probability. If 2-phase flow is possible this would increase the required valve size, but I would still try the conservative approach first until that is proven to be a problem.

The more you learn, the less you are certain of.

 

[FrankH2]

Have you considered other scenarios than exposure to solar radiation that could justify a thermal relief?
Say, could situations arise where the liquid is colder than average soil temp, and the pipeline is then blocked in and temperatures line out over the large distance. Or say, a minor bush fire nearby if vegetation control has failed...
Another issue to consider could be repair costs should the pipeline be damaged. Underground pipelines can be exposed to external corrosion creating the weak spot there. How large a section of the pipeline needs to be unearthed to find the point of leak ? Are there potential clean-up costs?
Could the absence of a TRV be interpreted as lack of due dilligence?
In my view, fitting a standard 3/4" TRV could be easier than sorting out the above issues

Frank HH