hydrostatic pressure increase 1

[StoneCold]

I want to calculate the pressure rise in a closed liquid full system when the temperature rises. Does anyone know where I can find this at. I have found the thermal relief equations that tell me the volume of material displaced but I want to know the resulting pressure if I did not relieve the system.

Thanks

 

[DLANDISSR]

BRADSTONE:
Not to relieve the system is not a sensible approach. Most of the time the pressure will rise and over stress the piping system.

Calculate the change in liquid volume.
Calculate the change in pipe vomume.
Subtract the two. This will give you the net volume change.
Assume that the pipe will elongate enough to accomodate the net change in volume.
Calculate the necessary stress to produce this elogation.

The need for a relief device will be come evident.

IF you do not want a relief device put a expansion joint in a dead end branch (the expansion joint should be tied) the movement of the joint will accomodate the expansion of the liquid. The tie bolts will keep the joint from over expanding.

 

[StoneCold]

I am really just interested in the resulting pressure buildup. We have a 50ft run of 1" pipe that is liquid full of Tetrahydofuran. The piping is blocked in on both ends. A filter housing in the pipe recently burst. My associates feel that the housing was defective and there is no design problem. I would like to know what the pressure rise is in the piping to prove to them that there is a problem with the design.

Thanks

 

[TD2K]

Bradstone, do a keyword search on this site, it's been discussed several times and there are lots of links. A rule of thumb is 40 to 100 psi per deg F increase so it's really impractical to design for a blocked in liquid case by making the system stronger, you really need thermal relief.

Some companies allow you to take 'credit' for the fact that typical block valves, unless they are actually bubble tight, will pass enough liquid (and it doesn't take much as you know from sizing thermal relief valves) to avoid having a problem.

 

[zdas04]

The "credit" (scary concept) that TD2K talks about does not apply to trunion ball valves or other devices that allow verification of a bubble-tight seal. I've only seen it applied to devices that seat based on shifting a component into a seat (i.e., floating ball valves and any gate valve).

 

[25362]

To quickly estimate the pressure developed by a "blocked in" liquid upon heating, divide the cubic thermal expansion (1/^oC) by its isothermal compressibility (1/MPa). Then you get Mpa/^oC. This is the worst case while assuming the pipe is not flexible at all.