5 replies to this topic

[WilliamN]

Dear peer professionals,

According to API 521, for blocked pipe, we can install a ¾ x1 valve by default for relieving thermal expansion, without performing any calculation. Another idea I am thinking is to install  a piece of vertical pipe, say 4 feet tall, few inches diameter, with closed top. The closed top is N2 filled vapor space, which provides the room for liquid expansion. I appreciate if any member out there could share their experiences sizing this vertical expansion pipe.

 

[Bobby Strain]

That won't do.

 

Bobby

[WilliamN]

Bobby,

I thought the vapor space would provide room for trapped liquid to expand/contract. Thus it can be used in lieu of the thermal PSV. The advantage of the vertical pipe over PSV is that the vertical pipe does not relieve fluid to the environment. Since the thermal expansion is cyclic from solar input, the expansion will calm down few hours later. Thus it sounds a good solution. This is the operating procedure I am thinking. 1) I will purge the line with N2, so the pipeline ( plus the small piece of vertical pipe) is filled with N2, 2) then I bring in the process liquid. The N2 in main pipe is displaced, and the N2 in the vertical piece is retained. Thus a vapor space is created for the system. Appreciate if you could comment which step won’t  work.

[latexman]

The N2 will absorb into the liquid and be carried away.  When there is no N2 left, there is no protection.

Edited by latexman, 18 September 2013 - 07:30 AM.

[ColinR33]

You are essentially describing a pulsation dampener.  These are used to dampen pressure pulsations in piping around reciprocating positive displacement pumps and utilize a "bladder" made of neoprene or similar flexible material (depends on what is required to resist attack from the process fluid) that is charged with Nitrogen to about 80% of the system maximum pressure.  As the pump piston moves back and forth, pressure pulses are sent into the associated piping.  The bladder expands and contracts, dampening out these pulsations.  This is not designed for pressure relief and a PSV is always present on the piping as well.  Sizing of these is specific to each application and based on fluid, pressure, pump cylinder size, stroke and speed.  I would not be comfortable using this for thermal relief of a pipeline as there are too many unknowns.

[Padmakar Katre]

Hello,

If I understand correctly, having this scheme in the event of thermal expansion or variations in flow demand can be justified but I seriously doubt that this will work in "Blocked Outlet" scenario. If my doubt does not make any sense please ignore my comment.

Edited by Padmakar, 18 September 2013 - 01:39 AM.