4 replies to this topic

[Enginerdo]

I was hoping to get more information on the causes and effects of vacuum condtions in pressure equipment.

I know that in large storage tanks or atmospheric vessels vacuum condtions are caused by flow in and out of the tank/vessel.

1) What would happen to a vessel if it did not have a properly sized PVSV/PVRV? I've heard that it would collapse, is this true? If yes, what are the physics behind it?

My other question is in regards to piping.

2) What can cause vacuum conditions within a piping system and what are the effects?

Thanks

[latexman]

Yes, it will collapse. I've seen the aftermath right after it occurred about 3-4 times in my 31 year career. A tank, 2 tank trucks, and a railcar. I've seen evidence of it happening and then repaired (as best they can) more times than that. Internal pressure makes a round shape rounder. It rounds out the imperfections. External pressure (same as internal vacuum) buckles it's imperfections. Prove it to yourself. Get an empty plastic soda bottle, a big one. Blow in it and see if you can break it. Now suck the air out. See?

Many things can create vacuum in a pipe. A pump's suction, a vacuum pump, condensing a vapor inside, an elevation increase in a liquid line, a reduction in flow area and increase in velocity, etc. The effect in a pipe is much less than in a tank because piping is inherently stronger due to smaller diameters and it being relatively thicker walled.

[breizh]

Hi ,
In addition to latexman'reply , I experienced once at a restart of a plant after a turnaround where the inbreathing line on a storage tank of phenol was plugged with phenol solidified and did not allowed the N2 to enter the tank to compensate the transfer of liquid from storage tank to a reactor . It may happen with blinds forgotten ,......
Sure others can provide examples .
Hope it helps
Breizh

[Enginerdo]

Thanks a lot, I will have to try the pop bottle experiment.

A follow up question for Breizh. How was the issue of phenol solidification mitigated? Heat tracing perhaps, or did it need to be cleaned every so often?

[breizh]

Hi ,
Identify the location of the cold spot , dismantle the connection to the tank , clean the part plugged (check valve ), reinstall the equipment and make sure the tracing was effective . Here it was a combination of small things which leaded to the problem , starting with insulation material removed during turnaround to install blind , steam tracing not effective ,....

Regards
Breizh