Basis for vaccum pressure design

[pipexp]

Dear Experts,
Can you suggest what should be the basis for design of a pressure vessel for vacuum pressure.
Regards,
Pranjal

 

[SnTMan]

pipexp, what do you mean by basis? Vacuum pressure? Code of construction? Design methods? Something else altogether?

Regards,

Mike

 

[MJCronin]

Pranjal....

By "basis" I assume that you mean the reasons for a certain design requirement.

Regarding vacuum design of pressure vessels, my experience has been that process chemical plants commonly require the "FV" (full vacuum rating) on most of the storage vessels that they purchase. This is because of the increased use of steam cleaning of vessels and piping.

Another reason to specify FV as a design condition is the fact that many tanks and vessels are repurposed in the facility as time goes by...

For smaller diameter vessels ( up to ~ 60 inches) this adds little cost to the vessel.

It is generally not considered wise to design a pressure vessel for a vacuum any less than a FV condition

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[pipexp]

Thanks MJ Cronin.
Can you please give a brief on how vacuum is created during steam out of a vessel.
Regards

 

[mbt22]

Vessel full of steam, vessel cools, steam condenses. The reduction in volume from steam to water drops the pressure if the vessel is boxed in or the vent is inadequately sized.

Matt

 

[dineshakabari]

In addition to the steam application, there is another cases where vapor services at higher temperature and chances of condensation is there without proper vent provision. In those cases also need to safe guard equipment by considering vacuum condition at design stage. As per my knowledge, if vessel is already designed for higher internal pressure than most of case the required thickness to sustain internal pressure is also suitable to withstand vacuum condition. So in this case it's just a question of verification by calculation. In some cases by putting the external stiffeners are also sufficient to make equipment to capable to with stand vacuum pressure.

 

[Ripz]

Simply put, if you do an analysis of the process conditions that can occur to this tank, and it shows the potential for creating a vacuum, then some mitigation has to be put into place. Either design thickness for Full Vacuum, install appropriately sized vacuum breakers or create system electronic interlocks.

I've seen a 5 mm thick vessel implode while being pumped out because all the other connections were locked out.

Tanks usually are usually stated to be designed for Full vacuum, since their internal design pressure calculations for atmospheric pressure would not provide sufficient thickness for vacuum conditions.

 

[AK23Static]

Pranjal,

One more conidtion when the Vessel experiences FV or External load:-
1.If Vessel is located in pit, soil load in closed pit on the vessel.
2.Also for open pit due to rain there is water in open pit.

Vessel may experience external pressure incase vessel is at atm pressure from inside during operation.

cheers
AK
Beginning of every success is desire