Full Vacuum against Pressure Relive Device

[MohdYaseen2010]

1) Do a Vessel/Tank that equipped with a Pressure Relieve Device (PR Valve, PSV, etc) can be exempted from being subject to Full Vacuum design?
2) ASME VIII Div 1 mentioned UG-28 as reference for Vacuum (External) Pressure Design while API 650 didn't mention anything about how to design a tank to Vacuum Condition ()?
3) Tanks are designed normally for Partial vacuum cause tanks are laying to API 2000 provisions with respect to emergency or normal venting conditions. Am I right?

Mohd Yaseen

 

[mk3223]

1. No. Both vessel and tank are required to consider under both vacuum and overpressure conditions.
2. Vessel can be designed with the wall thickness under the full vacuum condition.
3. Yes. API-2000 is the Code for the vacuum relief design of the tank.

 

[JStephen]

Common practice is to specify only the vacuum design required by the service, including the effect of relief valves, cleaning procedures, etc.
For vessels of small size or high pressure, the full vacuum may not make any difference, but for many vessels, it will.
API tanks are never designed for full vacuum. The standard tanks are adequate for partial pressures of 1" of water column. That may be extended up to 1 psi by use of Annex V. Maximum vacuum on a large tank may increase the cost considerably, and should not be specified without some thought.

 

[MJCronin]

I agree with the solid advice given by JStephen on flat bottomed (API-650) tanks

API (650)tanks are never designed for full vacuum. The standard tanks are adequate for partial pressures of 1" of water column. That may be extended up to 1 psi by use of Annex V. Maximum vacuum on a large tank may increase the cost considerably, and should not be specified without some thought.


I would add that once the newbie client learns how much that it would cost for even partial vacuum protection of the API-650 style tank, he quickly changes his mind. Then, either the process protection is redesigned or an ASME dished style vessel is specified.

Search these forums on "API-650" and "vacuum design" .... this has been discussed before

In the USA, there have been several analytical methods for vacuum design that have been developed and are now used worldwide.

Good information here:

https://archive.epa.gov/emergencies/content/fss/web/pdf/lieb_04.pdf

MJCronin
Sr. Process Engineer

 

[MohdYaseen2010]

Dears
Thanks for all your inputs however I am still having a doubts about some points;

Among the whole Tanks I have passed through on my previous designs, I found that their Vacuum (External) Design Pressure are set in range of -0.216 Kpag to -0.6 Kpag which is nearly similar to the values indicated by you (1 inch WC = 0.2463Kpag to 28 inch WC = 1 psig = 6.9Kpag), thus I am querying in which basis I shall select the specific number from this range to be my Vacuum (External) Design Pressure for the specific tank.

Moreover, As we are the same line with regard of Vacuum (External) Design Pressure rang, what do you think about the table enclosed in attached file (I have founded earlier in studied sheet);

Finally, I have noticed that for Tanks containing FW (Fire Water) or WI (Water Injection) are designed for ATM only & there is no mentioning for any vacuum (External) Design Pressure, do you think is it right?

Mohd Yaseen