Atmospheric pressure vessel in PVElite

[GheorgheCristian]

Hello, my coleague and i have a dis agrement about how to design a atmospheric pressure vessel in PVElite ( I know that PVElite is not intended for this kind of job but the firm we are working for has no other software)
- my view is that we should introduce something like 0.01 barg as an internal pressure ( PVElite gives an error if there is no internal pressure)( my logic is that API 650 does not take into consideration pressure but height of liquid )
- his view is that we should put 1 barg as internal pressure ( his logic is that because it's atmospheric , we should put 1 atm ( pressure exerted by the weight of air in the atmosphere of Earth ) = 1barg.
Which one of us is right ? And if there is a more correct way of calculating an atmospheric pressure vessel in PVElite pls do tell us.
Also another question : I am under the impression that PVElite understands by internal pressure , gauge pressure.
Am i right ?
Thank you all for response.

 

[SnTMan]

GheorgheCristian, PVE I am pretty sure works in gage pressures. By that logic you are more correct that your co-worker.

But you mention API 650. If your vessel contains liquid, I believe PVE will account for static head, which could serve as your design pressure.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[GheorgheCristian]

yes. it does contain liquid. i know that PVE takes into consideration the pressure exerted by the height of the liquid but if i put 0 as internal pressure PVE gives a warning( i think it has something to do with the fact that a 0 pressure gives a null formula for calculation of minimum required thickness)
My interest was in the pressure that is put as internal pressure.
I gave the example with API 650 because it deals with atmospheric storage tanks and that is why it doesn;t acount for internal pressure.
Thank you for your response SnTMan.

 

[SnTMan]

Agreed, you will need a non-zero DP. You could calculate the static head manually and use that, with no entry for SH in the program, that way you'd know it is applied consistently across the various calculations which I am not sure you could depend on in PVE.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[jte]

Yes, as SnTMan points out, gages read - well - gage pressure. The thickness required to contain 1 bar(a) would be rather thin...

As for API 650, I suspect we are saying the same thing in different ways but just to be clear: API 650 absolutely does include the hydrostatic pressure due to the liquid which is contained, but does not account for substantial vapor pressure above the liquid (which is where the design pressure / MAWP of a vessel is measured). That would be the reason why lower shell courses are frequently thicker than upper shell courses. And that's without getting into the bending situation at the bottom shell to bottom plate / ring.

 

[JG MechEng]

Depending on your requirements, you may not be able to use API 650 calculation. If you need to have a name plated vessel, you will be required by the AI to use the ASME code calculation. Confirm if you are in a state where ASME Section VIII is law, and when you start mixing standards, it opens up all sorts of questions...is nozzle reinforcement requirements and attachment design. Also, ASME does not require a min thickness like API, I would use some engineering judgement and calc the thickness at 15psi and see what tr is. If tr is equal to 0.1875in or less, I would use 0.1875 in and leave the name plated design pressure at 15. All this depends on your diameter, but if this vessel is of any thing larger than 6 in diameter, I wouldn't use anything less than 3/16 in. plate because of fabrication and attachment issues. When this type of issue has come up for me in the past, I start focusing more on fabrication issues than on the actual calc because thin material has its own challenges when it comes to designing supports and shop handling.


Also, if you put 0.1 in as your pressure and you add a liquid level, the software should develop a pressure for each shell section and the bottom head that includes the static head at the various levels...i know compress does this, not sure about PVE

The procedure for calculation of API thickness tells you that the calculation already includes 2.5psi of vapor pressure API 650 5.2.1(c). Also, you need to consider appendix f for roof design if you have pressure.

Sorry for the units and scratch the "may be law" thing! with the SI units, you are probably not in the US!

 

[JStephen]

API-650 is set up for flat-bottom tanks, and doesn't contain any provision for suspended bottoms.
API-650 does include allowances for up to 2.5 psi pressure in the vapor space- see Appendix F.
API-620 is similar but includes provisions for pressure up to 15 psi. It can also be used for suspended bottoms, but doesn't really give any guidance on the design or attachment of leg supports. It tends to be overly conservative in the design of the knuckle portions of F&D heads.
Meanwhile, I don't think ASME contains any provisions for a soil-supported flat bottom.

If no particular design code is specified, I would use the one most appropriate for the tank configuration.