Design of Vessel at Atmospheric Pressure

[takiyasamsama]

Hi,

I got a vessel, which the design pressure is even lower than atmospheric (around 0.035MPaG). The vessel design temperature on the other hand is at 300 degC and wrapped with a half-pipe jacket of 0.7 MPaG. Should I design the vessel at atmospheric pressure instead of 0.035 MPag? The reason for saying this would be that some of the manufactures, when we issue purchase order they quoted the design pressure of the vessel to be Full Water + 3 barg, sometimes Vacuum + 3 barg.

 

[prex]

I don't understand why you say that the design pressure is lower than atm.: to me MPag means MPa relative, so this is 0.35 bar design pressure.
If the 'g' is a mistake, and you mean MPa absolute, then this is a partial vacuum and it would be normal that the vessel is designed for vacuum.
Concerning the manufacturers, you should ask them why they quoted what they quoted. And normally it is up to you, the purchaser, to state the design conditions.

prex
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[JStephen]

If the design pressure is low enough, but the vessel is still built to a vessel code, the minimum thickness requirements and gravity loads will control the design anyway, and it won't matter what pressure is used. It may be that the vendors just figured the MAWP and quoted that as the design pressure.