Hi,

I have a vessel fabricator who has completed the U-1A for a vessel and indicated on Line 8 (heads) in the "Side to Pressure, Concave or Convex" box >> BOTH. I've marked it as wrong and returned it. They have countered that since the vessel has vacuum design conditions the pressure is acting on both sides of the vessel head. I disagree since whether the pressure (inside) is positive (MAWP) or negative (vacuum), we're applying that to the inside of the pressure vessel... hence the correct entry (for these vessel heads) should be "Concave". (pressure outside the vessel is always atmoshperic regardless of the internal condition).

Although this seems clear and logical, it is not clearly spelled out in Non-Mandotory appendix T.

Can someone confirm (or reject?) this interpretation and/or guide me to another source for directions on correctly completing the U-1A..?

Hi,

when I look into my Guide to Physics from skool, the definition of pressure is Force per Area. Force is a vector which has a direction and an amount. Look at it the simple way, and do not think about negative amounts, and you have a clear point of view on the SIDE TO PRESSURE.

The same approch you will find when looking into the design calc. If the manufacturer has performed an internal and an external pressure calc, the correct entry is BOTH.

Please consider there is more than one correct way of filling in the forms. When Manufacturer and AI accept, is will be reasonably okay, but there are revisions sometimes.

Does this help?
DK

Hallo,
I believe by reading thru Mandatory APX 9 you will get the answer. Please delete the configuration you have in your mind, how the pressure is applied gives you the answer = both