I was looking at a drawing for an existing pressure vessel a Client had the
other day. I was looking at it in regards to the support frame and
foundation. I noticed the drawing said it was a 10 psig design pressure with
a 1 psig operating pressure. I am not an expert in the boiler code, but I
did see that the vessel is 5' in diameter with a 3/16" thick flat top. The
top does not have any stiffener and was made as a circular flat head that had
the knuckle turned down (1-piece head) . It is my understanding that a flat
head with a turned knuckle (bend top with a radius) is only allowed on tanks
24" and narrower. I checked the formula for the thickness and arrived at a
5' diameter would have to be over 3/4" thick. The tank was supposed to meet
the ASME boiler code Division VIII.
I looked in the Pressure Vessel Handbook by Megyesy saw the same rules I had
learned thru osmosis. The head shown in the book as "A" has limits that this
existing tank far exceeds. The t/d is .003 which is much less than the .05
limit placed on this type of head.
Does anyone know if you can have a flat head (one-piece) greater than 24" in
diameter? If not, what are reasonable methods of retrofit?. The tank is 5'
OD and about 5' tall with a cone bottom. The Client has already confirmed
that the 10 psig shown on the drawing is incorrect.
Martin Structural Services, Inc.