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RE: Flat Heads-ASME Boiler Code Question

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This appears to be a UL-142 type head that has been applied to a pressure

You can try to analyze per UG-19 but it will probably be overstressed.

By the time you try to add external stiffeners and analyze, it will be more
effective to replace with an ASME F&D head.

Ron Hill
HILL Consulting Engineering
Birmingham, Alabama  USA
Email: ronhill(--nospam--at)

-----Original Message-----
From: MSSROLLO(--nospam--at) [mailto:MSSROLLO(--nospam--at)]
Sent: Monday, June 21, 1999 12:08 PM
To: seaint(--nospam--at)
Subject: Flat Heads-ASME Boiler Code Question

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
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
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
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
OD and about 5' tall with a cone bottom.  The Client has already confirmed
that the 10 psig shown on the drawing is incorrect.

Ron Martin
Martin Structural Services, Inc.