UW13.1
UW13.1
(OP)
When attaching hemi heads which are thinner than the shell plate, some fabricators cut back the hemi head and taper the shell plate to the head thickness ( 3: 1), while others put the hemi head, without cutting it back, on the shell plate, and use weld metal to provide the required taper. Is there any advantages to one over the other? How is it possible to reduce the shell thickness of the shell without compromising it's integrity?





RE: UW13.1
RE: UW13.1
Just another bit of Code trivia... the minimum thickness of the skirt of a formed head is determined as that required for a seamless cylindrical section. A Code book is not in-hand, but that's in UG-32 somewhere. UG-32(O), maybe?
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: UW13.1
As Steve Braune pointed out, the sraight flange of a head is basically considered to be a shell course by the code. As far as the code is concerned, the head ends at the tangent line. UG-32(l): "... When a skirt [straight flange] is provided, its thickness shall be at least that required for a seamless shell of the same inside diameter." [But what do you do with say a two piece 2:1 SE head which has circ seams on the straight flange?]
But to answer arcer's question: In theory, both approaches produce the same result. I've seen tapers provided both ways. My preference, however, is to have the taper machined from a thick plate instead of by weld buildup. Simply because I believe there is less likelyhood of quality issues and potential stress issues which could come up with welding. If its a relatively small change in thickness as you might see with a 2:1 SE to a shell, that's one thing. For a hemi head, I presume you have relatively high pressure, and the change in thickness between the shell and head is more substantial.
jt