Sect VIII Corner Joints
Sect VIII Corner Joints
(OP)
Is a size-on-size corner joint allowed in a vessel of non-circular cross-section? It appears that with the full-penetration joint option in UG-34, size-on-size is precluded by the 1.2*ts requirement. Can anyone find an exception to this in either UG-34 or UW-13?
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RE: Sect VIII Corner Joints
Cheers,
gr2vessels
RE: Sect VIII Corner Joints
I'm not sure where I picked up the term, but it's not in the code.
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RE: Sect VIII Corner Joints
RE: Sect VIII Corner Joints
'tw=2*trmin nor less than 1.2*ts but need not be greater than t'
By the UG-34 equations, 't' will most often be an order of magnitude greater than 'trmin', leading the designer to generally choose a plate material for the flat head thicker than the shell material.
There is a large stress concentration at that joint, and the 1.2*ts is accommodating that concentration. Otherwise, there would be no need for the 1.2*ts requirement, just force tw=t max.
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RE: Sect VIII Corner Joints
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RE: Sect VIII Corner Joints
With a 'size-on-size' joint, the weld requirement would not be satisfied as it is worded.
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RE: Sect VIII Corner Joints
Code [UG-34] sez: but need not be bigger than T. Thus a 3/8" x 3/8" Tee-joint need not have a fillet-weld bigger than 3/8" weld size.
Now, the reason it bothers you is probably that you have never seen a size-on-size square corner pressure-boundary weld on material thinner than 1/2" or bigger. Neither have I. A 3/8" shell 2-3 feet in daiameter will have a 'flat-cap' 1" to 1.5" thick.
RE: Sect VIII Corner Joints
I'm only offering this in the effort to clarify my thinking:
'tw=2*trmin nor less than 1.2*ts but need not be greater than t'
COULD be:
'tw=2*trmin but not less than 1.2*ts unless greater than t, then tw=t.'
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RE: Sect VIII Corner Joints
1.2 the t of the weld applied to the corner joint
if the inner plate is thicher than the shell, not a problem, you just fill the
joint 1.2 the st and you're in compliance,
not greater than t means once you comply with the 1.2 you need no
more weld deposit.. usually it is filled all the way if the plate is not too thick that it will add considerable cost. there are other rules if the plate is to be left unwelded
if the inner plate is the same t as shell then you will have to insert the
inner plate far enough into the shell to fill more weld,
a fillet will suffice.
RE: Sect VIII Corner Joints
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RE: Sect VIII Corner Joints
ASME compliance by putting the right amount of weld,
to hold the pressure. and that is the only way as the shell has to be covered, so you cannot just add weld w/o shell
so you put the plate inside the shell... to comply.
not only that, the fillet weld has to cover the groove weld.
RE: Sect VIII Corner Joints
UG-34(d) " The size of the weld tw in sketch (g) shall not be less than 2 times the required thickness of a seamless shell nor less that 1.25 times the nominal shell thickness but need not be greater than the head thicknes...".
Shell thickness = 3/8", head thickness = 3/8", weld size = 3/8"
RE: Sect VIII Corner Joints
I feel it is my responsibility to understand the engineering inherent in the code. I can understand why the weld would not need to be greater than 't'. I question this because the wording can be interpreted at least a couple of different ways. I understand the popular interpretation, I'm just asking if anyone has explored an engineering verification.
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RE: Sect VIII Corner Joints
RE: Sect VIII Corner Joints
Am I the ONLY one who can see this?
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RE: Sect VIII Corner Joints
Something that has not been mentioned is the consideration of the stress concentration(s) at the head corners when considering that the 2 adjacent sides of the head are welded to different plate thicknesses.
I also think UG-34 is designed for the head to be bound on all sides/ around the circumference by the same thickness 'shell'.
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RE: Sect VIII Corner Joints
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RE: Sect VIII Corner Joints
need not be grater than T,
if you comply with the 1.2st and the weld size first; then you need not be greater than T only if the ht is greater than the required. say you meet the required t 1/4", and yiour ht is 3/4', you only you do not need anymore weld pouring.
but if you decide to fill it up the groove, you need not be greater than T. it is very clear. it is a matter of interpreting the Code if you do not understand it.
I know it because I do a lot of flat heads designing.
All sections of the Code have same or similar requirements
as I have most stamps S,U,H,M,UM,R
RE: Sect VIII Corner Joints
A size-on-size joint as I've described above does not comply with the 1.2*ts.
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RE: Sect VIII Corner Joints
RE: Sect VIII Corner Joints
You can always ask for a Code Case to the ASME and if the/your Jurisdiction accept it, you will be okay.
to modify your joints and weld sizes.
genblr
RE: Sect VIII Corner Joints
However, they do have a little problem [here & there] in writing clear sentanceses & clauses.
RE: Sect VIII Corner Joints
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RE: Sect VIII Corner Joints
Because it is not needed and it will distort the materials.
or Even a girt or long weld, no reinforcing from now on.
This is the end of me on this post. I learned the lesson,
now I am in a position of manipulating the Code in
my favor. Have a great day you all.
RE: Sect VIII Corner Joints
It's not a manipulation of the code in my favor, as you put it. I'm reading the plain language given. It's written poorly, and my only point was that there is at least one interpretation of those words that is just as valid as the popular one, which in my opinion is more self-serving than the one I present here. I'm sorry if this challenged your methods. Had there been presented an explanation of the sentence in question in terms of the engineering methodology behind the sentence, there wouldn't be this back-and-forth.
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