Coupling 'Nominal' Wall Thickness

[BigTank]

What does everyone here use for the subject value?

The 'G' body wall dimension in B16.11, Tables 4 & I-4?
The pipe described in B16.11 2.1.1 and Table 2?

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[BigTank]

oh...clarification:

i need this value for section viii calcs...

thanks

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[JStephen]

Seems like I have seen calcs where the OD was taken from the dimensional tables and the ID was taken as the OD of the pipe that threads into it.

 

[jte]

BigTank-

Why do you need this value? For what (specifically) calc? Normally you'd just get a B16.9 component and you're done, no calc's.

jt

 

[BigTank]

jte-

vessel opening integral reinforcement calc (excess beyond nozzle required thickness and actual for the coupling).

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[BigTank]

clarification: i know that commonly couplings are sized such they are exempt per UG-36, but often, i calc. the reinforcement area even if not submitted (to the a.i.) for my own peace of mind

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[rumandcola]

Don't have the code with me but I believe it states in B16.11 that the coupling is caculated as an eqiuvalent straight pipe. Based on the type (eg 3000# threaded, 6000# socket, etc) you look up the corresponding schedule sch 80, sch 160.

 

[BigTank]

mbc2009:

if i remember correctly, you're right, but Compress doesn't follow the b16.11 rule.

what started the confusion was that b16.11 spec's a 1.12in o.d. for a 1/2" 3k# coupler. Compress was using 1.125in, as is shown in a few catalogs (penn usa, for example). splitting hairs (literally), but...

Compress was then subtracting the nominal pipe size o.d. (0.840) as jstephen says, and dividing by 2 to find the wall thickness. this is a pretty conservative practice. (i don't believe section viii addresses this question of wall thickness for a screwed fitting in a pressure vessel aside from a cursory treatment for external threads and minimum engagement.)

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[jte]

Well, ok… So you’re on a wild goose chase of your own choosing since as you noted, the opening is excempt from area of reinforcement calc’s. Perhaps the right answer is that there is no nozzle neck to provide excess area for integral reinforcement. See Int VIII-1-83-217.

jt

 

[GenB]

I see that the coupling is self reinforced,
but what about weld pass? it is needed to satisfy pw-15

 

[BigTank]

jte

i agree that i put myself on this wild goose chase. but then aren't most fine details in the code a sort of wild goose chase?

could you guide me to the interpretation you reference? i don't see it on the asme site (and it's not in my copy of the code).

i respectfully disagree with you regarding the lack of a nozzle neck to reinforce. the geometry is roughly the same as that of a nozzle neck save the threading (a cylinder of steel penetrating or attached to the outside of a vessel wall). couplings that are allowed per sect viii are forged such that the wall seems to be even thicker than a pipe of similar outside dimension at the sch 80 wall thickness min. b16.11 is the code that gives the guarantee. this may promise a certain level of reinforcement, BUT when it all comes down to it, it's still an opening that is concentrating the stresses in the shell, and there is a limit the stress the opening can accomodate.

the code may be written such that the shell would fail before the stresses at the opening associated with the coupling rise to the point of failure, but that isn't an excuse to neglect having a sense of this stress condition.

genb

UW-15(b)(1)(2): exempt from strength calcs if exempt from reinforcing requirements by UG-36(c)(3)

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[jte]

Question: Are threaded couplings welded directly to a pressure vessel to be designed per ANSI B16.11 as stated in UG-11, footnote 5, Section VIII, Division 1, thus disregarding the requirements of UG-45 for nozzle neck thicknesses, since no neck exists?

Reply: Yes.

Now, to chase this goose around another corner… How you attach the coupling matters: If you plan on an approach such as in Fig. UW-16.2(K) or (L), take a close look at UW-16(f)(3)(a)(5).

jt

 

[BigTank]

jt

yeah, i've been chasing that goose already. fortunately, however, i have had some success catching that one! (or at least snatching a few feathers when i get close)

i've actually looked closely at UW-16(f)(3)(a)(5). this applies in rare cases in our shop. we try as best we can to penetrate the vessel wall rather than attach from the outside only.

thanks for the interpretation quoted. did you get that from the asme site? is that an older interpretation (is the 83 referring to 1983?)

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[jte]

Yes, the 83 refers to an inquiry submitted in 1983. You’ll find it in Interpretations Volume 15 published in 1984. If you have an IHS subscription, you should be able to see it there.

jt

 

[GenB]

the idea of exemption is that the material of shell can embeds certain openings without suffering loss of strength,
example: you can calc an opening w/o reinforcing: Say a weldless handhole 3 x 4 in you calculate the opening you can do it without reinforcing and a lot of times I do not have to reinforce else I use a welded ring.
in the welded couplings or small pipe nozzles (exempt per Code)
the Code takes it as if the coupling is not there and still the vessel is safe. The Code addresses loadings as a different issue so it is the user after the vessel is completed who will be responsible is the user/installer
not the fabricator...