ASME Sec. VIII - Multiple Openings

[Sjqlund]

My question is regarding multiple openings. Say I have two openings: One nozzle opening large enough for some opening rule to apply, combined with a small opening, that alone would not need to be taken into account (e.g. a ventilation opening). Would that qualify for multiple openings, e.g. UG-39(b)? Or can i discard the small opening and consider the nozzle opening as a single opening?

UG-39 states the following.
"UG-39(a) General. The rules in this paragraph apply to all openings in flat heads except opening(s) that do not exceed the size and spacing limits in UG-36(c)(3) and do not exceed one-fourth the head diameter or shortest span"

However i'm still in doubt w.r.t. my question.

 

[MikeG7]

Interesting question. But what if the size and spacing requirements were met per UG-36(c)(3), and yet the smaller opening was close to the edge of the flat head such that UG-39(b)(3) was not satisfied? If all the conditions of UG-39 are met AND the opening is less than the size and spacing of UG-36(c)(3) then it would be reasonable to ignore the smaller opening.

 

[prex]

See the last sentence of UG-36(c): it tells you in practice (though not exactly) that the reinforcement of two openings cannot overlap.
If that condition is met, then UG-39(a) is in effect, otherwise you fall under UG-39(b), and you must treat the pair per the same: the smaller opening will subtract a tiny fraction of reinforcement to the larger one.

prex
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[Sjqlund]

Thank you MikeG7 and prex.

What do you say about this example. Nomenclature: d=diameter for nozzle opening, L= shortest span of head, dv = diameter for ventilation opening.

We have 1/4 L < d < 1/2 L and dv < 1/4 L. Then Since the dv (ventilation opening) do not exceed one-fourth of the head diameter, UG-39 cannot be used and U-2(g) must be used. (According to UG-39(a))


This is what they did in an earlier report i saw. Does it make sense? I have a feeling that they wanted to use U-2(g) though, to have a less conservative design.

 

[MikeG7]

Yes, it's a little confusing to me the way UG-36(a) is written. It says that (my interpretation) the rules of UG-39 basically only apply to all openings, EXCEPT ones which don't exceed the UG-36(c)(3) requirements AND don't exceed one quarter of the head diameter.

So in your case for the small opening you didn't give actual sizes so I can just give an example: if it is assumed that the opening of your vent is small enough that it does not exceed UG-36(c)(3) AND is not >1/4 "L" then we can proceed with the rules in UG-39, provided the spacing requirements of UG-39(b)(2) and limitations of UG-39(b)(3) are met.

When multiple openings are such that their size is significant and when there spacings are close leaving a narrow ligament which is likely to carry significant stress, you quickly run out of the limitations of the rules of UG-39 and you must prove your design by U-2(g). Like prex said, if you have to check for both openings, then the limits of reinforcements must be considered.

If your small opening, "dv" is insignificant (as determined by UG-36(c)(3) ) and it is spaced far enough away from your larger opening, "d" (per the spacing requirements of UG-39), then FEA is going to tell you if you can follow a less conservative route. I'm not sure if you can opt for div.2 rules if Div.1 is the design code and there are rules to cover your design situation. I'm not saying you can't, I'm just not sure if that is acceptable practice or not.

The rules become less cryptic the more you read them, except UW-11(5)(b). I've read it like a gazillion times and every time it reads differently. That's gotta be the winner!!

 

[prex]

IMO UG-39(a) is applicable when you have only openings complying with UG-36(c)(3) (and with d<1/4 L).
In your example this is not the case. Assuming dv is 'small ', you should:
1) determine the reinforcement required for the larger opening;
2) in doing this you'll determine the minimum required distance of reinforcement along vessel wall
3) if now the last sentence of UG-36(c) is satisfied, then dv does not require a calculation of reinforcement
4) otherwise go to UG-39(b)
So IMHO U-2(g) is not required, and I don't see what one would gain by its use.


prex
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[Sjqlund]

Again, thank for your responses MikeG7 and prex.

However, Prex, can you clarify your step 3)? Since UG-36(c) is only for unreinforced openings. So why would calculating the calculating reinforcement for the larger opening change anything?

 

[prex]

The last sentence of UG-36(c) says

The centerline of an unreinforced opening as defined in (a) and (b) above shall not be closer than its finished diameter to any material used for reinforcement of an adjacent reinforced opening.

So an unreinforced ('small') opening meeting this condition is considered isolated and stays unreinforced. Otherwise you need to check its reinforcement combined with the other opening.

prex
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[Sjqlund]

Ah, thank you for pointing that out. I read that as a sentence belonging to UG-36(3)(d).

 

[MikeG7]

Prex, if that's the intent, i.e. that the rules only apply if the openings are "small" and if d<1/4L, then we may proceed...

UG-39(b) is for openings with diameter up to 1/2 L, but which can't be applied if d > 1/4 L per your assessment

UG-39(c) is for multiple openings with d up to 1/2 L , but which can't be applied if d > 1/4 L per your assessment

UG-39(d) is an alternative reinforcement method for single opening if for d up to 1/2L , but which can't be applied if d > 1/4 L per your assessment

UG-39(e) is alternative reinforcement method for multiple openings if for d up to 1/2L , but which can't be applied if d > 1/4 L per your assessment

In each case, then we can do nothing with rules of UG-39 if d > 1/4 L so what are these rules for then?

 

[prex]

MikeG7, let me rephrase, something went wrong in your understanding of the syntax.
I didn't say 'the rules only apply if the openings...'; I said (or wanted to say) 'the rules apply when you have only small openings...', in other words 'when all the openings are small'.

prex
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[MikeG7]

Noted prex, I think we're singing from the same hymn sheet...

 

[Sjqlund]

This thread was very helpful, but I'm going to bring this thread up again! Its about openings at welds.

Lets say i have a opening due to a nozzle. The nozzle is welded onto the shell.

Furthermore, the openings are all less than one-fourth the smallest span. And they comply with UG36(c)(3) EXCEPT (not 100% sure, see below) UG36(c)(3)(d).

Would it activate UG-36(c)(3)(d) since the nozzles are welded on? If so, this would mean i'd have to go to UW-14, which again tells me to follow UG-37 to UG-42.. However the way i got there was from UG-39, so its a infinite loop!

Am i mis-interpreting it somewhere?

 

[prex]

Seems you are reading UG-36(d), not UG-36(c)(3)(d).
Could you describe in steps your problem, I'm not following you.

prex
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[Sjqlund]

You are right Prex. Seems like it was getting too late when i asked this question. Thank you!

 

[Sjqlund]

Can someone confirm my current interpretation:

Multiple openings with diameter smaller than one-fourth smallest span. Spacing requirements in 36(c)(3) not exceeded. Size requirements are exceeded however. This is since a nozzle is welded on top of the opening which 'activates' 36(c)(3)(a) in where the opening diameter is larger than 60 mm (head thickness larger than 10 mm).

Hence the openings must be reinforced using UG39(b).

 

[MikeG7]

Sjqlund, please attach a sketch to make it clear to understand.
Thanks[tt][/tt]

 

[Sjqlund]

Here's a drawing i just made:

http://imgur.com/pvb5a8U

My question is: Since the nozzles are welded onto the plate, would UG-36(c)(3)(a) govern? The nozzle openings are larger than 60 mm and plate is thicker than 10 mm.

 

[prex]

Assuming the required thickness is over 10 mm, UG-36(c)(3) is not applicable and you must check the reinforcement.
I don't see how, the fact that these are sit on nozzles, can affect this position. The same would apply for a set in nozzle, the diameter of the hole in the nozzle neck being the diameter of the finished opening in that case.

prex
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