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Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

(OP)
Having some trouble with the ASME VIII Div 1 UG-39 (b)(2). It says (for ease of reference):
"Multiple openings none of which have
diameters exceeding one-half the head diameter and no
pair having an average diameter greater than one-quarter
the head diameter
may be reinforced individually as
required by (1) above when the spacing between any pair
of adjacent openings is equal to or greater than twice the
average diameter of the pair.
When spacing between adjacent openings is less than
twice but equal to or more than 1 1/4 the average diameter
of the pair, the required reinforcement for each opening
in the pair, as determined by (1) above, shall be summed
together and then distributed such that 50% of the sum is
located between the two openings. Spacings of less than
1 1⁄4 the average diameter of adjacent openings shall be
treated by rules of U-2(g)."

My situation is that where the space between adjacent openings is less than twice but equal to or more than 1 1/4 average diameter.
I use the distance between each opening (sketch provided)
centre-to-centre as the space between openings. Hope that is correct?
To my question:
The average diameter of the openings exceeds 1/4 of the head diameter.
I don't see any way forward if this is condition is not satisfied.
Openings in the attached file are just holes (for a valev), no nozzles are attached.

Thanks in advance.
Mikeg7

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

Mikeg7, are these openings in a pressure vessel flat head? You cannot have 'just holes' in a flat head of a pressure vessel. What do you weld to those openings for pressure retention?
gr2vessels

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

(OP)
Gr2
This flat plate is a partition at some point in the shell of the cylindrical vessel. On one side of this plate is liquid at pressure. There is a valve seat that goes into each of the holes. When the valves open, the liquid in the can pass through the holes. Until the valves open, the plate has the full design pressure across it. That's the best way I can describe it.

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

I agree that the limitation 'no pair having an average diameter greater than one-quarter the head diameter' is applicable also to the second paragraph of UG-39(b)(2), as you imply in your first post. So it seems that you are left with U-2(g)

prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

It's just a quick suggestion, can you weld a ring over each of those holes to the valve required diameter, having the actual openings in the flat reduced to the UG-39 (b)(2) prescription?

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

You might design it as a doughnut, possibly a sort of loose reverse flange, ignoring the material inside a circle encompassing the openings. Or Appendix 14 might apply to the geometry. Kind of a U-2(g) approach, I suppose.

Regards,

Mike

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

(OP)
Gr2

Do you mean create a false nozzle outside of the valve? Yes, it could be done but requires additional welding and materials which won't go down well.

Prex

I believe that the 2nd paragraph of UG-39(b)(2) also has the limitation of 1/4 diameter. There is no way around this, because it again appears in UG-39(e) where the idea is to increase the head thickness instead of checking for reinforcing.

This is the approach that I was trying to use because there must be a thickness at which it is safe. However, the rules don't allow any method to be used to arrive at that thickness because of this limitation.

Prex, does U-2(g) mean FEA for this problem or just alternative rules cover this situation?

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

MikeG7, the FEA won't give you the magic go ahead around the code. It will tell you how much additional reinforcement you need for those openings (either increase the flat end thickness or increase locally the thickness for strength). Yes, the ring I have mentioned will provide the much needed additional thickness for reinforcement. If the holes have not been cut, by reducing the hole diameter you don't even have to recalculate the reinforcement, you will comply with the code requirement and also providing the required diameter for the valves.
The last option (not recommended), abandon the design.
Cheers,
gr2vessels

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

(OP)
gr2, prex
Further consideration has been given to the way forward for the client. The general feeling is there must be a thickness at which the design is safe. This is preferred compared to the (practical) suggestion of locally reinforcing the plate at the openings.
In order to prove by FEA, I would add rigid constraint at the plate circumference and apply a pressure force over the plate which remains after the holes are cut out.
1. in order to get valid result would it be necessary to add a pressure thrust at the edge of each opening (presume Yes is the answer)?
2. to compare to code allowable, should the stress control line (SCL) be placed directly at the circumference of the plate? This is where the stress is are expected to be the highest?
Mikeg7

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

I would not model only the flat plate - I would also add 5*sqrt(r*t) of the shell to the model. You would want SCLs all over the place. Be careful how you classify the stresses in the shell and flat head, especially far away from the holes. Do the analysis to Div 2 Part 5. Pay special attention to Table 5.6. If something is not clear about that table come back and ask us.

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

Of course you should add the pressure thrust for each hole. Also, as an alternative to the advice by TGS4, I would represent the periphery as simply supported (making it as fully clamped would definitely be wrong).
However I would suggest you that, for a single component, the cost of a FEM analysis (with all the problems of interpretation the will follow) is not worth the extra metal you would get with a simplified method.
SnTman above has the right suggestion. If the attachment to the shell satisfies the requirements of App.14 for an integral attachment, then App.14 is the way to go (the use of 2-13 is less straightforward, as you have no bolts). Even if you can't satisfy the attachment requirements, App.14 would give you an upper limit on thickness for checking the FEM calculation.

prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads

RE: Multiple openings in flat head to ASME VIII Div 1 UG-39 (b)(2)

(OP)
Thanks for the advice Prex, TGS4, SnTman...
In the time between I did run a FEA per TSG4 suggestion of adding a portion of the shell. This seems to support the advise that the edges are NOT fully clamped and are allowed some rotation. The advantage of adding the shell portion is that it is also worthwhile checking what influence the bending of the plate has on the shell. As a note: the FEA shows that the maximum total Von Mises stress intensities do not exceed 90% of the allowables. If that was the case, could the FEA route not be less intense since linearization is not necessary (question not a statement) in this case ?

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