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UG-39

UG-39

(OP)
We fall into UG-39(b)(2) as far as spacing and hole size, but since we fill the holes with heater rods and weld the rods to the flat head, is it really an opening?

RE: UG-39

Unless things have changed, Yes it is a penetraton.

RE: UG-39

The rules for ligaments can apply. the plate can become less efficient! thus requiring reinforcing/thickening
genb

RE: UG-39

heaterguy,
things have not changed in the Code since your last posting!
genb

RE: UG-39

(OP)
We hired an expert to do FEA on our flanges and FEA shows that our flanges do NOT need to be as thick as UG-39 dictates. I was just wondering if the holes are filled then are the filled holes still considered an opening. Is there ANY way to use the FEA instead of UG-39?

RE: UG-39

In your FEA you should not only discard any collaboration from the heater rods (material and weld presumably not per code), but also apply pressure over the hole (or on the hole border). Having done that, you shouldn't find a big difference with UG-39, except for the fact that your holes are not centered, so that they require less reinforcement, but the code doesn't allow to profit of that.
Concerning your first question, well of course it is an opening, as some material is cut from pressure boundary and is not replaced with something of equivalent strength (heater rods do not normally count as structural material).
And sorry, you have no (practical) alternative.

prex

http://www.xcalcs.com
Online tools for structural design

RE: UG-39

Resistance elements have no cnsidered strength in the tube and powder you fill them with so the Code will no allow its inclusion.
since they are small holes, you may get away with
just running ligament efficiency calculations.

genb

RE: UG-39

(OP)
Well perhaps we are doing our reinforcement calculation incorrectly since the FEA says our flanges are too thick.

How do you calculate the following UG-39(b)(2):

"...the required reinforcement for each opening in the pair...shall be summed together and then distributed such that 50% of the sum is located between the two openings."

RE: UG-39

see UG 42 view of 2 openings mean that the reinforcing should overlap. I see 50% there, between the 2 openings
c to center.
genb

RE: UG-39

I am familiar with some heater designs as we mfr electric steamers (sec I and IV)
Have you consider UHx-12 design?
if you heaters have u bends, may qualify for UHX design,
there is where the FEA takes consideration as the TEMA style tubesheets.
'hope this helps, let us know please.
GenB

RE: UG-39

Heaterguy, what you are describing in your opening question about welding heater rods to the flat head appears to be a similar situation with firetubes being seal welded to tube sheets of a firetube boiler, therefore, ligament calculations stated by GenB apply.

My question to you is, are you intending to detail out a manufacturer's data for the pressure vessel that you are fabricating?

RE: UG-39

chicopee sec I fire tube boilers are way different to any sec VIII-1 pc. larger inmersion heaters require partial
data report to be intended for unfired steam or HWB boilers or process heaters
therefore require calculations to comply with the Code.
genb

1 find the required and use the reminder t on the flange for your reinforcing, if more reinforcing is required,
use add-on metal, weld metal,
perhaps a stiffening ring will suffice.(do not ask me I do not know how to calc the stiffener)
genb
 

RE: UG-39

heaterguy,
to me that sentence sounds simply as:
- take d=half the centerline distance of the two openings (but of course not more than UG-37 limitations).
Another way to interpret that sentence, telling exactly the same, is that reinforcement material can never be used twice an that 50% of it must be located on each side of the penetration.

prex

http://www.xcalcs.com
Online tools for structural design

RE: UG-39

d in my previous post is to be understood as the limit of reinforcement along vessel wall, that, sorry, is not called d in UG-37 (unfortunately there's no symbol for the limits of reinforcement)

prex

http://www.xcalcs.com
Online tools for structural design

RE: UG-39

Read U-1(a)(3)... again.  I call this the Sound Engineering Practice Disclaimer.

If your FEA dude has done everything right, and I have found that it takes several iterations for them to get everything right, then you should be able to go with the FEA results.  However, be aware that if there is a problem and your FEA results turn out to be incorrect, whereas The Code would have given you the correct results, you will be hosed.  

My personal experience is to go with The Code if it has the application.  Why would you want to take the risk associated with deviating from The Code?  Steel is a lot cheaper than litigation.

Last but not least, if you have one, talk this over with your A.I.  Most of those guys know their stuff and are happy to help.

chili  

RE: UG-39

chili,

I have to disagree with your assessment that FEA can trump Code rules.  Referring to U-2(g), you can apply alternate rules IF there are no rules provided in the Code.  Unfortunately for heaterguy, the consensus seems to be that there are rules that apply in his instance.

RE: UG-39

(OP)
Would anyone agree with this?
tr=A/(p-dh), where A=0.5*dh*t
Or how about this?
tr=(dh/2)^2/(dh^2-(dh/2)^2)*t

tr is the reinforcement thickness
dh is the hole diameter
p is the distance between holes
t is the thickness required without holes

RE: UG-39

TGS4,

Perhaps I did not state my opinion correctly.  I have used FEA many times, but never if there was a clear example in The Code.  Unfortunately, in custom equipment design, there has been many applications where I could not find a relative application in The Code.  The bottom line is Sound Engineering Practice.  Using Code rules that are applicable would be considered as Sound Engineering Practice.

As noted..."My personal experience is to go with The Code if it has the application.  Why would you want to take the risk associated with deviating from The Code?  Steel is a lot cheaper than litigation."

chili

RE: UG-39

My AI will accept design on tubesheet analysis,
I belive he uses roar's design analysis
genb


RE: UG-39

chili,

I see you point - and we appear to agree.  Good to see.

I also don't see a problem using a tubesheet analysis for heaterguy's problem.

RE: UG-39

heaterguy,
your first formula appears to me as the correct one, don't understand the second one that BTW reduces to 4/3*t (?)

prex

http://www.xcalcs.com
Online tools for structural design

RE: UG-39

(OP)
prex,

Is the first one in Section VIII? What makes it correct?

The second one reduces to 1/3*t (I didn't realize that, thank you). It takes the volume of the hole and moves it above the hole in a cylindrical shape with a 2*dh outder diameter and a dh inner diameter.

RE: UG-39

I correct: Miller analysis,
genb

RE: UG-39

heaterguy,
reinforcement calculations are based upon reconstitution of metal cut by the opening in all sections through vessel wall made with planes containing the opening centerline. This procedure conceptually works only with areas, not volumes (of course because stresses act on surfaces), so your second formula has no meaning.
The first one is the application of UG-39 rules, as:
-make a section with a plane containing the centerlines of both openings
-area available between the two openings is tr(p-dh) (with your symbols)
-only 50% of it may be used for each opening
-the same 50% area is accounted for each opening on the other side
-the available area for each opening is again tr(p-dh)
This is the rule. Of course, as discussed above, this procedure doesn't account for the orientation and position of the holes: two holes aligned along a radius are very different from the same two along a circumference, as the first case deals with tangential stresses, the second one with radial stresses, and the two are quite different.
However that's it, at least for the moment...

prex

http://www.xcalcs.com
Online tools for structural design

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