Heat exchanger tube sheet thickness

[MikeG7]

Hi
I have to design a blind flange which has a a flat, full face gasket. There are multiple openings for heat exchanger tubes that pass through the blind cover. I tried to determine the thickness based on rules of UG-39 with multiple openings, but the spacing of the tubes rule that out. The tubes are not providing any "staying" to the tube-sheet because they are not attached at opposite end to anything. They are welded to the blind flange at one end and are loose at the other end, except that some baffles or support plates are provided to keep them from moving about.
Should I use the rules of UHX for this (not familiar with UHX at all) or by Appendix 2 with a ligament efficiency applied? What is the design approach you can suggest?
Picture attached.
Mikeg7

 

[SnTMan]

MikeG7, sorry for the bad news, this would normally be a Part UHX design. I would advise you to get some software, as I am not certain that Part UHX calculations can be done by hand.

If you are not bound by Sec VIII, Div 1, you could use the old TEMA tubesheet calculations. Much simpler that UHX.

If your design is not within the scope of part UHX, you might consider design per UG-34, excluding consideration of the ligaments. It can be demonstrated that UG-34 calculations produce a larger required thickness than TEMA.

Regards,

Mike

 

[MikeG7]

SnTMan (Mike)
Thanks for your suggestions. I could use TEMA in this case. But on your 2nd suggestion, per UG-34 I understand it may produce thicker plates than TEMA but that section does not deal openings in the cover, so wouldn't "excluding consideration of the ligaments" be under-estimating the thickness somehow? But it is a suggestion I would consider since it also takes into account if there is any edge moment from bolting (but in my case gasket is flat face) . Could you expand further on it's applicability in this situation?

 

[bernoullies123]

FEA analysis using division 2, part 5 might be an option.

 

[MikeG7]

Yes , an expensive option though ...

 

[SnTMan]

MikeG7, I really don't know *anything* about this situation. It may be I should not have mentioned the UG-34 approach. The particular set of assumptions involved may not be applicable to your work.

Best just use TEMA if you can.

Regards,

Mike

 

[MikeG7]

Mike, this forum is for sharing ideas and thoughts and all opinions are welcomed.

 

[SnTMan]

MikeG7, yeah, agreed. The UG-34 approach I mentioned is used in the design of rectangular tubesheets. Assumptions are made about pitch dimensions, plate dimensions, dimension "G" etc, etc. to calculate the total factor against design pressure. Under these assumptions and using a UG-34 efficiency of one, the total factor is higher for UG-34 than for TEMA, yielding a thicker plate. Might not be so if an appropriate ligament efficiency is used in the UG-34 side of the comparison.

Didn't mean to be mysterious about it . Still think TEMA would be your best bet.

Regards,

Mike

 

[gr2vessels]

My two cents;- what wrong with using UG-34(p)? It will yield a certain thickness (minimum thickness). Then use UG-39 for ligament check and increase thickness if required.
Finally, use TEMA for tubesheet calculation, in order to compare the results. Or FEA if available.
I understand this is not an optimizing, cost saving exercise for a particular case, it seems rather a generic discussion over a generic sketch. Accordingly, why would an FEA be expensive given the possibility of significant saving in material, fabrication, etc. when compared with a manual calculation per ASME or TEMA?
Are there other details of the construction which might be pertinent to the discussion?
Cheers,
gr2vessels

 

[MikeG7]

gr2vessels, I don't think there are any other aspects of the construction to take into account, besides that I mentioned before it is not just a tubesheet welded into the vessel but it is also a blind flange so the flange calculations could be relevant? However, with a full, flat face gasket as this one is, there no edge moment to consider and it is mentioned in UG-39 that it does account edge moment caused by bolting. Not worth discussing it further since there is no edge moment.

But besides all of this, I don't suppose I could use these rules of UG-34 with a ligament efficiency either. As with UG-39 (openings in flat covers), I would expect (although it is not stated in the code) that the size and spacing limits of UG-36(c)(3) should also be satisfied. This particular tubesheet has the holes closer than the restrictions of UG-36(c)(3) which states:
" no two unreinforced openings, in a cluster of three or more unreinforced openings...shall have their centers closer to each other than the following:
for formed or flat heads 2.5(d1+d2)"

So it was just a general discussion on the application of UG-34.

Looks like TEMA is the way to go, if it came out a bit thicker than would be required from FEA then so be it, really it's probably not worth the effort. From my point of view here client is not expecting to pay for FEA in this instance, it would be hard to justify that to them.

 

[SnTMan]

MikeG7, if this were Code work, and a case for which no explicit Code rules exist, then you could be justified using, say, UG-34 with ligament efficiency. Or another method which could be an extension of existing rules. U-2(g). If not Code work the same pretty much applies, just no need to invoke U-2(g).

Curious why you say it is both a tubesheet and a blind?

Regards,

Mike

 

[GenB]

Q. Do you call it a blind because is an ANSI fly,blind? What is the mat spec?

 

[GenB]

Will this be ASME Code Stamped ?

 

[MikeG7]

Not a code stamped vessel but it is design to VIII, Div.1.

The tubesheet is also the vessel body flange. If you look at the picture attached at the beginning of the post you can notice that there are some tubes that pass through the blind flange. There is no "shell side" to this vessel. It is to be understood that some tubes pass into the vessel from the outside via the blind flange and then some heat exchange happens between the tubes and the steam inside the vessel. This flange is to be designed and is not a B16.9 or B16.47 flange, it is made for the purposes of the application. That's why I brought up if it should also be designed as an App. 2 flange?
Thanks all!

 

[GenB]

If ASME stamped cannot use ANSI flange for tubesheets. so it is not allowed,
I do not understand how can be designed to Sect VIII-1 if the material is not allowed.

 

[gr2vessels]

MikeG7, you seem to have some terminology problems;- the sketch you posted shows a simple arrangement with a tubesheet bolted to a flange (you said an Appx 2 flange, OK). The tubesheet is typical, extended with a full face bolting flange. Don't mention again the bolting moments because it confuses the issues. Do mention, however, that the tubes are connected to the tubesheet by expansion into the holes or welding, because you called it tubesheet.
The tubesheet can be designed in various ways, depending on the tube holes pitch, arrangement, pressure and temperature, etc. Further, the extended flange of the tubesheet has a calculation of its own and could have different thickness from the tubesheet. You mentioned several times the vessel design to ASME VIII-1. That has nothing to do with the tubesheet design if it is not stamped with ASME U-stamp. Accordingly, you can design the tubesheet to UHX or TEMA code and the flange extension to Appx. 2, to match the existing vessel flange.
Cheers,
gr2vessels

 

[SnTMan]

MikeG7, I would say that this design is not within the scope of Part UHX. I would say therefore that it is a U-2(g) design. I would say that UG-34 could be applied using an appropriate ligament efficiency, if desired. I would say that alternately TEMA rules could be used.

I would say that Appendix 2 does not apply, as its scope is for gaskets contained within the bolt circle. If a flange calculation is the preferred approach, Taylor Forge Bulletin #45 would apply, perhaps with an ID equal to the tube circle.

I would say it would be permissable to pick from among these alternatives the one yielding the thinnest plate.

Best of luck

Mike

 

[MikeG7]

Thanks all, many good ideas and suggestion!
Great to get all your thoughts.
MikeG7