Heat exchanger tube sheet thickness
Heat exchanger tube sheet thickness
(OP)
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
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





RE: Heat exchanger tube sheet thickness
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
RE: Heat exchanger tube sheet thickness
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?
RE: Heat exchanger tube sheet thickness
RE: Heat exchanger tube sheet thickness
RE: Heat exchanger tube sheet thickness
Best just use TEMA if you can.
Regards,
Mike
RE: Heat exchanger tube sheet thickness
RE: Heat exchanger tube sheet thickness
Didn't mean to be mysterious about it :). Still think TEMA would be your best bet.
Regards,
Mike
RE: Heat exchanger tube sheet thickness
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
RE: Heat exchanger tube sheet thickness
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.
RE: Heat exchanger tube sheet thickness
Curious why you say it is both a tubesheet and a blind?
Regards,
Mike
RE: Heat exchanger tube sheet thickness
RE: Heat exchanger tube sheet thickness
RE: Heat exchanger tube sheet thickness
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!
RE: Heat exchanger tube sheet thickness
I do not understand how can be designed to Sect VIII-1 if the material is not allowed.
RE: Heat exchanger tube sheet thickness
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
RE: Heat exchanger tube sheet thickness
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
RE: Heat exchanger tube sheet thickness
Great to get all your thoughts.
MikeG7