Fixed tubesheets with eccentrically allocated tubes

[CuMo]

Hello all,
I have been asked to design a replacement waste heat boiler to ASME VIII-1 where the ends act as tubesheets and somewhat vice versa.

Probably this could illustrate things a bit better:

https://exotech.nl/images/c1.505:1/uploads/pictures/147_1.whb-3d.png?1452257628

I've also drawn a sketch (attached to this post) to illustrate the problem a bit better.
The tubes are not located in the central portion of the tubesheets but are rather located eccentrically in the lower section.
The remaining top section of the tubesheets is supported additionally by few 'S'-shape stays made from solid bar which are welded to the shell.

Are you aware of a provision in ASME VIII-1 that will allow to take this eccentricity into account
or the standard UHX method (where I believe the assumption is "tube OTL is concentric to the tubesheet OD") will be sufficient?

I would appreciate any help if someone has had this scenario before and could share a few thoughts on how to approach it safely.
It is the first time I encounter such design.

Many thanks!

 

[Dhurjati Sen]

Dear CuMo,

Hot flue gas would pass through the tube side and the Boiler Feed Water passes through the shell side, gets heated up and forms saturated steam (not yet super-heated). The steam goes up and there would be liquid-vapor separator at the steam outlet.

This is a very common design for waste heat boilers particularly in process units where these are located downstream of the furnace to utilize the waste heat of the flue gas.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[SnTMan]

CuMo, a previous employer designed and built waste heat boilers very similar, including the stays.

They were not in my product line, so no first hand experience on my part but I believe they were to Sec 1.

In my opinion this kind of design does not meet the general applicability for Part UHX, due to the tubefield eccentricity as you noted as well as the presence of the stays. There may be other reasons as well.

Having said that, Part UHX is routinely applied to designs that don't strictly meet the applicability such as no tube in window designs.

It would be nice to back up any Part UHX calculations with another type of analysis, similar existing design, etc. Otherwise I'd find it hard to trust.

Regards and good luck,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[CuMo]

Thank you both!
I have done some research, trial and error and it seems that UHX seems NOT to be the way forward for the following reasons:
Due to the high temperature of the gases that go through the tubes (might not be everybody's application) - the anticipated thermal expansion in them is great.
Since the tubesheets are fixed and there is no provision for shell expansion/compression - the UHX method would fail due to tube end loads exceeding the allowable and potentially resulting into tube buckling no matter what.
Tubesheets should rather be designed as thin flexible membrane tubeshees which would allow movement hence the presence of their round knuckles.
I've found a few examples which are somewhat relevant to this problem.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.659.5878&rep=rep1&type=pdf

&

https://www.borsig.de/uploads/tx_bc...h_Thin_Flexible_Tubesheet_Design_E_BORSIG.pdf

Further interesting read might be that:

https://brimstone-sts.com/wp-conten...ens-WHB-Integrity-Panel-Discussion.x54692.pdf

 

[MrBTU]

CuMo,
See UHX-10 (c). Since UHX is not applicable, U-2(g) applies. Your AI may accept the old TEMA methodology, or may require an FEA.