Tubesheet Design

[TJOrlowski]

Early appology if this has been discussed before; I did several searches but was unable to find anything relevant.

We have a customer who currently owns a shell & tube heat exchanger (TEMA NEN); he uses it more as a reactor vessel than a heat exchanger. He is looking to have his existing unit modified.

Currently it has 1-1/8" OD tubes. The owner wants new tube sheets and baffles installed, but he wants to use several different size tubes, ranging from 3/4" OD to 2" OD, with mostly 1" OD tubes (total of five different sizes). All sizes are standard condenser tube sizes.

Background: Design will be to Section VIII, Division I, unit will carry NBBI R stamp.

Just wanted to get some additional thoughts on how to go about calculating an appropriate tubesheet thickness. The existing unit was designed to Ed '04, A'05, and we know what the existing thickness is. We don't know what the tube-tubesheet attachment is, but we plan on double serrating every tube hole, and expanding and seal welding every tube.

-TJ Orlowski

 

[SnTMan]

TJOrlowski, short answer is this will be a U-2(g) design, perhaps by FEA. I am not familiar with any standard tubesheet calculation that accounts for multiple tube diameters, and current Part UHX calculations are pretty resticted as to scope. I don't suppose you have access to the originals?

I think you are going to have to get an early buy-in from the AI for whatever you propose to do as well.

Tough problem

Regards,

Mike

 

[SnTMan]

As an afterthought, I suppose you could do the calculations for each tube diameter as though only that diameter were present, and take the thickest result, although for a fixed tubesheet exchanger this is a gross simplification. Reliability would be very dubious.

Regards,

Mike

 

[TJOrlowski]

do the calculations for each tube diameter as though only that diameter were present, and take the thickest result,

This will most likely be our initial approach. Each ligament will be greater than or equal to the ligament that would be present if all the tubes were the same (ie the ligament of any 2" tube hole would be .482 in any direction, even if all surrounding tube holes are smaller).

I plan on doing UHX calcs and wiping the dust off the TEMA calcs as well; luckily our AI remembers the couple of times that ASME scratched what they had come up with and told S&T fabricators to refer back to TEMA.

Thanks for the input.

-TJ Orlowski