Shell and tube exchanger with stationary tubesheets 2

[19750412]

Hello everyone

I have a question referring design/construction of shell and tube heat exchanger.

Dose anybody meet in own design practice bellow described design case:

Shell and tube exchanger with stationary/fixed tubesheets with relief grooves at connection between tubesheets and shell./
Some amount of tubes go across part of relief groove, OTL has diameter covered part of it closer to the center of tubesheet.
Is such solution acceptable? My client said that yes but in my eyes it is wrong. At the point of contact between tubes with surface of groove additional stress concentration can occur and further we loose main task of groove.

Unfortunately, client till now dose not allow to increased I.D. of the shell and process engineer who design exchanger from the process point of view said that there is only small addition in exchange surface and reduction of tubes is really the last solution. Moreover, neither ASME in subsection UHX nor THEMA do not give any information/requirements for relief grooves.

Thank you in advance for any answer or opinion.

 

[unclesyd]

Can you post a sketch of your proposal?

This new to me and we have numerous fixed tubesheet exchangers.

 

[BPVFEA]

I have never seen tubes going beyond/on the groove diameter. It would not be good practice since stress patterns of Tube-Tubesheet joint & Relief groove would interfere giving stress levels higher.

1)You can ask client to show if they have done any similar design in past which is working properly.

2) UHX/TEMA does not address such configuration. Client has to prove that this design is safe. He might propose to do FEA. But in that case he should do detailed FEA & not any simplified FEA based on some assumptions. The operating conditions for FEA should be specified accurately. It is also necessary to carry out FEA for startup, shutdown, accidental, upset conditions etc.

In my opinion such configuration should be avoided. (especially if the exchanger is subjected to frequent cycles (fatigue).)

 

[19750412]

Hi BPVFEA and thanks for your opinion.
I have done in same way as you proposed. I have askesd client to confirm such design and his good experiance in this, but i have only received answer: Yes, we have used such solution in the past and our experiance is good.
But such answer dose not convince me and thereofore my question.

 

[BPVFEA]

Only one line reply can not do. Tell your client to substantiate his claim by mentioning the list of equipment along with project, customer, mfg year etc. I suggest you to independently verify if these equipment really exist & are working properly. Take everything in writing from your client.

As unclesyd said, post the sketch of this configuration. This is to make sure that what we have imagined is correct. (since we have never seen something like this)

 

[19750412]

Thanks for replay, please find attached sketch for better understanding. I will ask client to send me previous documentation approved by authority. This is not only problem of strength calculation but also problem of manufacturing, tubes shall be also expanded. FEA analysis is only one way to be sure that the construction is safe.
Thanks for help.

 

[unclesyd]

You got me on this one. I've seen welding lips on some fixed tubesheets, mostly CS, but never with a groove as your sketch shows. A welding lip would have a simple radius on the inside with no tubes in the radius tangent area. It could be fabricated with a little extra effort, but no lights have come on.

Can you comeback with the physical parameters and process fluids?

The only thing I've seen is we experimented with machining such a groove in SS tubesheets on vertical exchangers to mitigate Chloride SCC. We took our tubesheet vents from the groove area. The experiment failed in our case as the tubesheets would get a crown and the Chlorides would accumulate there.

 

[SnTMan]

19750412's sketch looks to me like a hubbed tubesheet per Fig. UW-13.3(b). I think there was some discussion awhile back about this configuration.

While I think the configuration is a little weird, assuming it meets the requirements of UW-13 etc. as to radius, TS thickness, etc. I would not be too concerned about stress concentration, this is Div. 1 design after all. The gain in surface above rated is surely negligible, lets don't assign a degree of accuracy to these calculations that does not exist.

Strictly speaking I doubt it is within the scope of UHX, but nothing unusual about that.

You for sure would not want to roll into the groove.

I'm glad it's not mine

Regards,

Mike

 

[19750412]

Thanks all for opinion. I absolutely agree with you SnTan, the configuration is strange. But i have met many times tubesheets with relief groove but never with tubes go across it. The sketch shows our first design assumption but of course it will no change much later. I thing that we reduce radius of groove firstly, but nevertheless we will not have enough space to locate tubes without going across the groove.

I have looked into UHX and have not find requirements regarding such construction.

I thing that at the end we increase diameter of shell to reach more space to locate tubes, but is only one condition - the client agreement.

Regards
Arti

 

[MrBTU]

As long as the tubesheet thickness at the bottom of the groove meets UHX, then you are complying with UHX. As stated above, roll tubes for the length they are in the tubesheet only, not into the groove.