Tube bundle layout different from drilling tubesheet layout

[Peter113]

Hello to all,
we have a multitube heat exchanger (minimum center to center diameter: 14") with tube bundle according to UNS 39274 (superduplex) cold formed and solution annealing(U-bends and 12"). The tubesheet layout is square pitch (1") and the U-Bends have been formed according to triangular layout (15/16"). Due to long delivery date of new forged tubesheet (UNS 39274) or new tubes, we would like to repair the U-Bends safely. Please could you indicate any advice about Non-destructive and Destructive examination?
Thanks in advance
Peter

 

[SnTMan]

Peter113, it sounds like you want to straighten (at least to some degree) and re-form the U-bends. While I can't address the metallurgical aspects, here are some practical considerations:

You need to determine which pitch is correct as this can affect the thermal rating and perhaps maintenance cosiderations.

If straightening and reforming will the straight length be as specfied? If not, rating could be affected.

I hate to think about thinning and general physical condition of the tubes after this. Smooth radii, lack of puckers, kinks, etc.

If this unit is to be built for another party ("the customer") do plan to get permission to proceed with this course of action? Personaly I would not accept such a proposal.

Bite the bullet, fix it properly.

Regards,

Mike

 

[Peter113]

Thanks SnTMan,
all thermal concerns have been considered. We are looking this issue from a metallurgical and mechanical point of view. We can give you for your information some details:
- Maximum radial displacement: 1.5" (opening and closing the bend).
- Total length oh tube bundle: 240"
- Distance between the U-Bends tangent line and the first baffle: 1"
- BWG: 16
- Tube OD: 3/4"

Our major concern is the first baffle because this is the most deformed region because the radial displacement of the tube is 1.5" in 1" distance (i.e, 56º). Our idea is to perform necesssary and realistic non-destructive/destructive to assure the integrity of the tube: For example, we have proposed the following:
- Thickness, ovality, visual inspection, diameters, eddy current testing, metallographic reply. Which is your opinion?

Thanks for your support and awaiting for your reply.
Regards
Peter

 

[unclesyd]

If this bundle is your's can you dispense with the first baffle from the bends to minimize the rework?

 

[SnTMan]

Peter113, I may not understand your configuration fully. I would suppose the innermost rows would require the most severe re-forming, and that successive rows may or may not require less severe re-forming, depending on the change in radius required. The physical NDE you list would seem to satisfy the mechanical concerns, but again I offer no opinion on the metallurgy. At a minimum it seems you would have to soln. anneal again, and would want to verify the physicals.

unclesyds' suggestion is worth a look, perhaps moving the last (first?) baffle could help.

Still, I suggest you get all your ducks REALLY in a row if this is not your bundle.

Regards,

Mike

 

[Peter113]

Thanks,
no removal of baffle is possible due to thermal considerations. No metallurgical concerns exist. Regarding the physical NDE, do you know any recognized Standard to be follow in order to verify the integrity of the tubes? Do you think necessary to perform a hydraulic test on the tube bundle prior to assembly the different parts of the HE?
Regards
Peter

 

[SnTMan]

Peter113, SA-688 may be of interest.

Good luck,

Mike