Tube expansion depth ratio in tube sheet thickness design 1

[mechengineer]

Hi heat exchanger design experts,

Does the tube expansion depth ration apply for the light expanded (closing the gap between tube and tube hole) of the tube to tube sheet joint? I think it should not, it should not consider the tube expansion depth ratio 'ρ' for the Effective Ligament Efficiency = (p✱ - d✱)/p✱, but code dose not clear mention it. ρ = tube expansion depth ratio = ℓ t x /h ,(0 ≤ ρ ≤ 1).

My understanding is,
Strength weld+light expanded(thickness reduction<2%)= Strength weld is joint type "a" in ASME VIII-1, Table A-2, Efficiencies fr.
Strength weld+heavy expanded is joint type "e" in ASME VIII-1, Table A-2, Efficiencies fr.

Regards,

 

[EdStainless]

First you can't measure a 2% reduction. You would need the original actual size of the hole, tube OD and tube wall.
Then figure out the what the ID size would be when you actually made contact.
But to your question, no the depth isn't very important as long as you stay away from the back face of the tubesheet.
Since a contact roll does not provide any mechanical support (tension, compression, or vibration) it isn't critical.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[SnTMan]

mechengineer, from what you describe, and for the purpose of Part UHX calculations I'd take ltx as zero.

Regards,

Mike

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

 

[mechengineer]

Hi SnTMan,
I agree with you. But some vendors insist that ltx is not zero, especially for inconel 625 tube sheets (expensive) to save material cost. This is because the code says itx is the tube extension length, but doesn't say whether it's a light or heavy extension. I request the venor to do mock up test(QW-193) for tube to tubesheet joint expended and tube (inconel 625) hardness test if they consider ltx is not zero for the light expended in design.
Regards,

 

[Christine74]

If your vendor insists on taking credit for the expansion depth in the UHX tubesheet design, why not just make him perform a full expansion of the tubes?


-Christine

 

[SnTMan]

Was about to ask the same, thanks Christine74.

mechengineer, why not full expansion?

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

 

[mechengineer]

@ SnTMan & Christine, Client requirement is "Strength Weld + Expanded". The light expanded is because the tube material is Inconel 625 to avoid hardening of tube (H2S service). This question seems to deviate from my concern about "ltx" application condition.

Regards

 

[Christine74]

Thanks for the clarification. To answer the original question, as far as I know there's nothing in the Code that tells you at what level of expansion tubes adds structural integrity to the tubesheet. For 2% expansion I would consider "ltx" to be zero but that's just my opinion.


-Christine

 

[SnTMan]

API 660 allows 4-5% wall reduction for non-ferrous tubes. Surely this is reasonable (but confirm) and would allow a non-zero ltx...

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