Enlarged Tubesheet Holes - - What to do??

[Abc Xyz]

Hello to all!

I am in a big fix currently. We have 02 tubesheets available for fabrication of new tube bundle (old tube bundle is being replaced). 3% holes of new tubesheets are exceeding the over tolerance limits of TEMA Table RCB 7.21 for Tubesheet Holes ID. As per design, heavy expanded TTS joint is required.
1.To compensate for enlarged Tubesheet holes, should we opt for welded TTS joint design??
2.Will welding the TTS joint provide any benefit in lieu of heavy expanded TTS joint?
3.What are the adverse effects of enlarged Tubesheet Holes once the exchanger is in operation??

Thanks.

 

[Some Curious Guy]

1) I assume that the tubes and tubesheet are of different metallurgy hence the owner specified strength expanded tube to tube sheet joint. Strength welding tube to tube sheet joint is a better option provided the material are compatible and the root gap of the weld is not of primary concern. If the tube is malleable enough also roll expand the tubes in addition to welding. This will ensure that weld would not directly face the tube vibration which will now be there due to oversized tubeholes.
2) Welding will no doubt offer a better leak resistance than an expanded joint. The disadvantage is that it is more labour intensive to replace tubes in case of repair. Choosing a tube to tubesheet joint depends on metallurgy , weldability , process condition , difference in shell side and tube side temperature etc so there are no absolute advantage or one over the other.
3) Oversize tube holes will have face more vibration. If the tube material is not malleable there is a likelihood of cold hardening of tube due to extra expansion.

Please avoid doing weld built up or sleeves as it may lead to local bulging and reduced structural integrity of the tubesheet. I would recommended that you honestly approach the owner with this issue. Not only you but even the owner is in a fix since reordering the tubesheet would be a costly proposition and derail the project schedule. Solution you both arrive would depend on process limits , metallurgy , weldability, manufacturing and operation feasibility. In extreme case you would be asked to plug the tube holes if sufficient margin is considered in thermal design.

All the best.

 

[r6155]

There may be some tubes with allowable variation in outside diameter, then fit them with 3% of the holes you mentioned.

Regards

 

[SnTMan]

Abc Xyz, first I largely agree w/ Some Curious Guy, particularly as to not attempting to repair the deficient holes. More harm than good. Also get buy-in from the client for any proposed fix. r6155s' suggestion may have merit as well, including selecting for thicker wall if possible.

Second, you will need to expand those tubes to some degree to close up the crevice between tube and hole.

Third, a seal weld rather than a strength coupled with some degree of expansion may serve the purpose.

I don't remember the exact details (and don't have the calculations available), but I used to deal with oversized holes by performing an analysis:

First, calculate thinning due to expansion of the tube to contact. As I recall assumes constant volume of the involved tube material with no longitudinal expansion.

Second, calculated thinning to achieve desired wall reduction, based on above starting wall thickness. Constant volume as well I think, but with longitudinal expansion.

Third, determine if resulting wall thickness is acceptable, based on relevant factors.

Best of luck,

Mike



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

 

[EdStainless]

Require tests expanding tubes into oversized holes and measuring pushout strengths.
This should tell you if the holes are usable as is.
Don't calculate wall thinning, measure it. Expansion control is done using torque not size measurements. If you go by size then you must know the actual size of every hole and the wall thickness of each tube. No one wants to measure all of those.
I have see oversized holes in used tube sheets reamed out larger and then having matching metallurgy sleeves expanded into them. Which are then reamed to the correct size.
If I was the end user I would reject the tubesheets and require that new ones be manufactured, but I am a prick about these things.

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

 

[GD2]

AbcXyz,
Seal weld may not give you the adequate weld strength required for these outside tolerance tube-holes. Strength will assure the design strength. Follow ASME VIII Div 1 UW-20 or other equivalent code guidance.
.

GDD
Canada

 

[Abc Xyz]

Thank you all for your guidance and support. And apologies for delayed reply.

Best Regards.

 

Oversize tube holes are indeed a problem.

I concur with Some Curious Guy - if 3% are affected, plug them if HX performance is not adversely affected. A good HX tech spec will talk about this and give a limit on the number of holes permitted to be plugged.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[r6155]

I suggest continuing with normal fabrication and the hydraulic test will show which tubes need to be plugged.
This percentage must be reduced from the final payment, prior agreement.

Regards