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Over Expanded Tube in Tubesheet- Rework or Redo?

Over Expanded Tube in Tubesheet- Rework or Redo?

Over Expanded Tube in Tubesheet- Rework or Redo?

(OP)
So we have a predicament. My guys over expanded the tubes and it resulted in warping of the tube sheet.

I have an intercooler much like a one pass tube bundle with tubesheets on both sides of the tubes (not U Bend). My guys over roller expanded, reducing the tube wall 22% when calcs say 10% max. Only one of the two, tubesheets is visibly warped (bowed in the middle) probably 1/8". Amazing after putting on the heads the flange is not leaking around the gasket area. But the tubes to tubesheet joints are leaking. The tubesheet is 304SS 3/4" thick with 2 TEMA grooves. Tube is 5/8" Cu/NI 049 wall.

We plan on leak testing the tubes to see if the tubes are damaged, but I'm concerned that the warping made the tubesheet holes elliptical and so rolling further will make things worst?

Any ideas to fix assuming none of the tubes are damaged?
1) Reroll further?
2) Could you put in smaller OD tube inside and re-sleeve?
3) Do we completely retube everything? If so tubesheet salvagable? If salvagable do I remachine the holes?

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

Start over. there are patches but they will cost as much or more than redoing this.
And patching this one will likely be a long term headache.

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P.E. Metallurgy

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

Explore the idea of seal welding.

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

No welding of CuNi to SS. Maybe you could with 80%Ni filler, but I wouldn't trust them.
Look at the strengths of your TS and tubes.
Are the tubes stronger?
Weren't they rolling with a torque control? That is the better way to limit rolling forces.
If you think that things are warped now wait until this gets temperature cycled.
Can you shorten the unit 1.5" and reuse the tubes? Then it would just be new tubesheets.

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P.E. Metallurgy

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

The reason about my statement "explore the idea..." is because I was not sure which was confirmed by the argument of EdStainless against seal welding. Another possible solution is the use of ferrules inside the tube ends (not outside tube ends). Again that possible solution should be discussed with a jurisdiction authorized inspector, an insurance pressure vessel inspector and a metallurgist about the proper ferrule composition. I would also contact the manufacturer for advice.

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

Rerolling tube ends will thin out the tube ends, therefore, ferrules inside the tube ends have been used to strengthen the tube ends.

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

If the tube ends are already thinned and cold worked, and the tube sheet distorted then I don't see saving this one.
If it was less severe you would remove tubes, ream the holes, roll in precisely machined sleeves, and then install new tubes. Though this is really only an option in low pressure service as you end up with a lot of joints.
The real problem that I see with welding is not that it isn't possible to weld these material, it is just difficult. The issue is that you may need strength welds and not seal welds. This raises many other issues.

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P.E. Metallurgy

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

Feedback is always appreciated about the steps that you have taken. Also before undertaking new similar new projects, have your crew get a course from a mechanical specialist about the work that you are doing. Insurance companies that provide boiler and machinery insurance coverage have such people.

RE: Over Expanded Tube in Tubesheet- Rework or Redo?

your work was good for nothing, no way of saving the tube sheet. you have to make a new bundle

luis

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