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Retube process key steps 3

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therunningbruce

therunningbruce

Chemical
Nov 17, 2020
25
Hopefully this is ok to ask

in the Re-tube process of a fixed tubesheet. Id like to validate my understanding of the process.

Is it as below

1. Grind out welds on all tubes
2. Pull all tubes out.
3. re-detail (tube sheet)
4. insert new tube sheet
5. reweld up tube sheet.

with a very large HX. is there a risk baffles collapse within the shell?
does that require an inspection ?
should they be inspected every re-tube ?
should the empty shell be cleaned and treated?

from a multiple series of you tube searches , linked it it seems in every case i can see all tubes are removed first and then new tubes are put back.

do you ever do it tube by tube.. say for a very large HX..

I am asking as ive seen a HX have significant iron build up at nozzle .. maybe from re-tube or just in service issues..So, to understand the most approprate steps id like to get myself clear on the retube process.
 
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I have worked on projects like this on big HX, steam surface condensers with 20,000 tubes.
Tube rolling and/or welding need to be validated on mock-ups.

All tubes are pulled. (rolled flat and chopped into short pieces for handling)
Tubesheet holes are cleaned (soft wire brush or flap wheel)
Every hole in each support plate is cleaned. (same way)
Tubesheet holes are gaged. If any are oversized they are reamed and lined.
New tubes are installed, the only lubricant allowed is water.
Tubes are set to correct position on one end.
They are welded and/or rolled in groups, skipping around the tubesheet to minimize risk of distortion.
The other end of the tubes are milled flush.
Then repeat fixing.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Not sure what is meant by Step 4 "Insert new tube sheet." A "retube" of a fixed tubesheet unit usually means that the existing tubesheets are salvaged. Are you just replacing one tubesheet or both?

But your concern about a baffle breaking loose or collapsing is a valid one, especially if the shell side has significant corrosion. To mitigate against baffle collapse you could install and few new tubes after extracting the existing tubes around the perimeter of the baffles. This will also protect the baffle alignment to facilitate tube installation.


-Christine
 
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sorry my bad typing
1. Grind out welds on all tubes
2. Pull all tubes out.
3. re-detail (tube sheet)
4. insert new tube sheet => insert new tubes on by one/
5. reweld up tube sheet. and seal
 
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Try calling the Atlantic Group or RETUBECO.
They are the largest re-tubers.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Slightly outside the scope of the OP-- When pulling out the tubes through the tube sheet holes be careful that the corroded surfaces of the tubes could damage the holes.
 
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