Retubing a warped heat exchanger bundle

[marty007]

Hello,

We have a fixed-tubesheet heat exchanger in our shop that we have been asked to retube. Here are a few quick stats:
[ul]
[li]32"ID[/li]
[li]15'-2.25" F/F Tubesheets[/li]
[li]282 x 1.25" OD x 16Ga Tubes[/li]
[li]4 Baffles[/li]
[/ul]

Our normal retubing procedure is to collapse, remove, and replace batches of tubes at a time. Doing this in batches allows the remaining tubes to support and maintain baffle alignment.

This exchanger is causing us problems however, because the entire bundle appears to be warped. If you shine a flashlight down one of the tubes, you can see a significant bow. We have removed a batch of tubes, but are unable to insert the new tubes because the tubesheet and first baffle are significantly out of alignment. When the tubes reach the first baffle, they are out of alignment by more than half a tube diameter, so even the use of bullets wouldn't help.

Is anyone aware of a method to fix this situation, short of cutting off one of the tubesheets and rebuilding the baffle cage?

I have one crazy idea, but I'm not sure if it would work, what do you think?
[ul]
[li]Remove most of the tubes, leaving a small quantity in place (4? / 8? / ...?)[/li]
[li]Take pieces of 1" OD solid round bar, round the ends like a bullet, and insert them into the ID of the tubes left in place.[/li]
[li]Hammer in the round bars, using the existing tubes as guides for the round bar, with the intent of realigning the baffle cage.[/li]
[li]With the baffles realigned, start inserting new tubes in the other tube holes.[/li]
[li]Once enough new tubes are installed, remove the round bar, and remove the last of the old tubes.[/li]
[li]Continue retubing as normal.[/li]
[/ul]

Has anyone heard of this approach? Could it work? Does anyone have any other solutions that don't involve removing a tubesheet?

Cheers,
Marty

 

[EdStainless]

So how do you clean and chamfer all of the support plate holes?
Are there no tie rods in this unit?
When I have seen this done they removed all tubes.
Cleaned and rechamfered the holes in the support plates.
Replaced the tie rods locating the support plates.
Then re-tubed.


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P.E. Metallurgy, Plymouth Tube

 

[marty007]

On a fixed-tubesheet heat exchanger, the baffles are not cleaned or re-chamfered. This would require cutting the weld between the shell and tubesheet, which is normally avoided.
Yes, there are tie-rods inside the unit. Tie rods hold the baffle locations axially in the unit, but provide almost no lateral support.

In this style of heat exchanger, the bundle is not removable, so we do not have access to the bundle without cutting a major vessel weld. We try to avoid cutting this weld if possible.

 

[EdStainless]

Can you get the tubes out?
If so you might try pulling the ones in the 'corners' and replace them with solid rods.
This should hold things in alignment while you pull the rest of the tubes and start re-tubing.

Any HX with warped tubes that I have seen worked on was cut open.
Because in most cases you couldn't get the tubes out with tubesheet and baffles in place.

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P.E. Metallurgy, Plymouth Tube

 

[marty007]

Yes, we're able to pull the tubes out (takes some mechanical tugging). But again, the tubesheet holes are so far out of alignment with the first baffle that we wouldn't be able to get a solid rod in. This is what led me to the of using an existing tube as a guide for a solid rod.

 

[metengr]

This is what led me to the of using an existing tube as a guide for a solid rod.

Excellent concept.

 

[ASMEQC]

Have you tried rolling the vessel? Rolling might bring the supports close to alignment.

 

[EdStainless]

Your rod could have a very long tapered point on it, to aid in picking up alignment.
If it is that distorted I think that you are going to need to have nearly all of the tubes out before you can get it straight enough to get tubes back in.
Driving 1" rod into a few tubes now to hold things isn't a bad idea (Put a slug of heavy oil into the tubes before driving), but expect to have to remove all of the other tubes before you can get new tubes in.

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P.E. Metallurgy, Plymouth Tube