Partial heat exchanger retubing and internal tube coating 1

[Corroneer]

Hi All,

Does anybody has experience with either, or both, of the following:

1. Partial re-tubing of the heat exchanger with a higher alloy, i.e. corroded tubes to be upgraded to CRA while keeping the intact ones and replace them as needed in the coming shut-downs?

2. Internal coating of heat exchanger tubes? A company claims that they have a proven record of internal coating of tubes. Anyone has tried this?

Corroneer

 

[EdStainless]

I have worked with customers on both of these.
Partial retube works provided you have some things in your favor.
As long as you are using the same alloy type so that CTE matches, and it helps if you are doing a section of bundle not just random tubes.
If you go this way replace as many tubes as you can, you don't want to leave some borderline ones that may fail soon.
As for ID coating I have seen it work well in moderate temperature water service (steam condenser).
It is a way to put some plugged tubes back into service and buy yourself a few years to get the entire unit replaced.
If it is not water/steam and if it is hot you need to stop and think carefully.

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P.E. Metallurgy, Plymouth Tube

 

[Corroneer]

@EdStainless, thanks for the reply. In fact the service is wet sour gas not water , hence changing the CS tubes to 904L or 625!

 

[Dhurjati Sen]

Dear Corroneer,

Let's go one step at a time.

1. How would you carry out the partial re-tubing?

2. Surely, in-situ, i.e. at the site. If no, then what's the point in partial replacement?

3. If yes, how many tubes would you want to replace? Must be more than 20% as you can run with that number of plugged tubes.

4. Also, how do you ascertain which tubes you need to replace? Must be by eddy current testing, which would specify different levels of wall thickness loss.

5. By now, you know how many tubes have survived and for how long.

6. Do you still require an upgraded in-situ replacement, or replacing with identical tubes seem the obvious solution?

Regards.



DHURJATI SEN
Kolkata, India

 

[Corroneer]

@Dhurjati Sen, thanks for the reply.

I know the situation of the tubes and we have around 30‰ to replace.

This is a recurring problem and, ideally, I would like to upgrade the material of the whole tube bundles to better fit the purpose, but I cannot justify the replacement of all the tubes, so I had the idea of doing it "step-by-step"!

 

[EdStainless]

I have never seen coating in a steel tube work well. Corrosion always undercuts the epoxy and you end up loosing tubes.
And partial CS, partial alloy is a poor option unless there is very low delta T. IF this sees any real tem swings the differential CTE will start breaking things.

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P.E. Metallurgy, Plymouth Tube

 

[Chumpes]

Hello
modification of tube material usualy requires reperforming the thermal rating and mechanical design, ferritic and austenitic alloys having different thermal conductivity and mechanical properties.
regards

 

[Corroneer]

Thanks for everybody who responded.