Heat Exchanger Tubes 5

[Inchtain]

Dear Colleagues,

We have a Condenser that experienced a rapid failure of its tubes.

If the cooling water treatment was improved, do we still need to think about altering the material used.

Saying that, I wonder if SA 334 Gr. 1 carbon steel material was a good choice for this Condenser tubes; and how to guarantee the supplier will provide high quality tubes and of the same specifications needed when ordering them.

The Condenser parameters and construction is as follows:

Designation Shell Side Tube Side
Design Pressure (kg/cm2) 26 18.5
Design Temperature (ºC) 100 70
Fluid Refrigerant Propane Cooling Water
No. of Passes 1 2
Construction Code ASME VIII Div. 1 & TEMA Class R
Stress Relief None Yes, only for Channel Chamber
Radiography Full Spot

Component Material Design Thick.(mm) Corrosion Allow.(mm)
Shell ASME SA 516 Gr. 60 25 3
Elliptical Heads ASTM A 516 Gr. 60 19 (Min. 17 after forming) 3
2907 Tubes ø = 19.05 mm (Ł = 9144 mm) SA 334 Gr.1 2.11 -
Tube Sheets SA 350 LF 2
Insulation No

And how to verify the baffles and tie-rods condition when re-tubing this condenser following the removal of the old tubes? and in case of tube break during the extraction, which is the best practice to remove the remained debris inside and clean the shell knowing that this Condenser is a fixed tube sheet heat exchanger?

I really appreciate your valuable feedback.

Thanks and best regards,

 

[0707]

Cs tubes, for cooling water systems will not be a good choice.

 

[EdStainless]

CS tubes in condenser service are rare.
You typically run as thin of tubes as possible which means zero corrosion allowance.
You need to look at what alloys that may be in your application.
With CS tubesheets it usually also involves coating the tubesheets (two or three layer high build epoxy)
When you retube every tube is removed, all baffle holes cleaned and gauged, all tubesheet holes are cleaned and gauged for size.
All of the internals should be inspected.
After all this is your only chance to see everything.

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P.E. Metallurgy, consulting work welcomed

 

[Inchtain]

Thanks for replying.

So, what other suggestions to upgrade the tubes material? and how to guarantee that the supplier will provide high quality tubes and of the same specifications needed when ordering them?

 

[EdStainless]

There are Cu based alloys (often CuNi) and stainless steels (alloys better than 316).
1. Select a material
2. Get to know the specs
3. Right a short spec (don't repeat anything in the ASTM) if you want additions
4. Buy from mills that you know, if you don't know them visit them.
This is part of the procurement cost.

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P.E. Metallurgy, consulting work welcomed

 

[0707]

Ed gave you the answer

 

[Dhurjati Sen]

You need to determine whether the corrosion is shell side, or tube side, or BOTH.

Check the tube edges (the portion that protrudes out of the tube sheet) to assess cooling water corrosion.

Pull out a failed tube to check shell side corrosion.

I will not worry much about the tie rods and the baffles at the moment.

Rushing for a material upgradation without a proper failure analysis is not desirable.



DHURJATI SEN
Kolkata, India

 

[MJCronin]

As always, EdStainless seems to be on point .... CS was a bad choice

... as a suggestion, I believe that you might be well served to explore the corrosion-enhanced properties of the Duplex Stainless alloy tubing (2205)over 304/316 series

Even the ultra-conservative ALFA LAVAL people seem to be standardizing on this 2205 alloy choice for their oilfield condensate sevices.

https://www.alfalaval.com/globalass...olers-and-condensers-for-large-gas-field.pdf.

https://ebin.pub/corrosion-control-in-the-oil-and-gas-industry-1nbsped-978-0-12-397022-0.html

https://nickelinstitute.org/media/8dab1e8a1825480/nickelpub10044_apracticalguidetousingduplex.pdf

MJCronin
Sr. Process Engineer

 

[EdStainless]

2205 is a good option. It has better pitting/crevice corrosion resistance than 316.
It has much better CSCC resistance, it isn't immune but it has usable resistance.
It has much higher strength, which usually leads to thinner tubes.
You would likely go down to 0.065" or maybe thinner.
And the CTE isn't that different from steel (much closer than an austenitic SS or Cu alloy).
It is also widely available.
When you order a duplex SS always specify A923, without accepting on the micro.
This will require a special corrosion test to verify that the HT was correct.

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P.E. Metallurgy, consulting work welcomed

 

[rscosta1976]

Without more details it is hard to provide a good answer.

There is no question that either copper alloys, super duplex SS and other corrosion resistant alloys would offer great benefits over carbon steel. However, I can think of
cases where carbon steel utilization is acceptable depending of the cooling water system type and respective water treatment program. As an example, many close loop CW systems present very low corrosion rates for well (chemically) treated systems.

Thanks

 

[EdStainless]

The catch with most CS cooling water systems that rely on treatment is that you have to have procedures in place that assure if treatment is lost that the system will be shut down.
Most plants will not do this, saying that it costs too much to shut down.
But they take a system that would have lasted 20 years and destroy it in one day.
What does that cost?
It is a rare discipline.

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[Krausen]

2205 is a good option. It has better pitting/crevice corrosion resistance than 316.
It has much better CSCC resistance, it isn't immune but it has usable resistance.
It has much higher strength, which usually leads to thinner tubes.
You would likely go down to 0.065" or maybe thinner.
And the CTE isn't that different from steel (much closer than an austenitic SS or Cu alloy).
It is also widely available.
When you order a duplex SS always specify A923, without accepting on the micro.
This will require a special corrosion test to verify that the HT was correct.

EdStainless - What are your general thoughts on the tube-to-tubesheet joint design when using 2205 tubes with CS tubesheets? Being that 2205 is a much harder/stronger material compared to CS, do you typically strength/seal weld these joints to avoid any potential issues with rolling the harder 2205 tubes to the softer CS tubesheets? If so, do you recommend providing a weld overlay of 2205 (or 300 SS material) to the tubeside of the CS tubesheet to help match the metallurgy of the tube-to-tubesheet strength/seal welds?

 

[EdStainless]

Ideally I would like to see 2205 tube sheets. You would need this for strength welds.
But it really depends on how corrosive the service is.
If CS tubesheets will hold up then use stronger CS grades so that they are closer to the strength of the 2205.
The yield strength of 2205 isn't that high, and with thinner tubes this shouldn't be an issue to roll.
I have seen much greater differences work fine.
Seal welding will work but if you are welding directly to CS you will likely need a Ni alloy filler (C276?).
The most common solution is no weld and to shop epoxy coat the tubesheets.
A three layer high build system will be very durable and seal very well.
I am not a fan of overlay for these lower alloys.
Duplex overlays are problematic because of trying to achieve phase balance (issues with both cooling rate and dilution).
Using a 316L overlay in two layers would likely cost as much as a solid SS tubesheet.
Just not worth it.

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P.E. Metallurgy, consulting work welcomed