Stainless steel in chloride environment 9

[Meysamsh]

Hello everyone.
I have little problem.
We have a potable storage tank that hase been made by stainless steel 304.
But the concentration of chloride is about 130 ppm. Corrosion is start in near the welding.
That was design problem, and we cannot change the material.
What is the solution? Can we paint the inside the tank? Or can we use the cladding?
Thank a lot..

 

[Meysamsh]

@gtaw
Sry i couldn't finde your email add.
This is the photo of inside the tank

 

[Meysamsh]

Photo of small mounts

 

[Meysamsh]

After cleaning the mounts

 

[EdStainless]

While these images are consistent with MIC you can't blame the corrosion on MIC until you rule out everything else, it is a fact of life that microbes are everywhere. In this case the root cause is the poor weld condition.
It wouldn't hurt to also have a plant to minimize the MIC opportunities.

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P.E. Metallurgy, consulting work welcomed

 

[Meysamsh]

@Edstainles
As you see, this mounds are every where. On weld and plate.
How we can considered that's the weld problem?

 

I agree the morphology is consistent with MIC, but good luck capturing any microbes. A conclusion of MIC is usually reached by inference, after clearing all other possibilities off the table, as EdS stated.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

Meysamsh, The question isn't 'are there any microbes', you will always have them in systems. If you can limit their numbers and limit the nutrients then they are not a huge problem. The serious attack that you see is along welds so it calls out to me as primarily a weld issue. Fix the welding and treat the water, then you will just have some surface stains.
Now here is a tip, microbes will always grow preferentially along welds. The welds have a different microstructure and even in good cases have some secondary phases, this results in micro-currents. Under normal conditions these currents are below the levels that causes corrosion but they are attractive to microbes.
This is why in general 304 and 316 are considered to have virtually no resistance to MIC. It because of how week the corrosion resistance of the welds is.

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P.E. Metallurgy, consulting work welcomed

 

[0707]

Meysamsh

SSTP304 cannot be used in potable water with 130 ppm chlorides storage tank. The solution is to change the storage tank material, you can paint, you can cladding, but soon or later you have to change your tank.

luis

 

[Meysamsh]

@Edstainless
Thanks for your great answer.

 

[Meysamsh]

@0707
We want to apply PTFE lining inside the tank

 

[0707]

Meysamsh

I hope you will be successeful.

luis

 

[EdStainless]

With any coating system the three most important items are:
1, Surface preparation
2. Surface preparation
3. Coating application

You might also look at the two and three layer 'paint' systems used inside of potable water towers.
I am not enamored with PTFE linings, getting good adhesion is a real issue without shop baked treatments.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

Contact Belzona if you want the best coating system.

 

[0707]

Belzona is a well known coating system.

luis

 

[EdStainless]

TBE, one option. But theirs pale when compared to 3 layer systems designed for continuous immersion service. I have seen Belzona and a German epoxy system used in waterboxed and such and they do very well. But for the inside of a tank I would look for a more specialized material.

You also have to be cautious coating SS. Be aware that any failure of the coating (blister, disbond, holiday) will likely lead to rapid localized corrosion of the SS.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I should have said "has" coatings systems. Belzona has a full product range including specialized tank coatings for continuous immersion. They have a rubber coating, Belzona 2121, that I think would be ideal for tank interiors as it resists chipping and cracking. Of course you may find their price unreasonable as you pay a premium for the one stop shop. There are many other rubber tank membrane systems.

I see that this is for a potable water application so that will of course limit your choice of materials.

 

[Meysamsh]

I'm so grateful for your great advices. I'll be considered them