Corrosion on Stainless steel instalation 1

[Josef M.]

I'm working on a project that involves using a huge carbon steel buffer tank in a stainless steel piping system (close water chiller system). I'm concerned about potential corrosion issues that could arise from this combination.

Has anyone here had experience with a similar setup? If so, what precautions or measures did you take to prevent corrosion and ensure the system's longevity?

What measures should we take to avoid corrosion on a 30 year lifespan? (coat the inside, air vent valves, corrions inhibitors,...)

Thanks

 

[EdStainless]

Are you worried about inside or outside?
What is the fluid? Water isn't very specific.
pH, conductivity, temperature, treatments, etc.

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[Josef M.]

I’m particularly concerned about the inside of the tank. Since it’s a buffer tank, most of the water will be stagnant, and when it flows, it could transport small particles from the carbon steel tank. The fluid is potable water. The pH should be around 6. Temperatures of the fluid are from 17 to 27ºC.

 

[EdStainless]

So there really are two concerns.
First simply having the CS tank last ignoring the SS.
This will likely require a very high-quality internal coating.
Look at the three-layer systems that are used in water towers.
There is a risk of accelerated corrosion of the CS near where it joins the SS.
A good internal coating will alleviate this risk also.
Biological control will be a paramount issue.
This can accelerate corrosion of both metals.

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[bimr]

What is the definition of "huge tank? Why don't you make the cs tank form SS?

If the entire system is SS and closed, you shouldn't be worried about corrosion.

 

[TugboatEng]

It says the water will be stagnant. In this condition, stainless steel may pit and leak faster than a carbon steel tank. This is especially true if any mud or debris accumulates on the bottom.

 

[mfgenggear]

No idea guesing
Coating would be my guess

 

[shvet]

close water chiller system

https://a.co/d/7haRypN

What is the definition of "huge tank? Why don't you make the cs tank form SS?

@Josef M.
I join to bimr's question. What does it mean? What is a reason to install a 'huge tanks' for chilled water loop bearing in mind that you have (I suppose) an unlimited source of steam condensate?

 

[Josef M.]

When I see huge is in comparing to the instalation, around 25000L. Maybe I should not refer to them as huge.
The water will not be stagnant, there will be pumps for circulation. But in the buffer thank theres always a bit more stillness, thats what I meant.
Do you think filters and air vents would help decreasing the corrosion?

 

[EdStainless]

Vent or don't vent, in the long run it doesn't matter.
What matters is your biological control and corrosion inhibitors.
If you can't keep the water clean and non-corrosive, then you are bound to fail.
I would coat the CS.

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[Josef M.]

Thank you very much. I will probably coat the inside.
By the way, could you explain the chemical reaction and the process that would happen in corrosion? For example, would the carbon steel corrode under normal conditions, causing the water to become more acidic, and then leading to more corrosion? Could the stainless steel contribute to increasing corrosion, even if they are separated at the joints? Is the corrosion rate the same as if the entire installation were made of carbon steel? If theres no oxygen why should we worry?

 

[EdStainless]

While low oxygen may help the CS it hurts the SS as SS needs oxygen to maintain passivation.
Yes, more metals and lower pH will encourage more corrosion.
Maintaining true separation between the SS and CS will be quite a feat.
And if the water has high enough conductivity, then you will still have some galvanic effects.
Any sediment or biological growth will cause significant amounts of corrosion on either material.
The difference is that in CS you will get general corrosion usually.
While in SS it will be very localized pitting.
99.9% of the surface will be fine and you will have a few through wall holes.

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[mfgenggear]

From an engineering aspect I seen different types of coating for different types of environments. I suggested coating the inside of both tanks, I had a relative do this as a business. For very corrosive environments. Bare metal. SS or carbon based is just not a reliable setup.
The minerals, and ther contaminates as stated, does a lot of damage. Homes with high mineral and low or high pH values.
If no corrective measures, chews up a bunch of valves, facets, and metal pipes, when the coating wears out.

 

[Josef M.]

Thank you fol all the commments. Some more question please.
Is an anti-rust painting enough for the coating?
Do you guys know if theres any corrosion inhibitors to add to water? We already will have air purge, ph control and corrision measure devices for the maintenance team.
Other thing, do you think that the system will be contminated by the carbon steel? or this term doesnt make sense?

 

[mfgenggear]

OP
Contact different companies that specialist
In coating for different environments.
Carbon steel will or can corrode 24 hours,
There fore can contaminate the entire system.

 

[EdStainless]

What other metals are in the system?
Any Cu, brass, or Al?
Finding an inhibitor for a mixed system is tricky.
Talk to experts.
The coatings for continuous exposure are usually three component systems.
A primer (often reactive to etch the steel) sometimes with lots of Zn in it to help protect the steel, then a protection layer, and a finish seal coat on the top.
And yes if the CS corrodes you will have Fe oxides everywhere in the system.
This can foul all sorts of things throughout the system.

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