closed airtight container and corrosion 1

[Canada580]

Hello,

I would think the corrosion rate is very low in a closed airtight galvanized steel container containing liquid mix (40% water and 60% antifreeze (Ethylene Glycol)). The container can have 50% air and 50% the liquid mix or so. The tank size is about one meter cube and this needs to be placed outdoor in cold and warm weather. I would think the corrosion rate will slow down extremely once the oxygen in the close contained is completely used. But I am not sure and feels the antifreeze may affect the corrosion rate. We are thinking the galvanized container to last about 50 years or so. Will someone who knows better on corrosion control can comment and add their opinion on this please? Thank you.

 

[TugboatEng]

You need to treat the water portion with corrosion inhibitors. Sodium nitrite or carboxylic acid are standard fare. The latter is considered a long life inhibitors. These are common treatments for automotive treatments. Standard life is 10 years but that's at elevated temperatures. I would expect much longer at ambient.

One problem is that the inhibitors work best on the submerged metal so you may want to consider a small expansion tank above the unit fabricated from corrosion resistant materials.

You shouldn't need to galvanize the tank.

 

[Canada580]

Thanks a lot TugboatEng. We use to galvanize all the steel we use in our application.
Two small questions:

1. What will be the mix ratio of carboxylic acid and water in general? in PPM ?
2. Does antifreeze will have any role in accelerating corrosion in the closed container ?

Thanks

 

[TugboatEng]

Anti-freeze, glycols, are not corrosive.

For the older generation of treatment, 3000 ppm sodium nitrite was the norm for an initial dose.

The newer carboxylate based systems generally go off specific gravity so I don't know a concentration off the top of my head.

These are commercially available options.

https://www.chevronlubricants.com/en_us/home/products/delo-xli-corrosion-inhibitor-concentrate.html

 

[SJones]

The problem that you face is that the glycol will degrade with time and temperature to produce acidic components that will attack the galvanising. Probably, for that reason, industry galvanising associations do not recommend galvanised steel for storage of aqueous alcohols. If you are regularly changing out the contents, and can keep an eye on the pH so that it stays above 6, you might have a chance.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

So is there a loop that this fluid circulates through?
Are there any other metals in that loop?
You need consider everything that the fluid touches.
And even though the sheet steel is galvanized what about your welds?
Will you post-weld galv?
If the welds will be left bare then all of the steel should be bare.
If only the welds are bare then you risk that any corrosion will be concentrated there.
What about venting, the air will heat and expand in the days so will there be a pressure relief.
And then when cooling at nights it will want to suck in more fresh air.
The biggest risk is in the headspace, especially just above the fluid level.


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P.E. Metallurgy, consulting work welcomed

 

[Canada580]

Thanks EdStainless. Please see my below comments in red on your questions: will you please comment further

So is there a loop that this fluid circulates through? No the same fluid will be there all the time.
Are there any other metals in that loop? No
You need consider everything that the fluid touches.
And even though the sheet steel is galvanized what about your welds?
Will you post-weld galv? Galvanization is the last step in fabrication so the welds are also galvanized.
If the welds will be left bare then all of the steel should be bare.
If only the welds are bare then you risk that any corrosion will be concentrated there.
What about venting, the air will heat and expand in the days so will there be a pressure relief. its airtight container and so no venting.
And then when cooling at nights it will want to suck in more fresh air. airtight container.
The biggest risk is in the headspace, especially just above the fluid level. why ?

 

[TugboatEng]

For you last question, corrosion inhibitors for water are film forming type. The surfaces require exposure for protection. This means the surfaces need to be clean and immersed.

Add to that, evaporation in the head space concentrates corrosive substances.

Thirdly, any galvanic protection is ineffective in the headspace.

 

[LittleInch]

Anything made of steel, galvanised or not, that can last 50 YEARS, is never going to guaranteed by anyone, or if it is then it is worthless.

what is this thing? Will the level rise and fall within the chamber - sounds like an expansion tank to me -

What sort of inspection can you do on it?

How often will the fluid be changed?

Can't you make it out of plastic? or GRE or something that doesn't corrode like Duplex. If it's going to last 50 years then it needs to be bullet proof. Galvanised steel isn't that.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

Either this is small or the sides are very thick. The pressure change will be large.
And how will it be sealed? A pipe plug would not be good enough to prevent breathing.
Find someone that will blow a plastic liner into your steel box.
And then allow it to breath.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[stevenal]

A sealed airtight vessel without a relief valve is a bomb. Even if built to withstand normal temperature/pressure changes, please consider the fire fighters who may encounter this thing. I expect there are code requirements regarding this as well.

 

[TugboatEng]

What exactly is the purpose of the anti-freeze water mix?

 

[Canada580]

Hi TugboatEng.

Its just a liquid container which is not allowed to freeze and can be use in vibration control of structure.

 

[TugboatEng]

Vibration control? This is important. Are you looking for a specific mass or do you need a specific viscosity. If you need mass look to concrete. If you need viscosity, there are plenty of non-corrosive fluids to look in to.