Material of Construction for hot brine (NaCl) solution

[rollingstein]

What's a suitable Material of construction for equipment handling hot brine (NaCl) solutions? Temperature is max approx. 100 C.

I'm conflicted if or not SS316 works? I looked up an old handbook and it reported a corrosion rate of 0.2 mm/year (@80 C) which seems not too bad to me. But I've heard others say that SS316 won't work.

Any thoughts?

 

[Bystander]

Three hundred series are subject to stress corrosion cracking. What pressures? How heavy are you planning on building?

 

[rollingstein]

Three hundred series are subject to stress corrosion cracking. What pressures? How heavy are you planning on building?

Thanks! This is supposed to be a multi effect evaporator for recycling water from a waste NaCl solution stream. The downstream effects should be under vacuum and the very first effect at or close to atmospheric.

Basically, the Temperature / Pressure parameters can float so long as I get a feasible evaporator design. The goal is to see if I can avoid using an exotic (read expensive) allow. Unless there is a more suitable alloy yet not terribly expensive.

The feed load is around 1000 Litres-per-hour so it won't be very huge but I guess not a tiny lab unit either.

The life doesn't have to be fantastically long. A useful service life of 3-5 years would serve.

 

[Bystander]

Corrosion rates at those conditions should be pretty reasonable matches to what you'll find in handbooks. Have you considered copper? People used to clad wooden hulls with copper and I don't recall that it required replacement. Which does bring to mind the electrochemical angle --- you might want to look at some sort of anodic protection system --- if you can tolerate zinc or other metals in your brine.

 

[Danger]

How about just any basic cheap metal like aluminum or regular steel with a thin ceramic coating?

 

[rollingstein]

Corrosion rates at those conditions should be pretty reasonable matches to what you'll find in handbooks. Have you considered copper? People used to clad wooden hulls with copper and I don't recall that it required replacement. Which does bring to mind the electrochemical angle --- you might want to look at some sort of anodic protection system --- if you can tolerate zinc or other metals in your brine.

Zinc contamination is totally ok. The salt will probably go to a landfill anyways. Or some low cost, low purity market.

Copper is interesting. I will look. How'd Copper compare against SS316 for price (fabrication + material costs). I don't see much plant equipment fabricated in Copper any more (outside of distillaries) so finding a vendor who makes multi effect evaporators in copper might be harder.

 

[Bystander]

That's probably the big determinant --- vendor experience with the material of interest.

 

[rollingstein]

How about just any basic cheap metal like aluminum or regular steel with a thin ceramic coating?

Aluminium would be good. But is it any better at NaCl resistance than SS316?

Steel with a ceramic coating sounds exotic to me. Do you know if this is a commonly used fabrication material for process equipment?

 

[Bystander]

Aluminum and hot brine? Have you got any pH measurements on the brine you're evaporating? You could try a sample in a cheap aluminum pan on a hot plate.
It might be tough to maintain integrity of ceramic coatings for what is presumably going to be a sheet metal fabrication. There are epoxy coatings which might be rated for the temperatures you're running.

 

[rollingstein]

Aluminum and hot brine? Have you got any pH measurements on the brine you're evaporating? You could try a sample in a cheap aluminum pan on a hot plate.
It might be tough to maintain integrity of ceramic coatings for what is presumably going to be a sheet metal fabrication. There are epoxy coatings which might be rated for the temperatures you're running.

Don't have a pH measurement but I could take some. I'm assuming it will be very close to neutral. i.e. pH=7.0.

I agree about the difficulties with ceramic. An epoxy coat is a good idea. For one epoxy sounds less brittle than ceramic. I'm suspecting ceramic being finicky like glass coats on MS. Also, if it is a spray-on ceramic / rubberized layer then a coat post fabrication might be not too difficult.

The worry I have is whether it can be a good heat transfer surface. After all, we need to evaporate stuff.

 

[Bystander]

Long as you don't trowel it on too thickly it shouldn't degrade performance too much.

"Dragonskin." Copyright/trademark/something --- and I can't get my hands on any of the "propaganda" sheets at the moment --- supposed to be magical for some purposes for gun nuts like me. Haven't really looked at it, because I don't want to "improve" finishes on my collection. Probably an epoxy, but can't be sure.

 

[Danger]

Aluminium would be good. But is it any better at NaCl resistance than SS316?

I actually meant that the ceramic coating would be applied to that or whatever other metal you choose. Since you mentioned that the device would be small, I thought that perhaps you could just pour in a ceramic slurry, slosh it around, pour it out, and then bake the remainder onto the surface.

The worry I have is whether it can be a good heat transfer surface. After all, we need to evaporate stuff.

That could be an issue. I hadn't thought of that aspect. I was just thinking that it seems pretty impervious to many chemicals, and salt is a fairly innocuous one in that regard.

"Dragonskin." Copyright/trademark/something --- and I can't get my hands on any of the "propaganda" sheets at the moment

Is this the stuff that you mean? http://www.smooth-on.com/Silicone-Rubber-an/c2_1115_1129/index.html
There is also a line of body armour with the same name, which perhaps uses the same substance (although it claims to contain titanium as well as silicone, and it has a lot of negative reviews from soldiers who have used it).

Frankly, I don't see why something that will be restricted to 100° C needs to be made of metal at all. Why not something like Torlon or structural nylon?

 

[Astronuc]

What's a suitable Material of construction for equipment handling hot brine (NaCl) solutions? Temperature is max approx. 100 C.

I'm conflicted if or not SS316 works? I looked up an old handbook and it reported a corrosion rate of 0.2 mm/year (@80 C) which seems not too bad to me. But I've heard others say that SS316 won't work.

Any thoughts?

316/316L would be better than 304/304L, but these days, 316 has been superseded by 6-7 Mo SS, and higher Ni content, like 254 SMO or 654 SMO, or AL-6XN, and 4-5 MO stainless steel like 904L.

There are some other considerations depending on pH, O-content, Fe-content, and so on.
http://www.stainless-steel-world.net/pdf/11004.pdf
http://products.asminternational.org/fach/data/fullDisplay.do?database=faco&record=386&search=
http://www.nickelinstitute.org/~/Media/Files/TechnicalLiterature/GuidelinesforNickelStainlessSteelsforMarineEnvironmentsNaturalWatersandBrines_11003_.pdf

Consider also - https://www.atimetals.com/news/corrosion-conference/Documents/CSC09-pdfs/PAPER_3A1_HOUSER.pdf