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Corrosion Issue

09/17/2010 11:57 AM

We are using a sodium chloride brine solution (12.6%) to separate materials in a sink float system. We are designing a new system to move from the prototype small scale set-up to a production model. there is a screw conveyor in the bottom of the tank to remove the heavies from the tank.

What type of stainless or other materials would handle the corrosion of the brine solution? Coatings?

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#1

Re: Corrosion Issue

09/17/2010 1:24 PM

A little more detail wouldn't hurt. Quality of answer=quality of question.

Tanks? piping? pumps? etc?size?

316L or higher will give outstanding service.

PVC, polypropylene, PET, TFE or just about any plastic will survive.

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#2
In reply to #1

Re: Corrosion Issue

09/17/2010 1:30 PM

My question is in regard to the tank and screw. The tank is approx. 8' long, 2' wide and 3 1/2' deep. the screw conveyor is 9" dia.

The data that i have read shows 2205 being superior to 316L. The local Fab company has consulted their metals supplier and they are concerened that even the 2205 may not be good at the 12.6% concentration level.

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#3
In reply to #2

Re: Corrosion Issue

09/17/2010 1:39 PM

It's all about cost.

Next up is titanium, then Hasteloy C-276.

Beyond that, I don't know.

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#4
In reply to #2

Re: Corrosion Issue

09/17/2010 1:40 PM

2205 should be fine. We use it on a NaCl solution for pumps that can't tolerate any corrosion, and it might even be overkill vs. 316L. In fact I will shortly having a customer testig 2205 and 316L side by side on the same equipment. Then we'll know for sure.

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#11
In reply to #2

Re: Corrosion Issue

09/18/2010 6:16 AM

As long as the brine solution is kept at ambiant temperatures and there are no chemical reactions happening to release free Chlorine, 316L will be OK. Free Chlorine is your ennemy here. 316L will be OK for the brine even at high concentration provided the temperature are kept below 50° C.

(Experience in a textile Dyehouse)

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#5

Re: Corrosion Issue

09/17/2010 5:23 PM

Sending the items to a gold plating shop might help, perhaps?

Yahlasit

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#6

Re: Corrosion Issue

09/17/2010 11:11 PM

Coatings are a bad idea because they'll just get eroded over time by the solids being conveyed and then you'll start getting pitting corrosion where the coating has worn through.

Look at one of the Cupronickel/monel alloys. they are very good for both brine service AND are very erosion resistant. Beyond that 2507 or 2205 are decent, then there is Alloy 625 which is one of the most corrosion resistant/Chloride stress cracking resistant alloys out there, C-276 is only slightly worse. 316 (and virtually all of the 300 series) will undergo chloride stress cracking, especially in the welds of the flighting and I would not recommend. BTW, welding 625 is much easier than welding either of the duplex stainlesses. Welding Duplex stainlesses is a PITA. It can be done, and it is done every day, but it often is difficult to get a good metallurgically sound joint that does not have long term strength or corrosion issues. It is a skill that is often beyond every day welders.

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#7
In reply to #6

Re: Corrosion Issue

09/18/2010 12:20 AM

How about rubber lining? Soft rubber is better than hard.

If rubber lining is not in easy access and not viable due to quantity, FRP/epoxy lining may also be considered.

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#8
In reply to #7

Re: Corrosion Issue

09/18/2010 12:49 AM

Go back to sleep.

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#10
In reply to #6

Re: Corrosion Issue

09/18/2010 5:25 AM

That's a good point regarding welding of duplex. However, it could be a good material for the screw, depending on the nature of the solids, as it is easily hardened to about 300 Brinell.

I expect Alloy 625 is quite expensive compared to the others. I'm in two minds whether there is any need to go beyond 316L for 12.6% NaCl, so duplex should be safe enough.

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#9

Re: Corrosion Issue

09/18/2010 2:20 AM

Check this.

By the way, what are the heavies? More information would not only be nice, but would elicit a greater amount of answer material.

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#14
In reply to #9

Re: Corrosion Issue

09/21/2010 8:22 AM

The heavies is a combination of plastic, glass, metal and copper wire.

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#15
In reply to #14

Re: Corrosion Issue

09/21/2010 9:09 AM

sounds fairly abrasive, may also tend to jam a lot too.

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#12

Re: Corrosion Issue

09/18/2010 11:11 AM

Austenitic Stainless Steel (AISI 316 or 316L) Austenitic Stainless Steel (AISI 347 or 321)

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#13

Re: Corrosion Issue

09/21/2010 3:05 AM

Plastics. Virtually all of them.

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