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Rust in stainless still


glisade

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We have an old stainless steel jacketed tank we bought some time ago that has some rust in it. We're hoping to use it as the base of a pot still. I've tried Bar Keeper's Friend, and a rust removing gel and both have helped but I still can't remove all the rust. The photo shows the bottom of the pot.

First, any other ideas on removing the rust?

Second, is it usable? What would happen it we ran it with the rust in it?

Thanks,

Ron

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+1 to Five Star Acid #5. I've had some devilishly difficult rusting issues on stainless barrels and after cleaning with strong basic caustic (we use NaOH) the Five Star #5 passivated (repassivated?) and prevented any further rusting.

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  • 2 weeks later...

Totally agree with Rob! Polishing it will be quite easily than passivation machine :)

Penny

pennyjiang@zjdayu.com

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polishing vs fixing the problem. Polishing will make it go away....butttt...............

The problem with polishing is that you put the rust all over the stainless you are trying to get it of of.

The reason the rust is there is a couple reasons...

1. some one let bleach set in the still, bleach eat in to stainless 304

2. you have cheap stainless and the steel in the stainless is just rusting

3. **** my pick*** a piece of steel touched and scratced the stainless, you now have steel inbedded in your stainless. The steel is rusting in the stainless.

If you have #3 and you try to polish it you will just spread the steel around and it will over time rust even more, EVERYWHERE. I will do this because you are rubbing it all over.

If you have #1, #2 and passivate the problem,it will remove the problem. Or a mild acid bath.

FYI to clean that up with my machine would take about 3-4 minutes.

If you need help please just ask.

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There is a business here that will dip rusty steel into and a solution that consumes the rust and leaves a clean surface. In Portland they are called American Metal Cleaning. They may tell you what their solution is if it's not proprietary. (though it probably is) Or you can send it to them I imagine. An old Ducati tank was $68. I've had them clean things that were heavily rusted and came back with no rust. As far as I can tell it eats only the rust and doesn't etch the steel. I agree that you don't want to spread the existing rust around and need something that will lift the rust away.

good luck

cp

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Any welding shop that does sanitary stainless welding should be able to passivate the stainless for you. There are some do-it yourself techniques worth trying.

I recommend you passivate the stainless after any grinding or heavy buffing. The rust resistance of stainless steel is dependent on the layer of chromium oxide on the surface. Usually it will form naturally but sometimes it doesn't. By passivating you help the chromium oxide layer form.

As has already been mentioned avoid embedding plain steel in the stainless steel. A plain steel wire brush or steel wool will leave microscopic pieces of steel embedded in the surface of the stainless steel. These will create gaps in the chromium oxide layer and rust will form. Do not use a stainless steel brush if the brush has EVER been used on plain steel. The brush will have steel particles embedded in the bristles which can transfer to the stainless surface. The same warning applies to the non metallic abrasives like the Scotch Brite (3M) pads, never use a pad on stainless steel if it has ever been used on plain steel.

The simplest and safest passivation is a strong citric acid bath. Almost as safe and much better removing rust is hot phosphoric acid (the commercial rust remover Navel Jelly is 10 to 30 percent phosphoric acid and a touch of sulfuric acid in a water based gel). Hot sodium hydroxide solution is next. The downright dangerous options are Hot concentrated Nitric acid and Hydrofluoric acid. The Hot Nitric Acid is pleasant compared to the Hydrofluoric acid (HF). A small amount of hot concentrated Nitric Acid spilled on skin will lead to a bad burn. A small amount of HF spilled on skin can be fatal.

A friend is a chemist at a pharmaceutical company. The production and maintenance staff will use Hot Sodium Hydroxide solution in the production system for passivation but if that doesn't work the part of the plant is evacuated and a special team comes in to use hot concentrated nitric acid.

I would at least try soaking in food grade phosphoric acid (or even Navel Jelly)

The Rust Store (http://www.theruststore.com/CitriSurf-Copper-Sulfate-Passivation-Test-Kit-P220.aspx) sells a kit to test passivation. They also have a one step rust removal and citric acid based passivation gel (http://www.theruststore.com/CitriSurf-2310-Spray-Gel-P330.aspx). I plan to use this product the next time I need to clean and passivate stainless.

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  • 6 years later...
On 9/11/2015 at 8:26 PM, EdInNH said:

The production and maintenance staff will use Hot Sodium Hydroxide solution in the production system for passivation but if that doesn't work the part of the plant is evacuated and a special team comes in to use hot concentrated nitric acid.
 

I want to know more about this Special Ops - Chemical Team.

aside from that, great info @EdInNH thank you

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