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topic 2088

Flash rust in wash tanks


(1998)

Q. We have a new finishing system installed in our facility.

The three-stage washer in this system has three mild steel wash tanks. All three tanks arrived at our facility with flash rust inside of them. After installing the washer, we have tried a couple of ways of removing this rust.

One was to clean the tanks out and over flow them until the water is clean. This attempt was moderately successful. The second attempt was to add a small amount of muriatic acid to each tank and run the washer tank spray pump of a short time to clean the rust. This worked for a few days before the flash rust returned. This finishing line is not in production yet so we would like to know the best way to clean these tanks of rust. We want to have the water in these tanks as clean as possible before we start regular production using this system.

L. Rivers
- Columbia, South Carolina


(1998)

A. Is it your tanks or your enclosure that is flash rusting? Out of what material is the enclosure made? While I am still a baby in this area, I believe that it is in the drying of the steel that most of the flash rusting occurs. If you can keep it wet, it should not rust. Easy to say, and hard to do when your not in production, or shut down for the night! When we clean our mild steel parts, we rinse them with a slightly (0.05% or so) acidic (phosphoric) rinse, this seems to keep our parts from flashing, but may interfere with the chemistry you plan to use during production. Hope that this helps more than it confuses!

Kelly Jones Draper


(1998)

A. Flash rust is going to be present on the carbon steel tanks.

What is your chemical supplier saying about your problem?

The chemical supplier will play a key role, or should be playing a key role in helping you understand the issue. If the chemical supplier has told you not to worry about it, it is possibly good advise.

I would urge you not to use muriatic acid to clean the tanks again. If your do not have inhibitors in the acid solution the rust can actually get worse.

When you add the chemicals to the baths using chemicals the rust in these baths and the housing above will decrease. The tank and housing of the rinse station will have reduced rust after the carry over of chemicals occurs.

If you have verified, note I said verified, that the rust is going to create a quality problem your only choice is to coat the sheet metal.

Tyrone Caley
- Jefferson City, Missouri


(1998)

A. While I am seeing a number of polypropylene washers and phosphating lines these days, and some quite cool ones built of stainless frames and heavy clear vinyl curtains, such equipment has traditionally been mild steel and has proven satisfactory in years of use, so I agree with Tyrone.

If it is alkaline-based washer chemistry, the tanks will not rust in service. In fact a very simple, and somewhat effective temporary rustproofing that some finishing shops employ on their work-in-process is to simply dip the steel part in a hot alkaline tank and let it dry on.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1998)

A. Ted's comment is particularly true if you use a heavily silicated hot cleaner. The silicate forms a poor man's ceramic coating that is very difficult to get off without blasting or use of fluorides.

A rust remover alkaline cleaner would be a lot better than HCl, but a lot slower.

You might want to use Naval Jelly [linked by editor to product info at Amazon] which will give the steel a poor man's phosphate coating.

James Watts
- Navarre, Florida


(2001)

Q. I have treated the interior of a snowmobile gas tank with Naval Jelly to remove heavy rust. The rust was converted to a black iron residue that remains lightly adhered to the surface. I have since filled the tank with water to figure out the next step.

What can I treat the reduced iron residue with to dissolve it into a solution that I can discard? I can't have any foreign materials floating in the gasoline mixture that will contaminate the carburetor.

Michael Gleason
- Red Wing, Minnesota, USA



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