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Ted Mooney, P.E. RET
Pine Beach, NJ

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Removing rust from 303 SS cyclones

I have several large cyclones used to collect aluminum powder. They are 303SS. At least two of the cyclones have rust on some of the internal surfaces. This is out of my area of expertise, but I believe the rust developed from many years of aluminum powder scouring the cyclone surface, exposing Fe.

I'm planning on passivating the cyclones. I'm thinking of utilizing a citrus based gel, due to the size of the cyclones and environmental constraints. Prior to passivating, I'd like to remove the rust, aluminum powder, and any other contaminates from the surfaces. I'm considering mechanical cleaning with abrasive discs, followed by a water rinse. Silicon carbide (available in coarse and super fine grades) and aluminum oxide (available in various grades) are being considered. Is either acceptable, or is one better than the other? Any insights are greatly appreciated!

There are several possibilities as to the cause of the problem, but the solution should not be too difficult.As you know, 303 is a high sulfur free machining grade of stainless steel, so what you MAY be seeing is sulfides rather than rust. It is, however, quite possible that you have developed rust over the years. You can easily test for this.

If you are going to abrade the surface you could use Scotchbrite® pads quite safely.

Once you have determined that it is in fact rust, there are jelled citric products on the market that will both remove the rust and re-passivate the surface of the steel. If it turns out to be sulfides there are other ways to handle this.

If you call us maybe we can help you. We are in Illinois, also.

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