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topic 11234

Iron deposits on S/S?


I recently purchased a 316L S/S vessel. After passivation I ran typical batches and a black surface appeared (that proves to be magnetic material). I know this was not a raw material problem. Is there a possibility that the vessel was not cleaned properly before passivation and therefor the passivation did not perform and during my product runs 'drew' out some surface iron?

Ursula Bischof
- Greenville, South Carolina


It's hard to say from this distance; but it is true that good alkaline cleaning to remove soils and oils is absolutely necessary before passivation if the passivation is to work.

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


Don't forget that stainless steel is still steel, an alloy containing iron. Stainless contains varying amounts of chrome and nickel to give it its resistance to corrosion. If you've run materials in the tank that attack the tank walls you can certainly affect the alloy at the surface, including causing intergranular cracking and corrosion in the tank walls. And yes, this sort of thing can leave material behind that will be attracted to a magnet. Out of curiosity, what type of materials do you run in these tanks?

Jeff Watson
Jeff Watson
- Pearland, Texas

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