`New England Aquarium exterior panel corrosion`

Passivation defeated by post-passivation mechanical abrasion. Mill-passivated 304 panels were ground to create fish-scale texture, which removed the protective chrome oxide. In marine environment (Boston Harbor chlorides), the oxide could not reform. Rust appeared along grinding marks and along bumper scrapes at the loading dock. Tom tested citric acid and Diet Coke (phosphoric acid) as environmentally acceptable cleaning agents.

If you want to go over to the New England Aquarium — how many people have been to the aquarium? What's the outside made out of? Stainless steel. What was the specification? They wanted to make the outside look like fish scales, and they were going to use 304 stainless panels, and they were to be passivated. I read the spec. Passivation means in the mill they took the coils of steel before they had been stamped into fish scales, and they passed them through a bath of nitric acid — about a 5 or 10% solution, not concentrated. It's an oxidizing acid. You clean the stainless steel in the nitric, but you also oxidize it to form the protective oxide. It's now passivated. You can passivate 304 stainless in 15 minutes in nitric acid.