Orange Stains on SS and Defect?

[kluparello]

I have all new brewing equipment and CIPed with sodium hydroxide then passivated with Nitric acid, then rinsed. All tanks are looking good except one. It had a small defect near the bottom of the cone (maybe metal shavings?) After passivation some orange stains remained? What could have caused this and what should I do?

[UnFermentable]

The top picture looks like the tank shipped with the racking arm or other parts inside the tank. I have seen this on new equipment a few times. If they don't properly wrap all the individual pieces then something stainless can rub and cause this "electro pencil" effect during shipment. You can 600 grit this down if it seems rough, but if it is still smooth to the touch, I wouldn't worry too much about it. You would need to re-passivate after buffing it.

The bottom picture looks like manufacturing oil to me. It should be removeable by chemical cleaning, but perhaps your solutions were not hot enough or high enough concentration to remove it. You can also try something like toluene, acetone, or Methyl Ethyl Ketone to spot clean, which will usually tell you right away if it is an oil based substance. Otherwise, the brownish color would indicate iron oxide (rust), and would mean you had an inadequate passivation process. Re-run both cleaning cycle and passivation at higher concentration, longer time, and higher temperatures. Just my $0.02!

[Rickdude]

Machine oil makes sense. Caustic doesn't do a very good job on heavy hydrocarbons, so I'd try a manual detergent and some scrubbing. A formulated CIP detergent would probably also work, but if you're using caustic I wouldn't bring in something special for this single use.

Rick