[Porchdog]

Pickling gel works pretty well. You probably want to sand or polish a bit first. Try to get the visible rust off. Grey scotchbrite works well.

It's also good to prep with a strong caustic - you want to start with the surface as clean as possible. a bit of heat also helps - like 100°F.

If the pickling gel is hard to find you can use citric acid or nitric acid - but a welding store should have the pickling gel.

Rinse thoroughly with distilled water.

Stainless is protected by a layer of chromium oxide. You want to strip off the oxide and any contaminants, then allow a new oxide layer to form in air.