Answer
Passivation is a chemical treatment for stainless steel spiral rings (ASTM A380) that involves immersion in a nitric acid solution. This process removes 'tramp iron' from the surface of the ring that may have been embedded during the coiling or handling process. By removing this free iron, the acid promotes the formation of a dense, protective chromium-oxide layer. For 302 and 304 series rings used in food processing or medical equipment, passivation is essential to prevent surface rusting and pitting. Without it, the microscopic iron particles would oxidize (rust) in the presence of moisture, eventually leading to localized corrosion and potential failure of the ring. Passivation does not change the mechanical properties of the steel but is critical for its environmental durability.
