Passivation

Passivation is an essential finishing step for stainless steel components that ensures long-term corrosion resistance by removing free iron contamination introduced during fabrication, cutting, welding, or machining. During these operations, microscopic iron particles from tools and dies embed themselves in the stainless surface; these free iron particles corrosively corrode in wet environments, initiating rust even though the surrounding stainless is protected.

Passivation employs nitric acid (per ASTM A967) or citric acid (per AMS 2700) to chemically dissolve embedded iron and allow the naturally occurring chromium oxide passive layer to fully develop and restore corrosion resistance. The process is quick, taking only 15 to 30 minutes, and is cost-effective enough to justify for virtually all stainless fabrications intended for healthcare, food processing, marine, or outdoor service.

Properly passivated stainless steel maintains its corrosion resistance indefinitely, while untreated stainless may develop rust spots months or years after fabrication.