Passivation - Stainless Steel

Stainless steels are not completely impervious to rusting. One common mode of corrosion in corrosion-resistant steel is when small spots on the surface begin to rust because grain boundaries or embedded bits of foreign matter (such as grinding swarf) allow water molecules to oxidize some of the iron in those spots. Passivation is a post-fabrication method of maximizing the inherent corrosion resistance of the stainless alloy from which the workpiece was produced.

Stainless steel filters passivated for better corrosion protection