Natural Corrosion Resistance of Metals
When metals are exposed to oxygen in the atmosphere, they form an oxide layer on their surfaces. Some of these oxides are brittle and flake away, exposing more material to the atmosphere. In other metals however, this oxide layer is strong and impermeable, forming a protective layer that protects the material below.
Processes to Reduce or Prevent Corrosion
There are a number of methods that can be used to prevent corrosion.
- Replace with a more resistant material
- Painting / coating
- Insulate dissimilar metals
- Use sacrificial anodes
The passivation of stainless steel is a process performed to make a surface passive, i.e., a surface film is created that causes the surface to lose its chemical reactivity. Stainless steel passivation unipotentializes the stainless steel with the oxygen absorbed by the metal surface, creating a monomolecular oxide film. Passivation can result in the very much-desired low corrosion rate of the metal.
The passivation of stainless steel is performed when free iron, oxide scale, rust, iron particles, metal chips or other nonvolatile deposits might adversely affect the metallurgical or sanitary condition or stability of the surface, the mechanical operation of a part, component or system, or contaminate the process fluid.
Passivation is performed on clean stainless steel, providing the surface has been thoroughly cleaned or descaled. Since the term “passivation” is used to describe distinctly different operations or processes relating to stainless steels, it is necessary to define precisely what is meant by passivation.