About Passivation

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. Steels containing more than 11% Chromium are capable of forming an invisible, inert or passive, self-repairing oxide film on their surface. However during handling and processing such as rolling, forming, machining, pressing, tumbling, and lapping, particles of iron, tool steel or abrasive particles may be embedded in or deposited on the surfaces of stainless steel components. If allowed to remain, these particles may cause corrosion of a stainless steel surface thereby adversely affecting the sanitary condition or mechanical operation of a part, component or system, or contaminating a process fluid.

Passivation, which consists of immersing stainless steel components in a solution of nitric or citric acid without oxidizing salts, will dissolve the imbedded iron and restore the original corrosion-resistant surface by forming a thin, transparent oxide film.

Passivation is also accomplished by electropolishing, an electrochemical process that is a “super passivator” of stainless steel and results in a more passive surface than the other methods mentioned above. For maximum corrosion resistance a combination of electropolishing and a nitric and /or citric acid treatment is recommended.


  • Improved stainless steel corrosion protection without plating.
  • Superior clean surface.
  • Eliminates iron contamination reactions with other materials.
  • No rust discoloration.
  • Surface prepared for priming and painting.


  • ASTM A 967, Chemical Passivation Treatments for Stainless Steel Components. We can meet both citric acid and nitric acid passivation procedures outlines in this spec.
  • ASTM A 380, Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment and Systems
  • AMS 2700 (replaced QQ-P-35), Passivation of Corrosion Resistant Steels
  • ASTM B 912, Passivation of Stainless Steels Using Electropolishing
  • We can passivate Austenitic (300 series) , and Ferritic / Martensitic (400 series) stainless steel alloys.
  • AMS C 5541 and MIL C 5541 .Passivation of aluminum by alodining.

Alodining / Alodizing

What is alodining?

Alodining is the chemical application of a protective chromate conversion coating on aluminum. The term Alodining has become a generic term for passivation conversion coating on aluminum materials, though in the strictest sense the term only refers to use of the specific Alodine product.

Benefits of alodining aluminum:

  1. It provides good corrosion protection un unpainted aluminum. It even protects when scratched. For example: alodined 2024 aluminum withstands salt spray 150-600 hours before forming white corrosion. Untreated 2024 corrodes in less than 24 hours.
  2. It provides an excellent electrically conductive surface. This helps to provide good electrical bonding in an airframe.
  3. Paint sticks to it extremely well. In some cases, it can substitute for primer.

Advantages of alodining compared to other coatings such as primer or anodizing:

  1. Adds no measurable weight.
  2. Does not alter the dimensions of parts (does not make holes smaller).
  3. Requires essentially no cleanup after application. Encourages treatment of all small parts as they are fabricated and installed.