What is passivation?

The word passivation can have different meanings.

It can refer to the process when a stainless steel spontaneously forms a protective oxide layer in contact with oxygen. Passivation can also mean cleaning a surface from substances that can create corrosion, e.g. iron particles. When we at Calamo talk about passivation, we refer to a treatment with light acid (oxidizing agent) to improve the protective oxide layer.

 

If you perform a mechanical polishing or grinding on the stainless steel, the surface becomes active and loses its passive properties. To regain the corrosion protection, you need to recreate the passive surface. If this is allowed to occur spontaneously with the presence of foreign particles on the surface, these will also remain in the passive layer. This can provide less protection against corrosion than if you create the oxide layer through a controlled process.

 

The different standards for passivation have, to some extent, varying views on what passivation means.

According to ASTM A380, cleaning, descaling and removing welding oxides is not passivation, but this may be necessary to achieve a satisfactory result.

ASTM A967 states that a pickled surface that is free of scale, iron and other foreign substances does not need further treatment to be considered passivated.

ASTM B912-02 as well as SS-EN ISO 15730 state electropolishing as a form of passivation.

 

Simplified, one could say that the measures taken to protect a stainless steel surface from corroding through a protective oxide layer are passivation.

 

If you want to know more about passivation or have questions about the different standards, contact our sales department at sales@calamo.se