Suncor Stainless Product Information Knowledgebase - Glossary
Technically, passivation is not cleaning but is a process of dipping fittings into an acid solution to rapidly form a chromium oxide on the surface of the material, creating a passive film that protects stainless from further oxidation (see PASSIVE FILM). In common commercial terms (meaning non-military and aerospace), passivating means cleaning to users, and the terms "passivating" and "cleaning" are used interchangeably. A wide range of cleaning methods using different mixtures containing nitric, phosphoric and other acids or simply exposing cleaned stainless fittings to air for a period of time will result in a "passivated" condition. For properly cleaned fittings, it is impossible to determine the method of cleaning or passivation that was used. AN/MS/NAS fittings sold by SUNCOR have been cleaned, descaled, and passivated to the applicable engineering specifications.
- PASSIVE FILM
The major characteristic of stainless is its ability to form a thin layer of protection called a "passive film" on its outside surface. This film results from a continual process of low-level oxidation, so oxygen from the atmosphere is needed for the passive film to exist. Once formed, it prevents further oxidation or corrosion from occurring. Even if chipped or scratched, a new passive film on stainless will form.
Removing surface impurities by using chemicals. Used mainly to clean parts prior to coating. This treatment is more aggressive than passivation.
- PITTING CORROSION
Pitting indicates deep corrosion in localized spots on a fastener. Dirt or grease on certain portions of a fastener may block oxygen from that surface, thus impeding the passive film which protects stainless from corrosion.
- PROOF LOAD
A test load that a fitting must undergo without showing significant deformation. It is usually 50% +- of yield strength.