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.
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 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.
A test load that a fitting must undergo without showing significant deformation. It is usually 50% +- of yield strength.