PASSIVATION

After pickling, the steel is able to autonomously restore the protective chromium oxide film, but this self-passivation process takes a long time and requires particular conditions. Passivation is a process that induces the formation of this protective layer by means of solutions that are more oxidizing than atmospheric oxygen, such as nitric or citric acid or thanks to the action of an external anodic current as in the case of electropolishing (ASTM B912)

These two types of passivation are termed spontaneous and induced.

Pickling and passivation treatments can be performed in accordance with ASTM A480 and ASTM 967 standards by immersion or spray using gels or liquids, with products completely free of or containing nitric acid, according to the customer's specifications.

After treatment, it is possible to check the effectiveness of the treatment using our passivation test, which also allows you to detect any contamination.

DECONTAMINATION

The decontamination treatment eliminates ferrous and other metal contaminants from the surface of the stainless steel. The presence of these foreign materials on the surface interferes with the formation of the protective film, favouring potential corrosive triggers. The immersion or spraying of special solutions allows the complete removal of these pollutants without altering the original appearance of the product; compared to pickling, there is practically no material removed. Decontamination always has a beneficial effect on the stability of the passivation of stainless steel and for this reason it is often improperly defined as passivation. Decontamination can be verified with specific reagents, compliant with the reference ASTMs, or with a cycle of wetting repeated over 24 hours .

Protective film formation check (ASTM compliant)

After the pickling and passivation treatment it is often necessary to check the effectiveness of the treatment. For this purpose, a simple passivation test was developed (potassium ferrocyanide test), which also allows the detection of any ferrous contamination due not only to incorrect treatment but also to environmental contamination. The presence of iron oxides will likely trigger corrosion.

For those who need to outsource the passivation of stainless steel, Delmet has state-of-the-art plants and products, which include immersion and spray techniques: a final inspection protocol ensures success.

The passivation process follows the pickling process and shares its operating methods, guaranteeing the usual processing quality offered at the Delmet production plants or, alternatively, at the customer's premises. Passivation increases the life of the treated item by up to 5 times and, as with all treatments, it complies with the ASTM reference standards.