Passivation

After the pickling treatment, the steel is able to self-restore the protective film of chromium oxide, but this “self-passivation” process takes a long time and requires particular conditions. “Passivation” is a process that allows accelerating the formation of this protective layer with the aid of specific preparations. We normally operate by immersion in tanks or, alternatively, by spraying. After the treatment, we can check its effectiveness by means of our passivation test, which also detect any contamination.

After decontamination from oxides stainless steel parts are able, over time, to restore their protective chromium oxide film.

This “self-passivation” process takes a long time and requires particular exposure conditions: the parts must be left exposed in well-oxygenated environments and must not come into contact with any contaminating agents that could give rise a corrosion.

“Passivation” is a process that accelerates the formation of this protective layer with the aid of a suitable acid mixture, and is not a substitute for pickling (as clearly specified in the relevant ASTM).

It is normally carried out by immersion in tanks or, alternatively, by spraying.

Products used include our nitric acid-based PASSIVANTE P (applied by immersion or spraying on large areas, or applied by brush to small areas) or our PASSIVANTE P2000 (without nitric acid).

After passivation the surface must be thoroughly washed with water to eliminate any solution adhering to the surface. When all operations have been completed the treated parts undergo final inspection to ensure that the process has been successful.

In some cases the stainless steel surface has to be decontaminated without altering the appearance of the treated component, ensuring the elimination of free iron from the surface and increasing the chromium/iron ratio.

It is for this purpose that POLINOX PROTECT (WITHOUT NITRIC ACID) has been developed. It is used as a post-passivation treatment for all stainless steel surfaces and welds that have already formed a passive layer, and is particularly suitable as a passivation agent after mechanical brushing and grinding, considerably increasing the component’s resistance to corrosion.

Protective film formation check (compliant with ASTM)

After pickling and passivation it is often necessary to check the effectiveness of the treatment.

A simple PASSIVATION TEST (potassium ferrocyanide test) has been developed for this purpose that enables the detection of any ferrous contaminations caused not just by incorrect treatment operations but also by environmental contamination. Any presence of ferrous oxide (with the test solution changing from colourless to blue) is likely to lead to the onset of corrosion.

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