Biological Pickle Solution for Stainless Steel

Biological Pickle Solution for Stainless Steel

As an alternative to the pickling of stainless steel, POLIGRAT offers for the first time with POLINOX-Protect an environmentally compatible, cost-effective and safe process that also results in a marked improvement of the corrosion resistance.

The pickling of stainless steel serves as a final cleaning of the surfaces to remove scale, iron dust and heat tinting, in order to permit the formation of an intact passive layer as corrosion protection. To this end the top layer of the material including the damaged passive layer is removed chemically by means of hydrofluoric acid, nitric acid or sulphuric acid. In this way a new, intact passive layer can be formed on the cleaned metal surface.

Because of the health and environmental risks associated with the use of these acids, and the heavy metals which are released during pickling, the pickling process is subject to strict regulations with regard to health protection and the treatment of wastewater and spent air.

POLINOX-Protect works according to a completely new, different principle: in contrast to pickling, existing passive layers are not removed with great effort, but they are changed and optimized in their composition and structure in such a way that as a result the corrosion resistance of the stainless steel surfaces treated in this manner is considerably better than that of pickled surfaces.

POLINOX-Protect is a watery solution consisting of a special combination of biologically degradable, non-toxic active ingredients, whose use does not result in the development of unpleasant smells or poisonous vapours. When it is applied the iron oxides in the passive layer which are detrimental to corrosion resistance are broken down into iron and oxygen. The iron thus released is removed from the passive layers as well as the scale and the heat tinting, as is the free iron and iron dust. The chromium and nickel oxides contained in the scale and the heat tinting are retained and form effective passive layers once the iron oxides have been removed.

In a second step after the treatment with POLINOX-Protect, a brief heat treatment at temperatures of 140°C – 220°C can be used to optimize the structure of the passive layers, with the result that the corrosion resistance of the stainless steel surfaces is improved to an even greater degree. It then achieves considerably higher values than those attainable through traditional processes such as pickling, electropolishing or passivating. Such levels are normally only found with higher alloyed material qualities.

The treatment with POLINOX-Protect improves the resistance of stainless steel against all forms of corrosion which occur at temperatures below 250°C. These are essentially pitting, stress corrosion, crevice corrosion, foreign corrosion and temperature-related discolouration.

Press information

POLINOX-Protect permits for the first time in a single process the effective inhibition of corrosion on stainless steel, the removal of corrosion products and the reinstatement of corrosion resistance at a higher level. Because the chemicals used are not dangerous, the application can easily be carried out in situ. The repeated regular application of POLINOX-Protect as part of the service and maintenance programme can therefore facilitate the use of stainless steel surfaces under environmental conditions in which it would otherwise not be sufficiently resistant.

POLIGRAT GmbH Valentin-Linhof-Strasse 19 D-81829 Munich
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