"Organic" Pickling and Passivation of Stainless Steel
The challenge in terms of sustainability:
Pickling and passivating of Stainless Steel is a final cleaning of surfaces from scale, heat discolourations and iron contamination to enable the formation of an undisturbed and uniform passsive layer for provision of corrosion resistance. Therefore hydrofluoric acid, nitric acid or sulfuric acid are used to chemically remove the upper material layer including the existing passsive layer and impurities to provide a metallic clean surface, on which a new and homogene passive layer can be formed. Due to high health and environmental risks the application of these acids is subject to restrictions and rigid controls by authorities also in view of air and water pollution.
The initial situation:
As alternative treatment to pickling and passivating of Stainless Steel POLIGRAT first time offers with POLINOX-Protect an environmentally friendly, economic and safe process, which additionally provides an substantial increase in corrosion resistance.
POLINOX-Protect is a water based solution of a special combination of chemicals, which are biologically degradable and not poisonous. The application does not produce nasty smells or dangerous fumes. Within the passive layer and within scale and heat discolourations POLINOX-Protect cracks iron oxides, which reduce the corrosion resistance into iron and oxygen. The free iron then is removed as well as iron contaminations. The Oxides of Chrome and Nickel remain untouched and form a qualified passive layer.
In a second step after treatment with POLINOX-Protect structure and consistence of passive layers can be significantly improved by a short heat treatment at temperatures between 140°C and 220°C. The resulting corrosion resistance is much higher compared to pickling passivating or electropolishing. It is comparable to higher alloyes qualities.
The treatment with POLINOX-Protect improves the resistance of Stainless Steel against all types of corrosion at temperatures lower than 220°C. These are mainly pitting corrosion, crevice corrosion, stress induced crack corrosion and temperature induced discolorations.
For the first time POLINOX-Protect enables in one single treatment to stop ongoing corrosion, remove the corrosion products and provide a higher corrosion resistance. Due to absence of special risks in application, POLINOX-Protect can be applied on site without restrictions. Repeated application for maintenance can stabilise the corrosion resistance also under conditions, for which it would not be sufficiently high otherwise.
The sustainable strengths:
POLINOX-Protect acts according to new and different principle: Different to pickling and passivating the existing passive layer is not removed but improved in its consistence and structure that finally the corrosion resistance is much superior to pickled and passivated surfaces.
Siegfried Pießlinger-Schweiger, CEO
Dr. Olaf Böhme, Head of Research & Development
Brief profile of the company:
Name: POLIGRAT GmbH
Year established: 1953
Solutions: Surface Technology for metal surfaces
Great Britain, France, Hungary, Switzerland, USA, Canada
Australia, Belgium, Finnland, India, Italy, Israel, Japan, Austria, Poland, Spain, Taiwan, Turkey, U.A.E.,