Appearance of the patina
Outdoor use: the patina forms naturally in the open air (over a period of three to four years). Variations in appearance will be observed, depending on the water condensation, evacuation and evaporation conditions. After a few years, the patina will stabilise, even in an industrial, sulphur-containing or rural environment. To ensure optimum patina formation and limit the formation of rust streaks, the oxidation process can be accelerated artificially by first descaling the surface (by sandblasting or shotblasting) and then subjecting it to alternate periods of dry and humid conditions.
Indoor use: to preserve the natural appearance of the material and at the same time avoid powdery oxide deposits that may cause staining, the following three steps are recommended:
- First remove all dusty deposits, stains or surface defects, then apply a chemical treatment to those areas where corrosion has not yet developed
- Clean the surface with water, brush and dry
- Finally, apply a colourless, matt, UV-resistant varnish
Use painted: as the surface has a high reactivity, it is recommended that the first coat of paint be applied on a clean surface immediately after pickling or sandblasting.
The presence of copper in the oxide layer contributes to the formation of a strongly bonded, elastic and compact patina on the surface of Indaten® 355 in the course of the corrosion process. The chromium and nickel contribute to the formation of insoluble alkaline sulphates, which will seal the pores of the oxide layer, thereby protecting the metal from water and oxygen. Silicon, and to a lesser extent phosphorus, also has a favourable effect on corrosion resistance.
Corrosion in a salt spray atmosphere (according to ASTM B117)
Tests were conducted in a chamber at a temperature of 35°C, in a humid atmosphere with a 5% concentration of NaCl. Weight loss was measured after 1000 hours. The sample was weighed before and after the test, and the rust was removed with an acid solution.
The samples were exposed to an industrial, marine atmosphere for 12 months.