Passivation - The Principle
Stainless steels are corrosion-resistant by nature, which might suggest that passivating them would be unnecessary. However, stainless steels are not completely impervious to rusting. One common mode of corrosion in corrosion-resistant steels is when small spots on the surface begin to rust because grain boundaries or embedded bits of foreign matter (such as grinding swarf) allow water molecules to oxidize some of the iron in those spots despite the alloying chromium. This is called rouging. Some grades of stainless steel are especially resistant to rouging; parts made from them may therefore forgo any passivation step, depending on engineering decisions.
A typical passivation process of cleaning stainless steel tanks involves cleaning with sodium hydroxide and citric acid followed by nitric acid and a complete water rinse. This process will restore the film, remove metal particles, dirt, and welding-generated compounds (e.g. oxides).
Galvex-Technology of passivation increases corrosion resistance drastically. Not only on SS but as well on Tungsten and many other materials.
Anodurit® - the next level
- drastically increased corrosion resistance