The corrosion-resistance of stainless steel is due to a ‘passive’, chromium-rich complex oxide-film that forms naturally on the surface of the steel. Mechanical fabrication actions disrupt the existing passive surface and result in a surface with a low chrome to iron ratio. It is therefore essential to clean the stainless steel after fabrication to restore its passive layer. Here are the main benefits of passivation.
1. Prevent Corrosion
When the passive surface layer has been removed due to welding or other fabricating, there is an increased possibility of surface contamination getting pushed or smeared into the metal surface. A common example is rust, particularly in an environment where the stainless steel will be exposed to the elements.
By cleaning the weld and restoring a passive layer on the surface, contaminants are removed from the surface and foreign materials are no longer able to disturb the metal.
2. Improve Aesthetics
Post-fabrication, especially welding, the metal surface is altered and free iron is released from the alloy. The chrome to iron ratio is also lowered in the heat affected zone of the weld. This results in imperfections such as discolouration of the metal.
Following electrochemical passivation, the metal is restored to its original polished state as any imperfections are instantly removed.
3. increase durability
Did you know that the re-creation of a passive layer allows the metal to endure more stress and weight without buckling? It’s under 3 nanometers thick, but this thickness and stability is critical to system longevity and product purity.
4. less agressive than other cleaning methods
Other methods of cleaning such as pickling use much stronger acids which can damage other surfaces they come into contact with. This also doesn’t create an immediate passivation, as there is a 24-48 hour period where the metal surface will still be prone to corrosion and foreign materials may enter. Alternatively, using Scotch-Brite or bead blasting will clean the surface, but not restore the passive layer, so it will remain susceptible to corrosion.
The advantage of electrolytic weld cleaning is that the passive protective layer can be instantly rebuilt while using less aggressive acids than traditional methods.
