[TheForge] Stainless contamination

[Hochewa at aol.com]

In a message dated 8/23/2005 7:22:29 AM Eastern Standard Time, 
debmiller at fuse.net writes:
Have a question regarding stainless steel rust contamination.
To All,
Stainless isn't stainless unless you make it so.  Making it so can happen by 
itself but there are times when it needs help.
Stainless can undergo corrosion if the surface is deprived of oxygen.  The 
space under the head of  a bolt or under a washer.  This is corrosion not 
rusting/oxidation.
The appearance of rust on the surface has a few sources.  Iron deposition 
either from particles from the air or brushing with a non-stainless brush are 
common sources.
Rust can form is the surface is activated.  The easiest way to activate the 
surface is to wash it with muriatic acid.  If you do this the only way to get 
it stainless again is to wash it again with muriatic acid to a rust free state, 
neutralize  and then wash it with nitric acid.  This is passivation.  If the 
surface has been scaled by heat and "cleaned", the surface may be chromium 
poor and rust will appear.  Again muriatic followed by nitric.
Passivation can happen naturally if the surface is clean and uncontaminated.

Hochewa