On Sat, 16 May 2009 11:03:08 +0200, "Steve Lusardi"
wrote:

Bruce,
Your tests were not valid because you did not reproduce corrosive cases.
Stainless is corrosion resistant only as long as the passive film of oxide
remains on its surface. This passive film can be removed mechanically and
electrically, but in both cases the material will attempt to absorb oxygen
from its environment to recreate the passive film. If the environment is
oxygen depleted, corrosion occurs very rapidly. Here is a case in point,
stainless bolts holding a cast lead ballast plug where water seeps in slowly
surrounding the bolt, but with very slow or negligible flow. As the hull
moves the leads ballast shifts around ever so slightly , but enough to
abrade the passive film. In short order, the surrounding water is depleted
of free oxygen. That is when corrosion starts. It is commonly called crevice
corrosion. Please also appreciate that stainless steel in homogenous, in
that it is an alloy of multiple metals.The corrosion resistance it displays
depends on this homogenous blend. Any disturbance of this blend also
endangers its corrosion resistance, like welding. This fact necessitates
repassivating the disturbed surface in order to restore the original
corrosion resistance. Repassivation is accomplished by removing the
non-homogenous metals from the surface that migrated there during the molten
state while welding. This is accomplished mechanically, electrically or
chemically with acid.
Steve


You didn't read the original post, that I quoted. The original post
stated:

Stainless steel does well in relatively dry environments with access to
oxygen. Look at your home cutlery, for example.
Then go buy a stainless bowl and fill it half full of water.
See how long it takes to develop its first pin hole.
A matter of weeks or less, quite likely.

Which was all I was debating. Not the fact that stainless will
corrode....

Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)