"Cynic" wrote in message
...
On Wed, 9 Sep 2009 18:27:44 +0100, "nightjar" cpb@insert my surname
here.me.uk wrote:

All stainless steel, irrespective of grade, is capable of rusting. Some
are
less likely than others to corrode in normal use, but even marine grade
stainless steel is capable of rusting, as a number of yacht owners
discovered about 30 years ago, when their ballast keels fell off.

There are even different grades of "marine grade" stainless. When I
built my yacht I did a bit of research. I used 316 stainless, which
is OK for salt water exposure but not the best. It was however more
easily available, being used in the food industry. I think 328 was a
lot better, but I may be misremembering. I only needed it for the
stanchions, nothing structural. It yellowed very slightly over the 5
years at sea, but still looked bright and uncorroded.

328 does not mean anything to me, but 316L, which is a low carbon version of
316, has better corrosion resistance. There is also implant quality 316,
which has been twice refined under vacuum, which is even better.


The other thing that can occur is electrolytic corrosion when the
stainless is in contact with a different metal. Don't bolt stainless
fittings to an aluminium mast!

Before cadmium became a devil metal, cadmium plated steel screws were the
thing to use in aluminium.

Colin Bignell