Date:         Wed, 15 May 2002 08:25:51 -0700
Reply-To:     Alistair Bell <albell@UVIC.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Alistair Bell <albell@UVIC.CA>
Subject:      Re: Subject: Re: Want to paint camper roof
Comments: To: Eric Unrau <eunrau@yahoo.ca>
In-Reply-To:  <000001c1fc1d$c6db5a80$9a27ad8e@bc.hsia.telus.net>
Content-type: text/plain; charset="ISO-8859-1"

Eric,

in the situation first described, there was an aluminium pop rivet
(relatively small) in a stainless bracket (relatively large). In that
situation the aluminium is the most active metal, providing protection for
the passivated stainless, thus the rivet will be eaten up.

A different situation is having stainless rivets in an aluminium mast, same
reaction will occur but over a much larger area (mast) and won't be
noticible/important.

BTW Stainless is not that inert. Actually can be an active metal but forms
an oxide layer (as does aluminium) in the presence of oxygen. Put stainless
(meaning the common alloys) in an anoxic environment (one example is ground
tackle, in the mud) and it will corrode. Another environment where it will
corrode is where a fitting is welded to a structure (both stainless) and
part of the weld is painted. Splashed by an electrolyte (water) and
contaminated with oil, grime, a region around the weld and paint interface
will rust. 

Stainless is funny stuff, can active passive and active all on the same
piece.!


BTW this corrosion is not the same as cavitation corrosion. (although in so
situations both processes may be going on)


Alistair


> From: Eric Unrau <eunrau@YAHOO.CA>
> Reply-To: Eric Unrau <eunrau@YAHOO.CA>
> Date: Wed, 15 May 2002 07:35:33 -0700
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Subject: Re: Want to paint camper roof
> 
> A bunch of H2O isn’t required to promote corrosion between dissimilar
> metals, just a few drops now and then.  Cyclists see this all the time
> when an AL seatpost is installed in a Cro-Moly Steel frame without a
> whole bunch of grease to prevent seizing --> permanent weld.  That said,
> I was always under the impression that Stainless steel is relatively
> inert and wouldn’t react much (at all) with AL.
> 
> 
> ~Eric~