Some background on stainless steels. Oxide films give stainless steels their corrosion resistant properties. The oxide film is continually created by reaction with atmospheric oxygen. If the oxide film is broken and not re-formed, stainless steel will corrode just like mild steel. You can see this by putting a rubber band around a piece of stainless steel sheet (prevents oxygen from reacting with the surface) and immersing the sheet in water. Salt water speeds the corrosion reaction considerably (although other mechanisms also come into play).
It is possible the sealant prevented the oxide from re-creating to form a protective film. There may also be a "double whammy" of trapped moisture under the sealant, resulting in rapid corrosion. Aluminium anneals at relatively low temperatures (as may be experienced in heat cycling) and so could easily flow under any applied pressure. Incidentally, aluminium also forms a protective film by with atmospheric oxygen. That's enough metallurgy for now! Stuart Miler Ablewisp Ltd 01803 843502 Robert A. Macy wrote: > True, even several miles in from the coast we lost > stainless steel wire coated with *very* thick sealant. The > stainless steel wire was especially selected to be > resistant to the elements. The coating was THICK. > > Because the stainless steel wire was under tension, it > became as chemically active as raw iron. We'd lose the > installation of wire in less than a year. Big lesson > there. > > It is my understanding that aluminum has the characteristic > that it loses contact pressure with heat cycling *unless* > there is constant mechanical pressure. This means that a > simple screw terminal with NO spring washer will completely > lose any clamping ability with temperature cycling. Also, > rivets lose their mounting pressure with heat cycling. > This characteristic is one of the reasons that one has to > be very careful with aluminum wiring terminals > deteriorating and losing their low resistance, which has > resulted in mobile home fires. > > - Robert - > > On Fri, 16 Jun 2006 11:25:12 -0700 > "Peter Tarver" <[email protected]> wrote: > >> >> John - >> >> Not much of anything metallic lasts long by the sea, >> especially such >> electrochemically unfriendly materials as iron and >> aluminum. However, >> there are commercially available aluminum pop rivets with >> aluminum >> mandrels, though I don't know how reliable or >> installation friendly they >> might be. >> >> I don't recall the OP stating anything about an ocean >> view for their >> product. Rivets might not be wise, regardless of >> material activity, in >> such an environment. >> >> >> Regards, >> >> Peter L. Tarver, PE >> Product Safety Manager >> Homologation Services >> Sanmina-SCI Corp. >> 2000 Ringwood Ave. >> San Jose, CA 95131-1749 >> V: 408-904-2081 >> F: 408-904-2095 >> M: 408-234-3529 >> [email protected] >> >> > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] > David Heald: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
