Michael Daly" <michaeldaly_at_rogers.com> wrote: (In response to Steve at "ACKC" <aldercreek_at_qwest.net>:) > Stainless steel comes in quite a variety of grades. I am sure the grade of > SS in your knife is quite different from the grade used in deck hardware. >> But both the knife and the deck fittings rust. I've yet to discover an alloy of stainless that doesn't corrode. There aren't many stainless fittings on a sea kayak - a handful of nuts and bolts and a couple of deck U bolts maybe - these may not be considered critical if there's a thin layer of corrosion. Rudder cables are another story - swaged ends that have non-stainless crimps might corrode faster and could fail if not inspected regularly. I've noticed that some have aluminum bits and aluminum and steel are a famously bad combination. I've never seen this happen, so it's conjecture on my part at this point.>> Steve and Michael have it right: there is stainless and there is stainless. And, there is no grade that will not corrode ... eventually. Salt water, because of the chloride ions in it, is very aggressive towards iron-based alloys, owing to complexation of the chloride with ferrous (and then ferric) ion. The bottom line, however, might be whether the lifetime of the fitting, knife, or whatever, is "long enough." In full-size marine applications, it is good practice to pull a few fittings, especially fasteners, after four or five years, and inspect. Even stainless needs this sort of scrutiny because it is particularly susceptible to "crevice corrosion" in which the corrosion occurs in __hidden__ areas of low oxygen, where the lack of oxygen reduces the protective oxides of chromium and allows attack of the underlying iron in the alloy. (I know this is counter-intuitive; before anybody goes off on a rant, check out the term crevice corrosion. It is a well-documented problem for stainless, and well-studied.) This means that a little visible rust for through-hull fittings and deck hardware may be a __good__ sign, inasmuch as it may mean the stainless is still in an oxidized environment. Note: I said "may," and not "is certainly." YMMV when it comes to corrosion of stainless. I leave the problem of maintaining a shiny stainless knife in pristine condition to others. For me, I am content to know that the stainless I can't see, that holds my deck lines on, and allows my rudder to steer, is probably in good shape. -- Dave Kruger Astoria, OR longtime chemist *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Thu Nov 07 2002 - 06:49:16 PST
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