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crevice corrosion
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inf2003



Joined: 15 Jan 2009
Posts: 137

PostPosted: Tue Jul 23, 2013 10:14 am    Post subject: Reply with quote

Thank you , Good explanation. Very Happy
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rigitrite



Joined: 19 Sep 2007
Posts: 265
Location: Kansas City

PostPosted: Tue Jul 23, 2013 10:16 am    Post subject: Reply with quote

A good way to prevent this kind of crevice corrosion from ruining your day (you can imagine how unhappy youíd be if that bolt failed at the furthest point from your launch: you lose a $100+ fin and have a nice long body drag back to shore), is to use a little anti-seize compound on the threads. Thatís what I do, and just inspect your stainless hardware from time to time. If you see some corrosion in the thread valleys, just get a wire brush and clean it off really well. Fixed!
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andydavis



Joined: 11 Apr 1999
Posts: 268
Location: Point Isabel

PostPosted: Tue Jul 23, 2013 10:37 am    Post subject: Reply with quote

rigitrite wrote:
A good way to prevent this kind of crevice corrosion from ruining your day...


what about the embedded nut? seems more vulnerable.
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spennie



Joined: 13 Oct 1995
Posts: 809
Location: Thousand Oaks, CA

PostPosted: Tue Jul 23, 2013 10:41 am    Post subject: Reply with quote

Interesting. That must be why they need to use aluminum nails on a pool deck. Not much fun to hammer in, but I guess they don't corrode away like stainless would.
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rigitrite



Joined: 19 Sep 2007
Posts: 265
Location: Kansas City

PostPosted: Tue Jul 23, 2013 10:53 am    Post subject: Reply with quote

The nut is probably brass, which doesnít suffer the same problems that stainless steels do. Most people also donít realize that some brass alloys have yield strengths about the same as mild steel: theyíre remarkably strong. The biggest danger the nut faces, is damaging the threads: brass is fairly soft, SS is pretty hard. Also, the nut doesnít experience the bending forces that the bolt does. The fin material around the nut will probably fail before the nut does.
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inf2003



Joined: 15 Jan 2009
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PostPosted: Tue Jul 23, 2013 10:53 am    Post subject: Reply with quote

so Is stainless steel a non ferrous metal containing little or no iron ore?
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superkraut



Joined: 18 Mar 2001
Posts: 201

PostPosted: Tue Jul 23, 2013 11:52 am    Post subject: Reply with quote

ouch - Stainless Steel such as the ubiquitous 316, is about 70% iron
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andydavis



Joined: 11 Apr 1999
Posts: 268
Location: Point Isabel

PostPosted: Tue Jul 23, 2013 12:47 pm    Post subject: Reply with quote

rigitrite wrote:
The nut is probably brass, which doesnít suffer the same problems that stainless steels do. ... Also, the nut doesnít experience the bending forces that the bolt does. The fin material around the nut will probably fail before the nut does.


yeah, brass actually has worse problems. Maybe you've never witnessed it, called dezincification...the zinc essentially just leaches away, leaving a rotten, spongy matrix.

I don't know what you're talking about. The bending moment on a bolt in a Tuttle or Power box is zero. With the a tightly fitting fin/box connection, any bending moment on the bolt itself, even if the fin impacts something, is probably about zero. Zero bending force on the bolt.
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rigitrite



Joined: 19 Sep 2007
Posts: 265
Location: Kansas City

PostPosted: Tue Jul 23, 2013 1:14 pm    Post subject: Reply with quote

Yes, heard of de-zincification, but I donít think thatíd be a problem in non-chlorinated water. It happens to plumbing componants that are bathed in municipal water for a long time is what I know about it.
My point about the bending forces on the bolt are from the picture at the start of the thread; there is a very small amount of bending force on the bolt to force that crack to progress. You are correct that most of the force on the bolt is tension, this also helps to progress the crack. If the forces where purely tensile, then the beach marks would make concentric circles around the final brittle failure (like a bullseye). When thereís bending, they march across from a specific initiation point to the rupture line (exactly like the picture).
Donít ever get me started on composites or non-metallic materials; the geek-out on this thread already goes to 11.

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windoggie



Joined: 22 Feb 2002
Posts: 2377

PostPosted: Tue Jul 23, 2013 1:15 pm    Post subject: Reply with quote

isobars wrote:
I put on a pair of rubber gloves before clicking on this thread.
I was wondering when you'd show up.
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