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crevice corrosion
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superkraut



Joined: 18 Mar 2001
Posts: 203

PostPosted: Tue Jul 23, 2013 1:30 pm    Post subject: Reply with quote

with the "right" sort of impact, there can be lots of bending force on the fin bolt, particularly with a Powerbox!
http://www.boardlady.com/4712.htm
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swchandler



Joined: 08 Nov 1993
Posts: 5891

PostPosted: Tue Jul 23, 2013 2:51 pm    Post subject: Reply with quote

For many years I was involved in the procurement of high tech machine parts for the defense industry. We used to make a proximity fuse for the Navy's Stinger missiles where the housing was manufactured from a high grade of stainless steel. After machining, the housing was electroetched and then passivated to remove any exposed ferrites and to oxidize the surface.

What I notice often with SS screws and other components used for windsurfing is that exposed ferrites lead to corrosion and rust staining of the surface. While I've never had a problem with failure of these components, you can see how the passivation layer has been compromised.
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keycocker



Joined: 10 Jul 2005
Posts: 3457

PostPosted: Tue Jul 23, 2013 5:06 pm    Post subject: Reply with quote

To further rigits excellent explanation - the crevice corrosion can be much worse in SS than other steel. Other steel gets a thin layer of rust over a large area. When the surface layer is compromised on SS in a tiny spot, all the electrochemical action is focused on a tiny spot so corrosion goes deeper and is not as visible on the surface as a big blotchy rust spot would be.
This can result in surprise failures of nice shiny parts, a real problem on boats.
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afolander



Joined: 22 Jul 2002
Posts: 74

PostPosted: Wed Jul 24, 2013 12:17 am    Post subject: Reply with quote

I think a more likely failure mode is chloride stress corrosion cracking combined with fatigue once the crack got big enough. This failure mode does not usually affect stainless steels at ambient temps except where high residual stresses are present, i.e. fasteners.

If it was crevice corrosion I think you would see more evidence of metal etching on the crack surface and more than one thread affected.
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spennie



Joined: 13 Oct 1995
Posts: 843
Location: Thousand Oaks, CA

PostPosted: Wed Jul 24, 2013 7:17 am    Post subject: Reply with quote

Who would have guessed the world was full of windsurfing metallurgists?
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Georges



Joined: 10 Apr 2000
Posts: 249

PostPosted: Wed Jul 24, 2013 9:01 am    Post subject: Reply with quote

I will buy you a new screw if it brakes THIS thread. Cool
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whitevan01



Joined: 29 Jun 2007
Posts: 503

PostPosted: Wed Jul 24, 2013 10:28 am    Post subject: Reply with quote

kiters: cool dudes
surfers: ultimate cool dudes
windsurfers: nerds
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afolander



Joined: 22 Jul 2002
Posts: 74

PostPosted: Wed Jul 24, 2013 2:23 pm    Post subject: Reply with quote

Guess I will never be an "ultimate cool" nerd.
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andydavis



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

PostPosted: Wed Jul 24, 2013 3:10 pm    Post subject: Reply with quote

whitevan01 wrote:
kiters: cool dudes
surfers: ultimate cool dudes
windsurfers: nerds


why you harshing on us?
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jibemeister



Joined: 27 Sep 1994
Posts: 17

PostPosted: Wed Jul 24, 2013 5:02 pm    Post subject: Reply with quote

Sounds like some sort of STD.
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