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09-07-2014, 07:50
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#91
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Registered User
Join Date: May 2008
Location: Nova Scotia until Spring 2021
Boat: Custom 41' Steel Pilothouse Cutter
Posts: 4,974
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Re: Amazing Underwater Photos of an Anchor Swivel Failing
Quote:
Originally Posted by Jim Cate
Absolutely correct, SVN, but one just can't convince these experts.
Jim
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I was under the impression that crevice corrosion was a function of limited exposure to the surrounding environment and the failure of passive oxide layers. So salt water and inexpert welding are a bad combo. Galvanic corrosion I associate with dissimilar metals in an electrolyte (like sea water); crevice corrosion I associate with confined spaces, like inside a heat exchanger.
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09-07-2014, 17:23
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#92
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 19,549
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Re: Amazing Underwater Photos of an Anchor Swivel Failing
Quote:
Originally Posted by S/V Alchemy
I was under the impression that crevice corrosion was a function of limited exposure to the surrounding environment and the failure of passive oxide layers. So salt water and inexpert welding are a bad combo. Galvanic corrosion I associate with dissimilar metals in an electrolyte (like sea water); crevice corrosion I associate with confined spaces, like inside a heat exchanger.
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The critical factor here is that if there were galvanic corrosion in the s/s vs galvanized couple, it would be the zinc on the chain that would be eroded, not the stainless swivel. Thus I continue to maintain that the dread "dissimilar metals" issue has nothing whatsoever to do with the failure of the swivel... or any other stainless part in such a system.
Cheers,
Jim
__________________
Jim and Ann s/v Insatiable II, still hanging out in Port Cygnet. Summer was nice... it was on a Tuesday... and now autumn is here and being pretty nice so far!
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09-07-2014, 19:02
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#93
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Registered User
Join Date: Feb 2009
Posts: 2,301
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Re: Amazing Underwater Photos of an Anchor Swivel Failing
Quote:
Originally Posted by Jim Cate
The critical factor here is that if there were galvanic corrosion in the s/s vs galvanized couple, it would be the zinc on the chain that would be eroded, not the stainless swivel. Thus I continue to maintain that the dread "dissimilar metals" issue has nothing whatsoever to do with the failure of the swivel... or any other stainless part in such a system.
Cheers,
Jim
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And you would be correct
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09-07-2014, 19:09
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#94
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Registered User

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 8,462
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Re: Amazing Underwater Photos of an Anchor Swivel Failing
Quote:
Thus I continue to maintain that the dread "dissimilar metals" issue has nothing whatsoever to do with the failure of the swivel... or any other stainless part in such a system.
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But couldn't it be that the dissimilar metals were in the weld itself.
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09-07-2014, 23:35
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#95
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 19,549
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Re: Amazing Underwater Photos of an Anchor Swivel Failing
Quote:
Originally Posted by DeepFrz
But couldn't it be that the dissimilar metals were in the weld itself.
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Phil, I'm not even sure that the failure was within a weld... didn't look like it to me. But what I was railing about was several posters vehemently saying to never mix s/s bits with a galvo chain rode... and that it would cause the s/s bits to fail... and that ain't so.
Bad welds under water... not such a good plan!
Jim
__________________
Jim and Ann s/v Insatiable II, still hanging out in Port Cygnet. Summer was nice... it was on a Tuesday... and now autumn is here and being pretty nice so far!
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10-07-2014, 00:28
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#96
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Registered User
Join Date: Sep 2011
Location: UK
Boat: Woods Flica catamaran
Posts: 400
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Re: Amazing Underwater Photos of an Anchor Swivel Failing
Quote:
Originally Posted by DeepFrz
But couldn't it be that the dissimilar metals were in the weld itself.
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Looking at the pictures I am sure that it was not welded. It looks more like a casting of some sort. You wouldn't try to fabricate something like that by welding.
Looks like a stress failure which may of started as crevice corrosion.
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10-07-2014, 03:15
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#97
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Senior Cruiser

Join Date: Oct 2007
Location: 29° 49.16’ N 82° 25.82’ W
Boat: Pearson 422
Posts: 16,143
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Re: Amazing Underwater Photos of an Anchor Swivel Failing
Quote:
Originally Posted by Jim Cate
Phil, I'm not even sure that the failure was within a weld... didn't look like it to me. But what I was railing about was several posters vehemently saying to never mix s/s bits with a galvo chain rode... and that it would cause the s/s bits to fail... and that ain't so.
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My personal experience and easily confirmed by a look at a chart of the galvanic series. All common grades of SS are LESS active than mild or alloy steel and the zinc by far more active than both. So if galvanic corrosion was to occur the zinc would be the first to go, followed by the steel chain.
__________________
The water is always bluer on the other side of the ocean.
Sometimes it's necessary to state the obvious for the benefit of the oblivious.
Rust is the poor man's Loctite.
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