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Old 09-07-2014, 07:50   #91
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Re: Amazing Underwater Photos of an Anchor Swivel Failing

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Absolutely correct, SVN, but one just can't convince these experts.

Jim
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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Old 09-07-2014, 17:23   #92
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Re: Amazing Underwater Photos of an Anchor Swivel Failing

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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.
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,

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Old 09-07-2014, 19:02   #93
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Re: Amazing Underwater Photos of an Anchor Swivel Failing

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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
And you would be correct
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Old 09-07-2014, 19:09   #94
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Re: Amazing Underwater Photos of an Anchor Swivel Failing

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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.
But couldn't it be that the dissimilar metals were in the weld itself.
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Old 09-07-2014, 23:35   #95
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Re: Amazing Underwater Photos of an Anchor Swivel Failing

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But couldn't it be that the dissimilar metals were in the weld itself.
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!

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Old 10-07-2014, 00:28   #96
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Re: Amazing Underwater Photos of an Anchor Swivel Failing

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But couldn't it be that the dissimilar metals were in the weld itself.
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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Old 10-07-2014, 03:15   #97
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Re: Amazing Underwater Photos of an Anchor Swivel Failing

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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.
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.
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