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Go Back   SailNet Community > On Board > Gear & Maintenance > Corroded Shackle
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Thread: Corroded Shackle Reply to Thread
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Topic Review (Newest First)
01-12-2009 09:04 AM
sailingdog Looks like bad stainless—probably not an austentitic 300-series grade anyways.

Be aware that stainless steel require oxygen for the chemical reaction that protects it to occur. Without sufficient oxygen it rusts like any other steel, just not as quickly—which is why it is STAINLESS not STAINPROOF steel...it stains less.

Marine grade stainless steels are non-magnetic...so check stuff when you buy it...

As for galling, it is very common on stainless steel-to-stainless steel contact situations. Using LanoCote, Tefgel or some other compound to prevent it is generally a really, really good idea.
01-06-2009 01:23 PM
xort Probably some variation on 400 series stainless, "Looks like stainless"!!!

Be glad you caught it when you did!
01-06-2009 11:43 AM
hellosailor dh-
"So what does that imply?" Let's see...No name, no brand stamp, extremely magnetic...Wait, that's a special alloy from that premier French marine outfitter, Count Erfeit.

I expect that some vendors turn a blind eye to some suppliers, who in turn are intentionally supplying junk as marine grade stainless.

As our Fearless Leader (and before him, Chairman Mao!) said, "Trust but verify". Especially if it is a "Jesus pin" holding your rigging up.
01-06-2009 12:51 AM
sailaway21
Quote:
Originally Posted by dhornsey View Post
I just checked the failed shackle with a magnet, and it is extremely magnetic. By comparison, even the cheapest stainless hardware I have on board was only very slightly attracted to a strong magnet. So what does that imply? Do you think it was just made of very poor quality stainless?

Thanks.
Absolutely!

Crevice corrosion occurs due to a lack of oxygen, a situation your shackle did not experience. One also notes that the threaded portion of the pin shows much less degradation than the rest of the exposed pin. Were oxygen deficiency related to the corrosion you'd expect it to be most severe in the threads, and it's not.

I'd even hazard a guess that you'll find the bow of the shackle somewhat less magnetic than the pin. The bow and the pin are then dissimilar metals from one another and the pin was the less noble. The pin would also be less noble than the padeye on the hull. Regardless of which exactly was the cause, the pin acted like a sacrificial anode and deteriorated due to galvanic action. To the extent that it was once shiny, it was stainless. (g)
01-06-2009 12:36 AM
dhornsey
Magnetic Shackle

I just checked the failed shackle with a magnet, and it is extremely magnetic. By comparison, even the cheapest stainless hardware I have on board was only very slightly attracted to a strong magnet. So what does that imply? Do you think it was just made of very poor quality stainless?

Thanks.
01-05-2009 02:25 PM
tweitz
Failing shackles

On another thread I previously had posted some pictures of a Lewmar shackle on my main sheet that failed suddenly, with no outward sign of corrosion. Lewmar rather quickly sent me replacements for all of the main sheet shackles and blocks, but I never got a satisfactory explanation of the problem. It looked to me from the failure that it was defective mettalurgy, like the oft-repeated poor quality Chinese forgings, but I thoguht Lewmar was supposed to be better. By the way, this shackle was on the boom, so it did not get much salt water, except spray now and then, and it in its third season.


01-05-2009 12:55 PM
dhornsey I couldn't find a logo anywhere on it, so it was probably just generic. I'll try the magnet test when I get home today.
01-05-2009 11:50 AM
hellosailor Are there any maker's stamps on the what is left? Or was it generic "Made in China" stainless?

There have been all sorts of improper alloys used over the years, including one lot of stainless from Mexico that was infamous because the foundry used scrap, and a batch of radioactive material got into their product. Which, IIRC, was "stainless steel" dinnerware. That was probably 25-30 years ago, but China is no better.
01-05-2009 11:31 AM
xort tommays has it...even good stainless will eventually corrode in the situation this stuff was in.

do put a magnet to it. I'm suprised at how often I get a small amount of stick from a magnet on stainless.
01-05-2009 11:22 AM
tommays Without knowing if it is 3 years old or 30 it is a tough call, At 30 it was just left unchecked to long at 3 there is something wrong
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