Does cast iron rust under water?

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I bought some 45 pound barbell weights at a garage sale to use as a boat mooring. They are in pretty good shape. I intend to leave them at the bottom of the lake; will they rust away? I don't care about some surface rust; I just don't want them to disappear.
If they will rust, I have some epoxy varnish. Presumably there will be no UV to degrade it; will it prevent the rust? Thanks.
(reading this, it sounds a bit silly; but I am serious)
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If you can keep the oxygen away, then it won't rust, at least, not very fast.
Unfortunately for you, the water has oxygen in it and it will 'oxidize' very quickly. Those cheap barbells filled with concrete are okay.
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Not really suitable for this use. Moorings need to be pulled up and inspected annually anyway. Moorings are usually based on a galvanized mushroom anchor that is not only very heavy, but works it's way into the bottom.
CWM
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Toller wrote:

Yes, they will rust.
Just recently salvers raised a Confederate submarine (sunk during the recent unplesantness) and it sure enought had some holes in its structure. Of course the submarine's iron plating was probably thinner than your barbells, but I wouldn't count on much more than 150 years.
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Probably not a fair comparison; I expect it was deeper than my 20', and I further expect that oxygen decreases with depth.
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Toller wrote:

"The craft was found under about 30 feet of water, about four miles off Sullivan's Island, South Carolina..." http://archives.cnn.com/2000/US/08/07/hunley.advancer/
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In salt water, on a mud bottom, I'd expect them to last 3-4 years. If you cast them into a concrete block, they'll last longer than you will.
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Goedjn wrote:

What works in my area for small boat moorings is a garbage can filled with concrete . You put a 2" or so pvc pipe through the can , fill with cement and you have enough weight and a nice hole to run a chain through.
The cast iron will corrode fairly quickly . Sealing them will help.
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snipped-for-privacy@yahoo.com spake thus:

So how do ship's anchors survive? Is it just that they're so massive? Do they have to weld new stuff onto them periodically?
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On Tue, 19 Dec 2006 15:39:42 -0800, David Nebenzahl

Modern lightweight boat anchors start out galvanized. I dunno about ship's anchors. I expect those have replacable zincs attached to them somewhere.
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wrote:

Cast iron and steel are not the same thing.
CWM
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Iron and steel are not the same thing WOW who woudda thunk it.
yes, iron and steel both rust under water it is the primer that stops them from rusting.
spake thus:

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wrote:

Apparently many in this thread think they are the same thing, and they also think all cast iron is the same.

Bwhahahahahahahahaha!
CWM
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Charlie Morgan wrote:

Pretty well sums it up. He apparently has never made any real observations of the rusting type and rate between the two. Yes they will both rust but cast will 'rust' very slowly in comparison.
Harry K
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wrote:

Depends on a lot of factors. Barbells, as someone pointed out, are probably a very low grade cast iron. Probably to the point of being somewhat porous. Iron and cast iron are not the same thing either. "Steel", likewise, is an alloy and covers a wide range of properties. A blanket statement that cast iron will rust more slowly than steel is incorrect, unless you specify more precisely which alloys and production methods you are comparing.
CWM
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I think they'll last many lifetimes.
-rev
Toller wrote:

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The Reverend Natural Light wrote:

So, do I.
Congratulations for thinking outside the box.
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snipped-for-privacy@yahoo.com wrote:

Yep. Cast iron rusts slowly, steel fast. I suspect the submarine was made from wrought iron which would also rust. Also the sub was in salt water which increases speed of reaction.
Harry K
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Cannot say anything as a metal expert, but I think the life of your barbells will depend on the content and quality of the cast iron. Being barbells, probably made in China, they used the cheapest, easiest to get iron to make the barbells. Since they only function to be a weight, there will be no need for a good quality iron to be used.
That said, I used to work for a gas utility, and they still had cast iron gas mains in use that were close to 150 years old. Ordinary steel mains required coatings and anodes to prevent corrosion but the cast iron needed nothing to keep it in good useable condition. I can only assume that the iron that was used to make them was a good quality iron made to a specific specification.

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I'm thinking a four foot section or so of rail road track (iron). Torch a hole in one end, tie it off and drop it where you like.
(I've got an anvil made from a track)
-- Oren
"Well, it doesn't happen all the time, but when it happens, it happens constantly."
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