chain disintegration

[mestrezat]

We pulled the Lewmar G4 chain from out locker a while ago and found that about 25 feet of it had become unsafe to use as anchor chain. Now it wasn't the first 25 feet. That was fine. As a matter of fact, the first 75 feet was fine. From 75 to 100 was worthless. From 100 to 300 feet was also fine.
Any one have any idea why the first part was fine and then a chunk was bad and then the rest if great. If it was saltwater corrosion in the locker, it should have gotten all the chain clear down to the bottom. It can't be abrasion as the first section it what sits on the ocean bottom. this is the section that is off the bottom on it's way up to the deck and not really much of that as we typically let out 150-180 feet of chain.
I'm a bit mystified.

[skipmac]

I would have guessed that the bad section of chain was sitting on the bottom of the locker and stayed wet but I think from your description you are saying that the section from 100-300' was the part sitting on the bottom of the locker?

If that is the case then my guess is that the links in that section of chain were from a different coil of wire in the production process and might have been an out of spec alloy? Would not think it was in the galvanizing step since the whole chain is galvanized at one time.

Is the damaged section clearing separate from the rest of the chain meaning is there a badly rusted link and then the next link to it in perfect condition or does the rusted section get worse gradually from link to link?

[Rubikoop]

I had a similar experience with some 3/8 chain I used for a mooring. I took the chain back to the chandlery 2 years after purchase and they replaced it. They believed they had a barrel of chain that had galvanization problems on some portions since I wasn't the first customer to complain. The replacement chain looked great from top to bottom 4 years later. May not be what happened to you.

[Vasco]

Last season I cut 80 feet of chain from a 200 foot length. The 80 feet came out of the middle. The section nearest the anchor that usually lays on the bottom was fine and so was the last bit towards the bitter end. This chain was used extensively. My theory is that the bit that lays on the bottom when at anchor is fine and so is the seldom used last 100 feet. I think the part of the chain that is off the bottom seems to corrode a lot faster than the rest. I know of no scientific basis for this but that's because I know nothing about the science of corrosion. There may well be a reason anchor chain corrodes like this.

[MarkJ]

I just cut off the bottom 20 meters of my chain. A nice blob.

Anyway you can join chain whith those stainless steal chain c clip joiners. they work well!

[sailorboy1]

Originally Posted by mestrezat

From 75 to 100 was worthless.

Is that the section of chain that normally is at the waterline when you anchor. If so it gets wet with seawater then gets exposed to air, over and over. Air exposure plays a great part in corrosion.

[JPA Cate]

I notice you are at Vuda Pt. Is it possible that your rusted section was exposed to the waters that get the runoff from the dump next to the Royal Suva Yacht Club? Two years running, we had our galvo eaten off. Our hypothesis is that it was from the acids there.

After that we have used the Tradewinds anchorage, instead.

[barnakiel]

If it is not the 'bottom section' (of the locker) then it will be the part that chafed against something and you failed to notice the damage.

b.