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Old 11-08-2016, 12:10   #16
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Re: Chain Strength Loss Over Time/With Use

Steel fatigues and fatigue will eventually cause failure of course, example is I give you a piece of coat hangar wire and you bend it back and forth until it breaks, that is fatigue.
But if I give you a railroad spike you can try bending it forever but since you can't exert enough force, it's not being fatigued, so while chain can of course fatigue, I believe we rarely exert enough force to fatigue it. Most stress my chain sees on a regular basis is when I break out the anchor and that really isn't much.
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Old 11-08-2016, 13:13   #17
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Re: Chain Strength Loss Over Time/With Use

rule of thumb: When the links start flaking off rust, think about replacing the chain. It may help you to measure with your calipers the most corroded chain links and when the wire diameter is down to 90% of new chain thickness, or if the links start changing shape (you should look up the dimensions of new chain links for the type you are using) replace the chain. Delay the inevitable by end-for-ending the chain when half-worn out. Remember the strength of a wire (chain is welded wire) is proportional to the square of the wire diameter, not to the diameter itself. 10^2 = 100. 9^2 = 81. So when your 10 mm chain link becomes reduced to 9 mm your chain strength is down by about 20%.
If you think chain is expensive to replace, remember it is even more expensive when it parts under load.
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Old 11-08-2016, 17:24   #18
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Re: Chain Strength Loss Over Time/With Use

During 15 years of often deep water anchoring (40 - 50 meters) in a fiord-like cruising ground, 28 tonne disp, high winds, I had my 200 meters of chain re-galved once, maybe twice. And I reckon the chain was old to start with. Maybe as old as the boat - 30 years? OR maybe as old aas the previous owner's refit (5 years).

I guess I'm saying the chain was under about as much usage pressure as a pleasure yacht anchor chain will every be.

Now that it's been pointed out on this thread, I reckon there were a few more chain jams over the windlass teeth. Needed to keep pressure by hand on it as it came up. The chain must have been stretching eh?

The 10% stretch test seems to make sense to this layman .. although 10% is a lot?

How much stretch would affect jamming on the windless teeth? 5%? 10%? I have no idea.

Realising that old chain can look new with a re-galv, is the fit of the chain to the windlass a reasonable test of when to replace the chain?

Hmmm . better to just measure with calipers and compare against the likely spec.

Was that chain drift? sorry thread drift.
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Old 11-08-2016, 17:54   #19
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Re: Chain Strength Loss Over Time/With Use

Steel is very forgiving. It has a High yield strength, 36,000# for A36 steel. So say a 5/16" anchor chain, for example, would have a yield strength of somewhere around 8000 pounds. That is loads below 8000 pounds would not deform or weaken the steel link. Loads above would start weakening the chain. I don't see 8000# being an issue as the anchor would pull out long before a 8000# load, before the chain reached it's yield point.

This is one reason springs on cars,etc. are steel as they do not suffer fatigue even with high cycle rates, for a very long time.

Rust, reducing cross section is the big limit on chain strength. Shock loads on the other hand could cause the load to increase over the yield point.




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Old 11-08-2016, 18:17   #20
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Re: Chain Strength Loss Over Time/With Use

https://www.google.com.au/url?sa=t&s...l0UZ-9woM6HynA

Its a big issue with oil rig moorings. That are heavily pretensioned and subject to continually changing loads from sea, swell, wind and tide 365 days per year.

I have actually seen yachts anchor chain break three times. Twice though fatigue on my parents old 12mm long link chain of uncertain origin. And once on a friend's yacht where he tried 6mm g3 chain on a 28 footer. Probably this failed though overload. Also back then we weren't using decent snubbers so shock loading was a bigger issue.

But I suspect the modern anchor chains are much higher quality than these failed chains were, and I doubt the typical load cycle scenario on the average yachts chain isn't going to cause any significant fatigue issues, but I'd be very interested to see that article.

Seems like chain by its very nature is prone to fatigue issues. I just don't think the average yacht chain gets loaded over the fatigue limit very often, if at all in normal use.

It will be interesting to see if the new trend to lighter high tensile chains changes this in the future. Fatigue is a very complex issue and as I understand it it is not really correct to show it as a gradual reduction in strength Ie G4 chain becomes G3 strength over time, its less linear with metals, and more to do with crack formation and propagation resulting in a relatively sudden and isolated reduction in strength. Ie its a probability of failure rather than a gradual predictable weakening of the material.

Composites I think are different, eg I think GRP slowly loses strength over stress cycles as the bonds and fibres individually fail, but cracks are less likely to propogate due to the fibres holding it together. So it may exhibit a loss of stiffness and strenth over time rather than sudden failure.

But this is not my area of expertise, so I am probably rambling outside my pay grade.. ain't the internet great!
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Old 11-08-2016, 18:26   #21
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pirate Re: Chain Strength Loss Over Time/With Use

Okay.. we've had all the technical data.. now for real life data.. for another bored shitless poster who.. according to stated experience should know the facts.
If you are using galvanised chain once the link ends get to 60% of the centre.. time for new chain.
If your using stainless chain you deserve anything that happens to you.. that goes for the shiny stainless anchor and swivel you Yanks love so much as well
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Old 12-08-2016, 09:20   #22
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Re: Chain Strength Loss Over Time/With Use

Fatigue cycle was firstly detected/understood by German engineers in XIX c.

THEY were working in railways, and cycles were in the order of millions....minimum half a million cycles.

Not the case of any anchor chain.

Visual inspection for chafe/rust is the old rule..... or possibly changing every 30years
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Old 12-08-2016, 09:32   #23
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Re: Chain Strength Loss Over Time/With Use

Steel has more elasticity than rubber

That doesn't sound right does it
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Old 13-08-2016, 01:00   #24
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Re: Chain Strength Loss Over Time/With Use

Thanks guys. I'll do some more looking around online, & if anything surfaces which fits with my original post I'll be sure to share it.
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