Stainless shackles

[By Invitation]

I was asked by Gunner to submit this post about stainless chain and shackles. Last summer I replaced my mooring chain with stainless thinking that this was a good thing to do and would reduce my need to replace my mooring chain every 3 years. Below are some pictures of the chain after one season in New England waters and also a picture of the broken shackle which was used for 3 weeks. Our 1902 Herreshoff was drifting out of Narragansett Bay during a storm last summer due to this broken "new" shackle and ended up on the rocks after a 9 hour drift. Amazingly enough, she only has some minor scratches on her keel. I will never ever use stainless chain or shackels again!!

Here is the chain after 12 months in the water:





Here is the 3 week old shackle:



I use only marine grade galvanised mooring chain and shackles and so far everything is fine. One hell of a lesson learned.

[irwinsailor]

Thanks Scott. What size chain was that? Is galvinized chain also a better choice for anchor rode?

[By Invitation]

Gunner,

I don't have the chain here but my memory thinks it was 3/8" chain and 3/8" shackle. I have galvanised 3/8HT for my anchor chain on the boat.

[irwinsailor]

I am wondering if most people on the board think that stainless steel anchor chain is not worth the extra cost?

[sv_makai]

Interesting breaks, it looks like a crack or failure of poor weld on the chains. The shakels look like it could be poor casting I don't see in the photos if there are any other deformities caused by being overstressed

Is there any crevice corrison or electrolisis. We have met several people while crusiing that have had knock off anchors fail in the castings and aluminum anchors on stainless chain that need zincs to prevent them from being eaten away.

Are the sources for your parts reputable or were they discount no name. We ran into a stainless bolt shop that sold everything as 314 stainless only to find out that it was 304. Not quite as good for saltwater boats.

[By Invitation]

All this stuff was purchased at a Marine Consignment shop and it is 316 beleive it or not. I make X-ray analyzers for alloy identification as a business and I tested these before I purchased them. The welds in the links are definetly the major weak point but they also tested as 316, could only be poor welding pratice that caused this problem. As far as the shackle is concered, there is no obvious marks or deformaties, it just plain snapped - piece of **** shackle. I will never again use stainless on my ground tackle.

[Jentine]

New England waters well. Unfortunately, the welds did not. I was of the opinion that the chain manufacturers used a but weld, but that is apparently not the case. The weld filler is the culprit. Who is the manufacturer of the chain you used.

[sv_makai]

We use stainless and will continue as perpound it is stronger. Like buying knocked off anchors this is one place where cutting corners is false economy.

We generally buy the best we can afford and sometimes even when we can't. We live onboard and making sure that it there is some quality control and product history helps us sleep at night.

[Richhh]

Both the chain links and the especially the shackle look like fatigue fractures.

I see no evidence of yield (plastic deformation) only that apparently of brittle fracture. Stainless is notorious for fatigue and should only be used at 30000 psi instead of its ~90000 psi yield strength in cyclically loaded applications. My forensic 'analysis from a distance' would be parts undersized and subjected to cyclic stress/strain. You need a safety factor of at least 3X when designing or applying stainless for cyclical stress. Regular plain vanilla carbon steel has a much higher 'endurance limit'.

Gimme heavy galvanized carbon steel ANY day over stainless ... at least you can see the typical 'ductile failure' beginning to occur.

[exposure]

I can't comment much on the failure of the shackle. It looks like a fatigue failure, but I would suspect there was some kind of material flaw that preciitated the problem, or it was truly overloaded in a cyclic fashion. Stress corrosion likely also played a roll once the crack started.

The chain is another story. When stainless is welded the carbon and chromium combine into chromium carbide. The result is that the carbon no longer helps strengthen the metal and the chromium no longer provides the protective oxide layer. The result is accelerated corrsion and a weak material at the heat affected zone (HAZ) of the weld. The way to fix this is to use a low carbon material for the based material and welding rod(316L or 317L), then properly heat treat and quench the weld to restore the chromium. I am guessing that neither of these was done when this chain was made. It probably would have been much more expensive to buy if it had been done.

This is one of the reasons you don't see boats made from welded stainless steel plate.

High chloride liquids (such as salt water) are a pain to deal with.

Woody

[delmarrey]

If you notice, most people put anoids (zinks) on their prop shafts and out drives. There is a reason for that!!!

Maybe a zink on both ends of the chain would have prevented the errosion and failure..................._/)

[GMac]

Just looking at the photos I would say that the chain is Chinese made, it looks (and has come apart) very much like it. The Chinese never seem to get any weld penetration especially in the stainless so you’re only hanging off a small bit of weld around the outside of the link. Using Chinese made for anything important is silly and, as you can see, dangerous.

Also using stainless on a permanent mooring is a big no-no.

It is a long link as well, which is the weakest of the differing chain formations i.e. short link and etc.

Using 10 or 12mm on a permanent mooring would also be regarded as quite lite.

You basically had the nearly worst possible chain set-up on your mooring. Don’t stress, you’re not the first to do this and I suspect far from the last. Use big self-colour (not galvanised unless it goes in and out of the water i.e. from buoy to boat) steel chain. Galvanised chain on a mooring can actually make it last less than self-colour sometimes, strange but true.

The shackle – A small stainless one a no-no. Again use a bloody big steel one, biggest that will fit the chain is your target and if it is bigger than the chain, so be it and very good.

As for stainless on an anchoring system it is perfectly fine as long as you make sure of a few things:
1, It’s not Chinese made
2, It has been made and tested by a reputable company
3, You get whatever ‘grade’ you need to get the strength you want, just like steel chains.
4, You have a big wallet

There is stainless anchor chain available and made in the EU that is stronger than most steel chains being used. It is fantastic for anchoring but the downside is no. 4 above.

I am no metalurgist, and if I weld something, it is better off epoxied, so I do not pretend to know what happened here, but looking at the t first pic, it sure looks like the weld penetrated sufficiently. It also looks like the weld was contaminated. I am comfortable saying I know what a bad weld looks like. I have done plenty of them. Although I am not a fan of stainless chain for mooring or anchoring, I think you may have just gotten a bad chain. As for the shacle, I agree that it is likely Chinese steel. Unfortunately, it is an established fact that Chines steel processing is substandard.
Since you purchased it at a consignment shop, there is probably not much hope of recourse, but FWIW, I can recommend a good maritime attorney.

[Alan Wheeler]

It has nothing to do with the quality of the chain. I imagine it is of good quality anyway. SST should NEVER EVER EVER be used in a permanant under water situation. Even the best will fail very quickly. What has happened here is is a commonly known and predictable failure. The weld material will always be slightly different to the parent material due to the fact it has been melted and cooled differently than the parent. Because SST needs oxygen to remain Stainless, once placed in salt water, the surface layer depleates very quickly. But it isn't a "perfect depletion. Some areas depleate, some not so well. So both insulative and conductive paths are formed over surfaces and withing crevices etc. Electrolysis starts within the weld/parent metal area almost imediatly and both galvanic corrosion and crevice corrosion work away at the joint.
As for the shackle, a similar situation has taken place. Probably a small stress fracture when it was forged has allowed the two above negative actions to take place.

SST should only ever be used in temporary submersed situations only. NEVER permanantly or long term submerged.
I am a little shy of SST anchor chains and SST anchors, but I am also not aware of any failures in such use either, so my shyness may not be necessary.

[CaptainK]

Man, those chains look like rejects from a S & M shop !!