An interesting S/S anchor chain saga

[Bajansailor]

Here is an interesting article in the September issue of the Caribbean Compass about one sailor's experience with an all 316 (allegedly) stainless steel anchoring arrangement - anchor, swivel and chain.
http://issuu.com/caribbean-compass/docs/compass_online_september10/2?mode=embed

Once you bring up the on-line edition, click on page 41, and then click again to enlarge the script.

He was talked into buying this new kit 4 years ago in the Caribbean, and it all seemed wonderful.
But then he relates how the chain cable recently broke in a squall one morning, fortunately with the crew on board and up in the cockpit. They re-anchored with the kedge, and went diving to look for the anchor, and found it ok, even finding the broken chain link, of which there is a photo.

Vyv, if you are reading this, what are your thoughts please?

 

[craigsmith]

You put "allegedly" in brackets which is probably a predictor of what you expect in response.

1) 316 stainless is relatively weak, something between half and two thirds that of a 400 grade steel as used in G40 galvanized chain. The commonly available higher tensile grade of stainless chain that is available is G50. If using 316 you therefore need to use larger sizes to bring the breaking strength back up to par. That said, the failure in the article is clearly from corrosion and not pure mechanical stress.

2) Stainless is expensive. Marine grade 316/L is very expensive. Even better grades like 2205 are ultra expensive. (Compared to equivalent galvanized steels). You should expect stainless items, like anchors and chain, to cost something between 3 and 5 times the equivalent galvanized products. If they don't, there's a compromise somewhere.

Now, to the article: EXPENSIVE SLIPPERY AND SHINY: A DEADLY COMBINATION. In other news, Judgment Day is tomorrow!

Referring to "stainless steel ground tackle", the author goes on to claim that because of the magazine's "policies", he will not identify the actual gear he's talking about. Well okay then because obviously all metals are identical (yes that was sarcastic and no apologies).

No matter because he immediately goes on to mention "the complete system... including the stainless steel ball-and-socket type swivel", promptly giving the game away to anyone who knows a thing or two, semi-confirmed by the later reference to the "European company". Anyone familiar with the range of products on the anchoring market will identify this as the German WASI "GTS" anchoring system including their "PowerBall" swivel. I don't know of any other that would fit the, ahem, clues.

In any case it is the chain that failed on the author, not the WASI anchor or the swivel, and: I don't believe WASI make chain, in fact they state so themselves as quoted by the author in the article, so the disguised attack on the manufacturer, as opposed to the supplier, is unwarranted. (That said, frankly 316 is too weak a material to make an anchor from, particularly the shank, metallurgical failures aside).

WASI's promo material refer simply to "AISI 316" chains and mentions no specific manufacturer.

So, we can summarize by saying the author has bought chain of an unknown origin. He does not reference its certification which we might assume he would given the nature of the article. Does it exist? How much did it cost and by reference what can we conclude about its intrinsic quality, considering my numbered points above? Based on this, do we have either:
a) a damning report on the intrinsic nature of stainless steel, God help whoever invented the infernal stuff, or
b) a story on the quality of product sold by a Caribbean supplier.

In case my position on this is unclear, there is no problem with stainless chain or any other anchoring component that is 1) high quality from 2) a reputable manufacturer which will have supplied a 3) proof certificate, and which is 4) adequately maintained [periodically pulled out of locker and cleaned].

 

[Bosun Higgs]

Whilst there is no doubt that what you get and what you pay for are linked, I disagree with some of Craig's comments. The tensile strength of 316 in the annealed condition ( ie its softest) is not much different from that of the mild steel than the vast majority of our anchor chain is made from. Sure the anchor equipment makers would love us to go wholly to tested chain and maybe thats what happens in NZ but that isnt going to happen here and nor is it necessary. Its highly unlikely in my practical experience that the tensile strength of the chain is the limiting factor in our anchoring system - something else usually gives way first.

And by the way Craig, I don't remember getting a proof certificate when I bought my Rocna.

 

[puddock]

Craig,
I have read quite a few of your posts/ replies and on the whole they make for interesting (if biased) reading. However, I can't help feeling that you are letting yourself down a bit by your abrasive, almost arrogant, responses to other peoples posts. Is there any need for it?
As I said, you have made some very valid comments but don't detract from them by being rude - it doesn't make good reading and tends to make people skip over what you are trying to get across. Yours is not the only valued opinion out there.

 

[craigsmith]

Apologies. My attitude such as it is above is directed not at the OP but the author of the piece in question, who is indirectly slandering a manufacturer/brand for something they bear no culpability for - don't know why I'm defending a competitor - and more directly slandering an innocent grade of metal on an uninformed and illogical basis. That's misinformation and it's all too common in the marine publishing world.

 

[DownWest]

We all know where Craig comes from, so I find his posts informative. When people have serious problems with gear, they are not always well directed in their unhappiness.
A

 

[gardenshed]

correct me if I am wrong, but isn't the real message that s/s anchor chain is picnic hook bling for your marina-queen mobo and that for all practical purposes, good quality galvanised link is what is needed.

s/steels are great for specific purposes but are not miracle cures. The lack of obvious signs of corrsion and degradation can lead to a false sense of security

 

[vyv_cox]

.

Vyv, if you are reading this, what are your thoughts please?

A little difficult to say based on one photograph but here goes.

The author says the grade is 316Ti, although he is mistaken in stating the function of this grade.

316 stainless steel contains a small amount of carbon. If this grade is welded the weld and the region immediately adjacent to the weld reached a critical, temperature at which the carbon combines with some of the chromium that gives the alloy its corrosion resistance. This narrow region therefore corrodes preferentially, sometimes quite rapidly. It is described as intergranular corrosion.

In order to prevent this problem weldable grades of 316 are supplied with a lower level of carbon, known as 316L. For further protection some alloys are also given very small additions of preferential carbide formers, of which the most common is 316Ti.

It appears to me that the link shown has suffered intergranular corrosion at the weld, suggesting that although the base wire may have been 316L or 316Ti, the filler metal was not. Based on the general shape of the other fracture in the link it appears that this is a fatigue fracture that occurred in the wire after the corroded weld separated.

If I can correct some of the misconceptions above, 316 stainless steel has almost exactly the same UTS as mild steel, from which Grade 30 chain is made. Probably the majority of us use this. 8 mm chain in these grades fractures at almost 4 tonnes in most cases. 316 is slightly more brittle but this would have little significance in anchoring.

Stainless steel chain has the big advantage that it stows far better than galvanised and can solve problems associated with small or imperfectly shaped anchor lockers. It also, of course, remains rust free for many years after carbon steel chain would need regalvanising. However, it needs to be purchased with care as there is some very questionable stuff on the market.

 

[William_H]

SS Chain

As I read Craig's comments the German company making the anchor swivel etc have bought in the chain to make a system which they then wholesale to dealers. I don't believe the maker of the anchoring system can be absolved by saying they did not make the chain. They surely have an obligation to ensure the chain is appropriate to the anchoring system. in other words the guilty party. olewill

 

[craigsmith]

As I read Craig's comments the German company making the anchor swivel etc have bought in the chain to make a system which they then wholesale to dealers. I don't believe the maker of the anchoring system can be absolved by saying they did not make the chain. They surely have an obligation to ensure the chain is appropriate to the anchoring system. in other words the guilty party. olewill

I don't know that. Maybe, or maybe they just suggest the use of 316L chain and leave the acquisition up to the supplier. They do supply chain but this was a shop in the Caribbean so the author would have to dig a little deeper.

316 stainless steel contains a small amount of carbon. If this grade is welded the weld and the region immediately adjacent to the weld reached a critical, temperature at which the carbon combines with some of the chromium that gives the alloy its corrosion resistance. This narrow region therefore corrodes preferentially, sometimes quite rapidly. It is described as intergranular corrosion.

In order to prevent this problem weldable grades of 316 are supplied with a lower level of carbon, known as 316L. For further protection some alloys are also given very small additions of preferential carbide formers, of which the most common is 316Ti.

It appears to me that the link shown has suffered intergranular corrosion at the weld, suggesting that although the base wire may have been 316L or 316Ti, the filler metal was not. Based on the general shape of the other fracture in the link it appears that this is a fatigue fracture that occurred in the wire after the corroded weld separated.

Given the uncertain origin and implicated quality, it may not even be 316. So sensitization on welding leads to IGC around the welds in the original steel. The welds ("fusing"?) may not have been passivated, exacerbating things. Or the wrong welding rods used - certainly I've seen otherwise high quality 316L plate fabrications fail very quickly when welded incorrectly (the weld rusted and gone completely within a season). Possibly combined with inadequate maintenance (e.g. leaving in damp salty locker and never cleaning).

In any case the conclusion is not...

correct me if I am wrong, but isn't the real message that s/s anchor chain is picnic hook bling for your marina-queen mobo and that for all practical purposes, good quality galvanised link is what is needed.

... but rather the real message is that buying cheap chain of unknown origin of suspect quality may well bite you, whether it be galvanized or stainless.

I'll repeat a point I made above: there is nothing wrong with the use of stainless steel in anchoring systems, providing they are not immersed permanently (e.g. mooring components). Tales of stainless steel failures commonly come back to cheap and poor quality products. Stainless is expensive – marine grade 316/L/Ti very expensive, and still superior grades like 2205 ultra expensive (relative to galvanized steel alternatives). Comparing quality Italian chain available locally, I find that 316L is approximately four times more costly than the stronger G40 galvanized from the same manufacturer, never mind G30. Typically, a stainless steel product may be expected to cost between 3 and 5 times the equivalent grade galvanized version. If not, you are getting what you pay for.

 

[Bosun Higgs]

It appears to me that the link shown has suffered intergranular corrosion at the weld, suggesting that although the base wire may have been 316L or 316Ti, the filler metal was not.

For some reason I cant see the piccie concerned, but if the failure was in a link of the chain then there would not have been any filler material. Chain forming machines do a simple butt weld or at least the ones we used to supply wire to operated that way.

 

[vyv_cox]

For some reason I cant see the piccie concerned, but if the failure was in a link of the chain then there would not have been any filler material. Chain forming machines do a simple butt weld or at least the ones we used to supply wire to operated that way.

Perfectly true of carbon steel chain. For reasons I don't know stainless steel chain is made by MIG welding the links closed. I don't even know whether this always the case but I have looked at quite a number of examples in which the welded joint is quite obvious. The one posted by the OP is one.

 

[Bajansailor]

Thank you everybody for all the interesting and informative posts above.
Vyv made a very pertinent observation about how S/S chain stows more easily than galvanised, and that factor must make it very attractive to folk who have to keep on kicking down the pyramid of chain that piles up in the anchor locker under the windlass.

In the photo of the broken link, there did appear to be obvious brown signs of corrosion; I wonder if this would have 'stood out' if the chain had been ranged out on deck and inspected, or if there might have been many other areas of discolouration on the links.
I can see how welding will locally affect the properties of the chain links - we welded a couple of S/S plates on to a tubular goalpost, and didn't polish them afterwards, and they have rusted happily.

I wonder which would have better wear resistance, 'ordinary' galvanised chain, or the same size in S/S?
I ask this because the 1/2" galvanised (originally!) chain on our mooring is wearing fast where the links are in contact with each other - where the chain is ranging along the sandy bottom at low tide I have had to add doubler chains as the 1/2" chain has (in less than 2 years) worn down to less than 1/4" thickness in way of the ends of the links - yet the chain is fine a few feet higher up, where it is always suspended (ie not in abrasive contact with the sea bed).

 

[vyv_cox]

It would be unwise to use stainless steel chain anywhere permanently underwater, it's a risk too far from the corrosion point of view. I don't know how the wear of stainless on stainless would compare with galvanised on galvanised but I doubt if it would be greatly different. However, I will suggest that 1/2 inch chain is a little light for a mooring in tidal waters. When I had one in Menai Strait the recommended size for bottom chain and riser was 3/4 minimum, although my bottom chain was actually 1 inch. My pickup chain from the buoy was 1/2 inch. These measurements were the same for smaller boats - my first was 27 ft and I did not upgrade for 29 ft and 34 ft.

It does depend a little on your local conditions. I recall being shown a chain that had held a small boat for one winter at the northern end of the Strait where conditions are far more exposed. It had almost completely worn through, whereas mine was used for six or seven summers and was still in good condition.

Edit - the pickup chain was renewed every two seasons, mostly as it was rusty by then and marked the decks. Not a great deal of wear by that time.

 

[craigsmith]

As Vyv says you shouldn't use stainless permanently deployed, it needs exposure to oxygen to renew its chromium oxide surface and will corrode uninhibited when deprived of that, e.g. buried under mud. The chlorides in seawater attack the stainless and if that process occurs faster than the stainless can renew its protection, it corrodes. Deploying anchor chain in most circumstances is perfectly okay, and quality stainless chain looked after will far outlast galvanized (without re-galvanizing). However it's a no-no w.r.t. moorings.

The direct question re wear. Initially the HDG chain will wear more slowly as the zinc is actually very hard. However once through the zinc, rust is what makes your metal vanish.

 

[Monique]

FWIW... "The hole in the water in which I throw money" has a Rocna SS anchor, SS swivel and 75 Meters of 12 MM SS chain. The kit was bought when the boat was commissioned 13 years ago.

Last spring, I took all the gear apart and can assure everyone that there is not the smallest hint of corrosion anywhere.

However, I have no idea which SS is used...

 

[AntarcticPilot]

As Vyv says you shouldn't use stainless permanently deployed, it needs exposure to oxygen to renew its chromium oxide surface and will corrode uninhibited when deprived of that, e.g. buried under mud. The chlorides in seawater attack the stainless and if that process occurs faster than the stainless can renew its protection, it corrodes. Deploying anchor chain in most circumstances is perfectly okay, and quality stainless chain looked after will far outlast galvanized (without re-galvanizing). However it's a no-no w.r.t. moorings.

The direct question re wear. Initially the HDG chain will wear more slowly as the zinc is actually very hard. However once through the zinc, rust is what makes your metal vanish.

Just an addition. Galvanizing is actually the addition of a sacrificial layer of zinc, which not only mechanically protects the iron, but also provides the equivalent of the anode on your hull - zinc corrodes preferentially to iron. So, you shouldn't see deterioration of the iron until the zinc is pretty much all gone.