s/s versus C70 chain

[oldvarnish]

I was reading the interesting anchor chain thread.

In terms of strength, would s/s chain be stronger or weaker than G70 (of the same size, of course).

 

[macd]

Weaker, although to what extent is hard to say since stainless chain can be highly variable in its precise metallurgy. Lots of references on-line, and such as this:
http://www.ybw.com/forums/showthread.php?257983-8mm-Stainless-Steel-Chain-for-anchor

(Post 18 is prescient in light of the debate on the recent chain thread.)

Not that it helps, but stainless was used by several Dutch warships, but perhaps due to their being minesweepers and not wanting to anchor in kingdom come. I think the RN favoured bronze.

 

[oldvarnish]

I'm just bumping this up in case Vyv pops out of his locker

 

[macd]

I'm just bumping this up in case Vyv pops out of his locker

Don't blame you. He was around a few moments ago.

 

[Minchsailor]

SS chain stows better in the locker as it is not so 'rough' as galvanised chain. However I heard that it is more rigid than wrought steel chain - this is more elastic and capable of shock loads better. May be critical in a blow. Cannot comment on the relative strengths.

 

[duncan99210]

No idea about relative strengths but SS is exceptionally expensive.....

 

[macd]

The stainless chain supplied by Hackett's, one of the major UK chain/lifting gear specialists, is to G50, which correlates to a UTS of 500 MPa. The figures for G40 and G70 are 400 and 700MPa respectively.

 

[vyv_cox]

The stainless chain supplied by Hackett's, one of the major UK chain/lifting gear specialists, is to G50, which correlates to a UTS of 500 MPa. The figures for G40 and G70 are 400 and 700MPa respectively.

Until I read your post I was going to say that 316 stainless steel chain is supplied to grade 30 but I see that you are correct. Metallurgically the production of grade 50 in this material is very interesting because, unlike carbon steel it cannot be heat treated for increased strength. I assume they use hard drawn wire stock to increase its strength (as with shroud wire). The weld would anneal the adjacent metal back to its original soft condition but presumably the overall strength of the link would still give it the necessary mechanical strength.

 

[oldvarnish]

Until I read your post I was going to say that 316 stainless steel chain is supplied to grade 30 but I see that you are correct. Metallurgically the production of grade 50 in this material is very interesting because, unlike carbon steel it cannot be heat treated for increased strength. I assume they use hard drawn wire stock to increase its strength (as with shroud wire). The weld would anneal the adjacent metal back to its original soft condition but presumably the overall strength of the link would still give it the necessary mechanical strength.

So for equal sizes, s/s chain G50 has less strength than galvanised G70??

 

[srm]

Probably not a great problem with ss chain, but if part of the ss is covered so that water can not flow freely over it you may get pitting corrosion along the boundaries. Apparently this is due to different oxygen levels setting up an electrolitic cell on the surface of the steel. Takes a while so you would probably have to really like the anchorage. I have had problems with marine grade ss oceanographic instruments that were in the water for a few months and barnacles started to colonize. Also, on rudder heel fittings (on a boat I purchased) where the exposed steel looked fine but the covered area was so deeply pitted as to be almost porous. No direct experience with chain but pitting corrosion may possibly occur in a damp chain locker through the same mechanism.

 

[J Neeves]

G70 chain (in America) is made, I have been told, from the same steel used to make G43 (or High Test) chain and is then Quench and Tempered to give it the strength, referred to has G70. I'm not sure how Maggi make theirs. But Peerless now have a G70 metric chain available from stock in Europe and I have no idea how it is made, maybe from their metric G40.

However for imperial the base chain is G43, Q&T and it becomes G70 - but now it needs to be galvanised and the heat of galvanising reduces the min break strength of 5/16th G70 to about 14,000lb, this compares with ungalvansied G70 5/16th" of min break strength of 18,800lb. Sorry I quote in lbs but I do not have the metric chain equivalents. Actual strengths of Gal G70 just meet that min strength of 14,000lbs. Maggi chain is actually a bit stronger, but the galvanising is not quite so good - it flakes when breaking (if flaking at break is relevant). Because G70 is made from G43 chain, the chain is made then treated, it has the WLL stamped into it (for conventional G70) and to meet this WLL for gal G70 the safety factor is reduced from 4:1 for G43 to 3:1 for Gal, marine G70. G70 is made to special order for West Marine and is not sold by Peerless (except to WM) and gal G70 does not appear in the Peerless catalogue. Stainless G50 chain, in America has a min break strength of 9,600lbs.

I have the metric G70 specs, somewhere. I'll dig them out.

But if you are considering G70 note that it is very, and I emphasise the very, difficult to find connectors that fit the chain and are sufficiently strong. Simply put - most shackles are not strong enough.

edit - you can have larger links welded on by Maggi, if you buy Maggi chain. But this is a 'one off' and you rely on Maggi getting those few extra links right. If you buy from Peerless I'm guessing you are on your own and can have the local welder put larger links on - but you would need to really trust the welder and his choice of steel. end edit

Jonathan

 

[J Neeves]

Peerless metric G70 comes in 2 or 3 sizes. 8mm and both DIN and ISO in 10mm.

The WLL for 8mm is 1,400kg and for 10mm 2,200kg. Proof Load is 35 (3,570kg) and 55 KN 5,600kg and ultimate break strength 68KN (6,930kg) and 108KN (11,010kg) respectively.

From the link measurements a shackle pin of the correct strength should fit edit, but I would check as Maggi's 8mm link would not take a 3/8th" 2t shackle (and 8mm 2t shackles are not easy to find) close edit.

They are making a G40 to DIN spec in 6,7,8,10,11 and 13mm and to EN818-3 in 10, 12 and 14mm.

Maggi's G70, called Aqua 7 for 8mm has the same WLL of 1,400kg but Maggi are working to a 5:1 safety factor and suggest the min break strength is 7t. I have found it impossible find a shackle pin (of a commensurate strength) to fit Maggi's G70 link but Maggi supply a 'C' link (but I have seen no independent tests for this product - though one would think it at least matches the chain in strength).

No one makes a 6mm G70 but you can buy, through West Marine a G70 1/4" galvanised short link (its approximately the same size as a 1/4" G43 link (or so I am told).

If I were buying I would check my gypsy for fit, edit, check that the shackles fit and that the shackles then fit the anchor! close edit

Jonathan

 

[J Neeves]

My turn to ask a question

I note a more frequent use of EN818 -2 and EN818-3 (referring to link size, or steel quality as well?)

Where do they fit in? Are these different to DIN - or just a 'European' version of the German DIN size.

Some of the windlass companies make gypsies to suit, the Peerless range of metric chain for marine windlass includes EN818-3. Is there a difference between EN818-2 and EN818-3 - as I have seen both quoted - but they seem the same size of link.

But it does not come up much on 'chain' threads here.

Any knowledge?

Jonathan

 

[macd]

So for equal sizes, s/s chain G50 has less strength than galvanised G70??

Yes, oldvarnish, in a ratio of 5:7. Those G numbers aren't just happenstance.

 

[oldvarnish]

thanks macd and J. Very good replies

 

[J Neeves]

No,

The G70 is a misnomer - it was G70 but once its been galvanised it loses some of that strength and the G70 becomes the strength of , say, G60 (but its still called G70 - simply to confuse (and maybe they could not think what else to call it!)

Vyv will correct this but:

You take, say G40 chain - heat (red heat) and quench it (in Oz they quench with water I think Vyv told me they use oil in other processors) this destroys its crystal structure. You now re-heat and cool, temper, under a very accurately controlled temperature cycle and recrystallise. The original steel chemistry and the strict re-heat cycle (the tempering) impart strength. By altering the chemistry and temper process you can make a whole new range of steels with strengths upto in excess of 1,300 MPa (G70 is nominally 700 MPa). The process results in steels that are strong, hard and at the extreme used as protective armour for military vehicles.

The tempering temperature of a 700 MPa steel is at about the same temperature as galvanising (Q&T processors are secretive and do not divulge temperatures) so when you come to galvanise you destroy (or undo) some of the tempering process and lose some of the introduced strength.

This is why you should not regalvanise G70 chain (or an original Rocna anchor, or an Anchor Right Excel, a Manson Supreme or the new Mantus shank) - as you will lose more and more strength. I do not know but guess the more you do it the closer it gets back to being whatever it was before it went through the Q&T process in the first place.

Tests on gal G70 short link chain show it to be near specification, just over the minimum strength of the specification. I have no idea how close to the min spec might be for a G50 stainless but I suspect close.

It is possible to galvanise G80 chain (Campbell the other big American chain maker has done so) same issues, loss of strength. There are other galvanising processes that can be used, Sheradizing being one - that has been modernised by a company called Armorgalv or Distekna, watch this (or another) space. Its for another thread

But G50, it comes in a normal steel spec as well as stainless, is weaker than Gal G70 for the same size.

There maybe other downsides to stainless as an anchor chain. But gal G70 used as an anchor chain is very poorly documented - there are few users and there are potential issues with regard to abrasion.

Hopefully Vyv will have time to correct any errors I have made (he knows and understands this much more than I) - and might make comment on the use of stainless as a chain.

Jonathan

edit And its Burn's Night tonight and tomorrow is Australia Day - an opportunity, if one needs one for amber alcohol. end edit


But if I can ask - what prompted the query?

Jonathan

 

[vyv_cox]

So for equal sizes, s/s chain G50 has less strength than galvanised G70??

Very conveniently, the grade figures are the UTS (ultimate tensile strength) for 8 mm chain, given in kN. As near as makes no difference there are 10 kN in a ton.

There is quite a bit of information about chain sizes, strengths, compositions, etc at http://coxengineering.sharepoint.com/Pages/Chaindefinitions.aspx

As Jonathan says, Grade 70 is Grade 40 after heat treatment. My private theory is that this steel, widely used for construction of almost everything, is available throughout China. Mild steel, used for Grade 30, is probably far more difficult to obtain bearing in mind the steelmaking processes there. So although the chain imported into UK By William Hackett, Bradney et.al. is described as grade 30, much of it tests as grade 40.

 

[vyv_cox]

Vyv will correct this but:

You take, say G40 chain - heat (red heat) and quench it (in Oz they quench with water I think Vyv told me they use oil in other processors) this destroys its crystal structure. You now re-heat and cool, temper, under a very accurately controlled temperature cycle and recrystallise. The original steel chemistry and the strict re-heat cycle (the tempering) impart strength. By altering the chemistry and temper process you can make a whole new range of steels with strengths upto in excess of 1,300 MPa (G70 is nominally 700 MPa). The process results in steels that are strong, hard and at the extreme used as protective armour for military vehicles.

Just for the sake of accuracy - annealed steel with a carbon content of about 0.2% will comprise ferrite (=pure iron) and pearlite (a mixture of iron and iron carbides). Heating the steel to about 850C dissolves all the carbon, forming austenite. Quenching from this temperature converts austenite to martensite, a very hard, brittle metal that is nearly useless for any construction purpose. However, tempering it, which is heating it to a temperature anywhere between about 500 and 700C, followed by quenching again, softens it and reduces its brittleness. Almost all engineering steels will be treated this way.

I assume that there is little call for grade 70 chain in China, so there are no(?) plants carrying it out.

The only downside to stainless steel that I am aware of is its cost. Some of the welding I have seen in SS chains is pretty poor but so it is in some galvanised. The differential oxygen levels referred to above is not an issue in anchor chain - there is plenty of dissolved air in seawater. Different for chain on moorings, where it might become covered in mud. I believe that a lot of stainless steel chain is produced in Spain, mainly for the fishing industry. People have reported being able to buy it at quite reasonable cost in the past.

 

[AntarcticPilot]

My turn to ask a question

I note a more frequent use of EN818 -2 and EN818-3 (referring to link size, or steel quality as well?)

Where do they fit in? Are these different to DIN - or just a 'European' version of the German DIN size.

Some of the windlass companies make gypsies to suit, the Peerless range of metric chain for marine windlass includes EN818-3. Is there a difference between EN818-2 and EN818-3 - as I have seen both quoted - but they seem the same size of link.

But it does not come up much on 'chain' threads here.

Any knowledge?

Jonathan

I'm guessing a bit here, but as I was part of the ISO standards world for about ten years, it is an educated guess!

The EN prefix almost certainly indicates that this is an ISO specification that has been adopted by the BSI. It's full specification should be BS EN 818-(1,2,3, or 4). I've just looked at the BSI web-site, and the information there backs it up. Note that this is a standard for lifting chains, not for anchor chains.

 

[vyv_cox]

My turn to ask a question

I note a more frequent use of EN818 -2 and EN818-3 (referring to link size, or steel quality as well?)

Where do they fit in? Are these different to DIN - or just a 'European' version of the German DIN size.

Some of the windlass companies make gypsies to suit, the Peerless range of metric chain for marine windlass includes EN818-3. Is there a difference between EN818-2 and EN818-3 - as I have seen both quoted - but they seem the same size of link.

But it does not come up much on 'chain' threads here.

Any knowledge?

Jonathan

Most Google sources of these standards want to sell you a copy at an eye-watering price. However, I have been informed, by a poster here I think (thanks) that you can access East European sites where the standard is displayed for free. Here is one that seems to be Turkish http://www.eginlioglu.com/default.asp?Sayfa=DINEN818_2

The suffixes appear to specify different chain grades.