Simon Wilson said:

Don't ever leave any metal in contact with a stainless steel hanger that isn't stainless steel.

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I use stainless maillons quite a lot. I also use carbon steel maillons because I have a big stock of them. If I'm going to leave a cave rigged for more than a day I now use stainless maillons. Stainless maillons cost about three times as much but they are more economical. I have thrown away dozens of rusty maillons over the years and I wish I had started buying stainless ones a long time ago.

Why do stainless maillons have a higher strength rating for the same diameter bar as the mild steel ones? It's always puzzled me. Do they need to be stronger, and so are manufactured to be stronger via tempering etc., or is it just a consequence of the material used being naturally stronger? If a hanger plate is only rated to 27kN, why do we need a 40kN maillon? I'm not complaining, as I've used them myself, but not for strength, just long-term placements - not that I use many, as I can't afford them in the numbers I'd need.

Mind you, someone gave me some 40kN 10mm hanger plates recently, but likewise, I doubt there's a 10mm throughbolt that's rated at 40kN either?

Genuine Peguet Maillon Rapide are not mild steel, they are made of a special purpose-made steel. The challenge in making Maillons is in getting the two threads to line up and so they make a special steel which has the property of being able to be bent very accurately. It is a medium carbon steel which is similar to the type of medium carbon steel that high tensile bolts are made of so it also has a high tensile strength.

Cavers choose to use 7mm long Maillons not because of their strength but because we need the opening size which suits our ropes. There is also another dimension requirement and that is the bar size of 7mm. That is because research has shown that the minimum radius which a rope should be passed over without loosing strength is approximately 3mm.

The steel that stainless maillons is made from is 316 and is chosen for it's corrosion resistance but this is achieved at the expense of diamensional accuracy. You will find that when you screw up a carbon steel Maillon the threads always line up but not with a stainless one. With stainless ones the threads sometimes line up perfectly and sometimes not, in which case you have to use a spanner. If your doing permanent rigging you will always carry a spanner to tighten the Maillons anyway.

No Maillons are heat treated after bending; the slight difference is strength is just to do with the tensile strength of the steel which happens to be slightly higher for the stainless steel.

If you do use a Peguet Maillon Rapide which is not of the same material as the hanger you will be going against the advise of the manufacturer.

Hanger plates are designed to comply with the EN and UIAA standards which require a strengths of 20kN and 25kN.

Thanks for the info Simon - very useful. I've certainly noticed SS maillions can be a bitch to tighten up, but assumed that was as much to do with its property of sticking to itself.

Pwhole also likes to Grease his Maillons when he puts them in for a long time, this seems to help create a seal against moisture in the threads.
This seems like good practice to me, do you grease your maillons Simon?

I have had to throw stainless Maillons away due to the misalignment Simon describes causing them basically seize up. The force then needed to unscrew them while held in a vice has trashed them, or at least trashed the threads.

He has actually answered a question for me.

royfellows said:

I have had to throw stainless Maillons away due to the misalignment Simon describes causing them basically seize up. The force then needed to unscrew them while held in a vice has trashed them, or at least trashed the threads.

He has actually answered a question for me.

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This could also be due to cold welding. We often see this at work if someone used an A2 stainless nut with an A2 bolt.

Yes. It's more often called galling. It's caused by friction so you need to keep the threads clean and lubricated. My guess is that if it was so bad it trashed a maillon then the maillon had continued to be used after the threads had been damaged by galling.

I've tried a few different lubricants for maillons over the years and the best thing is spray grease. For stainless maillons any lubricant will stop galling but the best compromise of effectiveness, ease of use and availability is spray copper grease which you will find at any car accessory shop.

Greasing carbon steel maillons will protect the threads but will do absolutely nothing to protect maillons from corrosion if they are left in contact with stainless anchors. It isn't the thread that corrodes; it's the part in contact with the stainless steel. The problem of dissimilar metals in contact has been discussed a lot on this forum. It causes galvanic corrosion and in a wet location it can be very rapid indeed.

Carbon steel maillons are very cheap but they are false economy compared to stainless if you leave them in place for any length of time.

Simon, do you get galvanic corrosion between different grades of stainless? (sorry if this has been coverd elsewhere, but I can't find it)

A couple of years ago, I noticed the carbon steel maillon connecting the stinless steel chain to the stainless steel anchor at the bottom of Blue pencil Passage in Swildon's was corroded nearly the whole way through (at both ends of the maillon!).

The only stainless maillons I had at the time were cheap 304 ones I'd got from work, so I used one of these for the chain. I've been meaning to check up on it (or replace it witha 316 one) but despite passing by in the streamway below many times since, I've never got around to popping up the chain to have a look.

Is the 304 maillon likely to have corroded and more importantly, could it cause corrosion to the 316 anchor?

For the sort of application we are talking about you can forget galvanic corrosion between 304 and 316; it will be insignificant.

Have a gander at a reactivity series for metals.
The further apart the two metals are in the series the faster galvanic corrosion will proceed.

Simon Wilson said:

Yes. It's more often called galling. It's caused by friction so you need to keep the threads clean and lubricated. My guess is that if it was so bad it trashed a maillon then the maillon had continued to be used after the threads had been damaged by galling.

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So your suggesting it's avoidable by cleaning the threads.
would you agree there are 2 alternatives:
1) cleaning with a toothbrush or jetwasher (if you can keep the maillons in one place)
2) cleaning with an ultrasonic waterbath https://www.google.co.uk/shopping/product/2558373110095736493?bav=on.2,or.r_cp.&psi=1lqYWMq6H4v_UOX_iqgP.1486379794456.3&dpr=1&bih=921&safe=active&ech=1&q=sonic+water+bath&tch=1&biw=624&prds=hsecnline&sa=X&ved=0ahUKEwi4pZydrPvRAhVkJcAKHVeeBxUQ2SsILw

and then when you've got them running again (assuming the maillon is still serviceable ie not rusty) then you can grease them and use them for a bit longer?

I've often wondered how well these ultrasonic cleaners would work on caving krabs etc.

It seems like a perfect solution, but I've never heard of anyone using them, so maybe I'm missing something, or maybe we are all missing something!

There was a thread on aditnow  concerning the ultrasonic cleaners,few folks on there use them and rated them.

http://ukcaving.com/board/index.php?topic=16035.0

I've got one of the cheap lidl ones.  Works great on things like crolls, krabs, pantins etc. It can fetch the anodised plating off things though.

Best result I've had is with my climbing cams.  Some of the smaller older ones were getting very prone to seizing etc, but a minute or two in the bath with some warm soapy water and they're as good as new, you can actually see all the grit and grim working its way out of the gaps.

Has to be said, I've only ever given my stuff one go through it (probably due for another session).  I do use it for other stuff as well, like my leatherman tool, swiss army knife etc.  I can imagine its great for cleaning up bits and bobs of disassembled componentry,  gears, springs etc etc.

Divers use them for regs and other gubbins.

The image of SamT fiddling with Krabs in the bath is somewhat disturbing and shouldn't be publicised!

But on a serious note, my Father-in-law used an ultrasonic bath to clean my wife's engagement ring and I have to say it came up as good as new so maybe it could be used for restoring kit?
I will have to ask him to try it out.