Saw this on ukcaving, I've seen them in mines, but never been on one. Makes you think, though I admit this one looks to be particularly badly corroded.

http://ukcaving.com/board/index.php?topic=15287.msg199410;topicseen#new 

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I'm amazed that anyone would leave ally krabs in-situ for more than a week or two to be honest. Even galvanised steel in contact with stainless will start rusting quicker than it would if not. I wanted to use stainless maillons on a job I was doing, but they were pricier, and I was worried they'd get nicked so used ordinary ones instead. They've been in about a year, and look OK, if a bit rusty at the contact point, but when I first did it we had to use ally krabs, and after only two weeks they were getting that first trace of 'jelly' on them...

Put your hand up if you would even have considered using that again having already seen it on the way up.

Not me.

Personally .... not a fekking chance!

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I think the 'lessons learned' should just have said.

'Don't ab off something that looks as sturdy as a Cadburys Flake'

I've seen stronger-looking bits of metal dredged out of the sea....

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Cross-posting of my thoughts:





Bang on: it's basic galvanic corrosion of dissimilar metals.

The effect will be worse in a wet environment and particularly if there are any metal compounds dissolved in the water.

It's broadly GCSE chemistry and in simple terms, the less reactive metal is 'saved' while the more reactive metal is 'sacrificed' according to the following list:

Potassium > Sodium > Calcium > Magnesium > Aluminum > Zinc > Iron > Tin > Lead > Hydrogen > Copper > Mercury > Silver

Stainless steel comes in somewhere less reactive than copper, so it's a pretty safe bet that it's not going to dissolve away unless you leave it somewhere like Parys Copper Mine.

This is why boats have lumps of zinc on the outside of the hull - as a sacrificial anode to prevent the important stuff such as the (bronze) propeller from dissolving away.

Simple rule of thumb would be to use only stainless components for something left in place and ensure that dissimilar metals are not used - the bolt and hanger will (almost) invariably be stainless, so a stainless maillon would arguably be the only safe bet.


Going back a bit and without wishing to open a whole new (old) can of worms, it's possible to get hold of stainless maillons at relatively sensible prices, but they won't be PPE-spec and may not be stamped with a safe working load.

Firstly, PPE maillons are PPE mostly because they come with a pile of paperwork. Once you've got over that hurdle, you'll find that a marine or industrial supplier can get their paws on a non-PPE (and possibly non-stamped) maillon at about half the price. Although they're batch-tested, they're not stamped and thus they're not sold for lifting or as PPE.

I'm in the marine industry and sell 8mm and 10mm maillons for marine use in both galvanised and stainless versions - the stainless 8mm has a tested breaking load in excess of 4 tonnes, so I'm happy to hang off them all day long. But, some people will still say "it's not PPE, so it's not safe": it depends on your definition of "safe" but I'm not going to worry about whether a maillon can take 2 tonnes, 3 tonnes or whatever of shock loading - because my body certainly won't.

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Cross-posting of my thoughts:





Bang on: it's basic galvanic corrosion of dissimilar metals.

The effect will be worse in a wet environment and particularly if there are any metal compounds dissolved in the water.

It's broadly GCSE chemistry and in simple terms, the less reactive metal is 'saved' while the more reactive metal is 'sacrificed' according to the following list:

Potassium > Sodium > Calcium > Magnesium > Aluminum > Zinc > Iron > Tin > Lead > Hydrogen > Copper > Mercury > Silver

Stainless steel comes in somewhere less reactive than copper, so it's a pretty safe bet that it's not going to dissolve away unless you leave it somewhere like Parys Copper Mine.

This is why boats have lumps of zinc on the outside of the hull - as a sacrificial anode to prevent the important stuff such as the (bronze) propeller from dissolving away.

Simple rule of thumb would be to use only stainless components for something left in place and ensure that dissimilar metals are not used - the bolt and hanger will (almost) invariably be stainless, so a stainless maillon would arguably be the only safe bet.


Going back a bit and without wishing to open a whole new (old) can of worms, it's possible to get hold of stainless maillons at relatively sensible prices, but they won't be PPE-spec and may not be stamped with a safe working load.

Firstly, PPE maillons are PPE mostly because they come with a pile of paperwork. Once you've got over that hurdle, you'll find that a marine or industrial supplier can get their paws on a non-PPE (and possibly non-stamped) maillon at about half the price. Although they're batch-tested, they're not stamped and thus they're not sold for lifting or as PPE.

I'm in the marine industry and sell 8mm and 10mm maillons for marine use in both galvanised and stainless versions - the stainless 8mm has a tested breaking load in excess of 4 tonnes, so I'm happy to hang off them all day long. But, some people will still say "it's not PPE, so it's not safe": it depends on your definition of "safe" but I'm not going to worry about whether a maillon can take 2 tonnes, 3 tonnes or whatever of shock loading - because my body certainly won't.

We have this problem a lot with hot water boilers. (Big industrial units) one company who thought they knew what they are doing, did hundreds of these.

A stainless cylinder, with copper + brass pipework and fittings, with black iron and galvanised steel fittings coming off the top of the boiler (cheaper than brass!)

Add water and wallah! A giant battery! The copper pipe in a period of ❤ months has gone thin and porus and is now coating the inside of the cylinder and there is water pouring out everywhere!

I can't believe people don't remember basic science, you would like to hope anyone clever enough to learn srt and rigging etc would know a basic rule about dissimilar metals...

Stainless steel is NOT the be-all solution that most folk think... It's OK to use where it might get scratched and there's plenty of oxygen around to recreate the oxide film that make stainless steel 'corrosion proof'. I'm an ex marine engineer and latterly the 'Man from the Ministry' who used to go around doing safety inspections of ships and nailing writs to masts of dodgy ships. Examining a wooden hulled small passenger vessel one day (Class VI for them in the know) the owner was very proud of the fact that he'd replaced the galvanised steel through bolts that held the engine bed to the hull with stainless steel ones since my visit the previous year. I asked him if he'd knock some out for me to see (as I half guessed what I was about to see). He was puzzled and not happy but since I was the Man from the Ministry, had to comply. Well, you should have seen his face when they came out - all well rotted to about half thickness. The damp hull timber had expanded over them and excluded any oxygen so once the oxide film had been breached / rubbed off, the bolts just rotted away through galvanic corrosion - bronze prop and hull fittings, ordinary steel engine bed inside hull, no earthing wires etc, etc.

A similar problem I saw were on some RN patrol boats with SS prop shafts. The prop shafts came out of the hull to a P bracket and then the to the prop. In the small gap between the P bracket and prop was a ring of pits in the prop shaft which had caused several prop shaft failures. Analysis of their operations showed that they'd been laid up in particularly stagnant water for several months. The oxygen in the seawater had been removed by H2S from rotting vegetation. The oxide film had been destroyed in the crevice hence the ring of corrosion pits. Some of the other patrol craft that were in regular service didn't have this problem - the prop shafts whirling around in well oxygenated water of the wake kept the oxide film intact...

So, beware using stainless as well unless you're aware of this fact.

BFN

Clive

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I use stainless break pins on my motorbike caliper, its a tough call between normal or stainless.

Normal rust/corrode and can restrict pad movement.

Stainless wear out pretty quick but don't rust.

Its not the wonder material people make it out to be