Corroded bolt :O

Brains

Well-known member
11427196_832651926814988_6290993294302132341_n.jpg


Posted on a facebook site in a language I cant read (French...): https://www.facebook.com/GrottesDeHotton?fref=photo
Guess a bad dose of corrosion!
 

Simon Wilson

New member
It looks like galvanic corrosion caused by a stainless steel hanger being used on a carbon steel throughbolt.

Stay away from any rusty bolts and only ever use carbon steel bolts for short term use - but surely everybody knows that.
 

royfellows

Well-known member
Simon Wilson said:
It looks like galvanic corrosion caused by a stainless steel hanger being used on a carbon steel throughbolt.

Stay away from any rusty bolts and only ever use carbon steel bolts for short term use - but surely everybody knows that.

I am sorry but completely disagree with you on this.

The difference in the galvanic index between two types of steel would be very minimal, beside the corrosion would occur at the point of contact not somewhere else.

I would say that the bolt has been inserted into pyrite bearing rock and the corrosion has been caused by the breakdown of the pyrite into hydrous iron oxide and sulphuric acid.

This is not going to be an issue in the huge majority of natural caves but is areal issue in mines. There has recently been occurrences of this in a very short time scale in mines in the Gwydir Forest.
 

Simon Wilson

New member
royfellows said:
Simon Wilson said:
It looks like galvanic corrosion caused by a stainless steel hanger being used on a carbon steel throughbolt.

Stay away from any rusty bolts and only ever use carbon steel bolts for short term use - but surely everybody knows that.

I am sorry but completely disagree with you on this.

The difference in the galvanic index between two types of steel would be very minimal, beside the corrosion would occur at the point of contact not somewhere else.

I would say that the bolt has been inserted into pyrite bearing rock and the corrosion has been caused by the breakdown of the pyrite into hydrous iron oxide and sulphuric acid.

This is not going to be an issue in the huge majority of natural caves but is areal issue in mines. There has recently been occurrences of this in a very short time scale in mines in the Gwydir Forest.

I'm sure there is some truth in what you say but it is complex and I don't have the knowledge of chemistry to understand it adequately. However, I think the bolt in the photo has been affected by a combination of factors two of which are the galvanic effect of the dissimilar metals and the chemistry of the substrate.

 

Simon Wilson

New member
SamT said:
amazing... looks reasonably  ok from the  outside too.

Experience has shown me that sometimes an exposed bolt head is highly corroded while the hidden part is much less corroded and sometimes it is the other way round. It might partly depend on whether the hidden part is kept relatively dry or relatively wet.

Also of course, as Roy has pointed out, the chemistry of the rock has a big effect.

Still I say, stay away from any rusty bolt.
 

royfellows

Well-known member
What I am looking at in the photograph is typical of the effect that I describe in that the main area of corrosion is along the length of the bolt which is where the most of the acid would gather. Discharges from some mines have PHs low enough to be used as battery acid!

If you look at the point of contact between the dissimilar metals the corrosion is minimal.
Differences in the anodic index (sorry in last post said "galvanic index) of 0.15V or less even in high humidity environments can be discounted.

A good example of my point regarding the contact area of the dissimilar metals is the way that fingers used to fall off clocks. The clock mechanism would be of brass including the main spindle, and the fingers of aluminium pushed on as an interference fit. Where the two metals contacted would be the area of corrosion, causing the fingers to fall off.

The big issue here is the question of how this is likely to affect the safety aspect of what we do.

My advice here is to be suspicious of any rock showing iron coloration. To make matters worse the use of stainless through bolts only buys time, in sulphuric acid they will corrode. There is no easy answer to this, even the epoxy seated bolts designed for purpose will in time fail.

Of course, there is also the question of the effect of low ph water on our nylon ropes.

Trust me to open a can worms!
:LOL:
 

Simon Wilson

New member
royfellows said:
What I am looking at in the photograph is typical of the effect that I describe in that the main area of corrosion is along the length of the bolt which is where the most of the acid would gather. Discharges from some mines have PHs low enough to be used as battery acid!

If you look at the point of contact between the dissimilar metals the corrosion is minimal.
Differences in the anodic index (sorry in last post said "galvanic index) of 0.15V or less even in high humidity environments can be discounted.

A good example of my point regarding the contact area of the dissimilar metals is the way that fingers used to fall off clocks. The clock mechanism would be of brass including the main spindle, and the fingers of aluminium pushed on as an interference fit. Where the two metals contacted would be the area of corrosion, causing the fingers to fall off.

The big issue here is the question of how this is likely to affect the safety aspect of what we do.

My advice here is to be suspicious of any rock showing iron coloration. To make matters worse the use of stainless through bolts only buys time, in sulphuric acid they will corrode. There is no easy answer to this, even the epoxy seated bolts designed for purpose will in time fail.

Of course, there is also the question of the effect of low ph water on our nylon ropes.

Trust me to open a can worms!
:LOL:

Agree with most of that but it is highly complex and very difficult to predict. All the more reason why we should assume that eventually all anchors will need to be removed no matter how good they appear at present.
 

paul

Moderator
Simon Wilson said:
royfellows said:
What I am looking at in the photograph is typical of the effect that I describe in that the main area of corrosion is along the length of the bolt which is where the most of the acid would gather. Discharges from some mines have PHs low enough to be used as battery acid!

If you look at the point of contact between the dissimilar metals the corrosion is minimal.
Differences in the anodic index (sorry in last post said "galvanic index) of 0.15V or less even in high humidity environments can be discounted.

A good example of my point regarding the contact area of the dissimilar metals is the way that fingers used to fall off clocks. The clock mechanism would be of brass including the main spindle, and the fingers of aluminium pushed on as an interference fit. Where the two metals contacted would be the area of corrosion, causing the fingers to fall off.

The big issue here is the question of how this is likely to affect the safety aspect of what we do.

My advice here is to be suspicious of any rock showing iron coloration. To make matters worse the use of stainless through bolts only buys time, in sulphuric acid they will corrode. There is no easy answer to this, even the epoxy seated bolts designed for purpose will in time fail.

Of course, there is also the question of the effect of low ph water on our nylon ropes.

Trust me to open a can worms!
:LOL:

Agree with most of that but it is highly complex and very difficult to predict. All the more reason why we should assume that eventually all anchors will need to be removed no matter how good they appear at present.

And always back up main anchors.
 

Maj

Active member
paul said:
And always back up main anchors.

But no good if your back up anchors are in the same condition as the one shown in the photo.
With no back up the shout when it fails might be FU...............................................
But with a couple of back up anchors in a similar state it might sound more like FU......      SH.......      Bol..................................
Perhaps a good reason to use a natural in the system if possible.
The shout might then be    FU....................          PHEW!

Maj.
 

cavermark

New member
If it was from a marine environment then salty water could have run into the bolt hole to provide an electrolyte - which would allow wastage away from the point of contact of the dissimilar metals?
 

bograt

Active member
Looks to me as if the main corrosion occurred where the expanding sleeve was, maybe this was a dissimilar metal junction causing an electrolytic reaction?

Might be worth checking for this when inserting through bolts, cheaper ones may use cheaper alloys for the sleeve.
 

royfellows

Well-known member
Cavermark
No, its an anode - cathode process whereby one metal dissolves in favour of the other. So the corrosion would be in the contact area.
Useful link: https://en.wikipedia.org/wiki/Galvanic_corrosion

Maj
If back up anchors placed in different area of rock would reduce chance of all being in a pyrite bearing area

I would not worry about this condition in natural caves and feel it very much a mine thing. The mines where this is likely to occur are also easily identifiable by their ochreous nature, I think if the old ladders have iron rungs reduced to matchsticks one would think twice about fitting bolts.

There is a mine in the Llanrwst area where there has been these issues, through bolts could easily be pulled out after a few days. Dont like to mention it by name as there is no official access, its not on CAL access list.

Bograt
Now that is an interesting idea. It would depend on the metal used in the sleeve, but there would have to be significant voltage difference in the anodic index and I struggle to see this as the manufacturers of sleeve bolts will be well aware of such potential issues.
 

cavermark

New member
Has anyone been able to decipher the translations to find out what rock type or environment the bolt is from?  I think all of the previous suggestions are possible.

The photo below shows galvanic corrosion between stainless and carbon steel in marine environment.  I'm under the impression that in a galvanic "cell", the wastage occurs on the point with highest electropotential (eg. sacrificial zinc anodes in seawater ballast tanks on oil tankers), but I'm no chemist.

Bograts idea sounds feasible - I'm sure I've seen cheap thrubolts with alloy sleeves (designed for building work not personal protection).

8179585895_5265edf229.jpg
 

royfellows

Well-known member
cavermark said:
Has anyone been able to decipher the translations to find out what rock type or environment the bolt is from?  I think all of the previous suggestions are possible.

The photo below shows galvanic corrosion between stainless and carbon steel in marine environment.  I'm under the impression that in a galvanic "cell", the wastage occurs on the point with highest electropotential (eg. sacrificial zinc anodes in seawater ballast tanks on oil tankers), but I'm no chemist.

Bograts idea sounds feasible - I'm sure I've seen cheap thrubolts with alloy sleeves (designed for building work not personal protection).

8179585895_5265edf229.jpg

I am open minded here, stainless = 0.85V, mild steel = 0.5, difference is 0.35V . Difference between aluminium and brass which we all know about is 0.5 approx.
So stainless and mild is higher than I thought it was which emphasis the need to 'look it up' rather than 'think'.
Lesson learned

Of course one could argue that the effect of salt water on unprotected mild steel on its own will be far worse than any galvanic action?

Going back to the original photograph, unless my eyes deceive me there appears to be some corrosion of the stainless hanger.

cavermarks comment about translating the description or whatever is a good idea, we may learn more.
 

tamarmole

Active member
For all their myriad faults the potential for corrosion is the main reason that a lot of mine explorers opt for rawl type bolts - they get taken out after every trip, cleaned and checked.
 
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