Bolts Subject to Irrigation Runoff

A question for the hive mind:

A handful of the routes in the Lower Gorge at Smith intermittently run with water fed by the land owner on the rim diverting their excess irrigation water over the cliff.  In addition to seasonally coating the holds with grime, dust, and odd discolorations, this had the effect of more rapidly corroding the plated hardware that was installed there in the 90s.  This past spring most of the old bolts were replaced with 316 stainless.  Since then some folks have expressed concern that the runoff could create an environment prone to SCC and have advocated for a follow-up rebolting effort with titanium.  We've never seen evidence of SCC at Smith or in Central Oregon and I know relatively little about it other than some very simple basics.

I'm curious what the folks on here more well versed with SCC and crags in more corrosive environments think of the situation.  To me it reads like a very low likelihood-high consequence scenario, but I also feel like I'm poorly equipped to make the call due to a general lack of experience with that problem.

Max Tepfer wrote:

A question for the hive mind:

A handful of the routes in the Lower Gorge at Smith intermittently run with water fed by the land owner on the rim diverting their excess irrigation water over the cliff.  In addition to seasonally coating the holds with grime, dust, and odd discolorations, this had the effect of more rapidly corroding the plated hardware that was installed there in the 90s.  This past spring most of the old bolts were replaced with 316 stainless.  Since then some folks have expressed concern that the runoff could create an environment prone to SCC and have advocated for a follow-up rebolting effort with titanium.  We've never seen evidence of SCC at Smith or in Central Oregon and I know relatively little about it other than some very simple basics.

I'm curious what the folks on here more well versed with SCC and crags in more corrosive environments think of the situation.  To me it reads like a very low likelihood-high consequence scenario, but I also feel like I'm poorly equipped to make the call due to a general lack of experience with that problem.

You've already done the right thing by replacing (most of) the plated bolts, so don't borrow more trouble.  

If, in a few years, the new stainless bolts show signs of corrosion or stainless bolts in other parts of the Gorge show corrosion, then think about Ti.  

John Byrnes wrote:

If, in a few years, the new stainless bolts show signs of corrosion or stainless bolts in other parts of the Gorge show corrosion, then think about Ti.  

That was my initial gut reaction to the situation as well, but another community member who's significantly more educated than I am on this stuff, is concerned that SCC can manifest without any visual indicators.  He seems to think that SCC could occur and we'd have no warning until a bolt just snaps on someone at low loads.  Thoughts?

Isn't coastal salt kind of a major part of scc? You don't have that in this scenario.

Max Tepfer wrote:

That was my initial gut reaction to the situation as well, but another community member who's significantly more educated than I am on this stuff, is concerned that SCC can manifest without any visual indicators.  He seems to think that SCC could occur and we'd have no warning until a bolt just snaps on someone at low loads.  Thoughts?

There's not much evidence of stress corrosion cracking or hydrogen embrittlement even occurring on 316ss in coastal environments, much less inland.  But if you're curious, read through David Reeve's blog https://cragchemistry.com/blog/

drewp wrote:

Isn't coastal salt kind of a major part of scc? You don't have that in this scenario.

Well, if David Reeve is correct, and I believe he is, then it's not the salt but the sulphate that promotes SSC (not SCC) in stainless steel.  See the link above.

i am curious what is in the water.  if it has fertilizer of some sort, and what would be in that. sounds a bit sub-optimal. is there any way to create some sort of diversion to safely channel to another path?

Once you have come across a cracked stainless bolt, then it is a hard not to be haunted by the possibility. However, we need to assure ourselves that there are solid reasons for such things happening, and be aware of the circumstances where this might occur.

I would certainly be alert to what irrigation overflow might be adding to the environment. As John Byrnes says, the serious culprit is sulphate, and there are some agricultural scenarios where this could be so. Application of sulphur would be one.

However, in my experience, for stainless steel to be attacked then the same conditions would be absolutely destroying plated carbon steel. Is this the case? Furthermore, I would expect to see mineral efflorescence at points where the ground water is weeping from cracks in the rock. Something like the one illustrated from Long Dong.

If you find any points of efflorescence like this, send me a sample, and I'll happily check it out for you.

If we ignore situations where we know that environmental sulphate is promoting SRB attack, then the number of cases of stress-cracking/embrittlement is really small compared with the sheer number of SS bolts out there. I know of two causes.

a) Substituting 303 for 304 or 316 seems guaranteed to end in stress cracking even in quite mild corrosive conditions. Why? I have a theory, but need to do a lot more work. For now, I'd use the magnet test to pick up non-316, which would exclude 303 and 304. Don't rely on test kits for molybdenum as some 303 can contain it.

b) Alloys 304 or 316 can be of poor quality and have excessive carbon content. Ideally the L grade should always be used, but is difficult (expensive) to check for, and so creeps into the supply chain. The problem of high carbon is that chromium carbide formation becomes trivial if heat treatment is not scrupulously controlled. This in turn results in a product prone to IGC even under mild corrosive conditions. The gradual development of stress cracks on the outer circumference of bends is something to look for.

That is all super helpful information.  Thank you!

-Re: slim, diverting the water at the source is an option being explored, but we're at the whim of a private land owner, so there are no guarantees.

-Re: David, I'll definitely keep an eye out for effervescence.  Does the color matter/does it need to look identical to your picture or is any effervescence a cause for concern?  The plated hardware that was there was relatively new and definitely corroded quickly.  I want to say the old bolts were less than 10 years old.  I didn't rebolt it and didn't see them when they came out, but the folks that did reported some of the most badly corroded bolts they'd ever pulled out of a route at Smith. (which isn't necessarily saying that much)  Regardless, we'll definitely monitor closely for any cracking and corrosion in general.  Is there potential for the bolt to be compromised and not show any signs of weakness? (corrosion, cracking, etc.)

Thanks again for everyone's insights!

Can the water be diverted elsewhere?

Max Tepfer wrote:

That is all super helpful information.  Thank you!

-Re: slim, diverting the water at the source is an option being explored, but we're at the whim of a private land owner, so there are no guarantees.

-Re: David, I'll definitely keep an eye out for effervescence.  Does the color matter/does it need to look identical to your picture or is any effervescence a cause for concern?  The plated hardware that was there was relatively new and definitely corroded quickly.  I want to say the old bolts were less than 10 years old.  I didn't rebolt it and didn't see them when they came out, but the folks that did reported some of the most badly corroded bolts they'd ever pulled out of a route at Smith. (which isn't necessarily saying that much)  Regardless, we'll definitely monitor closely for any cracking and corrosion in general.  Is there potential for the bolt to be compromised and not show any signs of weakness? (corrosion, cracking, etc.)

Thanks again for everyone's insights!

Colour doesn't matter. Often efflorescence is pretty much white.

It would be very rare for a stainless anchor to be absolutely free from surface corrosion, yet be hiding dangerous incipient cracks. Glue-ins tend to be more obvious in this regard as the crack tends to spring open.

However, sulphate rich areas prone to SRB attack, and employing expansion bolts, are trickier because there is plenty of space beneath the hanger and within the first few millimetres of the hole to make a nice anoxic environment for the bacteria. Often the only clue you have is the "black ring of death" that tends to form around the space where the washer meets the hanger. One of the tricky characteristics of a sulphate environment is that it suppresses the pitting corrosion you'd normally expect with say 304, and an old bolt on a sea cliff can look pretty tidy, yet be dangerously embrittled just below the surface.

This one is from Cabo da Roca on the Portuguese sea cliffs. There is no possibility of visually inspecting a route for bad bolts under these circumstances. The magic knowledge the installer requires comes from the positive identification of sulphate efflorescence, and then shunning all 304, and further, checking that all 316 is indeed not magnetic.

David Reeve wrote:

Often the only clue you have is the "black ring of death" that tends to form around the space where the washer meets the hanger. 

A better photo of the Black Ring of Death by Martin Roberts in Greece. Notice the black ring around the bolt/nut and at the washer/hanger interfaces. This photo has efflorescence too (Bonus!).

David Reeve wrote:

Colour doesn't matter. Often efflorescence is pretty much white.

It would be very rare for a stainless anchor to be absolutely free from surface corrosion, yet be hiding dangerous incipient cracks. Glue-ins tend to be more obvious in this regard as the crack tends to spring open.

However, sulphate rich areas prone to SRB attack, and employing expansion bolts, are trickier because there is plenty of space beneath the hanger and within the first few millimetres of the hole to make a nice anoxic environment for the bacteria. Often the only clue you have is the "black ring of death" that tends to form around the space where the washer meets the hanger. One of the tricky characteristics of a sulphate environment is that it suppresses the pitting corrosion you'd normally expect with say 304, and an old bolt on a sea cliff can look pretty tidy, yet be dangerously embrittled just below the surface.

This one is from Cabo da Roca on the Portuguese sea cliffs. There is no possibility of visually inspecting a route for bad bolts under these circumstances. The magic knowledge the installer requires comes from the positive identification of sulphate efflorescence, and then shunning all 304, and further, checking that all 316 is indeed not magnetic.

David and John, you have both been exceedingly helpful and I very much appreciate it!

One follow up question for David: the bolts in question are 5 piece, so theoretically it wouldn't be too hard to periodically remove the stud and hanger and have a look inside.  Seems like a step worth taking?  I imagine there still could be embrittlement deeper in the placement that could compromise the bolt, but at least you could easily see what was happening to the stud and most of the machine.

Thanks again for sharing your expertise.

Is the darker/black stud and discoloration of the face of the nut in the petzl hanger photo idicitive of SRB or more the ring around the washer in Johns photo? Or both?

Anyone know if N reducing bacteria have the capacity to cause problems with steel bolts? Similar to S reducing bacteria, they live in anoxic micro-environments, use oxygen in nitrate as an electron attractor, and pluck electrons off things in their immediate environment. They produce N gas instead of H2S. Ag field runoff can have a good bit of nitrate, and N reducers are present in the soil wherever you have the right conditions.

EDIT to add that I did some reading and, if I understood it correctly, N reducers do corrode steel but not as quickly as S reducers. Not sure about the practical implications of any of this, but its interesting to think about.

Dang, Tim. Your expertise goes well beyond raptors!

As to the idea of diverting the water… if you can offer the landowner free labor for this project as well as maybe throw in a couple more bonus improvements, he/she may be more willing to listen to your ideas. Also, make sure you listen carefully to any concerns the landowner might have, and address them. All this will go a long way to impressing said landowner with how awesome climbers are as well as getting what you want.  Saying this as a former rural land owner and awesome (but old and weak) climber…

John Byrnes wrote:

A better photo of the Black Ring of Death by Martin Roberts in Greece. Notice the black ring around the bolt/nut and at the washer/hanger interfaces. This photo has efflorescence too (Bonus!).

For the extra bonus, I've sampled that wall and that is sulphate. For the record, most of Kaly is sulphate-free. As far as I know, it is only at a couple of crags where hydrothermal seepage pushes the sulphur level and invite sulphur bacteria to the party.

Max Tepfer wrote:

David and John, you have both been exceedingly helpful and I very much appreciate it!

One follow up question for David: the bolts in question are 5 piece, so theoretically it wouldn't be too hard to periodically remove the stud and hanger and have a look inside.  Seems like a step worth taking?  I imagine there still could be embrittlement deeper in the placement that could compromise the bolt, but at least you could easily see what was happening to the stud and most of the machine.

Thanks again for sharing your expertise.

You could do that, but as a cautionary tale consider the bolt in this video. This is a 304 bolt snapped by a light hammer blow. It is totally embrittled but the action of SRB, but the damage is hard to see unless you get out a microscope. That tiny dark dot toward the centre turns out to be where the bacteria have tunneled in from the outside. 

Tim Meehan wrote:

Anyone know if N reducing bacteria have the capacity to cause problems with steel bolts? Similar to S reducing bacteria, they live in anoxic micro-environments, use oxygen in nitrate as an electron attractor, and pluck electrons off things in their immediate environment. They produce N gas instead of H2S. Ag field runoff can have a good bit of nitrate, and N reducers are present in the soil wherever you have the right conditions.

EDIT to add that I did some reading and, if I understood it correctly, N reducers do corrode steel but not as quickly as S reducers. Not sure about the practical implications of any of this, but its interesting to think about.

You bet that is a possibility. Nitrate reducing bugs are documented, although I've never encountered a situation where I've had reason to believe they might be active. I think the reason that sulphate reducers are so destructive comes down to the presence of sulphur. Sure the bug eats metal as it sucks on electrons, but this is only a minor part of what is going on. The real villain of the piece is it creates a strongly acidic environment rich in hydrogen sulphide. The sulphide poisons the catalytic recombination of cathodically generated atomic hydrogen at the metal surface. So instead of gaseous hydrogen building up, atomic hydrogen begins to diffuse into the metal. The rate of diffusion is accelerated something like 1000x if the stainless is rich in alpha-martensite, as is cold worked 304. So that is the second piece of the jigsaw puzzle. Put the two together, and you get embrittlement right through the bolt in a matter of several years. If the material harbors residual stress, as it must following cold working, then stress crack (SSC) must follow.

Blake M wrote:

Is the darker/black stud and discoloration of the face of the nut in the petzl hanger photo idicitive of SRB or more the ring around the washer in Johns photo? Or both?

I certainly would treat any dark coloration associated with cracks or closed regions as suspect. Think of the normal red color of rust. Nobody likes to see rust, but the bright red stuff is far less worrying that the dark brown/black stuff because the former means high oxygen levels and the later low oxygen levels. SRB are obligate anaerobes and thus dark corrosion products are a warning they could be present.

John Byrnes wrote:

Well, if David Reeve is correct, and I believe he is, then it's not the salt but the sulphate that promotes SSC (not SCC) in stainless steel.  See the link above.

Sulphate as you say John. David's sampling found calcium sulphate in Tonsai and aluminium Sulphate in Taiwan.