Zinc Failure Modes

This probably will turn into a shouting match of zinc vs ss, but before that happens I hope to gather some information. 

Long story short a development partner and I disagree about SS vs Zinc and which is more sustainable long term. 

***This is all in reference of 1/2" bolts***

My partners argument comes from a well known metallurgist in the climbing industry. Along the lines of 1/2" plated steel bolts can be pit rusted 1/3 of the way through and still have nearly full strength which is many factors of safety above what climbing would require. Further the cheaper material allows for nicer (5 piece) bolts to be purchased which are easier to remove, replace, and maintain leading to more holes being reusable. 

He also claims 1/2" bolts can/will last 50+ years without being a danger to climbers. 

My question to the community is: 

Are there documented cases of 1/2" zinc bolts failing **due to corrosion**?

What is the failure mode for in these cases?

Counterpoints to all the above points? 

How much longer will SS last over Zinc in the same conditions? 

While we are at it, is there anything wrong with using wedge bolts in solid (hard) rock? Was this a debate in years past as bad practice? 

For the sake of simplicity assume the high sierra for conditions. 

To be clear I'm curious and just like to have backing for my choices more sound than "well the community says to do it this way and so shut up and do it this way".   

Use stainless steel. There's lots of info out there (including on this forum). You might find this helpful https://www.hownot2.com/post/bolting-bible-metal. 

3/8" stainless wedges are fine in good quality hard rock, but you should check in with what other people are doing in your region. Do you have a local access society you can contact for advice? Here's some info on bolts https://www.hownot2.com/post/bolting-bible-mechanical-bolts

Dan The Man wrote:

Use stainless steel. There's lots of info out there (including on this forum). You might find this helpful https://www.hownot2.com/post/bolting-bible-metal. 

3/8" stainless wedges are fine in good quality hard rock, but you should check in with what other people are doing in your region. Do you have a local access society you can contact for advice? Here's some info on bolts https://www.hownot2.com/post/bolting-bible-mechanical-bolts

Yeah I've read and re-read the bolting bible. The local standard is almost all Zinc bolts here, I don't think the information in the bolting bible is going to change that, while a good resource it lacks real world examples of why zinc is bad. 

Sort of the reason for this post is to come up with real world reasons why to use SS over Zinc. 

To be clear I am on the SS train. I'd just like some reasonable arguments with real world examples to help sway other developers towards SS. Just saying to do it because the material is nicer or corrodes less holds no ground if the person believes both will need to be replaced and the difference is negligible on longevity. 

So again I ask for real world examples of 1/2" zinc bolts breaking due to corrosion and how long it took. I think that data would be very valuable. 

If you're living in an area where the community is still using zinc 5 pieces, and there are active community members monitoring and maintaining those bolts, it's not as bad as spraying zinc bolts in areas lacking community maintenance.

But just because there are community members currently maintaining the hardware doesn't guarantee that there always will be, eventually they should switch to stainless.

Stainless can last indefinitely longer, depending on if they're ever exposed to contaminates, which may be never in the sierras.  100 or 200 years from now I'd still trust a stainless bolt in those conditions if they visually looked OK, but not a zinc bolt

This recent thread has some good photos of rusted zinc-plated bolts https://www.mountainproject.com/forum/topic/124912846/plated-steel-bolts-corrosion-on-the-embedded-portion-of-the-bolt

Some of those photos are from Joshua Tree and relatively new bolts.

You should get some experince replacing heavily corroded 5 peice and wedge anchors using modern methods before you make generalizations about one being easier than another.  Rusted in 5 peices can be quite the pain in the ass to remove and drilling out the sleeves can often result in a wonky hole only suitable for a glue in,  while modern wedge anchor removal is pretty straightforward and can be very effective.  If I was bolting in granite I'd go for a quality 3/8" SS stud vs a plated 5 peice.  Sure the 5 peice is going to last a long time in arid environments, but passing along maintenance to someone in the not so distant future is poor form. Zinc can also kill lichens and make the rock streaky, and then when that's done you can count on some nice unsightly rust streaks.  

The reason you don't hear more about rust related failures is because the bolts USUALLY look quite bad before they are weak enough to fail under the forces of a climbing fall,  that isn't to say it doesn't happen though.  Massive rebolting efforts across the country, and the switch to SS I think is largely to thank for the fact that we don't hear of more rust related bolt failures.  

DrRockso RRG wrote:

You should get some experince replacing heavily corroded 5 peice and wedge anchors using modern methods before you make generalizations about one being easier than another.  Rusted in 5 peices can be quite the pain in the ass to remove and drilling out the sleeves can often result in a wonky hole only suitable for a glue in,  while modern wedge anchor removal is pretty straightforward and can be very effective.  If I was bolting in granite I'd go for a quality 3/8" SS stud vs a plated 5 peice.  Sure the 5 peice is going to last a long time in arid environments, but passing along maintenance to someone in the not so distant future is poor form. Zinc can also kill lichens and make the rock streaky, and then when that's done you can count on some nice unsightly rust streaks.  

The reason you don't hear more about rust related failures is because the bolts USUALLY look quite bad before they are weak enough to fail under the forces of a climbing fall,  that isn't to say it doesn't happen though.  Massive rebolting efforts across the country, and the switch to SS I think is largely to thank for the fact that we don't hear of more rust related bolt failures.  

Rust/lichen streaking is a good point.

Does anyone have numbers and sources for how long stainless lasts vs zinc? 

For example how old are the bolts in this thread? https://www.mountainproject.com/forum/topic/124912846/plated-steel-bolts-corrosion-on-the-embedded-portion-of-the-bolt 

Although those look to be 3/8 I think if they are less than say 20 years it could help in convincing people to move towards SS. **edit** I see the routes are 10 years old or so. however many of the photos include stainless/zinc mixed and so this is going to be dismissed due to the galvanic corrosion. (I'll pass it along in any case but I brought photos like this up).

As I understand it the reason to use SS over zinc is SS will retain strength longer than zinc (due to corrosion resistance). The question I am ultimately fishing for sources and backing to is how much longer will SS last over Zinc in the same conditions?

If I had a research paper, or experimental evidence, or even anecdotal bolt failures it could be convincing enough to outweigh the experts opinion that zinc lasts long enough, isn't a danger, and is more sustainable. 

**Also to reiterate I am not the one who is on the zinc train. To be abundantly clear the purpose of this thread is to gather actual evidence to support the SS claims in order to pass it along to help maybe change ethics locally and at large. 

Scrawny White Guy in a Yellow Shirt wrote:

Rust/lichen streaking is a good point.

Does anyone have numbers and sources for how long stainless lasts vs zinc? 

For example how old are the bolts in this thread? https://www.mountainproject.com/forum/topic/124912846/plated-steel-bolts-corrosion-on-the-embedded-portion-of-the-bolt 

Although those look to be 3/8 I think if they are less than say 20 years it could help in convincing people to move towards SS. **edit** I see the routes are 10 years old or so. however many of the photos include stainless/zinc mixed and so this is going to be dismissed due to the galvanic corrosion. (I'll pass it along in any case but I brought photos like this up).

As I understand it the reason to use SS over zinc is SS will retain strength longer than zinc (due to corrosion resistance). The question I am ultimately fishing for sources and backing to is how much longer will SS last over Zinc in the same conditions?

If I had a research paper, or experimental evidence, or even anecdotal bolt failures it could be convincing enough to outweigh the experts opinion that zinc lasts long enough, isn't a danger, and is more sustainable. 

**Also to reiterate I am not the one who is on the zinc train. To be abundantly clear the purpose of this thread is to gather actual evidence to support the SS claims in order to pass it along to help maybe change ethics locally and at large. 

The bolts in the pictures I posted are 10 years old.

To echo what Dr. Rockso said, the removal of corroded bolts is sometime horrendous. While hole for hole is optimal, it is not always achievable. It is 100% better for sustainability in the long run to install stainless so stewards in the future drill less and (hopefully) have an easier time replacing the older bolts.

As for length of time that plated bolts last, all I have is anecdotal evidence from the arid desert of Joshua Tree. I pulled a 1/2" stainless 5pc bolt from the 1990's last year that has a small amount of rust on the 303 stainless cone. The rest of the bolt was in fine working order. I have similarly pulled plated 5pc bolts that were placed in a similar time frame that were so corroded to the hole we had to drill out the sleeve and cone for removal. Generally in J-tree you can use a hook tool to remove the sleeves because the rock is soft enough to give a little. Whenever we have to resort to the drill out method, I know it is in very bad condition.

A similar anecdote, I attempted to pull plated wedge bolts from 1990 last year and they were so corroded the wedges snapped in the hole after just 3 to 4 spins. Absolutely un-salvageable (without core drilling equipment that is). It took 30 years until we had to hack, patch, and then drill another hole. At that rate, a developer could see up to 3 bolt holes drilled in their lifetime on just one placement on their project. I'd say that alone is enough of an argument for stainless to be the bare minimum.

Scrawny White Guy in a Yellow Shirt wrote:

oes anyone have numbers and sources for how long stainless lasts vs zinc? 

I understand it the reason to use SS over zinc is SS will retain strength longer than zinc (due to corrosion resistance). The question I am ultimately fishing for sources and backing to is how much longer will SS last over Zinc in the same conditions?

I already answered this upthread, the answer is indefinitely.  304 and 316ss don't lose their strength over time, they have to be exposed to contaminates to degrade them.  If they are exposed, then they can degrade very quickly.  So it just depends on your environment.

Jim Day wrote:

I already answered this upthread, the answer is indefinitely.  304 and 316ss don't lose their strength over time, they have to be exposed to contaminates to degrade them.  If they are exposed, then they can degrade very quickly.  So it just depends on your environment.

Right, I'm just asking for a source. I've heard this statement before (Numbers range from 50 to 200 years typically). But I have yet to find a reliable source for this. 

The best I've come across is on stack exchange: https://engineering.stackexchange.com/questions/45167/is-there-a-maximum-life-for-things-made-out-of-stainless-steel-or-cast-iron#:~:text=I%20read%20that%20%22316%20stainless,elements%20and%20not%20cared%20for%3F

But still not exactly a good source. 

I'm sincerely not trying to be a devils advocate here. But in order to convince my peers a paper in a journal would be the bees knees. Barring that a respected metallurgist to contradict [omitted name, metallurgist from OP who is well known in climbing community]'s opinion would likely do. 

Look a few threads down, David Reeve is probably the most knowledgeable expert who frequents this Forum:

https://www.mountainproject.com/forum/topic/124924111/sulphate-sea-cliffs-are-bad-news-but-what-gives-rise-to-them

I think you're better off trying to convince them from an ethics standpoint- in the sierras (and most areas except sea-side cliffs), we know that Stainless can last indefinitely, but that zinc plated will most likely become unsafe with a human's lifespan.  So by the time a zinc plated bolt you install becomes dangerous due to corrosion (which it certainly will be eventually), you will be too old to do the work of replacing it.   With stainless, the hope is that the bolt never becomes dangerous due to corrosion.

And if they say "well glue ins or stainless mechanical bolts might become dangerous fro contamination corrosion or glue degrading someday too" the distinction is "might", they're likely to outlive the cliff!

If the area is a dry arid place and not seeing a lot of water and it drys up pretty quickly after a rain or snow, then plated/zinc steel is just fine. No need for stainless steel. Especially since SS is so expensive right now. Greg Barnes, please correct me if I am wrong. 

Matt, you're wrong. Stainless is the way to go. Lots of severe corrosion in dry arid places, often after only a decade or two - Joshua Tree, Owens River Gorge, etc etc.

The only exception - where plated steel seems to last a very long time - is arid SOFT sandstone desert areas, in spots that don't see a lot of water (no water streaks, horizontal placements which pool water, etc). Soft means softer than Red Rocks and good Wingate - so basically we're only talking about select areas of southern Utah. The reason is that water is both infrequent, and most important, water evaporates straight THROUGH the rock. So there's no such thing as water staying in the hole to rust the bolt. And in soft sandstone (generally talking about the softer-than-Wingate formations), stainless 5-piece are quite likely to become spinners since you can't really clean the hole thoroughly - even a nylon brush wallows the hole. The newer Power-Bolt+ in 1/2" has a more effective dust cap and the bolts are known to tighten up more reliably in softer Utah sandstone. But this is totally a special case - both soft dry desert sandstone, and due to the particular bolt design. For any place that has rock that soft, best practice would be to use glue-ins for replacement - those using plated 1/2" PB+ are typically doing new routes, or replacements where you immediately have to rap off the anchor.

Hey look at that, HowNOT2 provides! 

https://www.youtube.com/watch?v=1GrHOi-P1T8 (posted only an hour ago, crazy)

Very useful and exactly relevant to the exact bolts in question (PS 5 piece) and concerns. 

Thank you all for the information in this thread I'll compile and pass it along.

Scrawny White Guy in a Yellow Shirt wrote:

Further the cheaper material allows for nicer (5 piece) bolts to be purchased which are easier to remove, replace, and maintain leading to more holes being reusable. 

While we are at it, is there anything wrong with using wedge bolts in solid (hard) rock? Was this a debate in years past as bad practice?

I don't have the data you're looking for, but my personal experience is that 5-piece bolts are often a pain to replace compared to wedge bolts. If the shaft is corroded to the cone to the point where it spins in the hole, cover your child's ears because I'm about to be frustrated. If the rock is hard enough, I like 3/8" SS wedge bolts. Super easy to replace with modern techniques. 3/8" because it allows a damaged hole to be expanded to 1/2" in the future if it ever needed to be replaced, and lighter and cheaper.

Greg Barnes wrote:

Matt, you're wrong. Stainless is the way to go. Lots of severe corrosion in dry arid places, often after only a decade or two - Joshua Tree, Owens River Gorge, etc etc.

The only exception - where plated steel seems to last a very long time - is arid SOFT sandstone desert areas, in spots that don't see a lot of water (no water streaks, horizontal placements which pool water, etc). Soft means softer than Red Rocks and good Wingate - so basically we're only talking about select areas of southern Utah. The reason is that water is both infrequent, and most important, water evaporates straight THROUGH the rock. So there's no such thing as water staying in the hole to rust the bolt. And in soft sandstone (generally talking about the softer-than-Wingate formations), stainless 5-piece are quite likely to become spinners since you can't really clean the hole thoroughly - even a nylon brush wallows the hole. The newer Power-Bolt+ in 1/2" has a more effective dust cap and the bolts are known to tighten up more reliably in softer Utah sandstone. But this is totally a special case - both soft dry desert sandstone, and due to the particular bolt design. For any place that has rock that soft, best practice would be to use glue-ins for replacement - those using plated 1/2" PB+ are typically doing new routes, or replacements where you immediately have to rap off the anchor.

Is that not what I pretty much said in my comment?

ASTM B117 tests will give you data on the appearance of corrosion, but not it's structural effect. First is a link to some 'zinc' coatings testing. SSTs (316 in the case of most climbing hardware) may also show minor signs at low hours in these tests, however the appearance of corrosion on SSTs is much less likely to have structural effects. See second link. 

EDIT: Lots of research has been done on the initial appearance of corrosion and lots has been done on the strength of materials. I don't know of much research that has been done in this middle ground of the structural effects of deep corrosion, as engineers/designers just don't operate in that realm of 'somewhat rusted through but still safe enough' because it's not safe. 

https://www.triangleoshkosh.com/resources/salt-spray-hour-data-sheet-on-electroplated-zinc/

https://www.worldstainless.org/Files/issf/non-image-files/PDF/ISSF_The_salt_spray_test_and_its_use_in_ranking_stainless_steels.pdf

Matt King wrote:

Is that not what I pretty much said in my comment?

No, nearly Greg's entire comment was about soft rock porosity as a key variable, not just weather. Gregg is saying that your logic only applies to very specific and uncommon rock.

Greg Barnes wrote:

...

The only exception - where plated steel seems to last a very long time - is arid SOFT sandstone desert areas, in spots that don't see a lot of water (no water streaks, horizontal placements which pool water, etc). Soft means softer than Red Rocks and good Wingate - so basically we're only talking about select areas of southern Utah. ...

I tend to hear about the dryness of an area being the key factor for longevity, but how about temperature? 

Another question I wonder about is this: Apart from the warm seaside locations (e.g., Thailand), has there been a documented case of a 3/8" bolt ever breaking in regular use (i.e., just hanging on it, or falling on it)? 

I've weighted a 1/4" bolt and had it break, and certainly have heard stories of that happening to others, but 3/8"? 1/2"?