Not all 304 SS is the same

For those interested in following the saga of the hydrogen-embrittlement of 304 SS climbing bolts. This one is a short post to keep the pot boiling while I work on my mega-analysis of the brittle fracture phenomenon at Cabo da Roca. I didn't expect to take 12 months, but that is how it is turning out.

Not all 304 SS is the same

It's worth remembering that 304 expansion bolts haven't been available in Europe for decades as they are not certifiable for outside use in the construction industry.

Thanks that's a fascinating read. I'm a solid state physicist and a quick survey of the literature shows quite a bit of research on hydrogen diffusion into metals which I had heard about but never thought of in the context of climbing hardware.

Emil Briggswrote:

Thanks that's a fascinating read. I'm a solid state physicist and a quick survey of the literature shows quite a bit of research on hydrogen diffusion into metals which I had heard about but never thought of in the context of climbing hardware.

It's one of those rabbit holes to dive down! I've worked with stainless for over 40 years and we learn it exists and what to do about it but related to climbing anchors some of Dave's work is certainly interesting. My comment earlier was related to the fact that we already know 304 is rubbish for mechanical bolts AND as far as I know no 304 mechanical bolts are currently available and certified for use as climbing anchors. My concern as a manufacturer is not shutting the stable door after the horse has bolted but which of the currently available bolts have a potential problem.

Emil Briggswrote:

Thanks that's a fascinating read. I'm a solid state physicist and a quick survey of the literature shows quite a bit of research on hydrogen diffusion into metals which I had heard about but never thought of in the context of climbing hardware.

Same. Hydrogen embrittlement is well known for many metals (316 etc.) especially when designing pressurized storage solutions for H2 gas, but it's interesting to see the amount present in the atmosphere may be have an effect on climbing hardware. 

I started placing stainless 5 piece bolts over 30 years ago in NC and WV. None of the ones I have looked at so far show any signs of corrosion. While not "certified for climbing" the 304  (main components) 5 piece bolts are still among the most common mechanicals in use in the US. 

curt86irocwrote:

Same. Hydrogen embrittlement is well known for many metals (316 etc.) especially when designing pressurized storage solutions for H2 gas, but it's interesting to see the amount present in the atmosphere may be have an effect on climbing hardware. 

In this case the mechanism is one of cathodic charging rather than exposure to a hydrogen atmosphere. The sulphide produced by the bacteria is a well known "hydrogen poison" and greatly stabilizes the atomic hydrogen concentration at the metal surface. There seems to be a consensus in the literature that the impact of hydrogen once it diffuses into the metal is the same, regardless of whether it comes via an external high pressure source of hydrogen gas, or via an electrolytic process.

timothy fisherwrote:

I started placing stainless 5 piece bolts over 30 years ago in NC and WV. None of the ones I have looked at so far show any signs of corrosion. While not "certified for climbing" the 304  (main components) 5 piece bolts are still among the most common mechanicals in use in the US. 

The whole question of the degree of martensitic conversion is pretty much irrelevant for the vast majority of crags. There simply isn't the environmental sulphate necessary to attract SRB to your party. So, no SRB, no sulphide, no cathodic charging and thus no deleterious impact of martensite. In our part of Australia which is subtropical/marine we have decades of experience with 304 anchors of all types and have never encountered a single case of SRB attack. However, down south of Sydney I am investigating a basalt sea cliff where we have a very clear example of SRB attack. The source of the sulphate is currently a total mystery. I guess the rule is "never say never" but I reckon "extremely unlikely" works better.

I made it to: "10mm expansion bolt taken from the sulphate sea cliffs of Praia da Ursa" and had to stop and roll my eyes. Maybe as the title suggests "not all 304 is the same", but NO 304 will ever be 316 or better yet, Titanium. On any sulphate sea cliffs or limestone of anywhere but near seawater especially would people please just use titanium?  

Deep respect to Jim, but I'm going to pick and choose which stainless I use, and a 1/2 x 7" 304 wedge anchor is hellalot cheaper than one in 316 and will last a long long long time in the pure mountain air solid basalt and tufts of the predominant rock in this area. It wasn't but a few years ago that we got bolters to stop using steel, and we have steel bolts in this area holding up fine (some surface rust, bolt dependant) easily after 30 years. 

That said, I did load up on a couple hundred 316 wedge anchors and Petzl hangers (they're also type 316 ss) in prep for the next project. 

Billcoewrote:

It wasn't but a few years ago that we got bolters to stop using steel, and we have steel bolts in this area holding up fine (some surface rust, bolt dependant) easily after 30 years. 

This isn’t entirely accurate. The past two years, I’ve been removing and replacing quite a few of those 30 year old bolts from the tuff and basalt you’re talking about and many of them are corroded to the point of breaking off in the hole when trying to remove them.  They’re still probably reasonably strong, but reusing the hole (and the rebolting process as a whole) gets a whole lot more complicated when the stud breaks off inside the innards of the old bolt.  We should do ourselves (and future rebolters) a favor and try and use the best tool for the job. 

Max Tepferwrote:

This isn’t entirely accurate. The past two years, I’ve been removing and replacing quite a few of those 30 year old bolts from the tuff and basalt you’re talking about and many of them are corroded to the point of breaking off in the hole when trying to remove them.  They’re still probably reasonably strong, but reusing the hole (and the rebolting process as a whole) gets a whole lot more complicated when the stud breaks off inside the innards of the old bolt.  We should do ourselves (and future rebolters) a favor and try and use the best tool for the job. 

When you say 30 yr 304's are breaking off in the hole, is this in comparison with new ones? I've found new 304's break pretty easily. Especially compared to a lot of the old 1/4" bolts I've pulled. I made the mistake once of sharpening my bits before a climb, reducing the bit diameter. I named the route Carnage because of all the broken 304's. That said, well placed fixe 304 bolts & hangers we placed in sandstone, rhyoloitic tuff, and dacite in the 90's appear in great shape.

If this thread has caused any of you to be hydrophobic, and you're swearing 304 off, I have 100 Fixe hangers in 316 SS with 3/8" holes that I'm willing to trade for similar hangers in 304. Not interested in selling; just a 1:1 trade. 316 is overkill where I'm working. 

I would note that, in most environments in which marked sulphate reduction is likely (anaerobic conditions coupled with soluble salts in the rock), 316 is likely inadequate, too.

Thanks for the fun reading!