Micro-Fractures in Climbing Equipments
I have always been very careful while handling climbing gear. Last year while returning from an expedition, I met a group that was returning from a tough-looking climb. They were selling off a few of their gear, which were pretty new. Most of the them were carabiners. Out of curiosity I asked them the reason and they replied that those equipment had fallen off a considerable height. I examined them only to find out a few minor looking scratches. They were in good shape.
The guy told me that they may have sustained micro-fractures.
Has anyone ever come across such an issue? Is there a way to scan and determine if the equipment is considerably damaged?
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This is sadly a very persistent myth that has been around rock climbing for far too long. Black Diamond says that as long as the gate action is fine and there is no major structural damage, the gear is fine.
As a side note, the fact that this group decided their gear was unfit to climb on, yet felt okay selling it to someone else who would climb on it, would make me question their character (to put it lightly).
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Aluminum and other metals undergo microcracking only when stretched beyond its elastic limit. Beyond the elastic limit, permanent deformation will occur. The elastic limit is, therefore, the lowest stress point at which permanent deformation can be measured. So if you slam a carabiner point blank at a concrete surface irreversible deformation will occur superficially (a scratch or dent), but the material as a whole will have rebounded perfectly. The elastic limit of aluminum is about 400 million pascals or about 58,000 pounds per square inch (far greater than any other point in the safety chain).
If a carabiner has a cross section of a quarter square inch you would have to pull with about 16000 pounds (58000/4) before irreversible deformation or load bearing would begin to be compromised. However long long before the ultimate load bearing capacity of the biner it would have to be undergo severe elongation. That is why as a rule, if the gate still works, the biner is still safe to use. If it has been stretched the half mm of clearance to interfere with the gate, it has been irreversibly deformed and should not be used for life or death situations unless there is no other option. Better reserve said biners for stretching your hammock or dangling them from the back of your jeep.
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Some articles about microfractures:
We dropped 30 carabiners from heights of 21, 40, and 109 feet onto concrete, filmed the impact on high-speed video, and tested their ultimate strength. ... There was no difference in breaking strength between brand new carabiners and ones that had been dropped, even from 110 feet.
http://www.outdoorsafetyinstitute.com/index.php/news/single/should_you_retire_a_dropped_carabiner/
Omega Pacific also tested carabiners that had been dropped from unknown heights off El Cap. If anything, O.P.’s report shows that a piece of gear gets stronger while flying through the atmosphere then impacting rock—those dropped carabiners broke at loads higher than their rated strengths.
https://rockandice.com/climbing-gear-tips/is-dropped-gear-still-safe/
Q. Is it okay to use carabiners that have been dropped? ... It's best to inspect dropped gear for dings and significant trauma. If only light scratching is visible and gate action is still good, there is a good chance it is fit for usage.
https://www.blackdiamondequipment.com/en_US/faqs.html#CLIMB
If you've ever seen a pull test, you know that carabiners actually stretch quite a bit before they ever break. Aluminum's inherent ductile nature prevents the danger of microfractures. ... REI employees have done controlled pull tests of carabiners dropped from 30+ feet onto a concrete floor and found no strength difference when comparing the "microfractured" carabiners to a control group.
Micro fractures did appear in what are now decades-old Chouinard carabiners. They radiated from the holes drilled to accept the gate pins, and you could clearly see the cracks. This was a manufacturing flaw and was corrected ... aluminum, the stuff climbing gear is made of, is soft. Take a hammer, beat on a carabiner and see if you can crack it. This is where we are today.
https://rockandice.com/climbing-gear-tips/are-micro-fractures-real/
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I consider a couple of factors when it comes to dropped gear:
- Some equipment is pretty easy to inspect. A carabiner has one moving part (the gate, possibly a second, if it's a locker). Nuts and hexes have no moving parts.
Cams on the other hand are not easily examined. - Equipment like non-locking carabiners, nuts, hexes, cams are often redundant. If the carabiner I clipped to a nut fails, that point of protection fails, but hopefully I have something else that catches me before I sustain a ground fall or factor 2 fall.
- Belay devices, belay carabiners, the climbing rope, my harness and my cordelette are not redundant. Most of these (except for the rope) are also pretty cheap.
- Some people are comfortable climbing with dropped gear, others are not. A climbing team is based on trust.
- Did I see what happened to the gear on its way down? Was it a 2000 foot drop, or did it slide down a slab and come to rest on a ledge?
- I am no metallurgist and it is impossible to prove a negative (in this case the claim: "dropped gear will not sustain micro fractures")
Here is how I make my decision whether or not to retire a dropped piece of equipment:
Can I easily inspect it, is it redundant, are the people I climb with OK with climbing on this piece of gear, am I familiar enough with the piece to know it is OK? - I keep it.
Any other situation or if I have just the slightest doubt - I retire it. I won't sell it to anybody else, in fact I destroy it to make sure no unsuspecting person inadvertently uses it.
A couple of final thoughts:
I think it is important to come to terms with the idea that every time you go climbing, you might lose some gear, may it be through dropping or retreat. Talk to your partner about this possibility, and how you will divide the cost.
I don't buy gear from strangers who personally would not climb on the gear any more.
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