Two Opposite and Opposed Carabiners: Possibly Weaker Than a Single Carabiner

With permission, I am reposting the results of some destructive testing conducted by Rob Stringer (Facebook).

Rob found that, in certain common configurations, it is possible to cause two 50kN-rated steel carabiners to fail as low as 24kN when loaded as a single unit. The carabiners failed at a low load because the sling forced the two carabiners together. When the carabiners were compressed together by the sling, the gates sustained damage which resulted in a double-open-gate failure, even though both carabiners are autolocking.

Video of the testing (failed at 26kN): vimeo.com/79189561

I found this information interesting because Rob's testing shows that a single carabiner may in fact be stronger than two opposed carabiners under some situations.

I might try to pull test some AL non-lockers O&O to see if I can replicate the results of his testing. If two locking steel carabiners are failing at loads that low, I am curious what would happen with the ever-common double non-locking aluminum biner O&O configuration.

video is not same as configuration above.
?

id be interested in what your tests show! thanks.

With all due respect.. these loads are crazy high for climbing factors, esp when used in a TR situation. The test itself is interesting though.

I have to agree with the above comment - the experiment doesn't look all proper.
1. The top uses shackle, not rope. Carabiners will be forced together to a lesser degree than with the rope.
2. The bottom uses girth hitched, sort of, webbing which slips and slides creating interesting loading effects.
3. Even though wear and age shouldn't be a factor for these carabiners, they looke very well aged.

Anyways - workflow for a your experiment -
- verify rating for single carabiners
- do not use setup in the video - loop of webbing on the bottom is variable best avoided.

john strand wrote:With all due respect.. these loads are crazy high for climbing factors, esp when used in a TR situation. The test itself is interesting though.

+1 Looks like the beginning of another "it will never kill you but let's argue it any way" thread. 26kn on top rope is damn near impossible.

Wow a single locker or double none lockers!
Standard is two lockers or three non lockers!
This is proven to be the most redundant. Combination of biners for a TR's master point!
If you use HMS biners at the master point
The rope generates all forces to the spine which is the strongest part of the biner.
Also pushes gates away from each other so there is no binding or cross load effect on the gate which is the weakest part of the carabiner.
Do believe most manufacturers show half strength on there biners when cross loaded or gate is compromised?
Finally it is silly you would ever generate that much force on a TR!
Have fun be safe!

1. A dynamic rope will never see a 20 kn load in a recreational climbing situation

2. A dynamic rope will break at less than 20 kn generally

3. You will never see these forces in TR

4. I dont believe there has ever been an accident of 2 properly opposed and locked carabiners in a climbing situation as a result of their failure ... Ever ...

Hmmmm

;)

interesting. However, for the reasons covered in the posts above, i see this as purely academic. It in no way discourages me from using two opposite and opposing non-locking carabiners as my standard TR anchor.

This is all wankery anyway but the people that are saying that the loads are way higher then will ever be achieved on TR, while correct, are missing the point. The point is that the two opposite and opposed lockers failed at LESS THEN HALF of the rated strength of the individual lockers due to an interesting failure mode. These were steel biners rated to 50 kN. Scaling to a pair of nominal aluminum lockers rated to 24 kN would imply the same failure mode causing failure at something less than 12kN, which might be concerning. This, of course, scales even lower for lower rated non-lockers, which might be more susceptible to this failure mode. This is 20kN's point.

He's not saying a TR fall will generate these kinds of loads (26kn). He is pointing out that with two steal lockers rated at 50 kn a piece, because of the opposite and opposed setup, failed at around half of what they were rated. So, if all things remained the same except with aluminum lockers rated at 24kn a piece, it is feasible that they might fail at 12-13 kn which in some rare scenarios is possible to generate in a climbing fall.

Great minds think alike Xam.

One of the limitations I see is that if you take a 50kN biner, it needs to have no history to it. To take used metals and test them to fail below their rating shows me that they probably have been subjected to fatigue before the testing began.

With the testing that already has been performed on biners, of course this type of test will only further support that biners are the weakest part of a given system. But, this doesn't convince me that two biners sharing a load introduces more danger to system failure than as if only a single biner.

Again, your experimental methods keep failing to show control testing; as with any garage-style testing itself isn't necessarily a bad idea, just give us some controls to compare. As well, you continue to draw absolute conclusions over one sampled result, not really all that convincing.

Folks theres never been a known failure of 2 opposed and locked carabiners in a recreational climbing situation that we know of. ... Ever ...

If someone has an accident report of such a failure please post it up ...

BD tested NEW 9.4mm ropes at around 13 KN static pull ... If you think the above scenario will fail at around 12-13 KN ... You should refuse to climb on 9.4 mm ropes

blackdiamondequipment.com/e…

There are MANY things that will kill you, this aint one of em ... But it makes for great intraweb arguments

;$

@bearbreeder you are absolutely correct. This is wankery. However, for the sake of argument consider an anchor using opposite and opposed BD ovals rated to 18kN with an open gate failure at 6kN. If the failure mode presented by 20kN is real, then you would expect failure of this anchor at 6kN. This may or may not be cause for concern but it is certainly interesting.

bearbreeder wrote:Folks theres never been a known failure of 2 opposed and locked carabiners in a recreational climbing situation that we know of. ... Ever ... If someone has an accident report of such a failure please post it up ... BD tested NEW 9.4mm ropes at around 13 KN static pull ... If you think the above scenario will fail at around 12-13 KN ... You should refuse to climb on 9.4 mm ropes blackdiamondequipment.com/e… There are MANY things that will kill you, this aint one of em ... But it makes for great intraweb arguments ;$

On a side note, a static pull is not analogous of a dynamic fall whatsoever. A dynamic rope is stronger when loaded dynamically. This is evident by the fact that the UIAA has stated that even the oldest ropes they could find would still pass at least one UIAA drop, which with an old rope, would typically produce no less than 9kN on the rope. BD said their oldest 9.4mm rope was failing at 6kN, which if that strength value could be replicated in a dynamic load, it would not hold a single FF2 fall.

Buff Johnson wrote:One of the limitations I see is that if you take a 50kN biner, it needs to have no history to it. To take used metals and test them to fail below their rating shows me that they probably have been subjected to fatigue before the testing began. With the testing that already has been performed on biners, of course this type of test will only further support that biners are the weakest part of a given system. But, this doesn't convince me that two biners sharing a load introduces more danger to system failure than as if only a single biner. Again, your experimental methods keep failing to show control testing & mathematical modeling; as with any garage-style testing itself isn't necessarily a bad idea, just give us some controls to compare.

This was not my study. I made that clear in the first few words of my post.

While I only linked one test video, the author broke over 20 samples, so this was not a single occurrence. Also, fatigue in carabiners is nearly unheard of when the carabiners are used in a manner relative to their intended application. The number of load cycles required to induce fatigue in a steel carabiner would be astronomical. Aluminum carabiners can typically withstand at least 10,000 load cycles to 8kN, and aluminum is far, far more susceptible to metal fatigue than steel is. In fact, steel has a zero-fatigue limit by which a load below a specific threshold will not cause any fatigue, no matter how many load cycles the carabiner is subjected to.

More info on what I am talking about: en.wikipedia.org/wiki/Fatig…

Xam wrote:@bearbreeder you are absolutely correct. This is wankery. However, for the sake of argument consider an anchor using opposite and opposed BD ovals rated to 18kN with an open gate failure at 6kN. If the failure mode presented by 20kN is real, then you would expect failure of this anchor at 6kN. This may or may not be cause for concern but it is certainly interesting.

There has never been an accident due to the failure of two properly opposed NON locking carabiners that we know of in a recreational climbing situation

In fact there is a reward for 40$ on RC for the first person to come up with a recognized genuine accident report of such ... No one has claimed it yet

In all the decades of climbing and using 2 opposed biners ... Not one

In the BD link i posted above they static pull tested old ropes to as low as 6-7 KN ... Yet we know that there has NEVER been a case of a broken rope in good visual condition that wasnt due to chemicals .... Ropes dont break, even old ones in climbing situations

If you are worried about 2 opposed non lockers, you should refuse to even TR on old ropes

Falls in climbing are dynamic

There are things that we really should argue about that WILL kill you like rock fall, crp belaying, gear placement, lowering/rapping, etc ...

But on the intrawebs we luuuv to argur about minute things that wont do anything ....

;)

26kN, way higher than any load a top rope anchor should ever take

20 kN wrote: This was not my study. ...

Arguing anecdotal footnotes on poor testing. All the more reason why tech discussion in this medium is close to pointless.

Xam wrote:@bearbreeder you are absolutely correct. This is wankery. However, for the sake of argument consider an anchor using opposite and opposed BD ovals rated to 18kN with an open gate failure at 6kN. If the failure mode presented by 20kN is real, then you would expect failure of this anchor at 6kN. This may or may not be cause for concern but it is certainly interesting.

If one is concerned about this failure mode on say BD ovals, one has to do the test on ovals rigged appropriately. You can't take a test done on steel lockers on a rigid shackle and just extrapolate the results to some situation with different biners rigged differently.

There's a difference between strength, and safety - while the claim was made that in some cases a single biner might be stronger than two opposed biners, it's not likely to be safer than two opposed biners.

@bearbreeder Your right! It's a subtle point and one might argue not an important one (your argument)...but it is nice to understand the argument so you can consider the limits of it. It seems to me that many up thread did not consider the argument completely by dismissing it due to the high forces in the test referenced.

@bobbin You right, of course. But scaling one engineering test result to another similar situation is used frequently in practice when time or cost prevents doing the specific test of interest...I am certainly not going to do it but 20kN said he was considering doing a similar one. As long a one considers the limitations of such a technique, it is certainly valid. (A infamous failure of this scaling technique is, of course, the O-ring failure in the challenger disaster.) Dismissing it outright due to the rigging not being identical certainly does not leave much room for discussion or understanding.

The argument of safety versus strength is not lost on me...and is certainly not one I originally argued against.

Yes, these loads are never seen in normal climbing situations.

Even for a grade VI bigwall, where all 4 members are jumping up and down and having a pillow fight on the portaledge, not likely.

Highlines on the other hand, where they're using amsteel lines and cable pullers, I'm sure they find this information interesting. It makes a serious shackle more attractive than carabiners.

Or suppose you're: pulling a stump, recovering a stuck truck, building your own house and hoisting a beam, moving boulders while landscaping, building an epic tree fort... these are all situations where you can generate huge forces, and where equipment failure can be disastrous. It's a reminder that subtle mistakes in rigging can compromise the safety of a system.