dropping carabiners

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dropping carabiners

Postby ek » Aug 3, 2010 4:56 am

I've been taught that if you drop an aluminum (alloy) carabiner down a pit, and it falls a significant distance, hitting a rock floor, that you should retire it. That it can sustain invisible damage this way, and potentially fail later when it's in use. But is that really true, or is it a myth?

Don't canyoneers drop aluminum 'biners long distances onto rock frequently as part of some pull-down techniques, and then reuse them? They seem to have no trail of dead bodies. And yet I've known climbers and cavers who will retire a carabiner that was dropped 20'.

Do we really have to retire our carabiners after dropping them...or can we just inspect them, make sure they're not cracked and that the gate still works, and continue using them?
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Re: dropping carabiners

Postby paul » Aug 3, 2010 6:10 am

http://www.onrope1.com/Myth1.htm

http://www.geir.com/mythbuster.html

There are plenty of other examples... :grin:

A friend of mine posed the same question while on a tour of the DMM factory in Wales. They showed him how the manufacturer name and strength details were placed on each carabiner using a very large press (efectively a bloody big hammer)...
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Re: dropping carabiners

Postby mgala » Aug 3, 2010 7:24 am

look at our cave pictures
at http://speleo.pl
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Re: dropping carabiners

Postby LukeM » Aug 3, 2010 8:52 am

FYI, I just did some digging and apparently you'll need to find a copy of R&I #81 (Sept 97) page 117 to get close to the primary source for the REI testing. It quotes the REI tests and Chris Harmston from BD.

I also came across a person claiming that that had in their possession test reports from CMI and Petzl that "show that any 'biner fall that does not disfigure the biner beyond a surface scratch has no effect on the rated strength on the 'biner." They didn't want to post the documents unless they could get permission, and they never posted them.

Also check out this discussion where NZCaver talks about hitting carabiners with a hammer and then testing them:
http://www.forums.caves.org/viewtopic.php?f=2&t=7840&start=15

From what I could find there's a great deal of controversy as to whether microfractures can ever develop in an aluminum carabiner.

Obviously, nobody has located a primary source of information here (except NZCavers first hand account). Hopefully with enough looking these mysterious test reports can be dug up and made available. I don't imagine gear manufacturers have much incentive to publish information that makes it possible to buy less gear.
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Re: dropping carabiners

Postby Chads93GT » Aug 3, 2010 9:23 am

Would you reuse the biner, even if it dropped so far that it reached terminal velocity? If so, then what is an acceptable impact speed that would make you think its still safe to use even after a visual inspection? 80mph? 70mph? 60mph? Maybe it will be fine, maybe not, but do you really want to be climbing on gear that makes you wonder if its going to fail at any moment and take your life? No thanks, I will keep my peace of mind, replace the biner, and feel safer knowing im not climbing on questionable gear.

If I drop a biner from any significant distance I would definately retire it to a gear clip.
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Re: dropping carabiners

Postby Amazingracer » Aug 3, 2010 9:50 am

ek wrote:Don't canyoneers drop aluminum 'biners long distances onto rock frequently as part of some pull-down techniques, and then reuse them?


We use that pull down technique all the time here in TAG. The carabiner is never actually dropped any significant distance (less than 10' if that), because the rope does not begin to free fall down until the carabiner has been pull down fairly close to the ground.

At any rate, at $15 a pop. Id rather just replace the thing that risking it. If it fell the distance of a short pit, i'd be fine using. But long drops, i would probably consider time for retiring. But thats just me.
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Re: dropping carabiners

Postby LukeM » Aug 3, 2010 10:10 am

Chad, I guess the question is what exactly is acceptable. Obviously, we put our metal and soft gear through a lot of abuse through caving. How do we know what is ok and what's not? Simple, people extensively test gear that has been subjected to all sorts of conditions and then the reports get passed around and become part of our collective knowledge. The ascenders, biners, and rappel devices I use on a regular basis all have a good amount of wear from abrasion, short drops, etc. For us to get comfortable with this level of abuse we had to be comforted by testing that showed it was ok. If I didn't have it on good authority that you can use static ropes for 5 years, 10 years, and possibly even longer, I might be inclined based on my own intuition to say "this rope has been subjected to so much caving in 3 years! How could it possibly be safe to use?"

I think this is an important topic to address and try to get to the bottom of. For instance, how can we train others in a satisfactory way if we can't give a reliable rule of thumb as to how much abuse is too much for our gear? Is it right to confidently tell people to retire their 'biners after any significant drop if they can be shown to easily survive very long drops with zero loss of strength? Is it right to tell others to just "go by their gut"?
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Re: dropping carabiners

Postby Stridergdm » Aug 3, 2010 11:35 am

ek wrote:I've been taught that if you drop an aluminum (alloy) carabiner down a pit, and it falls a significant distance, hitting a rock floor, that you should retire it. That it can sustain invisible damage this way, and potentially fail later when it's in use. But is that really true, or is it a myth?

Don't canyoneers drop aluminum 'biners long distances onto rock frequently as part of some pull-down techniques, and then reuse them? They seem to have no trail of dead bodies. And yet I've known climbers and cavers who will retire a carabiner that was dropped 20'.

Do we really have to retire our carabiners after dropping them...or can we just inspect them, make sure they're not cracked and that the gate still works, and continue using them?


Canyoneers are just really good at hiding the bodies. :-)

Seriously, the only carabiner I've retired was one that was handed to me at the bottom of Flowing Stone. I'm not sure exactly when I dropped it, but I think it was near the top of the 180' freehang. That one DID have a few minor blemishes from there it appears to have hit the bottom. So I did retire it. But more out of extreme caution than any real fear.

But I think generally the concern is overblown in most cases. But then again, what's $15 vs. your life?

Now we just all need to agree on "significant" distance and we can all be happy. (and carry tape measures for those times we're not sure if we're within inches of significant.)
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Re: dropping carabiners

Postby Scott McCrea » Aug 3, 2010 2:36 pm

Someone, I think it was KP at Black Diamond, tested biners that had been dropped from El Cap routes--1000+'. They all tested normal. Look thru the archives of KP's testing on the BD site. There is some good stuff there.
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Re: dropping carabiners

Postby LukeM » Aug 3, 2010 2:57 pm

Scott, is this what you were talking about?

http://web3.bdel.com/scene/beta/qc_kp.php

I don't see anything there about testing dropped 'biners, although you aren't the first person I've seen who's mentioned that someone at BD tested 'biners collected from the bottom of El Cap and found them to be normal. I would love to find the source for these claims.
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Re: dropping carabiners

Postby Marduke » Aug 3, 2010 4:06 pm

The problem isn't that a dropped biner forms a crack then has a lower residual strength when tested immediately, but rather that a significant drop could produce crack initiation. If the biner is then put back in service where it is cyclically loaded, the initial damage will propagate in what is called fatigue crack growth. Each load cycle grows the crack and lowers the residual strength. Eventually the crack will reach a critical size in which the biner will fail, most likely via ductile tearing.

Exposure to mineral rich aqueous environments (cave mud and sweat) will accelerate crack growth.

I have seen a croll which failed in exactly this manner, starting from a non-visible (in service) corrosion pit at the edge of the rivet hole. The owner never knew of a problem until his foot ascender gave way and broke into two pieces. The final step was a ductile failure. You could see the beach marks on the failure surface from every use session leading up to the final failure. Every time he put his gear away in a humid bag filled with sweaty gear, an oxide layer would form making marker bands.

Keep in mind that when unloaded, any cracks are most likely closed and not visible. They will open under load, when it is difficult to inspect (especially without actual inspection equipment or training).

For what it's worth, I am a Damage Tolerance Engineer for NASA.
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Re: dropping carabiners

Postby Stridergdm » Aug 3, 2010 10:54 pm

Marduke wrote:The problem isn't that a dropped biner forms a crack then has a lower residual strength when tested immediately, but rather that a significant drop could produce crack initiation. If the biner is then put back in service where it is cyclically loaded, the initial damage will propagate in what is called fatigue crack growth. Each load cycle grows the crack and lowers the residual strength. Eventually the crack will reach a critical size in which the biner will fail, most likely via ductile tearing.

Exposure to mineral rich aqueous environments (cave mud and sweat) will accelerate crack growth.

I have seen a croll which failed in exactly this manner, starting from a non-visible (in service) corrosion pit at the edge of the rivet hole. The owner never knew of a problem until his foot ascender gave way and broke into two pieces. The final step was a ductile failure. You could see the beach marks on the failure surface from every use session leading up to the final failure. Every time he put his gear away in a humid bag filled with sweaty gear, an oxide layer would form making marker bands.

Keep in mind that when unloaded, any cracks are most likely closed and not visible. They will open under load, when it is difficult to inspect (especially without actual inspection equipment or training).

For what it's worth, I am a Damage Tolerance Engineer for NASA.


The last line is actually pertinent. Thanks for including it.

I think the key though is the initial paragraph. No one doubts how it can occur. I think it goes back to as you say, "...significant drop could produce crack initiation." The question is how likely is that could. No one seems to have solid numbers on that. Is it 50% of the time? 5%? .05%? etc.

(btw, I may want to PM you some point about some NASA questions I have. :-)
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Re: dropping carabiners

Postby ek » Aug 3, 2010 11:04 pm

The question that comes to my mind is, could a drop significant enough to produce crack initiation nonetheless not produce visible damage?
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Re: dropping carabiners

Postby Marduke » Aug 3, 2010 11:30 pm

ek wrote:The question that comes to my mind is, could a drop significant enough to produce crack initiation nonetheless not produce visible damage?


Most definitely. The larger the damage, the shorter the life. Even with zero initial "damage", a fatigue crack would eventually initiate at a small particle inclusion or microstructure anomaly in the base material. When you incur damage, you are dictating a likely initiation location. The worse the damage, your life gets shorter by orders of magnitude. ie. a ding twice the size may shorten your life by a factor of 1000 (for example).

Obviously the material, size of damage, location of damage, environment, and loading history are all BIG factors in how long a "dropped biner" will last.

Personally, I don't loose sleep at night over "minor" dings on my biners since in practice I'm always redundant with 2 independent points of contact on rope at all times, EXCEPT for my harness half round, rack mallion, and a mallion I use for W3P2's. Since these three "critical" connection points are not redundant, they get "special attention".
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Re: dropping carabiners

Postby Marduke » Aug 3, 2010 11:45 pm

Stridergdm wrote:I think the key though is the initial paragraph. No one doubts how it can occur. I think it goes back to as you say, "...significant drop could produce crack initiation." The question is how likely is that could. No one seems to have solid numbers on that. Is it 50% of the time? 5%? .05%? etc.


I know it's not what you want to hear, but the honest answer is "it depends". Almost any drop will impart some amount of "damage" shortening the life, but how "significant" is it? ANY drop will impart some damage 100% of the time, but that damage may be totally insignificant. A 6" drop onto carpet can impart a microscopic scratch, but it will not effect the life of the biner.

Well,

How far did it drop?
What did it hit at the bottom? (dirt, rock, sharp rocks, how hard were they)
Was the full force of the drop imparted to the biner, or was it a "glancing blow"?
Is the "damage" a scratch, ding, dent, gouge, smear....?
What is the shape of the damage?
Material of biner?
Environment the biner is exposed to? (mud, humidity, sweat, salt air, bat guano, etc)
The loading history of the biner? (both amount of load, and cyclic count)
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