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When should you retire carabiners after a fall

Discussion in 'Archives - Yahoo Canyons Group' started by Tim Vollmer, Aug 9, 2012.

  1. Tim Vollmer

    Tim Vollmer Guest

    G'day folks,

    I thought this one might be of interest. One of my canyoneering mates has done some research and pulled together a post on what a range of experiments and experts from around the world have to say on the impact of falls on the strength of carabiners (You can read it here: http://fatcanyoners.org/bush-guide/dropped-carabiners/)

    Obviously the manufacturers advise to dump them after a fall, and given they are such an essential piece of safety gear most people would comply, but interestingly there seems to be little if any evidence to back that up. Even in some extreme examples -- a guy in the Blue Mountains has dropped them 255m onto a steel plate then tested them -- they seem to retain their rated strength.

    Obviously people will always make their own mind up on when it is time, but it does seem to throw into doubt the concept of these 'micro cracks' that are invisible to the eye but weaken the structure of the 'biners. That said, if anyone has any evidence to the contrary I'd love to hear about it!

    Cheers

    Tim Vollmer Mob: 0404 273 313 Email: tim.vollmer@gmail.com Web: www.fatcanyoners.org/
  2. TomJones

    TomJones Guest

    I beg to differ...

    I worked for Black Diamond for 12 years, one of the largest carabiner manufacturers in the world. We NEVER advised people to toss dropped carabiners. Manufacturer's recommendation is to inspect after any event and on a regular basis. If they function fully, then they are good to go. However, if an individual no longer has 100% confidence in their gear, then they should not use it.

    The "micro-cracking" phenomena is found in high-tech ceramics, a very brittle material, and in the over-eager minds of engineering students who are introduced to the concept in a sophomore engineering class. Fully hardened aluminum is not at all like high-tech ceramics, and micro-cracking has never been observed.

    I'm happy your friends did some testing, but their testing is very much not useful. In order to test for a specific problem, it is necessary to understand the system and the problem; their test protocol indicates they understand neither.

    But, good to know that steel biners self destruct. Since BD did not make steel biners, we never did any tests with them.

    Tom

    --- In Yahoo Canyons Group, Tim Vollmer <tim.vollmer@...> wrote:
    G'day folks,
    I thought this one might be of interest. One of my canyoneering mates has done some research and pulled together a post on what a range of experiments and experts from around the world have to say on the impact of falls on the strength of carabiners (You can read it here: http://fatcanyoners.org/bush-guide/dropped-carabiners/)
    Obviously the manufacturers advise to dump them after a fall, and given they are such an essential piece of safety gear most people would comply, but interestingly there seems to be little if any evidence to back that up. Even in some extreme examples -- a guy in the Blue Mountains has dropped them 255m onto a steel plate then tested them -- they seem to retain their rated strength.
    Obviously people will always make their own mind up on when it is time, but it does seem to throw into doubt the concept of these 'micro cracks' that are invisible to the eye but weaken the structure of the 'biners. That said, if anyone has any evidence to the contrary I'd love to hear about it!
    Cheers
    > Tim Vollmer > Mob: 0404 273 313 > Email: tim.vollmer@... > Web: www.fatcanyoners.org/
  3. Rick Fetters

    Rick Fetters Guest

    I would think that most falls would be within the elastic limits of the aluminum alloy and therefor not be a problem affecting the continued overall strength. If a fall went past the yield point then permanent plastic deformation occurred and there is a strong possibility that the gate would no longer close properly. IIRC most aluminum alloys that might be used for carabiners have a small range between yield strength and tensile strength so they quickly neck-down and break after reaching the non-elastic yield strength range. This has certainly been my experience when bending 6061 and 7075 in the workshop.

    doc

  4. Morgan

    Morgan Guest

    Interesting results, I think a more pertinent question for canyoneers in our area is how well do biners retain their strength when they have grooves that develop from repeated rappels with abrasive sand. (i.e how large do the grooves have to be in order to retire the biner) Anyone have a rule of thumb for this or do you not care? I know I have several awaiting near retirement due to large grooves.

    Morgan

    --- In Yahoo Canyons Group, Rick Fetters <rick.fetters@...> wrote:
    I would think that most falls would be within the elastic limits of the > aluminum alloy and therefor not be a problem affecting the continued > overall strength. If a fall went past the yield point then permanent > plastic deformation occurred and there is a strong possibility that the > gate would no longer close properly. IIRC most aluminum alloys that might > be used for carabiners have a small range between yield strength and > tensile strength so they quickly neck-down and break after reaching the > non-elastic yield strength range. This has certainly been my experience > when bending 6061 and 7075 in the workshop.
    doc
    > >
  5. khourde

    khourde Guest

    Morgan,

    That's a very interesting point. I wonder if there is someone here with an answer? I not only have this issue with some older biners, but also with descenders. How many millimetres of metal can you chew through before you have an impact on the item's strength?

    Tom,

    Interesting comments re the micro-cracking. That is extremely reassuring given that is the thing that seems to continually get brought up when people say you should retire old biners that have had a few to many drops / knocks. I've actually had another email from a guy whose friend has access to a mass spectrometer (or some similar fancy device used to examine aviation parts) and out of interest he examined some old biners. His findings were exactly as you suggested.

    One question. You said: "In order to test for a specific problem, it is necessary to understand the system and the problem; their test protocol indicates they understand neither." Do you have a suggestion for a more appropriate test that could be done? I'd be keen to pass it on.

    Cheers

    Tim



    --- In Yahoo Canyons Group, "Morgan" <morgan2ski@...> wrote:
    Interesting results, I think a more pertinent question for canyoneers in our area is how well do biners retain their strength when they have grooves that develop from repeated rappels with abrasive sand. (i.e how large do the grooves have to be in order to retire the biner) Anyone have a rule of thumb for this or do you not care? I know I have several awaiting near retirement due to large grooves.
    Morgan
    --- In Yahoo Canyons Group, Rick Fetters <rick.fetters@> wrote:

    I would think that most falls would be within the elastic limits of the
    aluminum alloy and therefor not be a problem affecting the continued
    overall strength. If a fall went past the yield point then permanent
    plastic deformation occurred and there is a strong possibility that the
    gate would no longer close properly. IIRC most aluminum alloys that might
    be used for carabiners have a small range between yield strength and
    tensile strength so they quickly neck-down and break after reaching the
    non-elastic yield strength range. This has certainly been my experience
    when bending 6061 and 7075 in the workshop.

    doc



    >
  6. RAM

    RAM Guest

    The ATC's when they wear get mighty sharp along where the rope runs over. I have heard that is why many retire them when that happens. As for biners with BIG grooves. I still use many that are cut half way through....but only for biner blocks. They are the only one's people don't abscond with! ;-) (Here, Ram, this is yours!)

    --- In Yahoo Canyons Group, "khourde" <tim.vollmer@...> wrote:
    Morgan,
    That's a very interesting point. I wonder if there is someone here with an answer? I not only have this issue with some older biners, but also with descenders. How many millimetres of metal can you chew through before you have an impact on the item's strength?
    Tom,
    Interesting comments re the micro-cracking. That is extremely reassuring given that is the thing that seems to continually get brought up when people say you should retire old biners that have had a few to many drops / knocks. I've actually had another email from a guy whose friend has access to a mass spectrometer (or some similar fancy device used to examine aviation parts) and out of interest he examined some old biners. His findings were exactly as you suggested.
    One question. You said: "In order to test for a specific problem, it is necessary to understand > the system and the problem; their test protocol indicates they understand > neither." Do you have a suggestion for a more appropriate test that could be done? I'd be keen to pass it on.
    Cheers
    Tim

    --- In Yahoo Canyons Group, "Morgan" <morgan2ski@> wrote:

    Interesting results, I think a more pertinent question for canyoneers in our area is how well do biners retain their strength when they have grooves that develop from repeated rappels with abrasive sand. (i.e how large do the grooves have to be in order to retire the biner) Anyone have a rule of thumb for this or do you not care? I know I have several awaiting near retirement due to large grooves.

    Morgan

    --- In Yahoo Canyons Group, Rick Fetters <rick.fetters@> wrote:


    I would think that most falls would be within the elastic limits of the
    > aluminum alloy and therefor not be a problem affecting the continued
    > overall strength. If a fall went past the yield point then permanent
    > plastic deformation occurred and there is a strong possibility that the
    > gate would no longer close properly. IIRC most aluminum alloys that might
    > be used for carabiners have a small range between yield strength and
    > tensile strength so they quickly neck-down and break after reaching the
    > non-elastic yield strength range. This has certainly been my experience
    > when bending 6061 and 7075 in the workshop.


    doc



    >
  7. charlybldr

    charlybldr Guest

    I work for Petzl. And our position on the dropped carabiner issue is similar to Black Diamond. If upon thorough inspection, the dropped carabiner does not exhibit excessive damage and functions properly, it's good to go.

    I believe the "micro-cracking" issue to be nothing more than urban myth. Who knows exactly where it began. Possibly from manufacturers who were simply doing the CYA thing after talking to those engineering students. That does not change the fact that if for ANY reason, you do not have faith in a piece of gear, you should retire it.

    As far as wear grooves are concerned, it is surprising how deep the wear groove can be before the carabiner is significantly weakened. Petzl recommends retirement when a carabiner exhibits one to two millimeters of wear. And honestly, that's not even close to how far a `biner can go before it is substantially weakened. But the same holds true: if for ANY reason, you do not have faith in a piece of gear, you should retire it.

    Ram's solution is a good one. Turn those grooved `biners into blocking `biners. Myself, I just retire `em.

    And of course, be cognizant of sharp edges on any piece of equipment. Sharp edges can cut ropes. Knock the edge down with a file or just retire the thing.

    Charly
  8. TomJones

    TomJones Guest

    The wear on a carabiner does not take place on the location of maximum stress; in fact, the wear point is one of the least-stressed places on a carabiner. Therefore, from a strength point of view, the carabiner can be about half-worn through before the standard tests show any problem.

    I have cut halfway through a carabiner on a single rappel. Therefore, I would not want to START a rappel with a carabiner that is half-cut through. My personal standard is to toss carabiners when they are 1/3 cut through.

    I think that "retiring" a carabiner to "blocking use only" is a VERY foolish thing to do. In the field, a carabiner is a carabiner, and anything that looks like a carabiner needs to function like one too. I do, however, take care to have some almost-new carabiners for my Pirana and for my Tiblocs. Once they get torn up a bit, they go to general utility; and when 1/3 cut through, they go to the carport for hanging up ropes.

    Tom

    --- In Yahoo Canyons Group, "khourde" <tim.vollmer@...> wrote:
    Morgan,
    That's a very interesting point. I wonder if there is someone here with an answer? I not only have this issue with some older biners, but also with descenders. How many millimetres of metal can you chew through before you have an impact on the item's strength? >
  9. rich_rudow

    rich_rudow Guest

    Sonny Lawrence told me this story so perhaps he'll chime in on the topic. A biner was half worn through in the usual area where the rope makes contact as it runs through the descender. He installed it on an assembly that would pull until something broke. The biner still failed at the gate. I don't go to half way through the AL stock before retirement, but I'll admit to getting close a few times on long trips when a replacement wasn't available.

    ATC's in particular do get razor sharp on the side opposite the brake hand exit if you push them too far. I remember a time when Todd and I did the first descent of the west arm of Fishtail Canyon. He was coming down on a 200' rap. About half way down I heard a few expletives when Todd realized that his ATC was sharp enough to cut the rope! He ended up having to be extremely careful to get out of the canyon because we didn't have a lot of margin to afford rope damage since we didn't know what drops were ahead.

    Anybody have concerns (like me) about the new version of the Black Diamond ATC XP? They are super light since they hollowed out the sides. I've used the new model without issue so far, but two things worry me: 1) the thermal dissipation on long raps seems like it can't be as good. How much hotter is my descender getting? One of the guys on an exploration trip once took measurements on the way down a 450' rappel (with the old ATC-XP) and temperature was around 250 F - toasty but not enough to damage a rope. Second, and a bigger concern in my mind, when on an awkward start over a choke stone its fairly common to have the descender contact the rock while sliding over. Sometimes there can be a fair amount of pressure on the side of the ATC in this situation. I never worried about the old ATC's fracturing, but the new ones have much less material on the sides and I've wondered if it would be easier to "break" the side right off. Obviously, this situation is counter to the safety instructions provided with the device and I try to be careful, but ..... is the new ATC more susceptible to an outright fracture if it's side loaded on a choke stone? Testing on that scenario would be worth while for canyoneering.

    Rich

    --- In Yahoo Canyons Group, "RAM" <adkramoo@...> wrote:
    The ATC's when they wear get mighty sharp along where the rope runs over. I have heard that is why many retire them when that happens. As for biners with BIG grooves. I still use many that are cut half way through....but only for biner blocks. They are the only one's people don't abscond with! ;-) (Here, Ram, this is yours!)
    --- In Yahoo Canyons Group, "khourde" <tim.vollmer@> wrote:

    Morgan,

    That's a very interesting point. I wonder if there is someone here with an answer? I not only have this issue with some older biners, but also with descenders. How many millimetres of metal can you chew through before you have an impact on the item's strength?

    Tom,

    Interesting comments re the micro-cracking. That is extremely reassuring given that is the thing that seems to continually get brought up when people say you should retire old biners that have had a few to many drops / knocks. I've actually had another email from a guy whose friend has access to a mass spectrometer (or some similar fancy device used to examine aviation parts) and out of interest he examined some old biners. His findings were exactly as you suggested.

    One question. You said: "In order to test for a specific problem, it is necessary to understand
    the system and the problem; their test protocol indicates they understand
    neither." Do you have a suggestion for a more appropriate test that could be done? I'd be keen to pass it on.

    Cheers

    Tim



    --- In Yahoo Canyons Group, "Morgan" <morgan2ski@> wrote:


    Interesting results, I think a more pertinent question for canyoneers in our area is how well do biners retain their strength when they have grooves that develop from repeated rappels with abrasive sand. (i.e how large do the grooves have to be in order to retire the biner) Anyone have a rule of thumb for this or do you not care? I know I have several awaiting near retirement due to large grooves.


    Morgan


    --- In Yahoo Canyons Group, Rick Fetters <rick.fetters@> wrote:



    I would think that most falls would be within the elastic limits of the

    aluminum alloy and therefor not be a problem affecting the continued

    overall strength. If a fall went past the yield point then permanent

    plastic deformation occurred and there is a strong possibility that the

    gate would no longer close properly. IIRC most aluminum alloys that might

    be used for carabiners have a small range between yield strength and

    tensile strength so they quickly neck-down and break after reaching the

    non-elastic yield strength range. This has certainly been my experience

    when bending 6061 and 7075 in the workshop.



    doc
  10. Tim Hoover

    Tim Hoover Guest

    I have switched to a steel carabiner for my rap device (thanks to Rich C for the suggestion). It is a tiny bit heavier but much less prone to wear than an aluminum one.   Any downsides to steel that I should be aware of?   Tim

    ________________________________ From: TomJones ratagonia@gmail.com> To: Yahoo Canyons Group Sent: Friday, August 10, 2012 10:55 AM Subject: [from Canyons Group] Re: When should you retire carabiners after a fall

    The wear on a carabiner does not take place on the location of maximum stress; in fact, the wear point is one of the least-stressed places on a carabiner. Therefore, from a strength point of view, the carabiner can be about half-worn through before the standard tests show any problem.

    I have cut halfway through a carabiner on a single rappel. Therefore, I would not want to START a rappel with a carabiner that is half-cut through. My personal standard is to toss carabiners when they are 1/3 cut through.

    I think that "retiring" a carabiner to "blocking use only" is a VERY foolish thing to do. In the field, a carabiner is a carabiner, and anything that looks like a carabiner needs to function like one too. I do, however, take care to have some almost-new carabiners for my Pirana and for my Tiblocs. Once they get torn up a bit, they go to general utility; and when 1/3 cut through, they go to the carport for hanging up ropes.

    Tom

    --- In Yahoo Canyons Group, "khourde" <tim.vollmer@...> wrote:
    Morgan,
    That's a very interesting point. I wonder if there is someone here with an answer? I not only have this issue with some older biners, but also with descenders. How many millimetres of metal can you chew through before you have an impact on the item's strength? >



    ---

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  11. TomJones

    TomJones Guest

    --- In Yahoo Canyons Group, "khourde" <tim.vollmer@...> wrote:
    Tom,
    Interesting comments re the micro-cracking. That is extremely reassuring given that is the thing that seems to continually get brought up when people say you should retire old biners that have had a few to many drops / knocks. I've actually had another email from a guy whose friend has access to a mass spectrometer (or some similar fancy device used to examine aviation parts) and out of interest he examined some old biners. His findings were exactly as you suggested.
    One question. You said: "In order to test for a specific problem, it is necessary to understand the system and the problem; their test protocol indicates they understand neither." Do you have a suggestion for a more appropriate test that could be done? I'd be keen to pass it on.
    Cheers
    Tim

    Well, since you asked...

    Bur first: since we are looking for a phenomenom (micro-cracking) which has never been observed in the material in question (7075-T6 aluminum), there is little reason to perform tests.

    But, a grad student has to have a thesis, right? So if you were going to look for it...

    Let's put this in the realm of science. What is the thesis?

    There are different ways of thinking about it that would lead to different theses, but I think the most believable thesis is: "a high drop onto a specific part of the carabiner might lead to a significant loss of strength that is not indicated by inspection." In other words, while most dropped carabiners will not be weakened, there may be a few specific orientations that result in significant weakening.

    Without knowing WHAT part to suspect, we have a problem solvable via the Monte Carlo method:

    http://en.wikipedia.org/wiki/Monte_carlo_method

    In this case, you would have to do a large number of drops to be sure to hit all possible impact points to hit the specific orientation that causes cracking. It would be good to record the impact point of each drop, then correlate any loss of strength with the impact point. This would allow you to find the "bad impact orientation".

    Or you could just do a very large number of drops and look for outliers. Maybe after you break them you could figure out where they impacted.

    The original test used a very small number of tests and compared averages. Perhaps your thesis is that dropping from a height makes all carabiners weaker, regardless of impact point - in which case looking at the average would be reasonable. My thesis is that only specific impact points would make carabiners weaker - therefore I do not care about the average, I care about the outliers.

    You also need a good control to compare your results to. The manufacturer's rating is rather useless for this, as it is only a very rough number. In order to run the test, you would want carabiners all from the same batch, and you would need to break quite a few carabiners of the control set in order to acquire a good understanding of the statistical distribution of break ratings, especially since (using my thesis) you are looking for outliers. Also, since aluminum ages, you want to perform your control break series contemporaneous with the drop tests.

    Once you have identified the critical impact location on the carabiner, you could then figure out how to get it to land on that point consistently. Perhaps little pieces of yarn tied to the carabiner at specific points could get them to orient for a specific impact.

    My suggested starting test quantities would be 100 for the control and 1000 for the dropped pieces. It would help to divide each of these batches into subgroups, then compare the stats on the subgroups for consistency, to see whether you have tested enough pieces.

    But again, I should point out that the THEORY suggests that finding a problem is highly unlikely. But then AGAIN, let me close with my favorite quote for the year:

    In THEORY, theory and practice are almost identical. In PRACTICE, they tend to be quite different.

    Tom
  12. TomJones

    TomJones Guest

    You mean, other than it hurts more when dangling, when it swings into your dangly bits?

    The tests Tim reported indicates if you drop it from a height it will likely break.

    Tom

    --- In Yahoo Canyons Group, Tim Hoover <frisbeedog02@...> wrote:
    I have switched to a steel carabiner for my rap device (thanks to Rich C for the suggestion). It is a tiny bit heavier but much less prone to wear than an aluminum one. >   > Any downsides to steel that I should be aware of? >   > Tim
  13. RSpanel

    RSpanel Guest

    Since male canyoneers must have steel dangly bits, a steel biner lets one create a Newton's cradle "in the field" - right?

    ~R

    P.S. - good thread - thanks...

    --- In Yahoo Canyons Group, "TomJones" <ratagonia@...> wrote:
    You mean, other than it hurts more when dangling, when it swings into your dangly bits?
    The tests Tim reported indicates if you drop it from a height it will likely break.
    Tom
    --- In Yahoo Canyons Group, Tim Hoover <frisbeedog02@> wrote:

    I have switched to a steel carabiner for my rap device (thanks to Rich C for the suggestion). It is a tiny bit heavier but much less prone to wear than an aluminum one.
     
    Any downsides to steel that I should be aware of?
     
    Tim >
  14. So Monte Carlo would be one of the worst methods available due to sheer size, time, cost, and repeatability (which I suspect is why you chose that as an illustration). There are other factors than angle of impact including magnitude.

    Better would be to use an analytic technique the aerospace industry uses often to find errors in manufacturing. You basically play the game with a finite element model as to what is the minimum size void/crack in the worst possible place. Once you determine that minimum size you then use a NDE method that can find voids half the size of your worst case.

    Sometimes, the game is changed slightly where you have a prescribed testing method that can detect voids of a certain size and your company doesn't want to pay for new equipment. You then examine the design and if you find out there is a possibility it could fail even after you tested it (because there was a void smaller than the detection level) you change the design.

    Oh and to the guy earlier who mentioned the mass spectroscopy (that test measures what type of material is in a sample) the test your buddy ran was probably some sort of non destructive evaluation which you can do with x-rays (or other form of radiation/waves you can, depending on the size of the crack you are looking for, use a longer wavelength) or a relatively newer technique where one measures voltage potential losses across various aspects of the a device thought to be good and compare to the suspect sample.

    Thanks for the rope Tom! Looking forward to using it next week in Ouray.

    GLD
  15. stefan

    stefan Guest

    On Aug 10, 2012, at 1:14 PM, Gareth Doskey wrote:

    > Better would be to use an analytic technique the aerospace industry > uses often to find errors in manufacturing. You basically play the > game with a finite element model as to what is the minimum size > void/crack in the worst possible place.

    it's worth mentioning as an aside that although these methods are practical and widely used, it is my understanding that finite element methods don't necessarily accurately capture the fracture of materials in all cases.

    stefan
  16. Tim Hoover

    Tim Hoover Guest

    Well, after nearly being neutered more than once by my piranha I think the extra pain from carabiner banging is not my main fear in that regard.   Good point about breakage. I'll be sure to try to avoid dropping it 250 feet (or was that meters?) onto a steel plate while I'm out canyoneering.   Tim

    ________________________________ From: TomJones ratagonia@gmail.com> To: Yahoo Canyons Group Sent: Friday, August 10, 2012 11:34 AM Subject: [from Canyons Group] Re: When should you retire carabiners after a fall

    You mean, other than it hurts more when dangling, when it swings into your dangly bits?

    The tests Tim reported indicates if you drop it from a height it will likely break.

    Tom

    --- In Yahoo Canyons Group, Tim Hoover <frisbeedog02@...> wrote:
    I have switched to a steel carabiner for my rap device (thanks to Rich C for the suggestion). It is a tiny bit heavier but much less prone to wear than an aluminum one. >   > Any downsides to steel that I should be aware of? >   > Tim



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  17. aj.outdoors

    aj.outdoors Guest

    Like Tom, I usually retire my carabiners after about 1/3 through. Sometimes I'm "VERY foolish" and have a few worn biners that are attached to my rope bags for blocking purposes only. I still carry good biners on my harness.

    Rich, the heat dissipation would be interesting to test. The holes in the sides might allow airflow too; which might offset the cooling (although I'm guessing you are right, that it would heat up faster since there isn't as much surface area to distribute/dissipate the heat. If you have one of the new ones, I have an old ATC-XP and a digital infrared thermometer... ;)

    Interesting thought on breaking the new XP's as well. There could also be an issue where it gets hung up on a small dimple/ledge. Don't know, I still use one of the old XP's...

    As for getting sharp, I've found that the Reverso's are the worst of all. I've had to use a file or dremmel tool on mine numerous times. I've found my ATC-XP to wear MUCH nicer...

    YMMV, A.J.

    --- In Yahoo Canyons Group, "rich_rudow" <rich_rudow@...> wrote:
    Sonny Lawrence told me this story so perhaps he'll chime in on the topic. A biner was half worn through in the usual area where the rope makes contact as it runs through the descender. He installed it on an assembly that would pull until something broke. The biner still failed at the gate. I don't go to half way through the AL stock before retirement, but I'll admit to getting close a few times on long trips when a replacement wasn't available.
    ATC's in particular do get razor sharp on the side opposite the brake hand exit if you push them too far. I remember a time when Todd and I did the first descent of the west arm of Fishtail Canyon. He was coming down on a 200' rap. About half way down I heard a few expletives when Todd realized that his ATC was sharp enough to cut the rope! He ended up having to be extremely careful to get out of the canyon because we didn't have a lot of margin to afford rope damage since we didn't know what drops were ahead.
    Anybody have concerns (like me) about the new version of the Black Diamond ATC XP? They are super light since they hollowed out the sides. I've used the new model without issue so far, but two things worry me: 1) the thermal dissipation on long raps seems like it can't be as good. How much hotter is my descender getting? One of the guys on an exploration trip once took measurements on the way down a 450' rappel (with the old ATC-XP) and temperature was around 250 F - toasty but not enough to damage a rope. Second, and a bigger concern in my mind, when on an awkward start over a choke stone its fairly common to have the descender contact the rock while sliding over. Sometimes there can be a fair amount of pressure on the side of the ATC in this situation. I never worried about the old ATC's fracturing, but the new ones have much less material on the sides and I've wondered if it would be easier to "break" the side right off. Obviously, this situation is counter to the safety instructions provided with the device and I try to be careful, but ..... is the new ATC more susceptible to an outright fracture if it's side loaded on a choke stone? Testing on that scenario would be worth while for canyoneering.
    > Rich
    --- In Yahoo Canyons Group, "RAM" <adkramoo@> wrote:

    The ATC's when they wear get mighty sharp along where the rope runs over. I have heard that is why many retire them when that happens. As for biners with BIG grooves. I still use many that are cut half way through....but only for biner blocks. They are the only one's people don't abscond with! ;-) (Here, Ram, this is yours!)

    --- In Yahoo Canyons Group, "khourde" <tim.vollmer@> wrote:


    Morgan,


    That's a very interesting point. I wonder if there is someone here with an answer? I not only have this issue with some older biners, but also with descenders. How many millimetres of metal can you chew through before you have an impact on the item's strength?


    Tom,


    Interesting comments re the micro-cracking. That is extremely reassuring given that is the thing that seems to continually get brought up when people say you should retire old biners that have had a few to many drops / knocks. I've actually had another email from a guy whose friend has access to a mass spectrometer (or some similar fancy device used to examine aviation parts) and out of interest he examined some old biners. His findings were exactly as you suggested.


    One question. You said: "In order to test for a specific problem, it is necessary to understand
    > the system and the problem; their test protocol indicates they understand
    > neither." Do you have a suggestion for a more appropriate test that could be done? I'd be keen to pass it on.


    Cheers


    Tim





    --- In Yahoo Canyons Group, "Morgan" <morgan2ski@> wrote:



    Interesting results, I think a more pertinent question for canyoneers in our area is how well do biners retain their strength when they have grooves that develop from repeated rappels with abrasive sand. (i.e how large do the grooves have to be in order to retire the biner) Anyone have a rule of thumb for this or do you not care? I know I have several awaiting near retirement due to large grooves.



    Morgan



    --- In Yahoo Canyons Group, Rick Fetters <rick.fetters@> wrote:




    I would think that most falls would be within the elastic limits of the

    > aluminum alloy and therefor not be a problem affecting the continued

    > overall strength. If a fall went past the yield point then permanent

    > plastic deformation occurred and there is a strong possibility that the

    > gate would no longer close properly. IIRC most aluminum alloys that might

    > be used for carabiners have a small range between yield strength and

    > tensile strength so they quickly neck-down and break after reaching the

    > non-elastic yield strength range. This has certainly been my experience

    > when bending 6061 and 7075 in the workshop.




    doc






    >






    >
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