Build My Own FeedQC LAB: Gear Doesn’t Last Forever - SLINGS & QUICKDRAWS
Before any piece of Black Diamond gear makes it on to the shelves, it spends months, sometimes years getting put through the wringer by our Director of Quality, Kolin Powick, and his team of Quality Assurance engineers. Through extensive and meticulous testing, both in the lab and in the field, KP and his team help ensure that you can count on your BD gear to be as durable, reliable and as strong as possible every time you head into the mountains or out to the crags. Our QC Lab posts aim to answer some of climbing's most common gear-related questions.
This month, KP and the crew present Part III of their Gear Doesn't Last Forever series (check out Part I and Part II), where they investigate the complex world of slings and quickdraws. Enjoy.
Slings and quickdraws (note: the webbing part of an actual quickdraw is often referred to as a dogbone) come in many different shapes, sizes, widths and lengths and are usually made from nylon, an ultra-high-molecular-weight polyethylene or some combination of the two. Dynex is the BD name for the polyethylene that we use. Other common brand names are Spectra and Dyneema. For argument's sake, they're all pretty darn similar, so I'll just go with Dynex. Some are sewn together using traditional (or not-so-traditional) bartacks, some are knotted together, and some use a Chinese-finger-trap-type attachment along with sewing.
The main differences between nylon and Dynex as it pertains to use in typical climbing situations:
- Nylon stretches a bit (ie. absorbs energy) whereas Dynex doesn't
- Dynex doesn't absorb water as much as nylon
- Dynex has a lower melting temperature (~145 °C) than nylon (~245 °C)
- Nylon holds a knot, Dynex does not
CE Requirements
Pretty basic stuff here-the meat of the CE standard for slings is they must meet at least 22kN when new. No durability requirements, no cyclic requirements, no wear requirements, etc.
Previous Testing
On one hand it seems the general feeling is that metal products should last forever (which of course they don't) whereas there appears to be some unwritten understanding that fabric type products do actually wear out. Even with that said, however, I have certainly seen some people whipping and rapping off some pretty sketchy draws and slings out there.
Over the years I've been removing worn out fixed gear from cliffs I frequent and testing it, and I've published some interesting findings:
http://www.blackdiamondequipment.com/en-us/journal/climb/all/qc-with-kp-from-the-archives-1#VRG
http://www.blackdiamondequipment.com/en-us/journal/climb/all/qc-with-kp-from-the-archives-1#testing
http://www.blackdiamondequipment.com/en-us/journal/climb/all/qc-with-kp-from-the-archives-1#cave
The takeaway from all of this—gear doesn't last forever. Old slings, especially those fixed on sport routes and rap anchors can have a high sketch-factor—but why?
How & Why Slings Wear with Time
Looking at all the slings and quickdraws we've tested over the years, I'd say there are two main factors that cause a reduction in strength:
- Abrasion
- UV
Now I wish I could say that we've done some high-tech super study on this stuff, but we haven't. We've tested old fixed gear (as stated above), and also helped a high school student do a science fair project a few years ago on the UV effects on slings.
His findings basically showed that nylon and Dynex have a reduction in strength when exposed to UV. Interestingly, his study showed that the drop in strength was similar between the two materials, and also it appeared that the major drop in strength (~16%) occurred during the first 10 weeks of exposure, whereas additional exposure resulted in only very incremental decreases in strength. Anecdotal testing from the field (cited above) doesn't exactly correlate to these findings, however, we must remember that there are other factors involved in real world use (falls, abrasion, etc.).
More Testing
We decided to try to compile a bit more data. BD athlete and tech rep Sam Elias stripped a bunch of old mank gear from Rifle, where they were installing steel perma-draws. He brought the gear to BD and we went to town with our tensile tester (remember-when new, slings need to meet 22 kN ultimate strength (4946 lbf)).
Results (dogbones stripped from Rifle)
The numbers represent lbf when failure occured.
|
Sample #1 |
Nylon |
3587 |
|
Sample #2 |
Nylon |
3145 |
|
Sample #3 |
Nylon |
3025 |
|
Sample #4 |
Spectra/nylon |
790 |
|
Sample #5 |
Spectra/nylon |
810 |
|
Sample #6 |
Nylon |
2988 |
|
Sample #7 |
Nylon |
3036 |
|
Sample #8 |
Spectra/nylon |
2011 |
|
Sample #9 |
Spectra/nylon |
2985 |
|
Sample #10 |
Spectra/nylon |
3627 |
|
Sample #11 |
Spectra/nylon |
4430 |
|
Sample #12 |
Nylon |
4586 |
|
Sample #13 |
Nylon |
2317 |
|
Sample #14 |
Nylon |
3890 |
|
Sample #15 |
Nylon |
2954 |
Yowsa—these were all found on popular routes that people, including myself, pitch off of all the time. They all were significantly less than the requirement when new, and a few (790 and 810 lbf) were well into the conceivable load range, even for a soft-catch sport climbing fall. Moral of the story—don't just blindly trust fixed gear.
And Even More Testing
We decided to do a few experiments here in the lab by setting up a few tests where we would compare new slings vs. old slings. We did our best to find representative 'old and well used' samples of what we had new, including:
- 10 mm Dynex dogbone
- 14 mm Dynex dogbone
- Variwidth nylon dogbone
- 18 mm nylon runner
- 10 mm Dynex runner
- ½" tubular webbing
- 1" tubular webbing
DISCLAIMER - these 'old and well-used' slings are non-scientific, totally random, not controlled, not a similar amount of exposure, wear, falls, etc.-just a bunch of old stuff that a few of us had lying around at home.
The tests we schemed up were:
New vs. old - ultimate strength
Basic stuff here—just to get a direct comparison of if and how much weaker old and worn slings can become
New slings - 500 cycles on our make-shift abrasion tester, then tested to ultimate strength.
This would allow us to see two things:
- how the abrasion affects the strength when compared to when not abraded
- how the different materials and material widths are affected by abrasion
New vs. old - 1000 cycles to 5kN (1124lbf) - then tested to ultimate strength
The idea here was to simulate 1000 falls of 5kN (a bit harsh but realistic) to both new and old slings, and compare to the ultimate strength of a new sling or dogbone.
New vs. old - cycled at 11kN (2473 lbf) to failure
This was a curiosity test. Exposing the slings to half their rated strength repeatedly until they broke. Not realistic in the climbing world, but maybe it would tell us something.
Results & Observations (comparative lab testing)
New vs. used - ultimate strength
Once again—no surprises—the older gear is weaker and sometimes significantly weaker than when new.
New slings - 500 cycles on our make-shift abrasion tester - then tested to ultimate strength
No surprise here—after beating up the sling for a bit on a rough edge, the ultimate strength is reduced.
Interesting that a few of the samples (both nylon and Dynex runners) didn't even make it through the abrasion portion of the test. This is possibly due to the fact that the webbing was more likely to twist and turn and be cut on an edge instead of having the stiffness of a dogbone which forced the abrasion to be consistently on across the width.
New vs. used - 1000 cycles to 5 kN (1124 lbf) - then tested to ultimate strength
Comparing after the 1000 cycles ultimate strength to no cycles then ultimate strength tested - it appears that the 1000 cycles to 5 kN had a very minimal effect on ultimate strength. Comparing the new vs. old samples, once again, the older worn slings had lower results. Two samples did not even endure the 1000 cycles.
New vs. old - cycled at 11 kN (2473 lbf) to failure
This is an unrealistic test as it pertains to the real climbing world, and gave us some results that are all over the map.
* Obviously this is all super limited data (ONE data point per test). In order to gain a more complete understanding, many more samples and controlled comparative samples should be tested.
Conclusions
As stated earlier, it seems that more climbers are willing to retire a piece of webbing material (or harness or rope) much quicker than a piece of metal gear-and this is a good thing. Our findings from testing old gear retrieved from the field definitely show a great reduction in strength of webbing products, sometimes to the point where field failure is a real possibility. I've definitely heard of several quickdraw or sling failures in the field (even a few in gyms) where the nylon draws are continually rubbing against the abrasive texture of the wall. Luckily there is usually another draw not too far below, so the climbers have come away unscathed short of their hearts being thrust into their throats momentarily.
Our makeshift lab tests also show the same. Webbing doesn't last forever, whether it's nylon or ultra-high-molecular-weight polyethylene. Abrasion and cyclic loading reduce the strength of webbing, and as the high school student science fair project showed, so does exposure to sunlight and the elements.
Now does nylon or Dynex fare better in real world weathering and use scenarios? Most literature you find states that Dynex is more resistant to cutting and therefore should do better in abrasion. Though nothing is conclusive, my findings from super non-controlled experiments by testing samples retrieved from the field actually show that nylon outperformed Dynex in ultimate strength after what is believed to be similar exposure to the elements, including abrasion.
One of the biggest takeaways if you ask me is that nylon stretches a bit, while Dynex/Dyneema/Spectra does not. It's important to realize when that makes a difference and adjust gear selection accordingly.
Next up: carabiners.
Climb safe out there,
KP
United States / English 
10 Apr 2013, 8:11AM
What exactly is Dynex? Is it not nylon 6 as opposed to nylon 6,6? If so then how is the differentiation between nylon and Dynex meaningful?
21 Jun 2012, 4:51PM
Are any of BD's, rope, sling and web materials treated for UV protection? Seems that the treatments available on the market would reduce the UV degradation of climbing soft goods. Unless, of course if BD is already using UV inhibitors. Thanks for the informative post.
21 Jun 2012, 12:58PM
I'm a bit confused why you don't actually do a scientific testing of this? It wouldn't be costly or incredibly difficult. Constant UV exposure to replicate certain number of days/years of sunlight exposure (can add humidity and tempeture variables as well), 5-10 samples per condition... basically what you've done here is useless other than to say something everyone should have already known- polymer based webbings make for sketchy periment draws. How about doing something to help with the knowledge of grossly approximate life spans for the draws i keep on my rack or the slings on your cams, etc....
20 Jun 2012, 7:13AM
Great read, I was hoping you might have answered the age-old question - when is it a good idea to retire your nylon/dynex soft goods? If you have the time/inclination, I'd love to see you hang some samples out to bake for multiple years, and test them to failure. Perhaps three samples a year for 5 years of each material - simulate a rappel anchor with minimal abrasion. It would allow us to finally get an idea of how these materials degrade over long periods of time without a lot of human abuse on them.
20 Jun 2012, 2:43AM
Hi,
Nice study that help us to consider that equipment will not last for ever. It's difficult to say, I'll trash my staff with which I've climb yesterday...
By the way, we can see on pictures that some times this is the stitching which brakes.
Did you consider the material of the thread for bartacks? It can be polyester or nylon, so the aging could be different against UV and abrasion?
19 Jun 2012, 9:32PM
Hi Guys, I love all the testing that you guys do, however could you put your results in kn as well as lbs.
Cheers
Pete
19 Jun 2012, 2:14PM
I thought it was interesting that the UV damage mostly comes in the first 10 weeks of exposure (16% weaker) and then tapers off. Although no explanation was given for this, it seems logical that this would represent damage to the outside layer of the materials and since the inner layers are naturally protect by the layer above it, they would very slowly degrade.
As a test, it would be fun to protect the outer layer from the sun (maybe a cloth sleeve over the dog bone) and see if it still degraded at the same rates.
19 Jun 2012, 9:24AM
Good work KP, once again... Your results reiterate the need to pay close attention to the shape of woven products (this includes harnesses as well as ropes). Wear is definitely a significant factor in my experience. Testing I conducted years ago supports all these findings and conclusions posted here. One factor I noted that was by far most significant and one that I could actually predict low strength was when there was a nick in the edge of the webbing material. This was most notable when the nick was at the edge of the biner contact surfaces or adjacent to the outside bartacks. Any nick in the edges would warrant immediate destruction from my rack and in some cases from my partners racks... Harmy.
19 Jun 2012, 9:17AM
Hi,
I was wondering if there had been any comparable load tests on unused 'new' rope that has been stored and unused but past its 'use by' date and new rope off the shelf.
This question comes about as a result of a query I received when some guys found new rope in storage but its been there for about 6-7 years. Never been used - no exposure to water, UV or even urine.. We always hear the 'natural degradation etc etc' of rope but I haven't seen any info on it. Answers?
Cheers.
3 Jun 2012, 11:10PM
and a few (790 and 810 lbf) were well into the conceivable load range,
These are not only near/below possible fall forces,
they are about 1/3 the strength of the next weakest
piece (2,300#) !!!? Did you do any pre-test examination
of the items to try to discern likely weaknesses?
Most literature you find states that Dynex is more resistant to cutting
and therefore should do better in abrasion
That's my reading & conclusion, although Jim Ewing of Sterling
has remarked that cutting & abrasion resistance are two different
things (but I'm not sure I understand why; conceivably, frictional
heat can play a role in the latter).
But also, I've read many times that HMPE (Dyneema, Spectra) is
nearly impervious to UV damage --"unaffected"--, and yet your
tests have consistently suggested otherwise, to the point of even
being more affected than nylon!?
As for "doesn't hold a knot", well, there are many knots
not tried for this. The thicker nature of typical HMPE webbing
poses some problems with knots typically used with tape or
which suit 1" tubular. The grapevine and double reever bends
should work. (IIRC, somewhere I saw some tests of the former.)
--dl*
====
1 Jun 2012, 11:57AM
I have a question about the reliability of old quickdraws that are relatively unused and have been sitting in a box for years. They've seen little to no UV and no chemicals. I also have ropes sitting in a haul bag that have been unused for years. Have you done any testing on aged ropes and slings with little to no use, abrasion or UV?
Joe Josephson
31 May 2012, 3:49PM
Good job! I am surprised that dynex was not more resistant to cutting. I would have thought otherwise, but good to know.
31 May 2012, 12:46PM
Not sure that QA is checking everything thoroughly before they go into production: This spring I bought ten brand-new Hoodwire/Hotwire quickdraws and within a month of use the rubber rope-end "biner keeper" had broken on every single one. Fortunately not a safety issue, but certainly a design or manufacturing problem. I've had no such problems on my other dogbones - including BD's Vari-Width nylon dogbones which are an awesome product by the way.