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Lifetime of Dyneema-sling

Discussion in 'Tech Tips and Gear' started by Jimmy Olsson, Nov 29, 2017.

  1. Jimmy Olsson

    Jimmy Olsson

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    I've seen dyneema slings been used in static anchors a few times. That can't be recommended right? Wouldn't weather and wind make them unsafe after a while? Even if you'd installed them yourself, there must be a lifespan... Even if the sling looks fine, for how long would you dare to use it in a static anchor?
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  2. Bootboy

    Bootboy Atwood Gear

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    Dyneema (UHMWPE) is the most robust synthetic fiber of any used in climbing gear. It will outlast nylon and even polyester in adverse conditions (Sun, wind, water, sand...) but not while within the limits of being trustworthy.

    That said, visual inspection is harder because it is white and much skinnier (a higher specific strength means that damage is more subtle).

    Nylon is much easier to inspect because the color and the feel (soft vs crunchy) change much more noticeably.

    I’ve not seen any specific data on the longevity of dyneema used for long term anchors, but I think the adage for inspecting anchors applies here:

    “When in doubt, change it out”
    Last edited: Dec 28, 2017
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  3. Brian in SLC

    Brian in SLC Brian in SLC

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  4. Rapterman

    Rapterman

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    Yeah- whacky- looks like it was cut.
    I have been manufacturing safety products with spectra and dyneema sling for over 17 years.
    I do NOT recommend that it ever be used for anchor sling left at a station:
    A. as Bootboy has said, it is very difficult to evaluate. Being expensive, people do not usually leave them unless they have no choice.
    B. girth hitching and/or tying knots in 100% spectra sling greatly reduce the strength- MORE than for nylon. Knots like the overhand may not hold at all!
    C. For these reasons, spectra is only sold as a sewn sling- never on a spool, so if used for a static anchor it will often be girth hitched or knotted (bad).
    D. Nylon is (relatively) cheap. Easier for everyone to evaluate.
    :)
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  5. Bootboy

    Bootboy Atwood Gear

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    All good points.


    To elaborate on the girth hitching issue, the passability of Dyneema as a rap station anchor material would have a lot to do with how it was attached. quick links would be superior to girth hitching.

    But still, if you encounter it, swap it out for (black) nylon.
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  6. Rapterman

    Rapterman

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    But
    Brian in SLC
    is the ONLY climber-type who knows what a quick link is
    ;)
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  7. Disruptive_Rescue

    Disruptive_Rescue

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    I remember reading the article from Alpinist, and discussing the issue with some people much smarter than I who specialize in material science. I had to start learning way more than I ever wanted to on the subject of material science (specifically fibers and manufacturing related to rescue) about 12 years ago. The benefit - was the appreciation that there is no "perfect" material for all situations and all environmental pathology. Every material has it's positives and negatives depending on a bunch of variables from skill level, environment, context, etc. The commenters above hit the points probably most relevant to your question...where I will try and avoid ADD tangents...

    As mentioned above, knots tied in dyneema greatly decrease strength - DMM did some interesting research - looking at strength reduction due to tying a "focal" or master point to rig into, and it was significant. When looking at fall factors, they basically had a reduction of ~half when an overhand knot was tied in the sling. The heat that is generated in a knot due to the friction when loading has a significant impact with UHMWPE. The melting point of UHMWPE is much lower than what you find with Nylon, and although DSM lists the melting point at 266-277 degrees F, DSM also states they don't recommend using dyneema in temps that exceed 176-212 degrees F for any long periods of time... but that being said, IKAR's Slovakia 2010 presentation "Dyneema during mountain and rescue operations Do's - Dont's - Critical Uses" presentation - illustrated a pretty well rounded view of dyneema in various operational contexts. They highlighted the fibers lightweight, low elongation, resistance to UV, alkali, acids, organic solvents - low water absorption, abrasion resistance, etc - BUT... they did note a decrease in strength beginning around 122 degrees F, stating that if dyneema slings are stored in a rescue bag, that bag shouldn't be left on a Tarmac, or close to any vehicle exhausts. As stated above, dyneema has a natural "lubricity" (insert joke here), but this is why the slings are typically sewn - double fishermans will typically slide through and not hold. In the end of the IKAR presentation, the take home point is..."Dyneema is a very efficient material when used correctly, but a very dangerous material when incorrectly used."

    If you do look into rigging Dyneema as a sling, check out "Is light right?" presentation by Zephyr Feryok, who tested dyneema in multiple configurations, even looking at rigging options for highlines (high tension) using dyneema slings. When testing the sling in a wrap 2 clip 4 configuration the mean strength was 64kN - this was the highest the testing machine would go up to, in which it didn't break - so they did 4 cycles on the same sling, maxing the machine out each tie without a sling break.

    Oh...and ADHD stray voltage...the heat issues mentioned above - specific to the frictional heat in an overhand knot that DMM tested - when they had the sling in a freezer prior to testing...the sling maintained most of its strength...

    Hope this gives you some info to research and make your own decision on dyneema utilization, not that my opinion matters, but I agree with Raptorman & Bootboy.
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  8. madman_lee

    madman_lee

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    Going along with the nylon comment. I've always had this idea about dynema slings; since they are much skinnier doesn't this mean small-damage can have large consequences?

    Following this logic is why I like nylon more than dynema and spectra. Nylon (with the larger surface area) should mean small-damage is lower consequence in comparison. I still have a 5 year old slack line with 1 inch nylon webbing with lots of small damage, yet it still hold strong under mass ammounts of tension and abuse.
  9. Bootboy

    Bootboy Atwood Gear

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    sort of.

    Cutting half of the fibers in a Dyneema sling will reduce its strength by half. Cutting half the fibers in a Nylon sling will reduce its strength by half.
    WHERE the damage occurs on slings of these two materials WILL make a difference, Nylon is stretchy and has the ability to diffuse the rise in stress on the fibers immediately adjacent to the damage. You get a less pronounced cascading failure effect with Nylon. Because Dyneema (UHMWPE) is exceptionallly static, asymmetry of force across the width of the sling causes a much more pronounced cascade effect. This, however, may in turn be made negligible due to the average width of Dyneema vs Nylon sling being used to support comparable forces. So who knows what the net effect of these two phenomena is.

    I suppose this could be tested, and perhaps it has, but I haven't seen any data comparing these effects side by side.

    The biggest reason that your slack-line is going strong is because you're not getting anywhere near its ultimate strength.
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  10. Rapterman

    Rapterman

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    We are all having fun piling on here....:D

    Madman-
    you do not actually know if your slackline is "still going strong":
    you only know that it is still going /has not broken yet...
    having some experience with testing slackline used by some local professionals, I can assure you that the strength of the webbing
    will degrade significantly with use, and then it will fail.
    Slacklining can put an amazing amount of force on a sling, especially if you are dynamically loading it.
    If you have lots of small damage, I would consider that damage to be CUMULATIVE.
    If you can detect a loss of stretch or bounce in your sling then I would retire it immediately- or have something soft underneath you...
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  11. Disruptive_Rescue

    Disruptive_Rescue

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    As far as assessing dyneema for strength loss (degradation) due to heat exposure - IKAR mentions that you can not appreciate with the naked eye. Maybe not a huge issue when using as an anchor within a canyon (?), but definitely an issue with urban use.