Using the same gear for slackline anchors and climbing. Safe or not?

Recently I came across something saying it's not safe to use the same gear (cams, nuts, carabiners) for setting up slackline anchors and for climbing. The person said something about "prolonged static forces" of setting up slacklines wearing on cams and such and no longer making them safe for climbing on.

After searching around the most I was able to find was some anecdotal accounts of biners not opening properly after extended use in slackline anchors, but no authoritative or scientific information.

I understand slacklines can generate tremendous forces; however, I can't see how a cam that didn't break under those forces would later break while out climbing. I'm no engineer though and I rarely slackline.
I'm just curious if anyone has any good info on whether this is a myth or not.

I don't know that its a myth, just that there's no data on the subject. Seems to me that until somebody does do the research, you're better safe than sorry.

I am going to school for mechanical engineering and we just learned about fatigue stress. Having the cam or biner loaded with that much force then constantly walking and weighting it will weaken your gear over time. They are probably still strong but maybe not to the given rating anymore. This of course depends on how long you have the gear in the slackline and how much your on it but, I wouldn't trust taking whippers on gear that has been strained by a slackline.

I have no idea if this is right but when I was working at bike shops was told aluminum has no 'fatigue limit' and each force added to result in cumulative damage to the structure while other materials like steel or ti had a force they could sustain before damage to the structure occurred. Is this true???? Thinking along the lines of what was said before and thinking of the materials in play. That said I am not savvy...

Medic741 wrote:I have no idea if this is right but when I was working at bike shops was told aluminum has no 'fatigue limit' and each force added to result in cumulative damage to the structure while other materials like steel or ti had a force they could sustain before damage to the structure occurred. Is this true???? Thinking along the lines of what was said before and thinking of the materials in play. That said I am not savvy...

This is true, but look how much use people get from handlebars, stems,seatposts, brake calipers, etc., to say nothing of aluminum bicycle frames. A properly designed and built aluminum structure can withstand a lot of use while a poorly designed steel or titanium structure can fail very quickly.

As for the OP's question, I suppose that if you used a cam with a micro-crack or big gouge in the lobes and used it to build a slackline anchor, you could enlarge the crack or gouge to the point where it weakened the cam and the cam failed well below its rated strength at an inopportune moment. Same thing goes for carabiners, nuts or whatever else you build your slackline anchor with.

How much would it cost to set aside some old nuts, biners, etc. to build slackline anchors with, and save your cams and other good stuff for climbing?

I'm not an engineer either, but I'm sure one will be along shortly to set all of us straight.

mark felber wrote: This is true, but look how much use people get from handlebars, stems,seatposts, brake calipers, etc., to say nothing of aluminum bicycle frames. .... I'm not an engineer either, but I'm sure one will be along shortly to set all of us straight.

Exactly. Low-cycle fatigue will give you notice before breaking, as in visible damage or deformation to the metal. Like, the biner gate won't close or open any longer. High cycle fatigue...?? Complicated. I am an engineer and I can't set you straight. That's like asking any old doctor to comment on your brainstem surgery. Fatigue definitely falls into its own special category, mostly surrounded by statistics of what might happen and how many loading cycles something might handle before destruction, with a cycles-to-failure standard deviation the size of those WTC pillars left standing. Anybody out there design aircraft or turbines?

I held a carabiner at 10-15 kN for a month in my pull tester before pulling to failure. Although I did not have a control to compare it to, the biner failed at its rating. I also recently pull tested a sling I was using for longlining. I had some 1" webbing I used to rig about 40 80'-150' longines. Each time I rigged the longline, the line was tensioned between 900lbf and 2,000lbf. Anyway, the sling failed at 21kN. A control sling failed at 23kN. The sling I tested was a bit torn up and had some minor damage which may have accounted for the strength loss. Also, I remember Bolt Products calming to do some cycle load testing on their steel bolts. I think Jim used some of his bolts to anchor a generator or something of the like and he claimed the bolt saw something like 100,000,000 cycle loads without damage. Realistically, I dont believe that moderate-term moderate loading is an issue with carabiners, at least not as it related to conventional slacklining.

As far as the question goes, is it safe to reuse slacklining gear for climbing, I would say yes, under most situations. I am not so sure that I would use a sling that has been loaded to 2/3rds its failure strength a ton of times for climbing, but carabiners that have been used in a primitive slackline setup are okay to reuse. In all honesty, a short primitive slackline setup is unlikely to have much more than 500lbf of standing tension on it and that much force is subjected to aluminum carabiners everyday in big wall environments where climbers are hauling heavy ass loads for long periods of time.

20 kN wrote: but carabiners that have been used in a primitive slackline setup are okay to reuse.

At the risk of sounding like an idiot, what is a 'primitive' slackline setup? Just webbing and biners? As opposed to something like a Gibbon kit?

My two cents worth: A fairly safe bet for tension load on a slackline is ten times your body weight, while you're on it. So, 1,500 to 2,500 pounds-force. That force is surprisingly static at the anchors, as the "bounce" is a function of dynamic load through the webbing which translates very little to the hardware. Dynamic/cycling loading on the anchor is only significant when getting on and off the slackline, but you still have the static load of whatever tension is left in the line (typ. 300 to 800 lbs-force).
Therefore, the load on the anchors is, perhaps, 1/4 of their rated load, and it's a very "controlled" load - not so dynamic/cyclic as it first appears and the residual tension in the slackline keeps everything in position so you're not introducing sudden dynamic force at varying angles like you would if taking a whipper on it.
Result: it's not much different than aid climbing on anchors or hauling on them and, other than normal wear and tear, I would think there is insignificant damage to them such that they can still sustain their full design load in a fall. It's ability to sustain that load, really, comes back to proper placement and the rock, which remains the critical point of its effectiveness no matter its load capacity.

Matt, you are correct in your assumption--primitive generally means just webbing and biners. I think it's more specifically referring to only using biners as a pulley system, not any other sort of pulley/ratchet/tensioner setup.

Cheers

Matt Roberts wrote: At the risk of sounding like an idiot, what is a 'primitive' slackline setup? Just webbing and biners? As opposed to something like a Gibbon kit?

It is a simple 1" nylon webbing slackline set up with carabiners in place of a pulley system. What I was trying to say is that if you are setting up a short line, dont worry about it.

nwslackline.org/344/howto-r…

Robert Stump wrote:My two cents worth: A fairly safe bet for tension load on a slackline is ten times your body weight, while you're on it. So, 1,500 to 2,500 pounds-force. That force is surprisingly static at the anchors, as the "bounce" is a function of dynamic load through the webbing which translates very little to the hardware. Dynamic/cycling loading on the anchor is only significant when getting on and off the slackline, but you still have the static load of whatever tension is left in the line (typ. 300 to 800 lbs-force). Therefore, the load on the anchors is, perhaps, 1/4 of their rated load, and it's a very "controlled" load - not so dynamic/cyclic as it first appears and the residual tension in the slackline keeps everything in position so you're not introducing sudden dynamic force at varying angles like you would if taking a whipper on it. Result: it's not much different than aid climbing on anchors or hauling on them and, other than normal wear and tear, I would think there is insignificant damage to them such that they can still sustain their full design load in a fall. It's ability to sustain that load, really, comes back to proper placement and the rock, which remains the critical point of its effectiveness no matter its load capacity.

Your statement is mostly correct. However, a shorter 1" nylon slackline will not generally see 1,500 - 2,500 lbf. I have tensioned 150' lines only a few feet off the ground and still not hit 2,500 lbf. Normally you will only see forces that high in a highline fall or longlines over 200'. Commonly, shorter 1" nylon slacklines will get tensioned to 300 - 500 lbf. Once you step on them, you can expect 600 - 900 lbf. With a jump or trick you might break 1,000 lbf - 1,300 lbf depending on how high you jump. Gibbon lines that have ratchets can spike loads above 1,500 lbf. pretty easily due to the fact that the webbing is very static and the ratchet makes it easy to overtension the line.

This graph shows a test where I stood on the line on three different points. The first peak represents standing 20% downline of the anchor from the side without the load cell. The middle peak represents standing in the middle of the line. The last peak represents standing 20% downline of the anchor from the side with the loadcell.