QC LAB: Wet vs. Dry runners, Part 2 - What about frozen runners?
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. Now running on a monthly basis, our QC Lab posts aim to answer some of climbing’s most common gear-related conundrums.
A few weeks ago, KP and the crew did some tests on the comparative strength of wet and dry runners. We received so many comments wondering about the relative strength of frozen runners compared to wet and dry, that they decided to do some follow-up testing. To view the original post, CLICK HERE.
We had a lot of people curious about how frozen slings stacked up in the wet vs. dry debate a few weeks ago, so we soaked a few slings in water and froze them for a day or so.
Then we tested them in our trusty tensile tester. The results are below.
A few things to remember:
- We're talking about a relatively small sample size, so this is by no means a comprehensive PhD level thesis on the topic
- Averages are not always the best way to look at data, especially when looking at a limited sample size
- This is static tensile testing data.It is possible that results differ if tested dynamically
First off-from our original data, it appears that wet runners are slightly weaker than dry. Why? I'm no chemist, but I asked a few friends in the industry that are way smarter than me. The basic layman's explanation I was given, was that one of the reasons nylon becomes weaker when wet is that the water lubricates the fibers and relaxes the molecular bonds.
An article about some similar, though dynamic, rope testing that the Italian Alpine Club did several years ago goes in to some more detail on a different theory:
Such a behaviour is in accordance with literature : the presence of water in nylon greatly lowers its Tg [a], the Glass Temperature (glass transition temperature of the material). Water acts like a real plasticizer, since it deeply modifies both the mobility of the amorphous part of the macromolecule and the characteristic temperature of mechanical relaxation of the material. This means that "in many respects, the addition of water to nylon is equivalent to raising its temperature by a substantial amount" (literature). In other words: testing a wet rope on the Dodero at normal temperature is about equivalent to testing the dry rope at 70-80 °C, conditions which cause a loss in performance. (To read the full article, CLICK HERE.)
But what about when frozen? I'm told that when the water in the nylon freezes it suspends that lubricating effect. And also according to the article, their test results showed that frozen ropes fared better than wet ropes, though not as well as dry ropes. In our testing, it appears that when frozen, the slings are actually stronger. Should we freeze all of our nylon gear before we go climbing? Of course not. Looking from one data point to another, or even at the averages, it appears that slings are stronger when frozen, but that is likely just due to the limited sample size. If you calculate the standard deviation, and even the 3sigma value for the data:
- The dry nylon 3Sigma value is 25.3kN where the value for frozen nylon is 25.8kN (still higher, but by not as much and remember once again, limited data)
- The dry Dynex 3Sigma value is 24.9kN whereas the 3Sgima value for frozen Dynex is 22.9kN.
So it's just a matter of the spread of the data. More data points would give us a better representation.
Bottom Line: nylon gear when wet/frozen is affected negatively from a strength perspective-likely not to such an extent to be of a concern in typical climbing scenarios, but under certain circumstances (multiple harsh falls, sharp edge, abrasion during a sliding fall over rough surface) it can be an important factor. I don't believe I've specifically heard of an accident that was attributed to the fact that nylon was wet, but that doesn't mean it hasn't happened. As with every aspect of climbing, it's our individual responsibility to arm ourselves with as much knowledge as possible in order to make good decisions in the mountains.
Be safe out there,