Tech Tip: What's With Microfractures?
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Posted 08/23/16
TECH TIPS 101: Microfractures ... feared, but are they real?
Last week, Terk from Nashville wrote:
“I took a rope access class with my department and the instructor told us carabiners may have microfractures we can’t see which could cause them to fail. Is that true?”
Great question, Terk ...
If there’s a bogeyman in Gearville, it’s the microfracture. Everyone’s heard about the major defect so small it can’t be seen; how they can be introduced by dropping a ‘biner from as low as waist high! What could be scarier?
But has anyone ever seen one?
A while back, we picked up a couple ‘biners from the blocks and talus at the base of El Capitan and brought them home to put on our tensile tester. We were surprised when they each broke over rating, so we made a call and, pretty soon, we got a box full of gear: ‘biners, cams, nuts & other hardware from at least a half-dozen manufacturers, including us, all recovered from the base of El Cap by our pals in Camp 4.
Thirty pieces of climbing gear in the box. We assumed each one had been dropped by climbing parties—no telling whether from ten or three thousand feet—but all passed the visual and functionality tests. The worst damage was a bent cam tip, presumably from impact with the scree where it was found.
We put on the lab coats, brewed up a fresh pot of coffee and got to breaking stuff. The results surprised us again: every item broke at or above its rating.
What about steel?
For that, we tortured a half dozen of our most popular professional-grade, plated-steel carabiners. We tied them to bumpers like newlyweds, beat them with hammers; pitched them from rooftops and mistreated them as creatively as possible.
Again, any goods that passed visual and functionality inspection broke at or above rating.
A scan of QA records doesn’t reveal anything, either. We regularly test raw material, work in progress and finished goods, which means we might break up to 11,000 ‘biners a year for quality assurance. We’ve tested at least a couple hundred thousand carabiners all these years and haven’t found a microfracture, yet.
So … what do we do with that?
Don’t climb on gear you salvage from the base of cliffs, regardless how sturdy our little box of kit turned out, that’s first.
Second, if you drop any piece of hardware from high up, you should just retire it. When you trust your life to a piece of equipment, you don’t need the doubt. Plus, it’s a good, professional practice, anyway.
Finally, your best bet is to rely on the visual and function tests. Look for variations to any original dimension, indicating the frame may have stretched. Look for scrapes, gouges or defects that can’t easily be buffed smooth with a few strokes of very fine abrasive paper (250-400 grit); retire the item if any are found. Check for functionality: the gate should open smoothly and close automatically. The locking mechanism should operate freely and with ease. Provided these conditions are met, you should feel pretty confident that your ‘biners are microfracture-free!
As always, the Old Wisdom applies: "When In Doubt, Throw It Out!"
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