This from Black Diamond's Web Site: Retiring Old Ropes by Kolin Powik

QC Lab: Retiring Old Ropes
We’ve all seen it at the cliffs, and I’m a major offender myself—climbing on old ratty ropes. Yeah, ropes are expensive and that’s the main reason people push their ropes to the limit—trying to squeeze every last ounce of use out of them until they become a dog leash or door mat. I’m not going to lie—I get sweet deals on cords, but still, I don’t like to be wasteful and usually end up climbing on my ropes a little too long.

Ropes can develop a sentimental value to some people—maybe it’s the cord you sent the “proj” with, or had a great trip up a Valley wall with—so you just don’t want to retire it. I had such a case—a special 9.4mm. I kept climbing and climbing and climbing on it. It was beat. It started out as a 70 m, then after endless days of constant whippers, it became a 65 m, then 60 m, then 55 m. I just didn’t want to see it go.

So one weekend I was taking REPEATED MONSTER whippers off the VERY LAST move of one of the many nemesis routes of mine. I had to skip the last clip because I’m too weak to clip it—and go for a huge chuck to the finishing bucket. I would sail onto the end of my trusty 9.4 mm time and time again. The last 10 ft or so of the cord were absolutely throttled—at the end of that weekend, it was time to say goodbye.

Of course, I brought it into the lab and figured I’d do some testing.

Testing

I decided just to test the ultimate tensile strength of the rope in different areas, and compare it to a brand new rope of the same model and make. We didn’t do anything fancy—just a figure 8 on each end, and pulled to failure in the tensile tester. We were just doing this quick and dirty for comparison's and curiosity's sake.

When tested like this, breakage at the knot is almost always the failure mode—and remember—figure eight knots can reduce the strength of a rope somewhere in the neighborhood of 25-30%.

Results

The first test we did was a piece from one of the totally worn-out ends. It broke at around 6 kN—and NOT at the knot.

Yowsa, I had just been whipping all over the place on that cord—and it broke at 6 kN, and NOT at the knot—scary stuff. Though the sporto falls I was taking were super soft (my wife was belaying and is light, and I am fat)—chances are the tension seen in the rope wasn’t anywhere near 6 kN, but if I had gotten slammed hard, low to the ground, etc??? It’s definitely possible to see these kinds of loads in the field.

We decided to do more tests on my cord—on the ends, and in the middle, as well as on a brand new 9.4 mm for comparison purposes. In all subsequent tests, the sample broke at the knot as expected, but we still saw some frighteningly low values.

New 9.4 mm KP’s 9.4 mm middle KP’s 9.4 mm end
15.6 kN 9 kN 6 kN*
13.8 kN 9.8 kN 8 kN
7.7 kN
*broke in the middle of the test sample

We tracked down another beat 9.4 mm from one of the QA guys—and put it through the ringer as well:

New 9.4 mm Used 9.4 mm middle Used 9.4 mm end
12.9 kN 11.9 kN 8 kN
13.6 kN 11.9 kN 9.8 kN
11.6 kN 8.6 kN
Still curious and given the results we’d seen—the boys in the lab and I decided to do the same with some other tattered ropes that were around. We did similar tests with more Beal ropes as well as Sterling, Edelweiss, Mammut, etc. We found very similar results:

The worn out, frayed, end pieces of any rope we tested were consistently significantly weaker than the middle sections of the same cord.
We DID manage to find other samples that broke in the middle (as opposed to at the knot) – and at relatively low loads—less than 7kN.
The end pieces, and middle pieces were consistently weaker than a section of a brand new cord.
Bottom Line

Ropes, like all climbing gear, don’t last forever—the ends of your rope take a beating—be wary of super frayed, worn, puffed out, beat up tattered cords. Yes, ropes aren’t cheap, but they’re also your lifeline—literally—so take care of them.
When the ends of your cord get all beat and tattered from dogging up routes, cut the ends off, or a buy a new rope.
I always cut equal lengths off BOTH ends so the middle mark is always in the middle.
Be sure to mark the new length on BOTH ends so you and your partners know what you’re dealing with.
And while you’re at it—tie a knot in one end—too often you hear of someone being lowered off the end of their rope—definitely not cool.
For me the most important thing… to train harder and get stronger, so I won’t be whipping in the first place.

Be careful out there,

KP