Serius Rope Outer Sheath Failure

Going by the data, it appears your used rope was ~75% of it's rated MBS.
Girth hitch would have contributed some percentage to that loss.
 
Steve Connally said:
Break testing results came in today


Hi Steve,

I've attached the testing data we got from your rope. We broke them in 6 foot sections with girth eye stitches on both ends. All 6 pieces broke at the stitch.

What this data means is that in a perfect statistical distribution, 99+% of the tests would break over the 3 sigma number of 5200 lbs.

Keep in mind the loss of strength compared to the manufacturer's MBS rating of 7900lbs.


So what's the rope overloaded at that specific time it broke at 1200lbs? What do you all Make of the numbers?
Click to expand...

Seems like it broke at a previously weakened point in the rope. I think the take away is that when rigging pieces of that size you need to be on a larger rope. I have a 14mm Sirius that is rated for 11,700(w/o splice). So basically 2mm larger buys you 3,000 ish in safety factor. Having a slightly bigger rope makes no real difference when working, but buys you some piece of mind. This is kind of a pet peeve of mine, the trend of using lighter rated equitment for removals. I mean 2mm in difference? Another example a cmi 5/8 aluminum block is rated at 28000lb mbs, the omi 2.6 has a mbs of 18,000 ish. That's like 10ooo in insurance for no real difference. Just my opinion and personal preference, not aimed at you steve. Sorry for the rant.
 
The rope had lost over 1000 lbs. of its strength when you broke it. That doesn't seem to indicate abuse... just quite a bit of use. That was almost poetic.
That would shift your WLL to: 5:1 = 1200 lbs. -- 10:1 = 600 lbs. -- 15:1 = 400 lbs.
 
Slack in the rope? Maybe not all the way tight a bit of fall. Three wraps held tight. well used rope. How quickly does 1200 lbs go to 5000 lbs. How much fall would it take. Although Sirius is supposed to be quite stretchy right?
 
As s random thought Steve.....Do you have a Magnaflux set or a local welder who probably has some. As a completely out of the box idea I would have the porty checked for cracks. They might not be visible to the eye but may appear undef inspection or under the pressures of tree work. I would hate to see it eat a new rope if the old rope was never really the problem. I do have a set at work but you can probably find one locally.
 
monkeylove said:
As s random thought Steve.....Do you have a Magnaflux set or a local welder who probably has some. As a completely out of the box idea I would have the porty checked for cracks. They might not be visible to the eye but may appear undef inspection or under the pressures of tree work. I would hate to see it eat a new rope if the old rope was never really the problem. I do have a set at work but you can probably find one locally.
Click to expand...

I'll look around.
 
You are welcome to hand deliver I can prob have it in and out of NDI in a day so the rest would be shipping time I can get it out ups like mighty quick. Shoot me a PM and I will get you info.
 
To answer one of your questions treebing. I could not find specs for Sirius so I used the numbers for Yale's 1/2 inch Double Esterlon. With 60 feet of rope in the system and with a 1200 pound branch you could remain in the green zone up to about a 1.1 foot drop. The green zone allows for maximum cycles. A 2 foot drop would nearly double the foot pounds of work required to catch the piece. And would put you well into the yellow zone, thereby reducing the cycles to failure. The formula can be found on Yale's website. http://www.yalecordage.com/arborist-rope/dynamic-energy-in-arborist-rope.html
 
Just from similar experiences, I think it was overloaded. System slack caused the failure. Say you put an undercut or standard box followed by a top cut with a large diameter pine limb with good tip weight, POP the limb jumps off the cut. As it jumpes off the cut the line dropped allowing the PW the fall 6-12" down the trunk. When limb weight caught the line, (considering it was around 3-500 over what I would hope to see regularly on that diameter line), it immediately sucked the slack from the system thus for a second putting all breaks on which caused glazing breaking the outer cover. Possibly? Just what I have seen happen on jobs.

Steve do you think removing system slack or pre tensioning is harder with the rig wrench?
 
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