Wire Rope Thimbles

[engpes]

I have a wire rope thimble (see attached photo) that has deformed during the load testing of the sling leg.

I have used a Crosby G-414 thimble on a 1" steel core IWRC wire rope.

My question is this:

1.) Should this sling be rejected?
2.) Is thimble deformation acceptable?

I was under the impression that the Crosby G-414 thimble would be adequate to take the full breaking strength load of the particular sling size.

Thank you in advance.

 

[dhengr]

Engpes:

I’d ask a few trusted sling suppliers this question, not just ones who wanted to sell you new slings. Would they warrant this sling?

Did you make the sling up or did they? What was the sling cap’y., vs. rope cap’y. vs. test loading? It looks like you pulled the sling and thimble over too small a pin dia., and slightly crushed and deformed the cable. This action would tend to open the thimble as shown, and then it doesn’t support the wire rope well around the bend. Was the thimble the right size for the rope used? Some types of ropes bend a bit tighter without detrimental deformation. It doesn’t look like you broke any wires. I believe a sling with thimbles only has about 70 - 80% efficiency when compared with the rope strength, depending upon how it is made up, and the type of wire rope used.

 

[engpes]

The sling was made by the sling supplier and was pull tested to twice its rated WLL (based on tension in sling at operational angle).

This same type of sling (with thimble) was also break tested. The breaking strength was greater than 5.0 times my assumed breaking stregth, so I believe this particular configuration can hold the minimum required load with a bit of margin.

Is it good practice to accept a slightly deformed thimble like this?

Thanks again!!!

 

[dhengr]

Engpes:

As long as no wires have been broken, and at that location in the thimble and load path, off the top of my head, I don’t think this is a serious cap’y. reducer. But, I would still ask the sling supplier for their opinion on this, since they are the one’s who guarantee their slings. In addition, I would do this for your own edification. What did you do wrong to cause the thimble and wire rope deformation, I’d bet on too small a pin vs. the thimble dia., and what do they think this does to cap’y.? What dia. pin or shackle do they say you should use with that thimble and rope? How did a similar thimble look after break testing to 5x, and why the differences? Obviously, the wire rope deformation would be looked at more critically out in the length the rope. Stress and strength (cap’y.) alone aren’t always the final word on these things, nor am I. What do OSHA and the below the hook code people say about these matters, and regular inspections, and extent of wear and damage before rejection? They are the people who can come down hard on you, even if no failure occurs. A breaking strength of 5x and a proof test of 2x seems fairly conservative if you also have a regular inspection program. In working with riggers and the like, they certainly never wanted a failure, but they sure thought the FoS was there for them to use up, and they really got in a twit when you started making a big deal out of what they thought were small details. I guess that’s where engineering judgement comes in. Maybe your liability insure re, would offer some guidance on these matters, an OSHA or ASME code they expect you to follow or some such.

 

[chicopee]

Looking at the deformation of the thimble, it seems that it was slightly under sized for the size of the wire rope.
The purpose of the thimble is to minimize wear and cuts of the end loops and plays no part in the lifting capacity of the sling. As long as the wires and strands forming the end loops have no breaks and deformation, you still can use the sling.
If you check a sling catalog, you'll note that there are no difference in the lifting capacity of slings with or without thimbles.

 

[MiketheEngineer]

A 5:1 safety factor is almost always demanded. I would NEVER accept anything that was deformed for any reason.

End of discussion - IMHO