Broken Wires in Wire Ropes

It is surprising how few operators know the allowable number of broken wires in a wire rope.

The discard criteria on a crane rope will vary significantly from construction to construction.  It is crucial to know the construction of the wire rope before you start the inspection.  To give you an idea of the difference in the allowable amount of broken wires for the different ropes, see the following examples from Australia Standard 2759 Wire Rope:

6×19 (12/6/1) – 3 broken wires

6×19 S (9/9/1) – 5 broken wires

6×36 SW (14/7 and 7/7/1) – 7 broken wires

8x19S (9/9/1) – 5 broken wires

18×7 NR – 1 broken wires

34x7NR -2 broken wires

** note:  this is the number of broken wires allowable over a length of 6 times the rope diameter.

To put this in perspective, if the hoist rope on your Franna AT20 Crane has 3 broken wires right next to each other the rope exceeds the limits for discard as listed in AS2759.

To make matters more confusing, the manufacturers of some higher performance ropes allow more broken wires in their ropes than that of the Australian Standards.

The standards go on to say that whilst the number of breaks is quite high, if the wire breaks are concentrated in on strand lower levels for discard are appropriate.  If more than one third of the outer wires in a strand are broken over a length of six times the rope diameter, the rope shall be discarded.  It should also be highlighted that broken wires alone are not the only factor in discarding a wire rope.

You can see that getting an experienced wire rope inspector with intimate knowledge of the relevant standards and manufacturers recommendations is a smart play when it comes to looking after your wire rope.  If you would like help with your wire rope maintenance and inspections, please contact the team at Crane Ropes Australia.