Introduction

This post will cover valley breaks in wire rope. By the end of this post, you should know the causes of valley wire breaks, be able to identify them and understand the discard criteria provided by ISO 4309.

This post applies to crane rope specifically.

The cause of valley wire breaks

Valley wire breaks typically occur due to inter-strand nicking. Inter-strand nicking usually occurs when the rope is under bending load during spooling and when running over sheaves. As the name suggests, inter-strand nicking is due to the forces occurring between strands (the valley region). The presence of valley wire breaks is a strong indication of internal deterioration in a wire rope. As plastic sheaves have become more widely used, it is common for wire rope to deteriorate internally without displaying external signs. Therefore, careful inspection is particularly important when using plastic sheaves.

Identifying valley wire breaks

Valley wire breaks are easily identifiable by their location. If a broken wire occurs in the valley region, it is said to be a valley wire break. The image below demonstrates several examples. Valley wire breaks are difficult to find, and the early signs may be a slight lifting of the wire above its neighbours.

Tip: Bending wire rope during inspection can often reveal the presence of valley wire breaks. You may also hear a cracking noise originating from inside the wire rope. Magnetic Resonance Testing (NDT or MRT) can often be used to detect the presence of internal deterioration.

Discard Criteria

As valley wire breaks are often symptomatic of internal strand and core damage, and due to the difficulty of detection, ISO 4309 has a low tolerance in terms of discard. Within a distance of one lay length (approximately 6 nominal diameters), only two valley wire breaks are permissible.

A simple way to remember this is that a valley typically has two sides- two valley breaks over 6d means discard.

ISO 4309 Deterioration Status- Each valley wire break adds 50% to the overall condition of the rope - a severity rating of 100% means discard.

Conclusion

Valley wire breaks are a serious issue if they occur and strongly indicate the internal deterioration of wire rope. Be diligent when inspecting the wire rope as these are probably the hardest type of wire break to spot!

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The Rope IQ team.

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