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Technical GuideWire Rope and Chain Discard Criteria
Broken wires, diameter reduction, corrosion and deformation in wire rope and lifting chain: ISO 4309-based discard criteria and how to inspect them.
Why rope wears out
As wire rope passes over sheaves and the drum, it repeatedly bends and straightens. Every pass both flexes the wires and rubs them against each other. Add the stress from the load, and the rope fatigues in a predictable way over its life.
That's why there's no "use it until it snaps" approach with rope. It's replaced once it reaches one of a set of defined discard criteria. These criteria are set so that action is taken while the rope still has safe carrying capacity left.
What's checked on rope
Broken-wire count: if the number of broken wires counted over a defined reference length (specified as a multiple of the rope diameter) exceeds the limit, the rope is discarded. The limit varies with the rope's construction and wire count.
Diameter reduction: if the rope's diameter has thinned by more than a set proportion of nominal — this often means the core has degraded internally.
Corrosion: internal corrosion between the wires matters as much as surface rust. Internal corrosion can leave a rope looking sound from outside while its carrying capacity has already dropped.
Deformation: birdcaging (the rope ballooning outward), crushing, kinking, twisting and flattening. Most of these are discard reasons on their own.
Heat and electrical damage: welding-arc strikes or overheating damage the wire structure; a discoloured section is a discard reason.
| Finding | What it means | Decision |
|---|---|---|
| Broken wires over the limit in a defined length | Fatigue has progressed | Discard the rope |
| Noticeable diameter reduction | The core may have degraded | Discard the rope |
| Birdcaging / ballooning | Internal structure has failed | Discard the rope immediately |
| Crushing, flattening | Cross-section weakened | Discard the rope |
| Signs of internal corrosion | Capacity has dropped | Discard the rope |
| Heat / arc damage | Material structure damaged | Discard the rope |
| Chain elongation over the limit | Material has yielded | Replace the whole chain |
| A nick or crack in a link | Risk of breakage | Replace the whole chain |
Exact limit values vary by rope/chain type and come from ISO 4309 and the manufacturer's documentation.
What's checked on chain
The most telling indicator on a lifting chain is elongation. The chain is measured over a set number of links and the elongation is calculated against its original size. Elongation shows the material has started to yield.
The second item is wear on the link diameter: the cross-section thins where links contact each other. Nicks, cracks, cuts, weld spatter and a twisted or bent link are also checked for.
A single link is never replaced on a chain — the whole chain is replaced. A link from a different manufacturer or a different grade is never spliced in.
How the inspection is done
With the hook at its lowest position so the full length is visible, the rope is run out and inspected by hand (gloved), end to end. The sections that pass over a sheave, first wrap onto the drum, and attach to the hook block wear more heavily; inspection is concentrated there.
Findings are recorded. Marking the section where broken wires were counted lets progress be tracked at the next inspection.
When rope or chain is replaced, the sheave grooves and drum grooves should also be checked — a worn sheave wears out a new rope quickly.
Technical terms
| Term | What it means |
|---|---|
| Discard criterion | A measurable finding that requires an element to be taken out of service. |
| Birdcaging | Rope wires bulging outward into a cage-like shape. An immediate discard reason. |
| Safety wrap | The minimum rope that must remain on the drum with the hook at its lowest position. |
| Drum | The cylindrical body the rope winds onto. |
| Sheave | The rolling element that changes the rope's direction. A worn groove eats through rope quickly. |
| ISO 4309 | The standard defining maintenance, inspection and discard criteria for steel wire rope. |
Frequently asked questions
How often should I inspect the rope?
A daily visual check is the operator's responsibility. A detailed inspection is scheduled according to the crane's duty class and utilization; it is examined at every periodic inspection regardless.
Does lubricating the rope extend its life?
Yes, if done with the right product and correctly. Lubrication reduces both internal friction and corrosion. But excessive or incorrect lubrication traps dust and acts like sandpaper.
A few wires are broken but not many — can I keep using it?
The criterion is a count: if it's below the limit over the defined reference length, the rope can still be used, but that section is marked and monitored. If the broken-wire count is climbing quickly, replacement is planned before the limit is reached.