Wire Rope Discard Criteria: How to know when your wire rope is done

A wire rope comes out of service when it meets any one of six discard triggers: broken wires above the limit for its construction, diameter reduction past the allowable threshold, corrosion, physical distortion such as kinking or birdcaging, outer wire wear, or a combination of faults that individually pass but together don't. The rope doesn't have to fail every test. One trigger is enough.

What follows is how each of those six is assessed in Australia, which standard applies to your rope, and where visual inspection stops being good enough.

Three Australian Standards get quoted in wire rope discussions and they cover different things. Getting this wrong is the most common mistake in wire rope guidance, and it leads people to apply winding rope criteria to a sling or the other way around.

AS 3569 – Steel wire ropes is a product standard. Construction designations, grades, minimum breaking force. It tells you what the rope was when it was made. It is not an in-service inspection standard. The current edition is AS 3569:2026, published May 2026, which superseded AS 3569–2010 and its 2012 amendment.

AS 1666.2 – Wire-rope slings, care and use is the in-service standard for lifting slings. If you are working with wire rope slings on a crane hook, this is your governing reference for inspection and discard. Current edition is AS 1666.2-2009, reconfirmed in 2019.

AS 4812 – Non-destructive examination and discard criteria for wire ropes in mine winding systems covers installed winding ropes: drum winding, friction hoisting, balance, rubbing and guide ropes. It is a specialised regime built around NDE. AS 4812:2023 superseded AS/NZS 4812:2003 in March 2023.

Most people reading this are working with slings, so AS 1666.2 is the reference. If you run winding ropes or crane ropes in mining, AS 4812 applies and the inspection regime is a different animal altogether. Don't mix them. More detail on the full standards landscape: Australian Standards for lifting equipment.

A rope is discarded when the number of broken wires exceeds the limit for its construction. There is no single number that applies to every rope, and anyone who gives you one is guessing.

The limit depends on how many outer wires the rope has and how many strands. A 6x19 rope and a 6x36 rope do not share a threshold. The count is assessed over a defined length – one rope lay, or a multiple of it – and the distribution of the breaks matters as much as the total.

Uniformly distributed

Breaks spread evenly across strands over one lay length

Why it matters

The expected pattern from normal fatigue. Assessed against the construction-specific count.

Non-uniformly distributed

Breaks clustered rather than spread

Why it matters

Points to a localised cause – a sheave, a fleet angle, a contact point. Lower tolerance than uniform.

Concentrated in one strand

Multiple breaks in a single strand

Why it matters

That strand is shedding load onto its neighbours. Treated more severely.

Valley breaks

Breaks at strand-to-strand contact points, inside the rope

Why it matters

The most serious indicator. Valley breaks occur where strands bear against each other inside the rope, so by the time one shows on the outside there is usually more damage underneath. They point to core deterioration or strand nicking and trigger immediate competent person assessment – not a “watch it and see” item.

Two other things to check while you're counting. Breaks within one lay length of each other in adjacent lay lengths compound. And any broken wire at or immediately adjacent to an end termination is a discard criterion on its own regardless of the count – the termination is where load concentration is highest.

Our wire rope sling examination checklist sets out what our inspectors work through on a sling, termination by termination.

✓CORRECT

Measuring across the crowns

Jaw faces on the crowns of opposing strands, with the jaws deep enough to cover at least two adjacent strands. The reading is the circumscribing circle – the rope’s actual diameter.

✕INCORRECT

Measuring across the valleys

Jaw faces land on the flats between strands. That is the flat-to-flat width, not the diameter – on a 6-strand rope it reads about 9% under.

Method: take two readings at 90° to each other at the same section and average them – ropes run slightly oval. Measure on a straight, unloaded section, never on the drum, and at several stations along the rope. Example shown: 20 mm 6-strand rope, fibre core.

Wire rope loses diameter in service. When the reduction from the nominal new diameter exceeds the allowable threshold, the rope is discarded.

Three things cause it – abrasive wear on the outer wires, core deterioration allowing the strands to close in, and corrosion removing metal. Only the first is visible. The other two are the rope collapsing from the inside while the outside still looks serviceable.

NEW – nominal diameter

What you record when the rope goes into service

Full, round outer wires. Measure the rope when it is new and record that reading as the reference – later readings are compared against it, not against the nominal size on the certificate. New rope is supplied slightly over nominal (typically −0 / +5%), so the certificate figure understates the starting point.

WORN – reduced diameter

What the caliper finds later

The crowns of the outer wires flatten and the strands settle in towards the core. The measured diameter falls below the reference – the grey dashed circle shows where the new rope’s outline was. The allowable reduction is read from the applicable standard for the rope type.

How you measure matters as much as the number. A single caliper reading tells you very little.

The point most inspection regimes miss: diameter reduction is a lagging indicator. A rope that has lost measurable diameter has been degrading for a long time before it crossed the threshold. So the finding isn't really "this rope is finished" – it's "something has been quietly eating this rope, and the replacement will go the same way unless we work out what." Sheave condition, fleet angle, lubrication interval, spooling practice. Replace the rope and fix the cause. Start with wire rope care and maintenance.

Significant corrosion of the rope, the fittings or the end terminations is a discard criterion in its own right – with or without broken wires. Under AS 1666.2 a corroded sling goes, full stop.

The problem is that the corrosion that kills ropes is the corrosion you can't see. External corrosion shows as pitting and rust staining on the outer wires and you can assess it by eye. Internal corrosion attacks the core and the inner wires first, in the spaces where lubricant has dried out and moisture has sat. A rope can lose serious internal section while the outer wires still look presentable.

This is why magnetic rope testing exists. MRT magnetically saturates the rope and reads the flux leakage, which gives you two measurements visual inspection cannot: loss of metallic area (LMA), the cumulative loss of steel cross-section, and localised faults (LF), discrete defects such as internal broken wires, with position data along the rope length.

Under AS 4812, LMA detected by NDE is a primary discard trigger for internal deterioration, assessed and documented by a competent person. And here is the detail that matters most: the relationship between LMA and actual loss of breaking force is not linear. Where corrosion is present alongside wear, the loss of breaking force can be substantially greater than the LMA reading suggests – by a factor of up to six.

Read that again if you run ropes in wet, salt-laden, acidic or chemically aggressive service. An LMA reading that looks tolerable can sit over a rope with far less breaking force than the number implies. Any rope in that kind of environment belongs on an MRT programme, not a visual-only regime.

Deformation is the easiest category to assess and the least negotiable. If the rope's geometry has changed, the rope is done.

Kinking

✕DISCARD

A kink is permanent. Once a rope has been pulled tight through a loop, the strands have moved relative to each other and the load path through the rope is no longer what it was designed to be. You cannot straighten it out. A kinked rope has no known working load limit any more – it is not derated, it is retired. If someone on your site has straightened a kink and put the rope back on the hook, that rope needs to come off it.

Birdcaging

✕DISCARD

The outer strands splay outward from the core, exactly like a cage. It is caused by torsional load or by a sudden release of tension – shock unloading, a rope allowed to go slack under twist. The strands are now carrying load in a way the rope was never designed for, and the internal structure has already shifted. Discard.

Core protrusion

✕DISCARD

The core pushes out between the outer strands. This is structural failure working outward from the inside – the core has lost its ability to support the strands in position. Discard, and treat it as a signal to look hard at the rest of that rope's length and at what caused it.

Waviness or corkscrew distortion

?COMPETENT PERSON ASSESSMENT

A helical set along the rope's length, from uneven wear, poor spooling or crushing on the drum. It needs competent person assessment rather than automatic discard – but a rope that won't sit straight won't spool straight either.

If the rope’s geometry has changed, the rope is done. Waviness is the one exception – it needs a competent person’s call rather than automatic discard.

Surface wear flattens the crowns of the outer wires and reduces the load-bearing cross-section. Enough of it and the rope goes.

For winding ropes, AS 4812 gives you a number: wear over at least two rope lays that has reduced the outer wire diameter by more than one third is a discard criterion.

For lifting slings under AS 1666.2, there is no percentage. Significant abrasion, flattening or notching of the outer wires is a discard criterion, but the threshold is expressed qualitatively and the call belongs to a competent person looking at the rope.

That difference is not an oversight. Winding ropes run in a controlled, instrumented, repeatable system where a quantitative wear limit means something. Slings get used across dozens of different lifts, loads and edges, and their wear patterns reflect that. The standard puts the judgement where the information is – with the person holding the rope. When it is time to replace, our wire rope and fittings range covers the assembly end of it.

This is the trigger most informal inspection regimes never apply, and it is the one that catches the ropes that hurt people.

A rope can sit below every individual discard threshold and still be unfit for service. Broken wires under the count. Diameter reduction inside tolerance. Light corrosion. Some flattening. Nothing that fails on its own – and a rope that should not go back on the hook.

AS 4812 addresses this explicitly: a number of faults, none of which exceeds any single limitation, may as a combined effect render the rope unacceptable.

Ranger's inspection teams reject ropes on this basis regularly, and the pattern is consistent: three or four sub-threshold findings that share a cause – run dry, run over a worn sheave, left in a corrosive environment between jobs – and a combined condition well past the point where anyone should be trusting it with a load.

The takeaway is the important part: discard criteria are the minimum triggers, not a pass/fail list that replaces inspection judgement. A checklist tells you when a rope definitely has to go. It cannot tell you that a rope is fine. A competent person can retire a rope that passes every individual criterion, and sometimes should. That judgement is what our inspection services exist to provide.

Take the rope out of service if any of the following apply.

Eight of the conditions that take a rope out of service. The rope does not need to fail every test. If any one of these applies, it comes out of service.

Damaged termination

Broken wires

Diameter loss

Corrosion

Kink / birdcage

Outer-wire wear

Heat damage

Missing ID

Most discard criteria can be applied by a competent person with a caliper, a good light and the right standard in front of them. The two that can't are internal corrosion and internal wire breakage – the two that take ropes out from the inside while the outside still looks serviceable.

Ranger has been inspecting, testing and certifying lifting and rigging equipment since 1998, nationally across NSW, QLD, VIC and SWQ. Our wire rope services cover MRT, visual examination, proof load and break testing, splicing, cropping and re-roping, and metallurgical failure investigation – on site, on vessels, in mines and on cranes. If you're running rope in corrosive or high-cycle service on a visual-only regime, an MRT baseline is the most useful thing you can do for it. For crane and winding applications, see our crane ropes range.