Start hereRules checked 20 October 2026
Wire rope fails from the inside out. Broken wires hide in the valleys between strands, corrosion eats the core where no one can see it, and a rope that looks merely dirty can have lost a large part of its strength. When a hoist rope parts, the load falls and the rope whips back with enormous energy.
That is why both the ILO code of practice and the SOLAS lifting appliance guidelines point to one international standard for the discard decision, ISO 4309, and why certification of the rope itself is one of the items a thorough examination checks. This lesson shows what to look for and when the answer is “replace it now”.
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In this lesson
- Keep, check or discard?
- In plain words
- In detail
- What the rules say
- Flag and class notes
- Key numbers
- What inspectors find
- Quiz: 6 questions
Try it
Keep, check or discard?
In plain words
A wire rope is made of many steel wires twisted into strands, and strands twisted around a core. It is designed to lose a few wires without danger, but only a few. Inspecting it means looking along its whole working length, especially where it runs over sheaves, onto the drum and near its end fittings, for:
- broken wires, counted over a short and a longer length of rope;
- loss of diameter, which can mean wear or hidden internal damage;
- corrosion, outside and inside;
- deformation: kinks, bird cages, flattening, core sticking out;
- heat damage, for example from welding or a fire.
When the signs pass the limits in the standard or in the manufacturer’s instructions, the rope is discarded. You never splice two damaged pieces together, and you never put a rope on a crane without a certificate.
In detail
What the SOLAS guidelines ask
MSC.1/Circ.1663 lists “certification and identification of ropes” among the items needing particular attention at inspections, and says damaged, broken, worn or corroded ropes, including their terminations, should be inspected and discarded according to the manufacturer’s recommendations, industry standards, international standards such as ISO 4309:2017, or class requirements acceptable to the Administration. The same text appears for anchor handling winches in MSC.1/Circ.1662.
ISO 4309:2017
ISO 4309, Cranes, Wire ropes, Care and maintenance, inspection and discard, is in its fifth edition, published in November 2017, which replaced the 2010 edition. It applies to rope on cranes, winches and hoists. Its discard criteria are organised by type of deterioration:
- Visible broken wires, counted over lengths of 6 d and 30 d (d is the nominal rope diameter), with the allowed numbers taken from tables according to the rope’s category number (RCN), which depends on its construction and the number of load-bearing outer wires. Ordinary lay and Lang lay ropes, and single-layer and multi-layer spooling, have different limits. Rotation-resistant ropes have their own table.
- Broken wires in particular locations: valley breaks, breaks at the termination, and localised groups.
- Decrease in diameter, measured against a reference diameter recorded when the rope was new.
- External and internal corrosion.
- Deformation: waviness, basket or bird cage, core or strand protrusion, kinks, flattening.
- Heat damage and electric arcing.
- A method to assess the combined effect of several kinds of deterioration at the same place.
Two points matter on ships. On multi-layer drums, the crossover zones deteriorate much faster than the rest of the rope. And on synthetic or synthetic-lined sheaves with single-layer spooling, the standard gives no discard criteria for visible breaks, because many internal breaks can occur before any appear on the surface.
The tables themselves are in the standard. Keep a copy, or the rope maker’s discard instructions based on it, with the crane’s maintenance manual.
The ILO code’s practical criteria
The ILO code of practice gives a short list that every deck officer should know. Wire ropes should be replaced when:
- they show significant corrosion, particularly internal corrosion;
- there is any tendency towards bird caging;
- there are signs of excessive wear, shown by flats on individual wires;
- the number of broken wires or needles in any length of ten diameters exceeds 5% of the total number of wires in the rope;
- broken wires appear in one strand only, are concentrated in less than ten diameters, or appear in the tucks of a splice;
- there is more than one broken wire immediately next to a compressed metal ferrule or similar termination.
If a rope has deteriorated, the defective parts should not be joined together. The cause of any defect should be investigated and put right, for example a seized sheave or a misaligned lead.
Care and maintenance
- Dress ropes regularly with a dressing free from acid or alkali, of the type the maker recommends, applied where the rope bends over a drum or pulley so it penetrates. Clean ropes used in dusty or abrasive cargoes first.
- Remove grips, wedge sockets and similar fittings during the thorough examination so the rope under them can be seen.
- Record each inspection, rope renewal and the certificate number in the crane’s records and the register.
Certification of a new rope
A new rope should be made to a recognised national or international standard, have its minimum breaking load certified by the maker, and be of a construction suitable for its use. Under the ILO model forms, wire rope is certified on Form No. 4: a sample is tested to destruction and the SWL is the breaking load divided by a coefficient of utilisation:
| Rope use | SWL | Coefficient |
|---|---|---|
| Part of a sling | under 10 t | 5 |
| 10 t to 160 t | 10,000 / (8.85 × SWL + 1,910) | |
| over 160 t | 3 | |
| Integral part of a lifting appliance | up to 160 t | 10,000 / (8.85 × SWL + 1,910) |
| over 160 t | 3 |
For a 10 t crane the formula gives about 5.0; for a 50 t crane about 4.25. The maker’s certificate and the rope’s identification must match the crane’s rope specification and the certificate attached to the register.
Slings
Wire rope slings with ferrule-secured eyes are individually proof tested, to not more than twice the SWL in straight pull. Hand-spliced slings are never proof loaded above their SWL; they rely on the maker’s certificate of the rope’s breaking load. Every sling is inspected by the responsible person before each use.
What the rules say
- MSC.1/Circ.1663 paragraph 3.5.1.5 says damaged, broken, worn or corroded ropes, including their terminations, should be inspected and discarded according to the manufacturer’s recommendations, industry or international standards such as ISO 4309:2017, or class requirements acceptable to the Administration. 2
- MSC.1/Circ.1663 paragraph 3.5.1.4.6 lists the certification and identification of ropes as an item requiring particular attention. 2
- MSC.1/Circ.1663 paragraph 4.6.4 requires loose gear, including slings, to be inspected by a responsible person before each use. 2
- The ILO code of practice, section 5.2.1.2 paragraph 6, lists the conditions under which wire ropes should be replaced, including more than 5% broken wires in ten diameters, bird caging and significant internal corrosion. 1
- The ILO code of practice, section 5.2.1.2 paragraph 5, says defective parts of a deteriorated wire rope should not be joined together. 1
- The ILO code of practice, section 4.2.3 paragraphs 2 to 5, requires wire ropes to be made to a recognised standard with the maker’s certified minimum breaking load, and ferrule-secured slings to be individually proof tested to not more than twice the SWL. 1
- ISO 4309:2017 sets general principles for the care, maintenance, inspection and discard of steel wire ropes on cranes, winches and hoists. 3
- The reverse of ILO Form No. 4 requires wire rope to be tested by sample to destruction and gives the coefficients of utilisation used to set its SWL. 4
Flag and class notes
- Liberia (SAF-020) accepts manufacturer’s recommendations, relevant industry and international standards, or its authorized classification societies’ rules for rope discard, and repeats the ISO 4309:2017 reference. 5
- Class rules usually set the minimum safety factor and certification for crane ropes, and some set inspection intervals. Check your RO’s rules and the crane maker’s manual, which takes precedence for its own equipment.
Key numbers
| What | Value |
|---|---|
| ILO code replacement limit | Broken wires in 10 d over 5% of total wires 1 |
| ISO 4309 counting lengths | 6 d and 30 d 3 |
| Ferrule-secured sling proof test | Not more than 2 × SWL 1 |
| Coefficient of utilisation, sling under 10 t | 5 4 |
| Coefficient, appliance rope up to 160 t | 10,000 / (8.85 × SWL + 1,910) 4 |
| Coefficient, over 160 t | 3 4 |
| ISO 4309 current edition | 5th edition, November 2017 3 |
What inspectors find
- Replacement ropes with no maker’s certificate on board, or a certificate whose construction or breaking load does not match the crane specification. 2
- Ropes dry and rusty because dressing is not in the planned maintenance system. 1
- Discard criteria missing: no copy of the maker’s instructions or the applicable standard, so crews cannot decide when a rope must go. 2
- Wire grips left on during the thorough examination, hiding damage underneath. 1
FAQ
How often should crane wires be inspected?
As the crane maker’s manual and your planned maintenance system set out, at least before use for slings and at each thorough examination. ISO 4309 and class rules give further guidance. Increase the frequency for ropes in heavy or abrasive service.
Can we cut off a damaged end and keep using the rest?
Often yes, if the remaining rope is long enough for the crane’s full range with the minimum turns on the drum, and the rest of the rope passes inspection. Re-terminating must be done properly, and the competent person may need to examine it.
Is a rope with no visible broken wires always safe?
No. Internal corrosion and internal breaks can be hidden, especially on synthetic sheaves. A local reduction in diameter is a warning sign.
Who decides to discard?
The responsible person can take a rope out of service. The final judgement on a doubtful rope belongs to a competent person using the standard and the maker’s criteria.
Quiz6 questions
Sources
- 1
ILO, Safety and health in ports, ILO code of practice (2005), sections 4.2.3, 4.2.4 and 5.2.1.2. https://www.ilo.org/sites/default/files/wcmsp5/groups/public/%40ed_protect/%40protrav/%40safework/documents/normativeinstrument/wcms_107615.pdf
- 2
IMO MSC.1/Circ.1663, Guidelines for lifting appliances (28 June 2023), Annex, paragraphs 3.5.1.4, 3.5.1.5 and 4.6 (copy hosted by ABS). https://ww2.eagle.org/content/dam/eagle/Images/rules-and-resources/regulatory-updates/solas-requirements/guidelines-hyperlinks/msc1-circ1663-guidelines-for-lifting-appliances%20%284%29.pdf
- 3
ISO 4309:2017, Cranes, Wire ropes, Care and maintenance, inspection and discard, 5th edition (November 2017), scope and clause 6 discard criteria (paid standard; catalogue entry). https://online.standard.no/en/iso-4309-2017
- 4
ILO model forms under Convention No. 152, Form No. 4 (Certificate of test and thorough examination of wire rope), instructions on the reverse, as published by the Danish Maritime Authority. https://www.dma.dk/Media/637721290870425149/Lifting%20Appliances%20-%20Certificates.doc
- 5
Liberia Maritime Authority, Marine Notice SAF-020 Rev. 12/25, paragraph 2.2.4. https://www.liscr.com/marketing/liscr/media/liscr/online%20library/maritime/saf-020.pdf
Rules checked 20 October 2026. VSL Safety is not an approved training provider and doesn't issue certificates. These lessons don't replace STCW training, or the manufacturer's training and certification that service technicians need.
