Wire Rope Selection per GB/T 24814-2009: Diameter and Discard
GB/T 24814-2009 "Cranes — Wire Ropes for Hoisting Mechanisms" is the core standard for wire rope selection and discard criteria in crane applications. The standard specifies wire rope construction requirements for hoisting mechanisms, minimum safety factors (ranging from 4.0 to 9.0 for duty classifications M1 through M8), drum and sheave diameter matching requirements, and discard criteria covering wire breaks, strand breaks, and diameter reduction. This article provides a clause-by-clause breakdown of the standard's key provisions.
GB/T 24814-2009 "Cranes — Wire Ropes for Hoisting Mechanisms" is an equivalent adoption of ISO 4309:2004 "Cranes — Wire ropes — Care, maintenance, inspection and discard." It serves as the direct technical basis for the selection, service, and discard of hoisting ropes in crane applications. The standard was developed under the jurisdiction of the National Technical Committee for Standardization of Lifting Appliances and was published and implemented in 2009. Kelude Heavy Industry selects and configures hoisting ropes for its CD1/MD1 electric hoists and QD-type overhead cranes in accordance with this standard.
Wire Rope Construction and Selection
The standard recommends the following constructions for hoisting ropes: 6×19W (Warrington), 6×25Fi (Filler), and 6×36WS (Warrington-Seale) six-strand round strand ropes, as well as eight-strand constructions such as 8×25Fi and 8×36WS. For multi-layer winding applications, rotation-resistant wire ropes in 35×K7 or 19×K7 constructions are recommended.
Core Selection: Fiber core (FC) ropes offer good flexibility but limited resistance to crushing, making them suitable for single-layer winding applications. Steel core (IWRC) ropes provide high resistance to crushing and are recommended for multi-layer winding and high-temperature environments. The standard recommends steel core ropes for duty classifications of M5 and above.
Nominal Rope Diameter: The hoisting rope diameter is determined based on the maximum static working load and the applicable safety factor. Common diameter sizes include 8mm, 11mm, 13mm, 15mm, 18mm, 20mm, 22mm, 24mm, 26mm, and 28mm.
Minimum Safety Factors and Diameter Matching
The standard specifies minimum safety factors for each duty classification: M1–M3 (light duty) 4.0, M4 4.5, M5 5.0, M6 (heavy duty) 6.0, M7 (very heavy duty) 7.0, and M8 (extremely heavy duty) 9.0. Higher duty classifications require proportionally larger safety factors.
Drum Diameter Requirements: The ratio of drum diameter D to rope diameter d (D/d) for rope-centered winding must meet the following minimum values: M4 ≥18, M5 ≥20, M6 ≥25, M7 ≥30, and M8 ≥35. For example, a M5 crane fitted with a 15mm rope requires a drum diameter of at least 300mm.
Sheave Diameter Requirements: Equalizer sheave diameters may be 20% smaller than those of the working drum or sheaves at the same duty classification. For instance, a M5 sheave requires D≥22.4d, while a M6 sheave requires D≥28d.
Discard Criteria for Wire Ropes
A wire rope must be discarded when any of the following conditions is met: ① The number of visible wire breaks within one lay length reaches the value specified by the standard (approximately 10% of wires for six-strand ropes); ② Wire breaks are concentrated in a single strand, exceeding 50% of the wires in that strand; ③ The nominal rope diameter has been reduced by 7% (fiber core) or 5% (steel core); ④ A localized diameter reduction of 3% of the nominal diameter is observed; ⑤ A complete strand break occurs — immediate discard is required; ⑥ Severe corrosion, wear deformation, or kinking is present.
Wire Rope Selection Reference Chart
| Duty Classification | Minimum Safety Factor | Min. Drum D/d Ratio | Min. Sheave D/d Ratio |
|---|---|---|---|
| M1–M3 (Light) | 4.0 | 18 | 14.4 |
| M4 | 4.5 | 20 | 16 |
| M5 | 5.0 | 25 | 20 |
| M6 (Heavy) | 6.0 | 30 | 24 |
| M7 (Very Heavy) | 7.0 | 35 | 28 |
| M8 (Extremely Heavy) | 9.0 | — | — |
| Wire Rope Diameter | minimumbreaking(k N) | M5Allowable(k N) | M6Allowable(k N) | Drum D(mm) | Pulley D(mm) | Recommended Lifting Capacity |
|---|---|---|---|---|---|---|
| 8mm | 37.6 | 7.5 | 6.3 | 160 | 179 | ≤0.5t |
| 11mm | 67.4 | 13.5 | 11.2 | 220 | 246 | ≤1t |
| 15mm | 132 | 26.4 | 22.0 | 300 | 336 | ≤2.5t |
| 20mm | 225 | 45.0 | 37.5 | 400 | 448 | ≤5t |
| 24mm | 328 | 65.6 | 54.7 | 480 | 538 | ≤10t |
| Krudd Recommended | CD1Standard Configuration M5Safety factor5.0, QD Typeaccording to working class Configuration M5~M7 | |||||
Frequently Asked Questions
Q: Why does the wire rope safety factor range so widely, from 4.0 for M1 to 9.0 for M8?
A: Higher work classifications mean more frequent operation and higher load factors, which translate into a greater number of bending fatigue cycles on the wire rope. A M8 crane can exceed 1,000,000 duty cycles per year, and a safety factor of 9.0 ensures the rope will not reach breaking point due to wire breaks before its fatigue life is exhausted. Lower-classified equipment runs far fewer cycles, so a lower safety factor is sufficient to meet the design life requirement.
Q: How much diameter reduction requires the wire rope to be scrapped?
A: According to the standard, a fiber-core wire rope must be discarded when its nominal diameter is reduced by 7%, while an IWRC rope must be discarded at 5%. Additionally, if a localized diameter reduction of 3% of the nominal diameter is observed — even if the overall diameter remains within tolerance — that section must also be scrapped. Diameter reduction is typically caused by internal wire breaks or core damage.
Q: Which standard governs the selection of electric hoist wire rope?
A: Wire rope for electric hoist hoisting mechanisms is selected according to GB/T 24814-2009. CD1/MD1 electric hoists typically operate at M4~M5 work duty, with a safety factor of 4.5–5.0. Common rope diameters are 11 mm for 1 t hoists, 13 mm for 3 t, 15 mm for 5 t, and 20 mm for 10 t. Kelude electric hoists are uniformly fitted with wire rope selected at a safety factor of 5.0 for M5.
Q: At what point must a wire rope be scrapped due to wire breaks?
A: A wire rope must be scrapped when the number of broken wires within one lay length (approximately 6 times the wire rope diameter) reaches the values listed in the table. For a 6×19 structural steel wire rope, scrapping is required when 12 wire breaks occur within a length of 6d, or 24 wire breaks within a length of 30d. Immediate scrapping is also necessary when broken wires are concentrated in a single strand and account for more than 50% of the steel wires in that strand. The clustering of wire breaks indicates severe local stress concentration and rapid crack propagation.
