Wire Rope Selection, Installation & Discard Criteria for Cranes

As Part 1 of the crane wire rope standard series, GB/T 24811.1-2009 provides comprehensive provisions on rope selection principles, installation methods, and discard criteria. The wire rope is the critical load-bearing component of the hoisting mechanism, and its safe use directly affects personnel and equipment safety. The following sections interpret the key requirements of this standard.

Standard Scope and Wire Rope Classification

GB/T 24811.1-2009 applies to the selection, installation, and maintenance of wire ropes used in overhead, gantry, tower, mobile, and jib cranes. The standard classifies wire ropes by construction into: single-layer ropes (1×7, 1×19, 1×37, etc.), double-layer ropes (6×7, 6×19, 6×37, and other mainstream types), and triple-layer ropes. By lay direction, ropes are classified as right regular lay (ZS), left regular lay (SZ), right Lang lay (ZZ), and left Lang lay (SS). The most common constructions for crane hoisting mechanisms are 6×37+FC (fiber core, 6 strands of 37 wires each) and 6×19W+IWR (independent wire rope core, 6 strands of 19 wires each, Warrington type). Rope cores are categorized as fiber core (FC), natural fiber core (NFC), synthetic fiber core (SFC), and wire strand core (WSC) or independent wire rope core (IWR). Fiber-core ropes offer better flexibility but lower crush resistance, making them suitable for cranes with multi-layer drum winding. Wire-core ropes provide higher strength and superior crush resistance, making them ideal for large-tonnage cranes with single-layer winding.

Wire Rope Selection Calculations

The standard specifies that the minimum breaking force F_min of the wire rope must satisfy: F_min ≥ S_max × n, where S_max is the maximum working load on the rope and n is the safety factor. Safety factors for different crane mechanisms: hoisting mechanism n=4~6 (corresponding to working class A1~A8); grab crane hoisting mechanism n=5~6; tower crane hoisting mechanism n≥5; mobile crane hoisting mechanism n≥3.5 (considering hydraulic system overload protection); telescoping boom mechanism n≥4; trolley travel mechanism n≥3.5. The safety factor is determined by the crane's working class, the hazard level of the loads being handled, and the frequency of use. For cranes handling molten metal, nuclear waste, or other hazardous materials, the safety factor should be increased by 1 to 2.

The maximum working load S_max is calculated as: S_max = (Q + q) / (m × η), where Q is the rated lifting capacity, q is the dead weight of the lifting spreader, m is the reeving ratio of the pulley block, and η is the sheave block efficiency (η≈0.97~0.98 for rolling bearings, η≈0.95~0.96 for plain bearings).

Wire Rope Installation and Maintenance

Installation quality directly affects wire rope service life. The standard sets clear requirements for installation and maintenance: before installation, the rope must be inspected section by section for visible defects (wire breaks, kinks, crushing, arc burns, etc.); ropes with obvious defects must not be used. During unreeling, the rope must be kept free of kinks and twists; a swivel or rotation compensator should be used to relieve internal stress. The fleet angle of the rope on sheaves and drums should not exceed 1.5°~2° (friction occurs when the drum and sheave centerlines are not parallel). Rope end terminations should use wedge sockets or clamp plate fixing, with the termination strength not less than 80% of the rope's minimum breaking force.

New wire ropes undergo constructional elongation during initial service (approximately 0.1%~0.5% of the wire rope length). After 24 hours of operation, rope tension should be re-adjusted and both end terminations re-checked for secure fixing. The rope should receive adequate lubrication, and the lubricant must be compatible with the rope construction. When the rope passes over sheaves and drums, it should be lubricated in a clean condition (oil film thickness approximately 0.5mm, with lubrication at least once per month).

Wire Rope Discard Criteria

The standard provides detailed discard criteria for wire ropes, based on the following six indicators:

Number and distribution of wire breaks — Discard the rope when the number of visible wire breaks within one lay length reaches 10% of the total number of wires (for example, ≥22 broken wires within one lay length for a 6×37 rope). If wire breaks are concentrated locally (e.g., the number of breaks in a single strand reaches 50% of that strand's total wires), or if an entire strand fractures, discard the rope immediately.

Diameter reduction — Discard the rope when the nominal diameter is reduced by more than 7%. Diameter reduction results from both external wear and internal corrosion; measurements should be taken at least 2m from the rope end under no-load conditions.

Corrosion — Discard the rope when visible external corrosion (surface oxidation, pitting) or internal corrosion (rust detected on the rope core via probe inspection) is present. Corrosion is more dangerous than wire breaks because it weakens all wires rather than a localized area.

Deformation — Discard the rope when structural deformation such as waviness, lantern shape, birdcaging, kinking, crushing, or flat spots is present. Deformation not only reduces rope strength but also causes abnormal wear on sheaves and drums.

Heat Damage — Wire rope that has been arc-burned, flame-scorched, or discolored by overheating (temper colors — blue or yellow) must be scrapped immediately. Heat damage locally anneals the steel wire, causing a sharp drop in strength that is not readily visible on the surface.

Loss of Elasticity — A wire rope exhibiting diameter reduction accompanied by a noticeable loss of elasticity (stiff to the touch, or failing to conform to the pulley when bent) should be scrapped.

Wire Rope Daily Inspection

Standard requirements mandate that operators and maintenance personnel perform a daily inspection of the wire rope. The inspection content covers the overall appearance of the rope—including wire breaks, deformation, corrosion, and lubrication condition—with particular attention to the drum connection point, areas passing over pulleys, equalizer sheaves, and the anti-twist device. Once the wire rope has reached 75% of its design service life (calculated by cumulative lifting tonnage or operating hours), the inspection frequency should be increased to twice per week. All wire rope inspections must be documented, with records including at minimum: equipment number, wire rope number and specification, installation date, cumulative service hours (or number of lifts), inspection date and results for each check, and the scrapping date and discard reason. Kelude provides crane wire rope configuration recommendations and periodic inspection services to ensure the rope remains in a safe use condition at all times.

Wire Rope Selection, Installation & Discard Standards Comparison Table

The comparison table below outlines the core parameter configuration for wire rope selection, installation, and discard criteria, serving as a reference for those involved in selection and usage.

Frequently Asked Questions