Mobile Crane Wire Rope Selection and Discard Criteria
GB/T 24811.2-2009 "Lifting Appliances — Wire Ropes — Part 2: Wire Ropes for Mobile Cranes" is the dedicated standard governing wire rope selection and installation for mobile cranes. Building on the general requirements of Part 1, this standard refines the selection calculations, installation and maintenance practices, and discard criteria for wire ropes used in mobile cranes, addressing the unique demands of telescopic boom structures, multi-pulley systems, and frequent spooling/unspooling operations.
GB/T 24811.2-2009 is the second part of the crane wire rope standard series, providing more specific provisions for the selection calculation and discard criteria of wire ropes used on mobile cranes. Mobile crane wire ropes operate under complex working conditions, requiring more targeted selection and discard requirements. The following sections interpret the core content of this standard.
Standard Positioning and Mobile Crane Wire Rope Characteristics
GB/T 24811.2-2009 is Part 2 of the GB/T 24811 series, specifically addressing wire ropes used on mobile cranes. The working conditions for mobile crane wire ropes are far more demanding than those for overhead and gantry cranes: the hoisting rope passes through multiple guide sheaves inside the telescopic boom, with frequent changes in bending direction; the rope is repeatedly spooled and unspooled (every lifting operation involves paying out and reeling in), subjecting it to combined alternating bending fatigue and tensile fatigue; and during boom extension/retraction, the telescoping rope moves with the boom, enduring additional tensile and bending loads. Furthermore, replacing wire ropes on mobile cranes is more complex than on fixed base cranes — the rope must be threaded sequentially through the guide sheave system inside the telescopic boom, where installation space is limited.
Wire Rope Selection Requirements
The standard sets out detailed selection requirements for wire ropes used in each mechanism of a mobile crane. Hoisting rope — a non-rotating (rotation-resistant) wire rope should be selected, such as 18×7, 19×7, or 35(W)×7 multi-strand rotation-resistant constructions. This is because the hoisting rope on a mobile crane passes over only a single sheave at the boom tip (with no equalizer sheave); the torque generated by the suspended load creates a tendency for the rope to rotate, and an ordinary wire rope (e.g., 6×37) would spin, causing the sling and hook to rotate and compromising positioning accuracy. The minimum safety factor for the hoisting rope is ≥3.5 (relative to minimum breaking force).
Telescoping rope — the telescoping rope (also referred to as the cylinder extension rope) is subjected to significant tensile forces during boom extension/retraction. The minimum safety factor for the telescoping rope is ≥4. A wire rope with good flexibility and wear resistance (such as 6×36WS or 6×26WS) should be selected. Luffing wire rope (used in the luffing system of lattice boom crawler cranes) requires a safety factor of ≥3.5. The luffing rope typically uses a 6×37+IWRC (independent wire rope core) construction, which withstands substantial static loads and dynamic shock loading.
Rotation-resistant rope
High wear resistance
35(W)×7
D/d≥14 (telescoping)
Multi-layer winding D/d≥18
≥5% of total wires
Sheave and Drum Matching Requirements
The standard specifies dimensional requirements for matching wire ropes with sheaves and drums on mobile cranes, which are critical to ensuring wire rope service life. The ratio of sheave diameter D to wire rope diameter d (D/d) — hoisting sheave ≥18 (hydraulic telescopic boom cranes) or ≥20 (lattice boom cranes); telescopic boom guide sheave ≥14; luffing sheave ≥16. The ratio of drum base diameter D_d to wire rope diameter — hoist drum D_d/d ≥16 (≥18 for multi-layer winding). The sheave groove radius R = (0.53~0.56) × d, and the groove depth h ≥ 1.5d. Larger ratios result in a larger bending radius for the wire rope, lower bending stress, and longer service life. Ratios that are too small accelerate bending fatigue fracture of the wire rope.
Special Requirements for Wire Rope Installation and Maintenance
Mobile crane wire ropes have special installation and maintenance requirements. During installation, the wire rope should be passed through a rotation device to release internal stress (particularly for rotation-resistant ropes, as improper installation can compromise their rotation resistance). When threading the rope through the sheaves inside the telescopic boom, it must not rub against the inner wall of the boom; guide rollers or wear-resistant liners should be fitted to protect the rope. During boom extension/retraction, the tension on the telescoping rope should be maintained constant (via a spring tensioner or hydraulic tensioning device).
Daily inspection focus — inspections of mobile crane wire ropes should pay particular attention to the following areas: the boom tip sheave (highest bending frequency and the most common location for wire breaks); the fixed end on the drum (stress concentration at the clamping plate); the guide sheaves inside the telescopic boom (not directly visible, requiring inspection via borescope); and the rope section in contact with the boom tip opening (wear of the wear-resistant layer). Inspection interval — a visual inspection before each day's operation, a detailed inspection once per week (including diameter measurement and broken wire counting), and a thorough examination once per month (including rope tension testing and internal lubrication condition checks).
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| Application Area | Recommendedstructure | Safety factor | D/d Ratio | inspection focus |
|---|---|---|---|---|
| hoisting rope | 18×7/19×7 Resistance Rotation | ≥3.5 | ≥18 | boom tip sheave Locationwire break |
| Telescoping Wire Rope | 6×36WS/6×26WS | ≥4 | ≥14 | Internal Guide Sheave Wear |
| Luffing Wire Rope | 6×37+IWRC | ≥3.5 | ≥16 | Fixing End and Joint |
| jib Wire Rope | 19×7 Resistance Rotation | ≥3.5 | ≥18 | Reeving Pulley Section |
| lattice boom Hoisting / Lifting | 35(W)×7 Resistance Rotation | ≥3.5 | ≥20 | Full-Length Appearance+Tension |
Refined Scrap Criteria for Mobile Crane Wire Ropes
A: Building on the general scrap criteria outlined in Part 1, the standard introduces more stringent, application-specific scrap criteria for wire ropes used on mobile cranes. These refinements account for the unique operating conditions of mobile cranes, including higher bending frequencies and smaller wire diameters, which accelerate fatigue and wear.
Wire Break: A rope must be scrapped when the number of broken wires within one lay length reaches 5% of the total wire count—a stricter threshold than the 10% specified in Part 1. This tighter limit reflects the faster propagation of wire breaks in mobile crane ropes, where individual wires are thinner and subject to more frequent bending cycles.
Wear: The hoisting rope must be scrapped when outer-wire wear, indicated by a diameter reduction exceeding 3% of the nominal diameter, is observed. Part 1 allows up to 7% before scrapping is mandated.
Corrosion: Given that mobile crane ropes are exposed to outdoor use, corrosion inspections should be performed more frequently. Any visible corrosion point (e.g., red rust spots) must be documented immediately. Scrapping is required when a continuous corroded area reaches ≥100 mm².
Telescoping Rope: If abnormal noises—such as rubbing or kinking of the rope inside the boom—occur during boom extension/retraction, cease use immediately and extract the rope for a thorough inspection.
Kelude Heavy Industry offers a wire rope life-tracking service for mobile cranes, providing dual-criteria replacement intervals based on cumulative lifting tonnage and calendar time.
Mobile Crane Wire Rope Selection & Scrap Criteria Comparison Table
The comparison table below summarizes the key parameters and configurations for wire rope selection and scrapping on mobile cranes, serving as a quick reference for engineers and operators.
| Wire Rope Application | minimum Safety factor | selection requirements | discard criteria |
|---|---|---|---|
| Main hoist Rope | ≥4.5 | Anti-Torsion+Anti-corrosion | wire break≥4Piece(10d) |
| Auxiliary hoist Rope | ≥4.0 | Anti-Torsion+Anti-corrosion | wire break≥4Piece(10d) |
| Luffing rope | ≥4.0 | High Strength+Wear-Resistant | wire break≥4Piece(10d) |
| Telescopic boom Rope | ≥3.5 | High Strength+Low Elongation | Diameter reduction≥5% |
