Nature and Quantity of Broken Threads

The overall design of lifting machinery does not permit wire ropes to have an indefinite lifespan.

For 6-strand and 8-strand wire ropes, the breaks mainly occur on the surface. However, for multi-layer strand wire ropes (a typical multi-strand structure), the breaks typically happen internally, making them "invisible" fractures.

The table takes these factors into account, thus, when combined with the factors in sections 2.5.2 to 2.5.11, it is applicable to wire ropes of various structures.

2 End of rope broken

When there are broken fibers at the rope end or in its vicinity, even a small number indicates high stress in that area, which may be due to incorrect rope end installation. The cause of the damage should be investigated. If the rope length allows, the broken fiber section should be cut and reinstalled properly.

Partial aggregation of broken threads

If broken wires are tightly packed together to form a local cluster, the wire rope should be discarded. If such a cluster of broken wires is within a rope length of less than 6d, or concentrated in any one strand, the wire rope should be discarded even if the number of broken wires is fewer than the listed value.

The increase rate of broken wires: In certain applications, fatigue is the primary cause of wire rope damage, with broken wires beginning to appear after a period of use. However, the number of broken wires gradually increases, with shorter intervals between occurrences. In this situation, to determine the increase rate of broken wires, it is essential to carefully inspect and record the progression. Identifying this "pattern" can be used to determine the future date for the rope's retirement.

5. Rope strand breakage

If a complete strand of wire rope breaks, the rope should be discarded.

Due to core damage, the rope diameter has decreased.

When the fiber core of a wire rope is damaged or the steel core (or the inner strands in a multi-layer structure) fractures, causing a significant reduction in rope diameter, the wire rope should be retired. Minor damage may be不明显 with conventional inspection methods, especially when all strands are in good stress balance. However, this condition can greatly reduce the strength of the wire rope. Therefore, any indication of internal minor damage should prompt an internal examination of the wire rope to ascertain the extent. Once damage is confirmed, the wire rope should be retired.

7 Decreased Elasticity

In certain situations, typically related to the working environment, the elasticity of wire ropes can significantly decrease, and continuing to use them is not advisable.

The elasticity reduction of wire rope is often difficult to detect. If inspectors have any doubts, they should consult with a wire rope expert. However, elasticity reduction typically accompanies the following phenomena:

a. Diameter Reduction

b. Wire rope twist distance elongation;

c. Due to the parts being tightly compressed together, there is a lack of space between the steel wires and between the strands.

d. Fine brown powder appears in the grooves of the rope strands.

e. Although no broken wires were found, the rope's significant difficulty in bending and the rapid decrease in diameter are much faster than simply due to wire wear. This condition can lead to sudden breakage under dynamic load, therefore it should be immediately scrapped.

Two types of wear: external and internal wear.

Internal Wear and Press Marks

This condition is caused by friction between the individual strands and steel wires within the rope, especially when the rope is subjected to bending.

b. External Wear

The wear on the surface of the steel wires of the outer strand in wire ropes is caused by friction with the rope grooves of pulleys and drums under pressure. This phenomenon is particularly evident during the acceleration and deceleration of lifting loads, where the contact area between the wire rope and the pulley is external, resulting in the steel wires being worn down into a flat surface.

Insufficient lubrication, incorrect lubrication, and the presence of dust and sand particles can exacerbate wear.

Friction reduces the cross-sectional area of steel wire rope, thereby decreasing its strength. When the outer wire's wear reaches 40% of its diameter, the rope should be discarded.

When the diameter of the wire rope is reduced by 7% or more from the nominal diameter, even if no broken wires are found, the wire rope should be retired.

External and Internal Corrosion

Corrosion is particularly prone to occur in marine or industrial-polluted atmospheres. It not only reduces the metal area of the wire rope, thereby lowering its breaking strength, but also leads to surface roughness and initiates cracks, accelerating fatigue. Severe corrosion can also reduce the elasticity of the wire rope.

External Corrosion

External wire corrosion can be observed with the naked eye. The wire should be discarded when deep pits appear on the surface and the wire becomes quite loose.

(2) Internal Corrosion

Internal corrosion is often harder to detect than the more common external corrosion. However, the following phenomena can be identified:

The change in rope diameter. The diameter of the rope typically decreases as it bends around the pulley. However, for the stationary section of the rope, it often increases due to rust accumulation on the outer strands.

b. The gaps between the outer strands of the wire rope have decreased, often accompanied by broken wires between the outer strands. If any signs of internal corrosion are present, the supervisor should conduct an internal inspection of the wire rope. If severe internal corrosion is confirmed, the wire rope should be immediately retired.

10 Transformations

Wire rope that loses its normal shape and develops visible deformities is referred to as "deformation." This deformed area (or malformed section) may cause alterations, leading to uneven stress distribution within the wire rope.

(1) Catenary Distortion - This deformation occurs on wire ropes with a steel core. It happens when the outer strands become loose or longer than the inner strands. Wire ropes with catenary distortion should be immediately retired.

(2) Ropewrap Extrusion

This condition often occurs alongside cage deformation. The extrusion of the strand indicates an imbalance in the wire rope. The rope strand with extruded wire should be immediately scrapped.

Wire Extrusion

This deformation occurs when a portion of wire or a bundle of wires arches into a ring shape on one side of the rope's groove against the pulley. This type of deformation is often caused by impact loads. If such deformation is severe, the wire rope should be discarded.

Tie Knot

Twisting occurs when a wire rope is tightly pulled into a loop, unable to rotate around its axis, resulting in deformation. This leads to uneven lay lengths and excessive wear. In severe cases, the rope may twist to the point where only a small portion of its strength remains. Wire ropes with severe twisting should be immediately retired.

(5) Local Diameter Reduction

Local reduction in wire rope diameter is often associated with core breakage. Special attention should be paid to inspect for such deformation near the rope ends.

Steel wire ropes with a severely reduced diameter in the rope circumference should be scrapped.

(S6) Partially flattened

The wire rope section was flattened due to a mechanical accident. In severe cases, the wire rope should be discarded.

(7) Bend

Bending is an angular deformation of wire rope caused by external influences. Wire rope exhibiting such deformation should be immediately scrapped.

(8) Damage caused by heat or electrical arc

The wire rope should be discarded once it has been subjected to special thermal treatment and exhibits a recognizable color on its surface.