Broken wire count is only half the conclusion

When broken wires are found, the usual response is to count them and compare the total with a discard table. The count matters, but the same number in different places and shapes can mean very different things. A dozen scattered over three lay lengths and five or six concentrated at one sheave tangent point should not be handled alike.

Broken wires are a result, not a cause. To judge whether the rope can stay in service, why it failed and whether a new one will fail again, read break location, break shape and distribution together. Counting alone turns equipment problems into rope quality complaints and can leave a failed rope on the machine. For the principles of discard, see the wire rope discard criteria

Location first: valley, crown and termination

Where a break shows matters more than the count. The crown is the outer face of a strand, in contact with the sheave groove, the drum or the ground; the valley is the recess between two strands, hidden by its neighbours and visible only when the rope is opened or lit from the side.

Crown breaks usually point to external wear combined with bending fatigue: repeated bending gives the outer wires the largest stress range, cracks start at the surface and the break ends up square. Valley breaks are harder to see, and the crack usually starts from contact stress between strands or from internal corrosion. Breaks near a termination deserve separate attention, because stress concentration at the fitting entry, the installation angle or corrosion can all cause them. For measurement, see wire rope dimensional inspection

Break shape: fatigue, tensile and corrosion

The fracture face is the evidence left when a wire breaks. A fatigue break is square, almost perpendicular to the wire axis, with no clear necking; a smooth zone spreading from the crack origin is visible, followed by a rough final fracture, like a paper clip broken by repeated bending.

A tensile break necks, takes a cup-and-cone shape with shear lips, and looks dull and fibrous. When a whole rope is overloaded, many wires break in one section, the faces mesh and the diameter shrinks. That says the rope has seen a force far above its working load, so replacing it is not enough: find out where the load came from.

Corrosion breaks sit between the two: the surface is pitted, the section is already reduced, the face is irregular and rust-stained. A pit is a crack origin, and cyclic stress grows it into a break, so these wires are not pure fatigue. Abrasion breaks are another type: the face is sheared and the wire end is worn to a point, which means the rope rubs against something hard, and the fault is in the layout, not the rope.

Distribution along the lay and the length

Counting broken wires must carry a length. Standards count within a defined length, commonly a 6d or 30d window; the window and the allowed count depend on the construction, the duty and the standard. "Eight broken wires in total" means nothing unless you say over what length and how many lay lengths they are spread.

Broken wires spread evenly over the whole rope, one or two per lay length, usually mean accumulated normal wear and a rope near the end of its life. Breaks within one or two lay lengths with almost none elsewhere look more like local damage: a bad groove, a crush, a bend point, or a section that once held water. Record the position along the length too; when breaks keep appearing at one point in the travel, it is the cause.

Random breaks versus clustered breaks

Random and clustered breaks lead to two different courses of action. A random pattern says the whole rope has aged at the same rate and needs replacing, but confirm that the new rope's grade, construction and lubrication match the duty, or the next rope will last just as long.

A clustered pattern calls for finding the cause before replacing the rope. Common causes include an undersized sheave or a groove worn to a sharp edge, a crossover crushing the layer below in multilayer spooling, a fairlead set at the wrong clearance, damage from a blow or a sharp edge in transport or installation, and local corrosion where water entered at a termination. A practical test: if a new rope develops breaks in the same place after a short run, the equipment is almost certainly at fault. For intervals, see wire rope inspection intervals

Reading equipment condition from the breaks

The sheave is the part breaks most often point to. As the groove bottom wears and the radius shrinks, the rope is pinched harder and contact stress rises; sharp groove edges cut the surface; and a failing bearing lets the sheave run out of line so the entry and exit angles keep changing, which adds fatigue. The break positions identify which sheave is involved.

Drum problems show up as crushing and crossover wear. In multilayer spooling the upper rope drops into the gap between turns below, the crossover point carries very high local pressure and dents the lower rope, which then breaks wires. Overload leaves a different signature: the break count rises sharply in a short time, the faces show tensile shape, the diameter falls and the rope elongates, so check the load records and the brake rather than the rope material.

Breaks combined with other deterioration

Broken wires never come alone. Wear reduces the section of the outer wires, fatigue makes cracks start more easily, and corrosion removes load-bearing area from the inside; when all three act together the break count understates the real condition. Judge a rope on breaks, diameter loss, lay extension, corrosion and lubrication together.

Diameter is one of the most objective measures. Use a caliper at the same point in two perpendicular directions, take the average and compare it with nominal, avoiding break clusters and flattened areas. A smaller diameter may come from wear, core contraction or internal corrosion. A clearly longer lay with a smaller diameter usually means the rope has been over-tensioned, and replacement should be considered even with few broken wires.

When to move to non-destructive testing

Visual inspection has limits: the part hidden behind a sheave, the inner layers on a drum, the core and the inside of a termination cannot be seen. Consider non-destructive testing when the count approaches the discard line, breaks appear in valleys, the diameter is abnormal, or the rope cannot be fully seen.

Wire rope NDT mainly uses electromagnetic methods, including LMA for loss of metallic area and LF for local faults. It scans the whole rope without removing it and finds internal breaks, corrosion and local deformation. Results need a baseline and interpretation experience; the method does not replace visual inspection and cannot be the only basis for discard. For methods and conditions, see wire rope NDT

Records and decisions

A useful break record contains at least the date, running hours, break position, the lay length involved, the break shape, whether corrosion or wear was present, the load condition at the time and photographs. After a few entries the rate of deterioration becomes visible, instead of waiting for the count to exceed the limit.

Decide in this order: confirm whether the breaks meet the discard condition, judge whether the cause is local or general ageing, then decide whether to repair the equipment, replace the rope, or both. Replacing the rope without fixing the equipment repeats the problem; fixing the equipment without replacing the rope leaves a rope whose remaining life is already reduced. Count the breaks, but read them: location says where the problem is, shape says why the wire broke, distribution says how much life is left.