Why diameter comes first

A wire rope carries load through its steel section. A loss of diameter usually means a loss of steel section: outer wire wear, strands bedding tighter, core failure or corrosion. A gain in diameter is not automatically good either; it can indicate core protrusion, internal corrosion, a kink or crushing.

Diameter is only the entry point. Discard decisions combine broken wires, corrosion, deformation, termination condition and diameter change; no single number stands alone.

Establish a reference diameter

Diameter inspection is a comparison against a baseline, not a single caliper reading. After installation, record a reference diameter on a straight section away from the ends and clear of crossover zones, using a consistent method. Return to the same positions and directions at every later inspection.

If no reference exists, record the measured value, the measurement positions, and the rope's size, construction, core and installation date. Nominal diameters of different constructions or core types cannot be compared directly.

Measure across the crowns, not the valleys

The caliper jaws should straddle the crowns of the outer strands, not drop into the valleys between them. A valley reading measures a local depression, not the outside diameter of the rope.

Take two readings about 90 degrees apart at the same cross-section and record both. Sample several points along the length, with extra attention near sheaves, drums and terminations. Crossover zones on a multi-layer drum wear harder and should be recorded separately, never averaged into the adjacent parallel zones.

Reading a reduction in diameter

A uniform, gradual reduction is typical of normal wear and strand bedding. A local, sudden reduction deserves more attention: it may indicate core failure, local damage or heavy corrosion. A local increase calls for a check for core protrusion, internal corrosion, kinking or crushing.

ISO 4309:2017 and GB/T 5972-2016 give diameter-reduction criteria by rope type, core and rope category, and treat the result as one contributor to an overall severity assessment. Do not apply one fixed percentage to every rope, and do not treat a value below a threshold as permission to keep running.

Stop the equipment and have a competent person assess the rope if you find a sudden local change, exposed core, broken strand or heavy corrosion.

What else to inspect

Broken wires are the most direct signal. Distinguish visible crown breaks, valley breaks and a broken strand; count breaks over the specified reference lengths, noting that rotation-resistant and single-layer ropes have different criteria. Breaks concentrated at a termination, sheave entry or crossover zone carry more risk.

Corrosion inspection covers external rust, the gaps between strands and the core. A consumed zinc layer, surface pitting or rust bleeding between strands all suggest internal deterioration. Deformation includes waviness, bird-caging, crushing, kinking, bending and heat damage; none of these is merely cosmetic.

Terminations are part of the inspection too: fitting slip, broken wires at the end, cracks in a swaged sleeve, a loose wedge-socket tail, thimble wear and corrosion can all leave the assembly rated below the rope itself.

Assess defects together

Real discard decisions rarely turn on one measurement. Broken-wire counts, diameter loss and corrosion can each look acceptable while their combined effect already meets a discard condition. The applicable standard provides a method for combining severity, not a set of independent pass marks.

Keep a complete record: date, equipment, rope specification, installation date, measurement positions, reference diameter, measured diameter, broken-wire counts and locations, corrosion level, deformation, termination condition, conclusion and inspector. Only then can the next inspection be compared.

Inspection intervals and stop-work conditions

Set the interval from the applicable standard, the equipment's duty class, frequency of use, environment and the rope's known rate of deterioration. Shorten it for heat, abrasives, moisture, marine exposure and frequent bending. Inspect immediately after an impact, overload, slip or abnormal noise.

Stop work on any sudden local diameter loss, exposed core, broken strand, kink, crush, heavy corrosion, abnormal termination or heat damage, then decide discard under ISO 4309:2017 or GB/T 5972-2016. The original breaking-strength table is not a substitute for an in-service inspection.

Make the record comparable

The breaking-strength table answers what a new rope can pull; an in-service inspection answers whether this rope is still fit to work. One cannot replace the other. Published breaking data is in the wire rope breaking strength guide for reference.

Construction and termination options are set out in the wire rope construction guide

When ordering a replacement, hand the old rope's inspection record to the supplier; it is more useful than a diameter alone.

The short rule

Measure on the crowns, compare against a baseline, record several points and judge the combination. Diameter is the first check, not the only one.