Wire Rope - Measuring Rope Diameter

MEASURING ROPE DIAMETER

Every periodic inspection must include diameter measurement at critical points and recording of measurements for future comparisons.

Most inspection standards are specific on permissable reductions in diameter. The criteria for the installation and industry involved should be known by the inspector before starting to take measurements.

Measurements are proper only when made across the crowns of rope strands, so that the true diameter is the widest diameter at any given point on the rope. Always rotate the caliper on the rope, or the rope inside the caliper, to take a measurement.

Reductions in diameter are caused by several factors, including:

Initial Pull-Down -

All ropes are manufactured larger than nominal diameter. When placed in operation for the first time, strands of a new, unused, rope will seat in and the diameter will be pulled down from its original diameter. Therefore, the first measurements should be made and recorded for future reference after the time of such a rope's initial loading.

Normal Wear -

In normal usage, the outer wires, particularly on the crowns of strands, will exhibit wear (see surface wear on 6 x 25 illustration below). Various inspection standards are specific as to the amount of such metal loss permissible.

This picture simulates 6x25 fw construction wire ropes
with surface wear (only) of 1/3 the outer wire diameter.

Internal Rope Damage -

When the core of a wire rope has begun to deteriorate, diameter reduction is often the first detectable outward sign. Impending internal breakdown should always be suspected when a sudden or significant diameter reduction is noted, and if possible, an internal rope examination should be made.