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WIRE_ROPE_NSPECTION

The following is a fairly comprehensive listing of critical inspection factors. It is not, however, presented as a substitute for an experienced inspector. It is rather a user’s guide to the accepted standards by which ropes must be judged.

1. Abrasion

Rope abrades when it moves through an abrasive me rum or over rums an sheaves. Most standards require that rope is to be removed if the outer wire wear exceeds 1/3 of the original outer wire diameter. This is not easy to determine and discovery relies upon the experience gained by the inspector in measuring wire diameters of discarded ropes.

2. Rope stretch

All ropes will stretch when loads are initially applied.

As a rope degrades from wear, fatigue, etc. (excluding accidental damage) , continued application of a load of constant magnitude will produce incorrect varying amounts of rope stretch.

Phase 1. Initial stretch, during the early (beginning) period of rope service, caused by the rope adjustments to operating conditions (constructional stretch).

Phase 2. Following break-in, there is a long period—the greatest part of the rope’s service life-during which a slight increase in stretch takes place over an extended time. This results from normal wear, fatigue, etc. On the plotted curve— stretch vs. time—this portion would almost be a horizontal straight line inclined slightly upward from its initial level.

Phase 3. Thereafter, the stretch occurs at a quicker rate. This means that the rope has reached the point of rapid degradation; a result of prolonged\subjection to abrasive wear, fatigue, etc. This second upturn of the curve is a warning indicating that the rope should soon be removed.

3. Reduction in rope diameter

Any marked reduction in rope diameter indicates degradation. Such reduction may be attributed to:

  • excessive external abrasion
  • internal or external corrosion
  • loosening or tightening of rope lay
  • inner wire breakage
  • rope stretch
  • ironing or milking of strands

In the past, whether or not a rope was allowed to remain in service depended to a great extent on the rope’s diameter at the time of inspection. Currently this practice has undergone significant modification.

Previously, a decrease in the rope’s diameter was compared with published standards of minimum diameters. The amount of change in diameter is, of course, useful in assessing a rope’s condition. But, comparing this figure with a fixed set of values can be misleading. These long-accepted minimums are not, in themselves, of any serious significance since they do not take into account such factors as: 1) variations in compressibility between IWRC and Fiber Core; 2) differences in the amount of reduction in diameter from abrasive wear, or from core compression, or a combination of both; and 3) the actual original diameter of the rope rather than its nominal value

As a matter of fact, all ropes will show a significant reduction in diameter when a load is applied. Therefore, a rope manufactured close to its nominal size may, when it is subjected to loading, be reduced to a smaller diameter than that stipulated in the minimum diameter table. Yet under these circumstances, the rope would be declared unsafe although it may, in actuality, be safe.

As an example of the possible error at the other extreme, we can take the case of a rope manufactured near the upper limits of allowable size. If the diameter has reached a reduction to nominal or; slightly below that, the tables would show this rope to be safe. But it should, perhaps, be removed.

Today, evaluations of the rope diameter are first predicated on a comparison of the original diameter—when new and subjected to a known load—with the current reading under like circumstances. Periodically, throughout the life of the rope, the actual diameter should be recorded when the rope is under equivalent loading and in the same operating section. This procedure, if followed carefully, reveals a common rope characteristic: after an initial reduction, the diameter soon stabilizes. Later, there will be a continuous, albeit small, decrease in diameter throughout its life.