- 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 is for
the most part useless. These long-accepted minima are not, in themselves, of any
serious significance wince 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 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 tis nominal size may, when it is
subjected to loading, undergo a greater reduction in diameter than that stipulated in
the minimum diameter table. Yet, understand 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 loadwith 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.
Core deterioration, when it occurs, is revealed by a more rapid reduction in diameter
and when observed it is time for removal.
Deciding whether or not a rope is safe is not always a simple matter. A number of
different but interrelated conditions must be evaluated. It would be dangerously
unwise for an inspector to declare a rope safe for continued service simply because its
diameter had not reached the minimum arbitrarily established in a table if, at the same
time, other observations lead to an opposite conclusion.
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