Wire Rope Inspection - cont - TM-5-3810-305-10

Wire Rope Inspection - cont - TM-5-3810-305-10_110

TM-5-3810-305-10 Crane Wheel Mounted Hydraulic Light 7 1/2 Ton (Rough Terrain Crane) Model LRT 110 Manual
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TM5-3810-305-10 3. Reduction in rope diameter: Any marked reduction in rope diameter indicates degrada- tion. Such reduction may be attributed to: a. Excessive external abrasion. b. Internal or external corrosion. c. Loosening or tightening of rope lay. d. Inner wire breakage. e. Rope stretch. f. 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 under- gone 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 standards are not, in themselves, of any serious significance since they do not take into account such factors as: a. Variations in compressibility between IWRC and Fiber Core. b. Differences in the amount of reduction in diameter from abrasive wear, or from core compression, or a combination of both. c. The actual original diameter of the rope rather than its nominal value. As a matter of fact, all ropes will show a sig- nificant reduction in diameter when a load is applied. Therefore, a rope manufactured close to its nominal size may, when it is subjected to loading, undergo a greater reduc- tion in 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 allow- able 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 orig- inal 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. 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 differ- ent but interrelated conditions must be evalu- ated. 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 observa- tions lead to an opposite conclusion. 4-46

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