How do I know if my kernmantle lifeline is still safe to use?
Even among rope manufacturers, there is not a definitive set of rules to be used in determining when a rope should be removed from service. However, the following is a list of generally agreed upon guidelines. When in doubt, it is always best to be conservative and replace the rope in question or downgrade it to a non-critical application.
Visual Inspection of the rope may reveal many signs that the rope has been weakened and should be retired. These include:
- Evidence of broken fibers or significant abrasion - Minor abrasion to the skin of the rope may not affect its performance. However, if the core of the rope is exposed or the diameter of the rope has been reduced anywhere due to damaged or cut fibers it is absolutely essential that the rope be replaced.
- Evidence of burns or melting - This may be caused by either abrasion or exposure to heat. Signs of melting suggest the rope has been compromised, and should be retired.
- Evidence of dirt - Kernmantle ropes are designed to protect the load bearing fibers from dirt and grit. However, excessive dirt may indicate that the rope has been weakened by the dirt particles abrading the individual fibers in the rope. This is of particular concern if the dirt cannot easily be cleaned off the rope, or if it seems as though the dirt has penetrated through to the core of the rope.
- Evidence of oil or grease - If the exposure is recent and minor, it may be possible to wash the rope using a mild detergent. However, extreme caution should be exercised, as oil often contains other contaminants, which may chemically damage the fibers in the rope.
Knowledge of the History of a rope may reveal factors indicating the rope has been weakened and should be retired. Where a rope is being used in life critical applications, it is a good idea to keep a log that records the history of the rope's use and maintenance. In fact, some standards mandate record keeping and replacement criteria. Some variables to consider include:
- Shock Loading - This puts an extensive strain on a rope in a short period of time. Often, a rope will not fully recover to its original strength. Generally speaking, once a rope has been shock loaded it should no longer be used in life critical applications.
- Exposure to Chemicals - Different chemicals will react differently with different types of rope. As a general rule, if a rope has been exposed to any type of chemical (including fumes) it has likely been weakened and should be retired or downgraded.
- Extensive Knotting - Knots will weaken a rope by as much a 50%, because they involve bending the rope quite sharply which distorts the fibers that make up the rope. Over time, the rope will be significantly weakened and should be retired from use.
- Run through Pulleys - Running a rope through pulleys, sheaves, bollards, chocks or other "bends" weakens the rope as it distorts the fibers. The amount the rope is weakened depends on the size of the "bend" the rope is being run over relative to the diameter of the rope. Over time there can be significant degradation of the rope.
- UV Exposure - UV rays from the sun or fluorescent lighting will weaken all ropes over time, including those that have been constructed with high quality UV stabilized fibers. The rate of degradation is largely dependent on the type of fiber used.
