Frequent falls (factor <1), frequent abseiling or toproping, considerable dirt (sand, dust, chalk) and mechanical abrasion (e.g. rough, sharp rocks) can reduce the safety reserves of a mountaineering rope. If the rope sheath is so badly damaged that the core is visible, the rope must be replaced immediately. To evaluate how long a rope is still away from this discard limit, the so-called "kink test" can provide an indication.
How the kink test works
Smooth out the rope at the point to be assessed to compensate for irregularities in the sheath yarns which may arise, for example, from long hanging in the belay device or other punctual loads on a rope. Bend the rope by 180° and using your thumb and forefinger evaluate how easily the rope strands can be pressed against each other without leaving an eye (a small opening between the ropes). When the “kink test” clearly shows no eye in some areas, compared to the rest of the rope, it is an indication that the sheath yarn tension has dropped in these areas. The rope sheath is altered by flexing or mechanical abrasion and approaches the wear limit. Thus, by means of a visual and haptic evaluation, supplemented by the impression of how easily the rope can be compressed in the "kink test", the state of wear and thus the distance to the wear limit can be estimated. This is because as soon as the core is visible, the rope must immediately be excluded from use, which can lead to an unpleasant situation in some applications.
Evaluation of the kink test depending on the application of the rope
How much distance to the wear limit is tolerable depends on the application area, environment, and inspection frequency. For example, it is conceivable that a rope can be used for indoor climbing up to the wear limit if the user checks the rope before each visit. On the other hand, less wear is to be tolerated for ropes that are to be used intensively for long periods of time for alpine climbing.