Drilling lines are highly stressed ropes. In order to utilize rotary drilling lines equally, they will be slipped and cut-off in regular intervals. The basis of these intervals is the amount of work done by the rope in various drilling operations. Slip and cut lengths as well as limits of rope work are fixed in an API-Specification. Rope work can be measured and monitored easily, but it does not describe the rope deterioration process well enough. In most cases the cut-off rope pieces are still in quite good condition. In some cases the discard state is reached much earlier than indicated by rope work. In the following a calculation method will be introduced which takes more into consideration the fatigue behaviour of the applied rope construction. Using that new calculation method service life of drilling lines can be extended enormously.
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