Improved Drilling Line Fatigue Model Reveals a Need for Revising Slip and Cut Procedures

This paper presents a state-of-the-art bending fatigue model for wire ropes and applies it to optimize slip and cut intervals of drawworks drilling lines. The new model considers many parameters and variables, such as specific line tension, sheave-to-line diameter ratio, optional reverse bending, drum diameter, and excessive bending curvature at the crossover intervals of multilayer drums. The new model transforms block motion and hook load statistics into a high-resolution distribution of cumulative fatigue damage along the drilling line. In turn, the model justifies that the cut length and the energy transfer (in ton-miles) per cut length can be substantially increased relative to common practice today. The calculated fatigue damage distribution can also be used to pick peak fatigue damage line spots, most suited for focused inspection and optional strength testing after it is cut away.