By Colin Rice
Colin Rice Exploration Drilling Advisory - www.colinrice.co.za
The second alternative to standard steel wire ropes is ultra-high strength steel wire rope.
The strength of a steel wire rope is directly proportional to the metallic cross-sectional area of the rope and so the more densely packed the wires are, then the higher the metallic cross-sectional area will be and the stronger the rope will be.
All conventional steel ropes are manufactured from round (circular) wires and so there is a physical limit to how densely wires of a certain size can be wound. If however shaped wires are used, then a much greater density can be achieved resulting in a higher metallic cross-sectional area. By using shaped wires it is possible to manufacture “ultra-high” strength ropes. The picture to the right illustrates how shaped wires are used to increase the metallic cross-sectional area.
These ultra-high strength ropes are only manufactured from very high tensile strength wire (2160 MPa) and so offer much greater breaking strengths than standard construction ropes.
The table below summarises the mean breaking loads for a range of steel wire ropes used in the drilling industry and also the breaking strength of an equal size ultra-high strength steel rope.
The table shows that in 16 mm size the increase in mean breaking load is very small but in 19 and 22 mm sizes, these ropes will significantly increase hoisting capacity and so will allow drill rigs to drill to significantly greater depths.
Both HMPE and ultra high strength steel ropes will allow drill rig hoisting capacity to be substantially increased. Both are however, significantly more costly than commonly available steel ropes but the reduction in risk associated with hoisting activities far out ways the increase in cost. If you would like more detailed information on these alternative rope designs, please email DrillSafe.