WorldWide Drilling Resource

59 WorldWide Drilling Resource ® JULY 2015 Knowing the Ropes Adapted from Information Provided by WireCo ® WorldGroup When choosing wire rope for use in drilling applications, consider the type of operation to be performed. Different tasks demand different properties, and the right rope for each task can be critical to the overall success of a project. Primary properties need to be evaluated, includ- ing the following rope design characteris- tics: Fatigue Resistance Fatigue resistance involves metal fatigue of the wires making up a rope. To have high fatigue resistance, wires must be capable of bending repeatedly under stress. I n c r e a s e d fatigue resistance is achieved in rope design by using a large number of wires. It involves the basic metal lurgy and diameters of wires. Typically, a rope made of many wires will have greater fatigue resistance than another rope of the same size made with fewer, larger wires since smaller wires have greater ability to bend as the rope passes over sheaves or around drums. Abrasion Resistance Resistance to metal loss and defor- mation is called abrasion resistance. Metal loss is the wearing away of metal from outer wires of a rope. Metal de- formation occurs when the shape of a rope’s outer wires is changed. A r o p e w i t h fewer, but larger, outside wires per strand will deliver more abrasion re- sistance. Strength A wire rope’s strength in the U.S. is generally meas- ured in tons of 2000 pounds. In published material, wire rope strength is shown as minimum breaking force (MBF). When placed under tension on a test device, a new rope will break at a value equal to, or greater than, the MBF shown for that rope. A rope should never operate at - or near - its MBF. Crushing Resistance Crushing is the result of external pressure on a rope, which damages it by distorting the cross-section shape of the rope, its strands, its core, or all three. Therefore, crushing resistance is a rope’s ability to withstand or resist external forces, and is a term typically used to compare ropes. When a rope is damaged by crushing, the wires, strands, and core are prevent- ed from moving and adjusting normally during operation. In general, ropes with an inde- pendent wire rope center (IWRC) are more crush resistant t han f i be r - co r e ropes; regular lay r opes a r e mo r e crush resistant than lang lay ropes; six- strand ropes have g r e a t e r c r u s h resistance than eight-strand or 19- strand ropes; and compacted-strand ropes are more crush resistant than standard round-strand ropes. Bendability Bendability refers to a rope’s ability to bend easily in an arc. Four primary fac- tors affect this capability: 1. Diameters of wires making up the rope. 2. Rope and strand construction. 3. Metal composition of wires and fin- ish such as galvanizing. 4. Type of rope core - fiber core or IWRC. Some rope constructions are natu- rally more bendable than others. Small ropes are more bendable than big ones; fiber core ropes bend more easily than +%2 $+ ) $ % 5 "$,- + 2 .%2 -# ' / + , '- -$(', 4 ".% -(+2 &) - (0 ' 6, " ' 2 &) - (. 4 ' % $, .,,$(' (' $ '-, ' ! -2 4 ,- % % + $ % % $'" (',- +. - $(' #'$*. , !(+ '/ ,-$" -$(' (! (- % %% &) -, 4 . ,.+! 1)%(+ -$(' !(+ .%% , (++$ (+ -+(+ $% 4 ' & '2 &(+ +' ('-$'.$'" . -$(' + $-, .- ((+ - -$ $,)% 2, 4 (%! .-$'" + ,$ '-6, $'' + 0 + , 4 '- +- $'& '- ' ((+ +$3 , 1#$ $-(+ ' )(',(+ ())(+-.'$-$ , + / $% % .+! %% 2 %%$ (-- $-2 +2% ' 2015 NDA Convention September 17 - 18 Knowing the Ropes cont’d on page 60.