Failure analysis of hoisting steel wire rope

Abstract

During a very short operation of a steel rope in a hoist system of a drilling rig it was significantly damaged. The wires of the upper layer of cable strands were damaged. This damage was not caused by fatigue of material; therefore it was necessary to determine the reason of the rope damage. The visual inspection of the damaged spots showed that during the operation there was a progressive release of the wires from the outer layer of the outer rope strands; subsequently released wires were rolled when passing the hoist system and they started to break. In order to find out the reason of the damage the samples of the damaged rope were collected as well as the samples of the new rope from the reserve. According to the nature of the damage we decided to perform mechanical tests of the new (yet not used) rope and thereafter metallographic tests of wire ropes from the outer layer of the strand. The analysis of the mechanical tests results of the new rope revealed the fact that the rope had been manufactured in other rope grade – different from the class declared by the manufacturer. It was also found that the wires of the top layer reporting damage were made of wires of different rope grades. Mixing wires having low and high strength in the upper layer of the rope strand caused different straining of wires in the specific (given) layer thus wires having lower strength begun to release from the strands and deform which led to the development of fractures at the weaken places.