Failure analysis of wire rope of ladle crane in steel making shop

A 6 × 36 construction wire rope conforming to IS 7904: 1995-X grade of high carbon steel failed after nine months of service. Visual observation revealed broken strands with dry damaged core and inter-strand nicking along its length. The dry core indicated insufficient lubrication. The fractured end of wire rope exhibited crown/chisel shaped marks and fractography using SEM showed striations confirming initiation by fatigue. The appropriate bending fatigue upon consideration of factor of safety, sheave diameter, rope diameter, co-efficient of sheave shape, working load and metallic area was estimated to be six months. Microstructural examination exhibited drawn pearlite in the matrix. Improper lubrication led to fretting wear between the internal wires resulting in failure of individual strands while rest of them were unable to carry the tensile load in service. Additionally, bending fatigue was predominant when it passed through the sheave during which inter-strand nicking occurred. Changing of the schedule of the wire rope from 9 to 6 months was recommended. Proper inspection by NDT and application of heat resistant lubricant like super micronized solid lubricant -molybdenum should be implemented to avoid such failures in future.