FAILURE ANALYSIS OF A WIRE ROPE BELONGING TO THE TRACTION SYSTEM OF A CABLE CAR

摘要

Failure analysis of a wire rope belonging to the traction system of a cable car was conduced. The specific failed wire rope, a 6×19 Seale type with nylon fiber soul, had been in service for three years by the time of the accident. The whole system had been in service for 30 years without similar reports of such a failure. Project loads for the specific traction system attended the reference standards and the loads were much lower than the specified resistance at the moment of the failure. The microstructure of the wires had no metallurgical problems and its hardness was in accordance with the specified resistance limit. Nevertheless, it was observed that the fiber soul was completely degraded at the fracture region, which resulted in insufficient oil lubrication and absence of corrosion protection. Corrosion has developed at the interior of the wire rope, resulting in corrosion-fatigue failure. Several cracks were found throughout the interior part of the cable. The failure occurred at the wire rope section inside of the pulley system which is the region that imposes the severest cyclic load conditions to the rope, therefore prone to fatigue failures. The failure originated inside the cable, turning it impossible to detect it during the daily visual inspections and diameter measurements. The reasons that have led to the degradation of the soul remain unknown. As a consequence of the occurrence of this failure, a complete review of the maintenance and inspection procedures was realized in order to increase the system security.