Metallurgical failure analysis of a Guy rope assembly

A Guy rope assembly, used in stabilising a steel lattice transmission structure, failed during a heavy windstorm. The assembly was in service for over three decades. We were given the mandate to determine the reasons for the failure of the assembly and to suggest measures to prevent such failures from occurring. The study involved the in-depth examination of the chemical composition, microstructures, mechanical properties and fracture morphologies of carefully sectioned specimens. Results indicated that the failure of the Guy assembly is due to the failure of the tube housing the wire rope. Failure occurred due to local microstructural weakness (decarburization and unusually large ferrite grain size) of the tubing. Fractography indicated that failure is due to tensile overload and the mechanism of failure is micro void coalescence (MVC). Wire rope of the Guy Assembly appears to perform well. It bends to accommodate the load without breaking. Its composition corresponds to that of AISI 1080. The tubing and the end plates were low carbon structural steels corresponding to grade 1012 and 1015, respectively and lacked the high strength–toughness needed to withstand the dynamic loading resulting from the heavy winds. To solve this inherent weakness of these conventional low carbon structural steels the adoption of modern strong, tough, weldable HSLA steels has been suggested.