Fracture analysis of collapsed heavy-duty pulley in a long-distance continuous conveyors application

In this paper we present a case study of a heavy-duty pulley that failed after 2.1 × 107 cycles. The pulley was installed as a take up on a continuous conveyor under a load of 350 kN transmitted by the counterweight tower. The failure was analyzed using (a) finite element analysis by Ansys, (b) field data analysis, and (c) fracture macro examination. The prior FEA analysis showed that the pulley was designed according to its field application and moreover when re-simulated, by applying higher loads, revealed high potential towards its safety factor. The field examination showed that the conveyor did not suffer any overload that would contribute to the pulley collapse. The macro failure analysis revealed stress discontinuities and fatigue symptoms such as beach marks and even chevron marks within the welding region. In the meantime the welding region did not show evidence of thermal affected zone (TAZ), which is the key to its mechanical strength. The case analysis showed that the pulley was designed in accordance with British Standard [British Standards Institution, BS 5400:1980. Steel, concrete and composite bridges: Part 10: code of practice for fatigue; 1980] but a welding failure generated unexpected stresses and weakness on the welding region which generated fatigue and the final fracture.