Investigation of premature fracture of a tail pulley in the field

An unexpected (premature) failure happened in Tail Pulley during operation in field. Consequently, a complete analysis in terms of fracture and fatigue performed. The analysis aimed to determine the failure root-cause by the analysis of the project and materials. The analysis covered the tensions undergone by the pulleys under operation and the material´s mechanical strengths. The results showed the project conforms the classical mechanics calculations. The failure, on the other hand, characterized as ductile fracture – Fatigue - with crack propagating along 45° referencing the cylinder longitudinal axis. The crack initiated at a flaw found at the weldment region, which resulted a shorter lifetime (collapsing). The sharpen flaw generated a shortcut in the failure process and jumped it straight to the phase of fracture - Stage II fatigue – called crack propagation.   Key words: Tag pulley, stress raiser, critical stress, fatigue.