Metallurgical failure analysis of a welded drive beam of a vibrating screen

A metallurgical failure analysis investigation was performed to evaluate the influence of the weld detail on the high cycle fatigue failure of a drive beam of a vibrating screen from the mining industry. The built-up drive beam was composed of three low alloy steel I-type beams joined by longitudinal butt welds. Carbon steel supporting plates for the exciters were transversally welded on the drive beam, with fillet lap welds that overlapped the longitudinal beads, generating a particular weld detail. The drive beam fractured at its mid span after 60 days under regular operating conditions, with the origin of the crack located at the weld beads overlapping. The weld detail was subjected to a metallurgical characterization by means of macro analysis, metallography and hardness testing. Its influence on the fatigue strength of the drive beam was analyzed using a recommended design guideline for structures operating in the giga-cycle regime, stress concentrator considerations and reported maximum stress values for deck and drive beams of vibrating screens operating at similar conditions. The overlapping of the weld beads generated a critical geometrical stress concentrator that served as a crack nucleation point; the crack propagated by a high cycle fatigue mechanism, diminishing the fatigue strength of the drive beam and producing its rupture.