Forensic Engineering | Engineering & design
FIELD Engineers was engaged to investigate a dragline boom point sheave failure for a major Australian mining company. The sheave was found out of position, running hard against the swivel frame and a bearing failure due to lack of lubrication was initially suspected. This was a reasonable assumption, as the issue was identified while investigating potential problems linked to a non-operational lubrication line. However, while bearing failure was plausible, the theory required confirmation to be useful for preventing future incidents. So as the site got back to work, engineers looked deeper to establish the true cause.
Engineers inspected the removed sheave and bearing, comparing the components with assembly drawings. This inspection showed the bearing was drier than expected but had no signs of failure, even after cleaning and non-destructive testing. Instead, engineers found one side of the bearing retainer was completely missing, and the other severely damaged. The missing retainer had allowed the sheave to walk along its shaft, until it was running hard against the frame. Further investigation showed the likely cause of the missing retainer was its bolt holes being modified, to allow them to match the bolt pattern on the sheave. This change reduced the bolt head seating area, which then deformed, letting the bolts loosen and ultimately led to the retainer detaching.
FIELD Engineers’ investigation revealed a hidden issue: modifications in the boom sheave retainer bolt holes can lead to failure, a conclusion that was reinforced by a similar historical failure identified during the investigation. This outcome allows the asset owner to manage the root cause through improved control of modifications, preventing future incidents, and demonstrating the importance of thorough forensic engineering to find the true cause.
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