BMT WBM, a subsidiary of BMT Group Ltd., has developed—and applied for a patent on—an innovative modification and repair scheme that it claims will dramatically improve the fatigue performance of cluster joints on existing tubular dragline boom designs.  According to the company, once implemented, this modification can significantly reduce maintenance and inspection workloads for tubular boom draglines with long-term deterioration of existing clusters.  

Draglines have long booms comprising a number of tubular chords with interconnecting lacings welded to the chords at cluster joints. Stresses are concentrated at the cluster joint weldments and over time, fatigue cracking becomes endemic.   

Charles Constancon, director of Canadian services at BMT WBM, said, “A boom replacement can cost in the region of $20 million and would require a three-month machine outage. With this proposed modification, the cluster design can be upgraded and repair costs reduced to approximately $2 million—an extremely attractive incentive for mining companies.”

The construction comprises a Reimann plate that provides an interface between the main chord and tubular lacings at a cluster joint. The design allows the lacings from the chord to be cut away, providing easy access to remove damaged or previously repaired material. The exposed chord can then be inspected and fully weld-repaired before installing the plate. 

Constancon said, “Aside from the limited maintenance schedules and the outage costs associated with lowering the boom, such an operation is viewed by operators as a dangerous exercise exposing them to a potentially high-risk task with major financial consequences.  

“This modification and repair approach can not only significantly extend the lives of existing tubular boom and mast structures, but can provide excellent access for weld repairs to take place, therefore minimizing the safety risks for operator,” he added.