BMT WBM, the subsidiary of BMT Group, has announced the development of a modification and repair scheme which it says will dramatically improve the fatigue performance of cluster joints on existing tubular dragline boom designs. Once implemented, the company says that 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 commented: “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. This design allows the lacings from the chord to be cut away, thereby 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. Charles Constancon explained: “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 minimising the safety risks for operators.”