Gantry crane removal study.

Required scope of work.

NXGEN was contracted to provide an engineering study and commercial budget into the removal and replacement of 2 No. overhead gantry cranes in a steel mill Melt Shop in Alabama, USA.  Each existing crane weighed approximately 426Te, whilst the new cranes would weigh 470Te.  The existing cranes were installed when the plant was being constructed, and as such the method of installation could not be used to replace the cranes.  It was necessary to replace the cranes during a 4 week shutdown.

Study of traditional methodology.

The traditional methodology to remove the cranes from the Melt Shop would be via land based cranes, lifting components through the roof of the building.  Whilst the use of land based cranes is well established and practiced, significant challenges / constraints to their use at this site were present including;

  • Significant weather delay risk
  • Piecewise lifting of crane components requiring disassembly and assembly of cranes at height
  • Simultaneous operations
  • Space constraints to site a crane
  • Ground improvement risks


Despite these challenges, a feasible solution was proposed using an LR1750 as the main lift crane to remove the gantry crane components.  The main drawback of the crane approach was the likely programme duration of nearly 7 weeks; 3 weeks longer than the desired shutdown duration.  This primarily due to the requirement to complete 85% of the works by commercial value during the shutdown period.

Alternative methodology.

The Melt Shop building is flanked on the North by the Black Warrior River, which presented an opportunity to use a large Shear Leg / Stiff Leg crane from the river to lift the cranes in large sections directly to / from the rails.  NXGEN proposed the construction of an extension to the existing gantry crane girders, cantilevered out from the North End of the Melt Shop building, supported by piling in the river.

The major advantage to this approach was that large parts of the works could be completed outside of shutdown;

  • Construction of the cantilevered frame
  • Disassembly of the existing cranes
  • Construction of the new cranes
  • Pre-commissioning of the new cranes

Key Services Delivered:

By moving nearly 50% of the overall works outside of the shutdown period, the NXGEN shear leg solution reduced the required shutdown period to just over 3 weeks, well within the allowed 4 week window.

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