Although two failures of lifting clutches thankfully didn’t injure anyone, they caused extensive damage and the potential for injury was very high.
A few weeks ago, the anchor engagement pin on a plate type lifting clutch broke during an attempt to rotate a 14.8 tonne pre-cast concrete panel using a 100 tonne and 80 tonne mobile crane. It appears the clutch pin failed when the panel was at about 45 degrees.
Although the pin broke totally in two, the panel did not drop due to the geometry of the lifting clutch, and how it was being loaded at the time. However, the break had potential for the pre-cast panel to drop to the ground, especially if the lifting clutch orientation was different.
The lifting clutch was in fact brand new with only a few lifts that had occurred on that very day. There was documentation on site that the lifting clutch had been provided with a proof test of twice its working load limit, before being sold. The clutch was marked with “7 T WLL”.
The incident follows one in 2019 in which the lifting clutch link on a 5-tonne lifting clutch failed when a 100-tonne crawler crane was lifting a 16-tonne concrete wall panel.
The cause of the latest incident is not known at this stage but the fact that the lifting clutch was brand new at the time of the incident is a concern. It appears that the completion of a proof test on the clutch before being supplied was no guarantee that failure would not occur.
In the 2019 incident, it appears the main cause of the failure was a substantial, undetected crack in its cross-section. Surface rust indicates the crack may have been present for some time. The crack was close to a weld and started on the inside of the lifting clutch link, so it may have been difficult to notice by visual inspection. The lifting clutch link was inspected and proof tested by a third-party lifting gear organisation six months prior to the incident.
These incidents highlight the need for a back-up lifting system to lift pre-cast elements as highlighted in Section 13.2 of the Tilt-up and pre-cast construction Code of Practice 2003. Although the second incident occurred on a tilt-up site, the same type of lifting clutch is commonly used for pre-cast element erection.
A rigorous inspection and testing program is needed on lifting clutches, possibly beyond the current minimum industry benchmarks. AS3850.1:2015 Prefabricated concrete elements: Part 1 General requirements specifies non-destructive testing (NDT) of cast components of lifting clutches at manufacture, but does not specify NDT during the 12-monthly inspection.
Therefore, to help prevent unexpected failures, consider carrying out NDT to inspect for cracks at the 12-monthly inspection. The inspection should include dimensional checking to determine that tolerances remain within the manufacturer's specifications.
Inspection records should be maintained for every lifting clutch and should include the:
- identification number of each clutch assembly
- inspection organisation carrying out the 12-monthly inspection
- name of the competent person carrying out the inspection
- inspection method used (including the NDT method if used)
- results of the inspection (e.g. pass/fail).
The rigging crew erecting concrete elements should carry out a detailed visual inspection of the lifting gear prior to use.
More information on the erection of tilt-up and pre-cast concrete elements: