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Liebherr HC Type Tower Cranes

Published December 20, 2007
Last updated 20 December 2007

Background
Cause of accident
Cranes affected
Inspection difficulties
What needs to happen
Prohibited services

Background

A 2.7 tonne concrete kibble dropped four metres to the deck on a construction site near Ipswich on 31 October 2007. The kibble was being lifted by a Liebherr 185 HC tower crane and the hoist drum went into free fall. The crane was manufactured in 1983.

Cause of accident

A preliminary investigation of the incident has found that the final output shaft on the gearbox of the tower crane fractured so that the hoist drum was able to freely rotate. The hoist brake on this type of tower crane is located on a gearbox shaft before the final output shaft. Therefore when failure occurred the hoist brake was ineffective.

The causes of the failure are being investigated. However, metal fatigue appears to have occurred due to excessive bending of the output shaft as a result of misalignment of the shaft with the hoist drum. Following strip down of the particular gearbox, another crack was found in a keyway on the brake shaft. On removal of the hoist drum from the shaft, the drum bearings were found to be excessively worn. Photograph 1 shows the assembled gearbox. Photographs 2 and 3 show the failed output shaft.

Photograph 1 - Liebherr

Photograph 1: Liebherr “HC” Type Gearbox

Photograph 2 - Failed shaft in bearings

Photograph 2: Failed shaft in bearings

Photograph 3 - failed shaft end view

Photograph 3: Failed shaft end view

Cranes affected

Information received so far has indicated that all “HC” type Liebherr tower cranes are fitted with a similar type of gearbox to the one involved in the recent incident. As far as WHSQ is aware, all “HC” type tower cranes were manufactured prior to the 1990’s and are therefore due for a 10 year major inspection. Failure of the output shaft in “HC” type cranes will cause the lifted load to free fall.

Inspection difficulties

The type of failure in the tower crane involved in the incident could not have been predicted by observing the gearbox in normal operation. To detect the crack in the shaft the gearbox needs to be stripped down and bearings need to be removed from the shaft. The fracture occurred at the point where the shaft steps down for location of the bearing between the gearbox and the hoist drum. Any cracks at this location are therefore obscured from view unless the bearing is removed.

Management of risk

All owners of Liebherr HC type tower cranes must implement a procedure where the following is carried out:
  1. Check of the alignment of the output shaft with the hoist drum shaft to the manufacturer’s tolerances (this must include assessment of bearing alignment, bearing condition and integrity of fasteners).
  2. If the alignment in point (1) is outside of tolerance, unless otherwise justified by a professional engineer, immediate removal and total strip down of the gearbox and non¬destructive testing (NDT) of all drive shafts for cracks is required.
  3. If the alignment in point (1) is within acceptable tolerance, continued operation of the crane until project completion and removal from site is allowed. However, total strip down of the gearbox and NDT of all drive shafts for cracks as part of the 10-year inspection is required.

Shaft alignment is to be checked by an independent competent person in accordance with the manufacturer’s instructions. The shaft alignment is to be quantitatively measured and compared with the manufacturer’s specifications and documented.

Strip down of the gearbox will require removal of bearings from the shafts. NDT should be undertaken by an independent NATA accredited organisation. Once the gearbox has been inspected, re-assembled and aligned, a competent person should certify that the work has been undertaken and that the gearbox complies with the manufacturer’s specifications. This certification can form part of the 10 year major inspection report for the crane. The 10 year major inspection is a requirement under the Workplace Health and Safety Regulation 2008 , and must be overseen and certified by a professional engineer).

Note: it is critical that the gearbox output shaft is correctly aligned with the hoist drum. Failure to ensure this is likely to lead to catastrophic failure of the output shaft.

Workplace Health and Safety Queensland (WHSQ) will consider professional engineer’s certification on recently completed inspections, testing and realignment of the gearbox components.

Prohibited activities

The following will be supported by statutory notices:

  1. Prior to inspection of the output shaft alignment – no lifting of loads over workers and no lifting of workers in work boxes.
  2. Following inspection of shaft alignment and evidence that alignment does not comply with the manufacturer’s tolerance - total prohibition of crane until the gearbox has been removed, stripped down, inspected and re-fitted to the crane. Variation of this prohibition notice may be considered if there is sound engineering justification, with supporting evidence, from a professional engineer with relevant experience in this area (e.g. the equipment manufacturer).

Further information

Telephone: 1300 369 915
Website: http://www.deir.qld.gov.au/

Liebherr HC Type Tower Cranes (PDF, 65 KB)