IMCA has issued a Safety Flash describing an incident of main crane failure during a load test at which the crane’s main block wires broke and caused the testing load to fall into the water.
What went wrong
Mechanical failure was found on the clutches of certain of the main hook double drums. Since the main hook wires were reeled on four drums, when the load at the hook reached maximum (barges completely out of water) the clutches of two drums, #3 & #4 (starboard side of the hook ) slipped on the transmission disk and the drum lost torque, while the other two drums, #5 & #6 (port side of the hook) were still pulling. This generated an unbalanced load on the main hook, beyond any normal compensation system, with concentration of stress on the port side half of the block assembly where the load ultimately exceeded the wire Maximum Breaking Load with consequent breaking of wires and the total loss of the load.
Cause
There was a clutch pad failure to the recently installed clutch pads, in which they lost their holding properties at maximum crane load. During the investigation it was found that the failure of the clutch pads was linked to the lack of proper burnishing of new pads.
Lessons Learned
- Perform burnishing of clutch pads as per manufacturer’s procedure.
- Implement a clutch torque test to verify the holding torque of the pads as per new manufacture’s procedure.
- Include in the planned maintenance systems the pads burnishing procedure and torque test with the frequency recommended by the manufacturer.
- Revision of crane FMEA, including review by competent persons.
