Hoist rope defects and a defeated limit switch
During a pre-start inspection on a 25 t rough-terrain crane, the operator finds three broken wires in one lay over a 6-diameter length on the main hoist rope, and three more broken wires over a longer section near a sheave. The rope is 16 mm, 6x36 IWRC, and the maintenance record shows it was replaced 14 months ago but has had no rope inspection since. The sheave groove has a visible ridge and the rope sits high in the groove. The boom lift limit switch has a cable tied back because it 'nuisance-tripped' during a previous lift. The site supervisor says the crane is needed for a 30-minute lift and the broken wires are 'only surface'. The crane has a current annual inspection certificate displayed. The load is 8 t at 10 m radius; the chart capacity is 9.5 t. The operator is newly certified and unsure.
1. What defects are present, and can the crane be used for the 30-minute lift? Give the reasoning and immediate actions.
Read the worked answer
The crane must not be used. There are three significant defects. First, broken wires are present in two zones, including a concentration in a 6-diameter length, and the rope has had no inspection for 14 months. The broken-wire count must be assessed by a competent person against the manufacturer's or ISO 4309 discard table for this 6x36 IWRC rope and its duty; 'surface' wires are still load-bearing wires and a concentration near a sheave is serious. Second, the sheave groove has a ridge and the rope is sitting high, which means the rope is not properly supported. That accelerates fatigue and can damage both rope and sheave. Third, the boom lift limit switch has been tied back. That is a defeated safety device, not a nuisance.
The 8 t load at 10 m radius is within the 9.5 t chart capacity, but that does not make the crane safe. The defects are independent of the load percentage. Immediate actions are to stop the lift, lower any suspended load if it can be done safely, isolate and tag the crane out, remove the key from the ignition, and report to the supervisor and crane owner. A competent person should inspect the rope and sheave, replace or repair as required, reinstate the limit switch, and function-test it. The crane should not return to service until those actions are recorded and a new pre-start inspection is completed.
2. The supervisor argues the annual inspection certificate proves the crane is safe. How do you explain the difference between annual inspection and daily pre-start, and what records should be completed?
Read the worked answer
The annual inspection is a periodic examination by a competent person. It reflects the crane's condition at that time and does not cover defects that develop later, damage from the last lift, or a safety device that has since been bypassed. The daily pre-start is the operator's check of the crane as presented for use today. A current certificate is not a warranty that the rope, sheave or limit switch are serviceable now.
I would explain this calmly and record the defects on the pre-start checklist, including the rope location and broken-wire count, the sheave condition and the tied-back limit switch. I would apply a lockout tag, raise a maintenance request and notify the person responsible for the crane. The crane should be quarantined until a competent person inspects it and the repairs are signed off. Replacement rope or sheave work should be recorded, and the limit switch should have a function test recorded before return to service.
If the supervisor continues to pressure the operator, I would escalate to the site manager or safety representative. The operator's stop-work authority is not overridden by a certificate or by a 30-minute production deadline.