Inspection Findings on a 5-Ton Bridge Crane
A monthly inspection is being done on a 5-ton single-girder bridge crane. Findings: the 1/2 in 6x37 IWRC hoist rope has 7 broken wires distributed in one lay, 3 broken wires in one strand, a 4 in long birdcage 6 ft from the drum, and a measured diameter of 0.470 in at the birdcage. The hook has a 2.00 in throat that now measures 2.19 in; the safety latch is missing. With a 4,000 lb test load, the hoist brake drifts 3 in in 60 seconds. The upper limit switch and the pendant emergency stop both function. The supervisor wants to use the crane for one 800 lb lift to finish the shift.
1. Which findings remove the crane from service, and which are acceptable or need monitoring?
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Separate the findings by removal criteria:
Removal items:
- Birdcage / rope distortion. A birdcage is a permanent structural distortion of the rope. It is a removal condition regardless of the broken-wire count, because the strand geometry has failed and the rope can part under load.
- Hook latch missing. A hook in hoisting service must have a functioning latch. Without it, a sling can slip off the hook under a slack or angled condition. The crane should not be used until the latch is replaced.
Not removal by themselves, but record them:
- 7 broken wires in one lay is below the 12-in-one-lay criterion, and 3 in one strand is below the 4-in-one-strand criterion. These counts alone would not remove the rope, but the birdcage already does.
- Diameter 0.470 in vs. 0.500 in is about a 6% reduction. That is not by itself over the usual 10% removal line, but it confirms wear and must be tracked.
- Hook throat 2.19 in vs. 2.00 in is about 9.5% increase, below the 15% criterion, so the throat is not the reason to remove the hook; the latch is.
- Brake drift of 3 in in 60 s with 4,000 lb is a performance concern. It does not by itself prove the brake is failed, but it must be compared to the OEM tolerance and re-tested after any adjustment.
2. Can the crane be used for the 800 lb lift? Explain the reasoning.
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No. The load weight is irrelevant to this decision.
The birdcage is in the load path. A distorted rope can fail at a fraction of its rated strength, and the failure is not proportional to the load; an 800 lb lift still puts the operator and the area under a rope that has already lost its strand geometry. The missing hook latch is also load-path and load-control related: a light load can still slide off a tilted hook. A light lift is sometimes argued as 'safe enough,' but removal criteria are not scaled by load weight.
Permitted actions: the crane stays out of service until the rope is replaced and the hook latch is restored. If a load must be moved, use another crane or manual means.
3. What documentation and control steps should follow the inspection?
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- Tag and lock: attach a clear 'DO NOT OPERATE' tag at the pendant control and at the bridge, with date, inspector name, and the specific defects. Lock out the disconnect if repairs are not starting immediately.
- Written record: enter the birdcage location and length, the broken-wire counts, the diameter measurement, the hook throat measurement, and the brake drift result in the inspection log.
- Notification: inform the supervisor in writing that the crane is out of service, and state what is required to return it (new rope, new latch, brake check).
- Return to service: after repair, re-inspect the new rope and latch, re-test the brake with a rated load, re-test the upper limit and e-stop, and record the results before the tag is removed. Only the person authorized by the site should remove the tag.