Crawler Crane Boom and Wire Rope Periodic Inspection
A 90-ton lattice-boom crawler crane has been working 250 hours since its last periodic inspection and is scheduled for a 6,000-lb pick at a 40-ft radius; the load chart allows 18,000 lb at that radius. During the walk-around, you find a 1.5-in. crack at the toe of a weld where a boom lacing meets the top chord, two adjacent lacings bent about 10 mm out of line, and seven broken wires distributed over one rope lay on the main hoist line near a sheave. The hook has a missing safety latch and its throat opening measures 3.56 in. against an original 3.50 in.; the hook shows no twist. The boom-tip sheave groove is worn about 0.08 in. The crew says the pick is light and the crack can be 'watched' until the end of the shift. The crane is on a congested site and the boom is in the air. You are the inspector.
1. Which findings require immediate removal from service, which can be corrected before the next lift, and which need manufacturer criteria? Explain your priorities.
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Immediate removal from service: the boom chord/lacing weld crack and the main hoist wire rope. A crack at a boom top-chord lacing junction is in a primary load path; load reduction does not make it acceptable, and 'watching' it is not a repair. Seven broken wires distributed over one rope lay on a 6x19 running rope exceeds the commonly applied removal criterion of six randomly distributed broken wires in one lay, so the rope must be replaced. The missing hook latch and sheave-groove wear must be corrected before the next lift; the hook throat increase is only about 1.7% (0.06 in. on 3.50 in.), below the usual 15% rejection guide, but the latch still makes the hook deficient. Bent lacings adjacent to a crack warrant dimensional comparison with the manufacturer's boom chart and likely engineering review. The 6,000-lb pick should not proceed.
2. The supervisor proposes lowering the load to 3,000 lb and using the auxiliary hoist, arguing the main hoist rope and boom tip are then not loaded. Evaluate this proposal.
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Reducing the load to 3,000 lb and switching to the auxiliary hoist does not cure the structural defect. The boom still carries the load, and the crack is in the boom, not in the main hoist line. The auxiliary line may also run over boom-tip sheaves, and its load chart and reeving may differ. Isolating the main hoist rope could address the rope finding only if the rope is clearly taken out of service and not used; it does not address the boom crack, the bent lacings, or the missing hook latch. A smaller load can still propagate a crack and change boom stiffness. The correct decision is to stop the lift, lower and secure the boom if that can be done safely, and repair per the manufacturer.
3. What repair, verification, and documentation steps are required before the crane returns to service?
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Document the exact locations and measurements, photograph the crack and rope, tag the crane out of service, and notify the owner and responsible person. The boom repair should follow the manufacturer's written procedure using a qualified welder and, where required, an engineer; the repair area should be inspected and NDT'd as specified. Replace the main hoist rope, hook latch, and sheave if the manufacturer's groove-wear limit is exceeded. After repair, perform a post-repair inspection and any load test required by the manufacturer or applicable standard, then record the repairs, parts, NDT results, and return-to-service authorization.