Climbing Operation With Hydraulic Pressure Drift
A 12 t hammerhead crane with a 60 m jib is being climbed from 60 m to 80 m using a hydraulic climbing frame and five 4 m mast sections. At 09:40 the jib anemometer reads 9 m/s with gusts to 13 m/s; the manufacturer's climbing procedure allows climbing only up to 10 m/s at the jib and prohibits climbing in gusts above that. While holding a section at mid-stroke, the climbing pressure gauge drifts from 120 bar to 95 bar over about 10 minutes. The crew reports that one guide pin will not seat fully. The concrete pour is scheduled for 13:00 and the supervisor wants the climb finished. The crane is not carrying a load. The operator is asked to keep going and 'watch the gauge.'
1. Should climbing continue? Identify the controlling limits and the significance of each symptom.
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Climbing should not continue. The wind is the first controlling limit: 9 m/s average is below the 10 m/s limit, but the 13 m/s gust is above the procedure's prohibition, and the crane presents a large sail area during climbing. The pressure drift is more serious. A climbing system that cannot hold pressure at mid-stroke may have an internal hydraulic leak, a bypassing check valve, a damaged hose or a cylinder seal failure. The gauge falling from 120 bar to 95 bar while holding means the load is being held by something other than a stable hydraulic column, and a sudden drop could occur. The guide pin that will not seat indicates misalignment or interference in the climbing frame or mast section. Continuing would combine an unstable hydraulic hold, a structural alignment defect and gusting wind. The scheduled pour is not a technical justification. The correct decision is to stop, land the climbing frame onto mechanical pins or blocking as required by the procedure, and treat the crane as out of service for climbing until the defects are corrected.
2. Outline the safe recovery sequence to put the crane in a stable condition.
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First, stop all climbing movement and keep personnel clear of the climbing frame, mast entry and the area below. Do not rely on the hydraulic system to hold the section while people work on it. Follow the manufacturer's procedure to lower the section onto the mechanical support pins or blocking, relieve hydraulic pressure, and isolate the power unit. The guide pin and its guideway should be inspected for damage, debris or distortion, and the hydraulic system should be checked by a competent person for hose damage, check-valve leakage, cylinder seal bypass and correct pressure. Any failed component should be replaced with the manufacturer's approved part. The climbing procedure should then be reviewed against the actual wind readings, and the climb should restart only in a sustained wind below the limit with no gust above it. A re-check of pins, bolts and hydraulic pressure should be made before movement resumes, and the area should remain barricaded.
3. What authorizations and records should exist before climbing restarts?
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Before restart, the climb should be authorised by the competent person responsible for the crane and, where the procedure or site rules require it, by the manufacturer's representative or a professional engineer. The authorisation should confirm that the hydraulic defect has been repaired, the guide pin seats correctly, the wind limit has been met, and the climbing crew has been re-briefed. The records should include the original pressure readings and the drift, the inspection findings, the replacement parts, the repair sign-off, the wind readings at the time of restart, and the revised climb plan. The crane log and the site's permit-to-work or climbing checklist should show who authorised the restart and when. If the repair changes the climbing procedure or the crane configuration, the load charts and operating procedures must be updated before the crane returns to service.