Tower Crane Climbing With a Pin That Will Not Seat
A tower crane is being climbed to add a 6 m mast section on a 30-storey building. The climbing frame is powered by hydraulic rams, and four guide pins are supposed to seat fully before the mast section is bolted. The wind is 9 m/s, gusting 14 m/s; the manufacturer's climbing limit is 12 m/s. During jacking, the operator notices that the upper left pin will not enter its seat. The hydraulic pressure gauge reads 180 bar against a normal 150 bar. The fitting crew says the pin will seat when the crane takes the load, and one fitter wants to tap it in with a hammer while the ram is pressurised. The slewing section is partly unbolted, and the area below the climbing frame is not barricaded because the crew expected the job to take only 20 minutes.
1. What is the immediate hazard, and why is the pressure rise significant?
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The immediate hazard is that the climbing frame is not fully engaged, so the load path may be relying on the hydraulic rams and a partly seated pin rather than on the designed mechanical seats. The pressure rise from 150 bar to 180 bar suggests the ram is meeting extra resistance, possibly from misalignment, binding, debris or a damaged pin or seat. Forcing the pin with a hammer while the system is pressurised risks a sudden release, a dropped mast section, or a hydraulic failure. The gust of 14 m/s is above the 12 m/s climbing limit, so the crane should not be climbing at all. The unbarricaded area below is also serious because any dropped pin, tool or mast section could strike a person. The crew's statement that the pin 'will seat when it takes the load' is unacceptable: the crane must not take load through an unseated pin.
2. What sequence should be followed to make the crane and area safe?
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Stop the climbing operation and stop the hydraulic pump. Keep all personnel clear of the climbing frame and barricade the area below. The load should be held on the mechanical safety system, not on the hydraulic rams; the manufacturer's procedure should be followed to lower the climbing frame onto its mechanical stops or to insert the approved safety pins. Pressure should be relieved only in the way the manual specifies, and no one should put hands or tools near a pressurised pin. The partly unbolted slewing section should be secured according to the manual. The pin, seat and hydraulic ram should then be inspected by a competent person for alignment, damage and debris. The climb should not resume until the wind is below the manufacturer's limit and the pin seats fully without force.
3. What must be checked and authorised before climbing resumes?
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The pin and seat should be inspected for deformation, cracks and foreign material, and the hydraulic pressure should return to the normal range when the ram is operated without load. The climbing frame should be checked for verticality and full engagement of all guide pins. The slewing section bolts should be checked and torqued to the manufacturer's values. The area below should be barricaded throughout the remaining climb. The operator, rigger and supervisor should review the manufacturer's climbing procedure and confirm the wind limit. A competent person should authorise restart in writing, and the event should be recorded, including the pressure readings and the corrective action. A test operation of the climbing system without the mast section should be completed before the new section is lifted.