Weekly Inspection Findings: What Stops the Crane and Who Clears It
Weekly inspection of a three-year-old 60 m jib tower crane working two shifts. Findings: (a) the hoist rope, 16 mm 6×36 IWRC, has six broken wires in one lay within a 30 × d length and a birdcage about 4 m from the dead end; (b) the hoist limit switch lever is cable-tied out of the way because it 'kept tripping'; (c) two slew ring bolts below the cab have no torque stripe and rust is weeping from the joint; (d) the anemometer cups are seized and the wind readout shows 0 m/s while the site flags are stiff; (e) the third-party thorough examination certificate on file is dated 13 months ago and the crane has worked continuously since; (f) the chart in the cab is for a 55 m jib. The site manager wants the crane back in service after the shift because the concrete pour is booked for 06:00.
1. Sort these findings: which remove the crane from service immediately, which need action before the next lift, and who can authorise return to service?
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Immediate out of service:
- (b) A defeated limit switch is a safety device out of service. Defeating it is never acceptable, and the reason it kept tripping must be diagnosed, not hidden.
- (a) A birdcage is a rope distortion indicating core or strand damage; the rope comes out of service regardless of the wire count.
- (c) Missing torque stripe plus rust weeping at a slew ring joint suggests loss of preload or corrosion in a critical connection. No operation until the bolts are checked by the manufacturer's procedure; a failed slew ring connection is catastrophic.
- (e) An expired thorough examination means the crane has no valid certification to work.
Before the next lift:
- (d) A seized anemometer means wind limits cannot be demonstrated; if the site relies on it, the crane is effectively out of service until it reads correctly.
- (f) A 55 m chart on a 60 m jib crane means every capacity used has been wrong. Replace with the correct chart and verify the LMI configuration.
Return to service requires the competent person's sign-off plus a functional test of the limits and LMI; the operator may refuse, and the 06:00 pour does not override any of this.
2. How do you deal with the hoist rope, and what else must be checked because of it?
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The birdcage alone settles it: a birdcage is a permanent distortion from core protrusion or strand displacement and is a discard condition irrespective of how many wires are broken. Add six broken wires in one lay concentrated in a 30 × d length and the rope is at the end of its life in that zone.
Do not simply quote a number and argue about it. The process is:
- Compare the wire counts, position and distribution against the rope-specific discard table in the applicable rope inspection standard and the manufacturer's manual, by a competent person.
- Remove the rope from service and fit a new rope of the correct specification.
- Investigate the cause before the new rope goes on: seized or worn sheaves, incorrect groove size, misaligned reeving, drum spooling problems, tight sheave at the dead end, or a shock load.
- After re-reeving, reset and function-test the hoist limit and the LMI, and record the rope change and the running-in inspection.
3. The limit switch was tied off 'because it kept tripping.' What does that tell you, and what is required before the crane lifts again?
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It tells you the switch was doing its job, or the crane had a fault that made it operate early. A hoist limit that trips repeatedly usually points to one of: incorrect switch setting, slack rope or a mis-set slack-rope device, brake slip letting the hook block creep up, two-blocking by the operator, or a malfunctioning switch. Tying the lever back converts a protective device into a collision waiting to happen: the block can be pulled into the trolley, shock-loading and dropping the load.
Before the crane lifts again:
- Remove the tie and find the actual cause; repair the switch or correct the setting, brake or operating practice.
- Function-test the upper limit so it stops the hook block with the clearance stated in the manual, and test at slow and normal speed.
- Function-test all other limits and the LMI, and check the slack-rope device if fitted.
- Record the defect, the repair and the test, and require the competent person's sign-off.
A pattern of defeated safety devices should also trigger a review of the maintenance regime and the operator's briefing, not just a single repair.