Sling Returned to the Shack with a Kink, Birdcage, and a Bad Hook
You are the rigger on a night shift at a fabrication yard. A two-leg bridle built from 3/4-in, 6x37 IWRC wire rope slings comes back to the rigging shack after a lift. The tags read 9,800 lb vertical per leg. Inspection finds: a kink about 4 ft from the eye that will not pull straight; birdcaging over roughly 6 in of one leg; four broken wires in a single strand within one lay; a forged hook whose latch hangs open and will not seat; and a hook throat that measures 1.19 in against a 1.00 in original dimension. There is light surface rust but no pitting. The foreman says it is only four wires, the crane is waiting, and tells you to tag it and send it out.
1. Sort the six findings into those that by themselves remove the sling from service and those that would not. Can any of them be downgraded, derated, or deferred?
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Removal on their own (any one is disqualifying):
- Kink that will not straighten - permanent deformation of the rope structure. The wires on the inside of the bend are already stressed past yield; the geometry will never be right again.
- Birdcaging - the outer strands have separated from the core. This is a structural failure of the rope lay, not a cosmetic flaw.
- Hook throat opening 1.19 in vs. 1.00 in original - a 19% increase. Hook throat spread is a classic removal criterion (commonly 15%) and it also tells you the hook has been overloaded or shock-loaded.
- Latch that will not seat - a hook in service must have a functioning latch. A latch that hangs open is a removal item, not something to tape, wire, or work around.
Judgement call, and moot anyway:
- Four broken wires in one strand in one lay - this is at or past the threshold many 6x37 sling criteria use (commonly three per strand in one lay), and it would require a check against the applicable removal table for that construction. It never gets that far here.
- Light surface rust without pitting is not by itself a removal criterion; it is a note-and-monitor item.
No downgrade path exists. There is no derating table that converts a kinked, birdcaged sling with a sprung hook into a usable lower-capacity sling. The defects are cumulative and independent: even if you argued the broken-wire count, the kink, the birdcage, and the hook each stand alone.
2. The foreman has told you to tag it and send it out. What do you actually do, and what happens to the sling?
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The decision is not the foreman's to override on the floor - but the way you handle it matters more than winning the argument.
- Stop it physically. Take it out of the rack and out of the flow of traffic so it cannot be picked up by mistake.
- Tag it clearly - out of service, date, initials, and the specific defects. A generic tag invites someone to cut it off.
- Render it unusable. Industry practice for a condemned wire rope sling is to remove it permanently from service - cut the eyes or the body so it cannot be re-tagged and returned to the rack. Tagging alone fails the first time the tag falls off.
- Report it up the chain, to the lift director or competent person, not just back to the foreman. Schedule pressure is not a rigging criterion.
- Write it down. Log the defect and the disposition. If the same sling shows up again next week you want the paper trail to show it was condemned, not lost.
Finish with the constructive move: pull two good legs from the rack and get the crane working. A rigger who only says no gets bypassed; a rigger who says no and supplies the replacement gets listened to.
3. Before you condemn the hook, what else should be examined, and why does the throat measurement point at something beyond the hook itself?
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A hook gets checked as a whole, not just at the throat:
- Twist or bend out of plane - check the hook against a straightedge; any bend is removal.
- Wear on the saddle and at the bowl, measured, not eyeballed.
- Cracks - the bowl and the area behind the saddle are the classic crack locations; a hook this suspect warrants a surface exam (dye penetrant) rather than a visual pass.
- Latch and latch spring - function, not presence.
- Stamp and capacity - legible identification and a rating that matches the sling.
The throat spread is the important clue. Hooks do not open up from normal service; a 19% spread means the hook has been overloaded, shock-loaded, or side-loaded, or the sling has been pulled at an angle across the saddle instead of seated in the bowl. So the hook is evidence, not just a part:
- Inspect the other end of that same bridle, and the other slings from that lift.
- Ask what the last lift was and what the load weighed, and check it against the 9,800 lb rating.
- Look at the master link, shackles, and crane hook from that lift for the same story.
One sprung hook on a returned sling is a question about the whole lift, not just one component.