supposedly the hook failed and boom slingshot over the top.
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Liebherr Orion crane failure under 5500t load test 7
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LittleInch
Petroleum
I'm still just surprised that the design is basically a giant Jesus Nut.
The bearing areas on the nut from the hook block don't look very big to me.
And the hook looks like it is able to swivel around.
Any difference in hook load or rigging would seem to put a large bending moment on that thick, but reducing diameter shaft.
To break in what looks like pure tension is difficult to understand.
I'd love to see more drawings of the hook assembly though.
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The bearing areas on the nut from the hook block don't look very big to me.
And the hook looks like it is able to swivel around.
Any difference in hook load or rigging would seem to put a large bending moment on that thick, but reducing diameter shaft.
To break in what looks like pure tension is difficult to understand.
I'd love to see more drawings of the hook assembly though.
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Also: If you get a response it's polite to respond to it.
charliealphabravo
Structural
LittleInch said:
I'm still trying to convince myself that it was loaded in pure tension. Looking at the rigging, the mooring lines would need to have been looped around to opposite sides of the hook in order to ensure uniform loading. Was this done? If not, it would be difficult to avoid putting a large moment on the shaft. I wonder what is the load rating if only one or two adjacent hooks are loaded?
Edit:
From this second view I'm gonna say there was almost no hope of ensuring a uniform load.
With this design, when load is applied, the pin will stretch and constrict. But still, at only less than half the design load, the moments had to have a flaw to exploit.
Added: To break in pure tension, implies necking, which would be visible.
Added: To break in pure tension, implies necking, which would be visible.
LittleInch
Petroleum
Looking at that photo above, maybe it's the camera angle but if looks like the main lines are not vertical. The barge clearly can't move any closer but if it's trying to lift at an angle it won't help.
It looks like such a clean break that there must be some massive inclusion.
I hope the design didn't mix up lbs weight with kg....
But for five thousand tonnes that shaft looks mightily small to me. I reckon you would need a 1m diam shaft. Not easy to make in high strength steel.
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It looks like such a clean break that there must be some massive inclusion.
I hope the design didn't mix up lbs weight with kg....
But for five thousand tonnes that shaft looks mightily small to me. I reckon you would need a 1m diam shaft. Not easy to make in high strength steel.
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I interpret that drawing to show a bearing behind that nut that allows the hook to rotate. I would call that a slewing bearing if it was in one of my machines. Slewing bearings like this can be rated to loads in this range. The rating of the bearing for pure thrust is highest. If any moment is applied, the thrust capability of the bearing is greatly reduced. This is the load chart for a bearing of that type.
If the hook is free to rotate on that bearing, then the tapered area above the bearing is just a guide and not an interference fit, as I first assumed. I would look for fretting damage from rubbing on that area for crack initiation. We have seen this sort of failure in large piston rods in reciprocating compressors.
How is this area lubricated?
Johnny Pellin
If the hook is free to rotate on that bearing, then the tapered area above the bearing is just a guide and not an interference fit, as I first assumed. I would look for fretting damage from rubbing on that area for crack initiation. We have seen this sort of failure in large piston rods in reciprocating compressors.
How is this area lubricated?
Johnny Pellin
charliealphabravo
Structural
I found a better shot of the rigging. This view makes me wonder if the mooring lines slipped off the reaction bollards causing an impact load on the shaft. That could explain the clean break. You can see that the bollards are not in line with the load and that the inside ears of the bollards do not have much of a rim to prevent a large diameter line from rolling off, especially when doubled as they were.
LittleInch
Petroleum
I'm assuming that photo was after the incident.
But it's the design of the shaft and hook attachment I just don't get.
Why is it tapered?
How does that bearing work?
What are the strange tapping holes?
What's the plate on the bottom?
Nothing looks right.
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Also: If you get a response it's polite to respond to it.
But it's the design of the shaft and hook attachment I just don't get.
Why is it tapered?
How does that bearing work?
What are the strange tapping holes?
What's the plate on the bottom?
Nothing looks right.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
The plate at the bottom is probably there to lock the nut so it can't unscrew. The holes coming in radially in the outside diameter of the nut could be for the tooling used to install and remove the nut (spanner holes). The bearing looks like a cylindrical roller bearing that I would call a slewing bearing or slewing ring. We use them in coker drill stem rotary joints that operate with loads in the range of 100 tons while spinning at maybe 30 rpm. The drawing does not make it clear that this is a threaded nut. But, if it was hydraulic, I would expect to see clear indications of the o-rings and back-up rings in the fit and the hydraulic connections. I suspect it is most likely threaded. The pin is tapered just because it needs to transition from the small nut to the larger area at the other end where the horizontal pin passes through. It is probably better to make this transition with a gradual taper than large steps.
Johnny Pellin
Johnny Pellin
charliealphabravo (Structural) 6 May 20 19:40 said:
It appears that the lifting points are canted longitudinally but not rotated towards the center of lift. This of course leaves all of the inside lines vulnerable to slipping off. I see some cinching cables, highlighted below,
but I struggle to understand this system.
Added: I see it now, when the hook is at the determined height, the canted planes pass through the center of lift.
The hook manufacturer chimes in. I think we already knew this though.
Brad Waybright
It's all okay as long as it's okay.
Brad Waybright
It's all okay as long as it's okay.
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4
- #34
With such components of existential importance to the system and without redundancy, and especially when lives are at risk:
Rules should require a pre-test in a safe working environment, step-by-step increase of load, thorough check for cracks prior and after.
But I don't know whether this is perhaps already the case with load hooks?
I don't know whether the enquiry (at least the technical part) shall be public, or being made public. But I'd very much like it to be made public, in all detail.
Such sudden death of a big size forging is quite unique to my professional experience. The more with the certificates and checking that must have undergone this particular one.
I have seen once a cluster of forgings that had been heat treated incorrectly, they just fell apart during transport, due to internal stress state.
Does anyone know whether there's a requirement to have a material sample going with the main hook components during heat treatment, in order to do a metallographical analysis?
Roland Heilmann
Rules should require a pre-test in a safe working environment, step-by-step increase of load, thorough check for cracks prior and after.
But I don't know whether this is perhaps already the case with load hooks?
I don't know whether the enquiry (at least the technical part) shall be public, or being made public. But I'd very much like it to be made public, in all detail.
Such sudden death of a big size forging is quite unique to my professional experience. The more with the certificates and checking that must have undergone this particular one.
I have seen once a cluster of forgings that had been heat treated incorrectly, they just fell apart during transport, due to internal stress state.
Does anyone know whether there's a requirement to have a material sample going with the main hook components during heat treatment, in order to do a metallographical analysis?
Roland Heilmann
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2
- Thread starter
- #36
LittleInch
Petroleum
That's actually very interesting.
The hook falls off and the block doesn't move for several seconds.
It's the fact the vessel is ballasted on the side that causes the large motion and movement of the crane arm backwards.
Seems like a bit of a design flaw to me. If the load had to be suddenly lowered in operation then the ship clearly can't ballast level fast enough to prevent large motion of the vessel and crane arm.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
The hook falls off and the block doesn't move for several seconds.
It's the fact the vessel is ballasted on the side that causes the large motion and movement of the crane arm backwards.
Seems like a bit of a design flaw to me. If the load had to be suddenly lowered in operation then the ship clearly can't ballast level fast enough to prevent large motion of the vessel and crane arm.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
JohnRBaker
Mechanical
Yes, I was thinking the same thing, the tilting of the ship as quickly as it did probably added enough inertial momentum in the boom structure that this contributed to the failure. And as LittleInch noted, there was very little movement caused by the failure of the hook itself, as nothing happened until AFTER the ship tilted toward the wharf, that's when all the 'excitement' stated to take place.
John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:
The secret of life is not finding someone to live with
It's finding someone you can't live without
John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:
The secret of life is not finding someone to live with
It's finding someone you can't live without
LittleInch
Petroleum
J Stephen. The massive difference with something like this monster is that the counterweight doesn't move....
It's clear that is the motion of the vessel which causes the crane jib to flex back until it goes beyond the vertical.
If the job wasn't as vertical as it was it might have survived. I do wonder though if this scenario ( loosing the load very suddenly) had been properly analysed.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
It's clear that is the motion of the vessel which causes the crane jib to flex back until it goes beyond the vertical.
If the job wasn't as vertical as it was it might have survived. I do wonder though if this scenario ( loosing the load very suddenly) had been properly analysed.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
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