supposedly the hook failed and boom slingshot over the top.
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Liebherr Orion crane failure under 5500t load test 7
- Thread starter tommj
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Was the loading really only 50% of rating? It seems to me that lifting something off water is harder than lifting the same weight off dry land due to surface tension.
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JohnRBaker
Mechanical
Actually, because the 'weight' was a barge, floating in water, as it was being lifted out of the water the suspended load would have increased as the effect of buoyancy was reduced. As for surface tension, I suspect that compared to the weight of the barge, that it was negligible.
John R. Baker, P.E. (ret)
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Compositepro
Chemical
"It seems to me that lifting something off water is harder than lifting the same weight off dry land due to surface tension."
I suggest you think that out a little bit more. You are probably thinking about suction effects that may occur when trying to pull something out of mud, but that too is not relevant here.
I suggest you think that out a little bit more. You are probably thinking about suction effects that may occur when trying to pull something out of mud, but that too is not relevant here.
Well, I was looking at some Youtube videos to see what happens in similar cases. And, there aren't too many cases where the load is dropped like that, and even fewer with a crane that can go backwards, and where they show what happens to the crane.
In the first clip on this video, it looks like the crane turned over rearwards due to load release, but it's hard to tell for sure what was happening with it:
In this clip, there's a pretty signifcant load release and you can see the boom (and crane) bouncing around pretty good, but not flipping over backwards, either:
In the first clip on this video, it looks like the crane turned over rearwards due to load release, but it's hard to tell for sure what was happening with it:
In this clip, there's a pretty signifcant load release and you can see the boom (and crane) bouncing around pretty good, but not flipping over backwards, either:
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charliealphabravo
Structural
I'm uploading that new linkedin video that shows the beginning of the failure to ET for posterity. At least I think that is what I did. It says jpg and png only but it still created the link for an mp4.
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/video/upload/v1589138202/tips/orion_linked_in_failure_video_furjwm.mp4[/url]
Edit:
I don't think that they ever intended for the barge to come clear of the water. Those lifting points seem too close together for such a long load. At any rate, the real-time load would be metered/monitored by the crane.
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/video/upload/v1589138202/tips/orion_linked_in_failure_video_furjwm.mp4[/url]
Edit:
I don't think that they ever intended for the barge to come clear of the water. Those lifting points seem too close together for such a long load. At any rate, the real-time load would be metered/monitored by the crane.
Dynamic control of counterweight to maintain crane stability - like an automatic ballasting system - or moving counterweights used in some tower cranes ( creates a situation where counterweight position (or moment) is critical to a safe lift - and sometimes structural integrity of the crane.
In this case in addition to the obvious situation with the hook, there is (to me) a question hull stability design.
So on a barge or ship mounted cranes is the backwards boom stability with maximum dynamic hull rotation in a loss of load event a required consideration when designing the load chart?
In this case in addition to the obvious situation with the hook, there is (to me) a question hull stability design.
So on a barge or ship mounted cranes is the backwards boom stability with maximum dynamic hull rotation in a loss of load event a required consideration when designing the load chart?
LittleInch
Petroleum
FacengrPE said:
Well I think it will be now!
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Alistair_Heaton
Mechanical
Trying to think of somewhere in Europe that could do a static pull on a 5000 ton test piece. Never mind geometric issues.
850 tons was the max I knew of 20 years ago.
They used to test the offshore cranes in Aberdeen harbour with a similar setup but a lot smaller barge. They were though the recertification checks.
I think this will be covered by DNV who were always pretty hot on logging of heat treatment and NDT.
850 tons was the max I knew of 20 years ago.
They used to test the offshore cranes in Aberdeen harbour with a similar setup but a lot smaller barge. They were though the recertification checks.
I think this will be covered by DNV who were always pretty hot on logging of heat treatment and NDT.
This test could only have had one acceptable outcome, and that was successful completion. Perhaps there was some monitoring of power and stress point metrics to verify calculations, but that catastrophic failure could have only had one result.
Brad Waybright
It's all okay as long as it's okay.
Brad Waybright
It's all okay as long as it's okay.
LittleInch
Petroleum
It's curious though as to why the barge has eight strong points, but only 4 were in use. Was the hook supposed to be higher to make the rope loads more "vertical". See the picture from CAB - 6 May 20 17:54
But once that boom went past vertical then the result was not in doubt.
I guess there were very good reasons why the crane is on one side of the vessel, but the ballasting arrangement to allow any load to be moved on or off the vessel would be significant and involve a lot of water movement between ballast tanks. Fundamentally this is the key to this failure.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
But once that boom went past vertical then the result was not in doubt.
I guess there were very good reasons why the crane is on one side of the vessel, but the ballasting arrangement to allow any load to be moved on or off the vessel would be significant and involve a lot of water movement between ballast tanks. Fundamentally this is the key to this failure.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Alistair_Heaton
Mechanical
I think its a test barge that they use in that port for all of the crane certifications and recertifications.
Its not the first time its been used and it won't be the last time either.
They don't lift off the actual deck they lift off barges and then position. The ones I have seen so far building off shore windfarms have all used jack up rigs next to the work site.
But they are wanting now to have one vessel putting foundations and piles in then build the complete mast plus turbine and blades on the shore or maybe on the deck then lift the whole lot into position in one lift. Before it would be piles then mast, then turbine on top then fit the blades. And fitting the blades apparently was extremely weather dependant.
Its not the first time its been used and it won't be the last time either.
They don't lift off the actual deck they lift off barges and then position. The ones I have seen so far building off shore windfarms have all used jack up rigs next to the work site.
But they are wanting now to have one vessel putting foundations and piles in then build the complete mast plus turbine and blades on the shore or maybe on the deck then lift the whole lot into position in one lift. Before it would be piles then mast, then turbine on top then fit the blades. And fitting the blades apparently was extremely weather dependant.
It seems to me that it wouldn't be too hard (in a relative sense) to test that hook. You could come up with hydraulic jacking arrangements, you wouldn't need to actually do it on a crane.
In the US, smaller lifting hardware typically uses a factor of safety of 5 or so. They may lower that in a case like that, especially if they can analyze the heck out of it. But still, it had to have failed at just a fraction of its intended strength.
I'll bet barge has a pretty good ding in the deck now.
In the US, smaller lifting hardware typically uses a factor of safety of 5 or so. They may lower that in a case like that, especially if they can analyze the heck out of it. But still, it had to have failed at just a fraction of its intended strength.
I'll bet barge has a pretty good ding in the deck now.
charliealphabravo
Structural
JStephen said:
Is that certain at this point? Firstly, the crane is only good for the rated load under narrow constraints which surely include restrictions on uniform loading of the hooks. Secondly, I understand that safety factors might be as low as 1.3 for these heavy lift systems. Thirdly, the rigging system doesn't give much confidence of a uniform load application. I can see a rather large moment being applied to the hook which might quickly put you well past the stresses expected at the 50% load reported by the crane sensors. Finally, I can't really see them getting this far in the process without testing and certification of the hook prior to installation.
JStephen-
You're right in that of all of the component parts of the crane, the hook would probably have been one of the easiest to conduct a static load as a separate part. In fact, I guess we don't really know whether such a test wasn't performed prior to shipping. We also don't yet know the failure mode, so it's possible that it might have passed in a different configuration. Ropeblock might be having similar thoughts in hindsight as I'm sure their liability is probably into seven figures.
BTW, from reading the press releases It seems to me that Liebherr was quick to note that the hook came from a 3rd party vendor and I get the feeling they're trying to throw them under the bus. I would say that unless that equipment was purchased/provided by somebody else like the customer, then it's part of Liebherr's equipment it and it's theirs to own. Ropeblock makes a similar notation that the failed part comes from an outside supplier, but they seem to defend that supplier's design, construction, materials, etc. a little more than Liebherr.
Brad Waybright
It's all okay as long as it's okay.
You're right in that of all of the component parts of the crane, the hook would probably have been one of the easiest to conduct a static load as a separate part. In fact, I guess we don't really know whether such a test wasn't performed prior to shipping. We also don't yet know the failure mode, so it's possible that it might have passed in a different configuration. Ropeblock might be having similar thoughts in hindsight as I'm sure their liability is probably into seven figures.
BTW, from reading the press releases It seems to me that Liebherr was quick to note that the hook came from a 3rd party vendor and I get the feeling they're trying to throw them under the bus. I would say that unless that equipment was purchased/provided by somebody else like the customer, then it's part of Liebherr's equipment it and it's theirs to own. Ropeblock makes a similar notation that the failed part comes from an outside supplier, but they seem to defend that supplier's design, construction, materials, etc. a little more than Liebherr.
Brad Waybright
It's all okay as long as it's okay.
JohnRBaker
Mechanical
I suspect that the mindset of the people responsible was that they were NOT testing the hook. They were focused on the crane and its structures, and had made certain assumptions about the other components.
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
I'm curious to know how far into the testing program they were. These thoughts are easy to come by in retrospect, but perhaps some thought needs to be given ahead of time to the consequences of plausible failures. I'd imagine a "lesson learned" coming out of this is to evaluate the repercussions of a hook failure when the boom is at such a high angle, and that there should probably be progressive testing at lower angles (and necessarily lower loads) before getting to that point. Again, I'm not saying I would have thought that before seeing this, just thinking about what could have been done to limit damage if the hook were destined to fail.
Since the crane only controls 1/2 degree of freedom of the boom in an application where 1 full degree of freedom is a possibility; perhaps there will be some design change to add the other 1/2 degree of control with a second mast located below the boom and a smaller cable reel to restrain the boom in a potential recoil in case the load is lost for any reason. OTOH the same 1/2 degree of control is true for tower cranes - if they have counterbalance a heavy load I'm not sure that sudden loss of the load can be withstood by the tower bearing and not topple off, which seems to be a rare occurrence, no doubt due to the high standards for fabrication of components.
The system may not have the moment capacity to test the hook at a low angle. Although this is interesting to think about. The moments have to zero out. Is the system safe from the failure mode of flicking the boom over at a low angle? This may not be too hard a problem to solve with energy methods.Pete K said:
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