6100 lbf load on 3 ton hoist

[someguy79]

I got a request from a fellow engineer at the plant asking about doing a planned engineered lift per ASME B30.2. The hoist they want to use is rated for 3 tons (i.e. 6000 lbf), and the item they want to pick is 6100 lb.

ASME B30.2 3.2.1.1(a) says “Planned engineered lifts shall be limited to powered cranes having a load rating of 5 tons and above.” I’m not yet sure how that difference will affect us. To me this seems like the proposed lift is outside the scope of ASME B30.2 and perhaps not allowed.

Is there another reference out there that would cover this subject more thoroughly? (e.g. OSHA section? CFR 1910.XX?)

BTW, I am planning to ask the manufacturer for guidance. They're usually quite interested in this sort of thing. Also, standards are nice, but the local authority having jurisdiction will govern.

 

[tygerdawg]

The answers can be searched for and found using OSHA website search utility. Can't remember exactly: hoists require safety factor of 4X? 6X? Can't remember. You can actually ASK an OSHA expert and find out for sure.

None of that matters, though.

What will the plaintiff's lawyer say during, and the jury decide after, the trial if/when your 6000 lbf-capacity hoist fails while trying to lift a 6100 lbf load? I think I know.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[fegenbush]

tylerdawg is correct. There are places to cut corners in business. This is not one of them. Hoists and cranes are cheap. Lawsuits and human lives are not.

 

[Tmoose]

Could you rig up a snatch block to ~ double the lift capacity?
Or, is the 6000 lb limit for the trolley/support structure?

 

[someguy79]

tylerdawg & fegenbush,

Yes, I understand that there are serious safety and legal implications for doing something incorrect with lifting equipment. I do not want to belabor that point.

I really just want to find the best acceptable method for moving the equipment. If that happens to be brining in some other lifting device for this one event, so be it. I do have to prove that's necessary though. No one wants to spend an extra $15,000 for something that could've been done via an alternate procedure for $5,000 or less in planning and analysis costs.

When it comes to searching OSHA or other systems for rules and standards, I don't want to miss anything. There might be a specific rule that says this is or is not allowable in some way. That's the sort of information I'm hoping to find (or maybe find leads for) here.

Tmoose,

Although blocks would get the cable tension down, I believe the 3 ton rating includes the trolley. I don't think there are any additional/alternate pick points to use in the area. I'll have to double-check on the pick points though.

 

[dhengr]

Someguy79:
I certainly would take with the crane manfu’er. How old is the crane? What is the controlling design feature? A 6100lb. lift with a 3 ton cap’y. (6000lb.) crane is only a 2% overload w.r.t. the rating. I’m pretty sure that you will find in OSHA that cranes have to be load tested to 125% of cap’y. on some regular basis to be/stay certified. The same 125% applies to most all lifting components. And, this type of equip. is designed to a safety factor far greater than 1.25. I don’t think I would worry much about a carefully planed lift of 6.1k, as long as everything is in good shape. In the final analysis, it kinda comes down to a management decision with some good engineering judgement and guidance in making the determination to save $10 or $15,000.00, vs. some very small potential risk and liability. I’ll bet this kind of overload has happened more often than you would care to know, without anyone asking for your approval.

 

[IFRs]

Although I think the risk is low that your crane will fail and someone will be hurt, it is not my risk to take. Can you mitigate that risk by evacuating the building and moving it by remote control? Can you lift it not in the middle of the trolley or the middle of the rail span, where the capacity may be higher? Can you drain out the oil and get it to be 100 pounds lighter? Can you attach helium balloons to pick up 100 pounds? Can you put a cart under it to take off 100 pounds?

 

[tbuelna]

You need to look at the lifting condition the hoist system is rated at. If the 3-ton hoist rating is based on some extreme lifting condition, and you can show your lift will be performed at conditions that put less than max stress on the hoist structures, then you might be OK. On the other hand, you will also need to account for the added mass of any lift fixtures/spreader bars used, which can be significant.

I gave the ASME B30.2 document you noted a quick scan and it does state a "planned engineered lift" is limited to powered lift systems rated at 5+ tons. But even a single planned engineered lift using a powered hoist rated at 5+ tons would require a substantial amount of documentation and analysis.

If this is a single lift requirement, I'd suggest hiring a crane or heavy fork lift for the day.

 

[someguy79]

FYI, we'll probably be modifying the 6100 lb cofferdams to remove some weight. That's going to be a lot cheaper and easier to use than modifying the hoist and/or rigging.

Thanks to all of you for the comments and ideas.

 

[gerhardl]

What am I missing here? 6 100 lb, lbs = 2.766 913 457 metric ton

 

[rb1957]

OP's using short tons (US ton = 2000 lbs) vs "real" tons = 2240 lbs

another day in paradise, or is paradise one day closer ?

 

[drawoh]

rb1957,

You mean short tons (2000lb) versus long tons (2240lb), as opposed to metric tonnes (~2208lb). Be careful, I have my MDCCCIIIV Mechanic's Calculator around here somewhere.

--
JHG

 

[rb1957]

as someone (Churchill?) said of the UK and the US ... "two peoples separated by a common language"

another day in paradise, or is paradise one day closer ?

 

[tbuelna]

Please be careful about disparaging the imperial system of measurements with regard to ASME B30.2. Below is a cover page provided with the document. Pay particular attention to the last sentence of the notice, "Heed this notice: Criminal penalties may apply for noncompliance.". Also note that section VII states, "The values stated in customary (ie. imperial) units are to be regarded as the standard"

God bless the United States of America.

 

[rb1957]

fortunately I'm neither a citizen nor a resident of the good ole USofA ...

so they can "stick it", up until the time when some guy knocks on my door (or worse, I see the laser sight on my house ...)

another day in paradise, or is paradise one day closer ?

 

[JStephen]

Is that page actually furnished with the standard? Or is that one of the copyright-violators-but-it-doesn't-count-because-it's-a-law publishers that stuck that in?

Someguy, sounds like you got it covered. Anyway, a rental crane would be the other alternative, and it should be a LOT cheaper than $15,000, assuming you in a metropolitan area that has any kind of rental crane service.

There have been similar posts about "What do you do if your beam is overstressed 2%?", with a split in opinions between the "It's only 2% so it doesn't really matter" and "An overstress is an overstress no matter how small" camps. With no good definitive answer.

 

[LittleInch]

tbulena,

that spec is interesting - it adds metric units in brackets after a lot of the numbers except for tons and also doesn't define ton (no long or short or no of lbs or kgs), therefore the original supposition may still be correct, i.e. someguy79 hasn't said why he's using short tons. Might be a good idea to double check the rating of his hoist....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[someguy79]

Littleinch,

Here in the US "ton" means 2000 lb. If it's not obvious to an inspector just by looking at the tags on the lifting equipment, it will be assumed to be the typical units of measure here. If the manufacturer says it's rated in long tons, I need them to say so in writing and keep that info nearby and conspicuous in case an inspector comes by.

The CFR reference included above means that it's part of the Code of Federal Regulations (i.e. it's a national law).

rb1957,

Don't worry, I'm not going to show up at your door, and I don't think anyone else is going to bother about this either. BTW, I think that laser guided munitions use a wavelength that's not visible. So you don't have to worry about seeing a laser designating your house as a target.

 

[rb1957]

"BTW, I think that laser guided munitions use a wavelength that's not visible. So you don't have to worry about seeing a laser designating your house as a target." ... oh great ! that's so reassuring ... that I won't know it's about to happen ! maybe they do that for humanitarian reasons ??

another day in paradise, or is paradise one day closer ?

 

[LittleInch]

Fascinating. When metrication arrived the ton to tonne (pronounced tonny) was one of the few that was so close it could really be used without conversion, but your ton is quite different. I'm still surprised it didn't add a conversion, but maybe it assumes everyone knows....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.