Can Dynamic Load exceed the SWL of rigging if the static load is ok

[escapizm]

Q) I have an existing rigging assembly with a hook rated to 25Te WLL, the static load is 22Te, applying a DAF of 1.3 gives 28.6Te. is the hook ok?

Tks

 

[phamENG]

I wouldn't chance it, at least not without contacting a rigging expert for an official (and documented) opinion. Best resource is probably the manufacturer.

 

[Craig_H]

Some context would be helpful here, what is the origin of your Dynamic Amplification Factor? I assume this is for lifting in an offshore environment, and the dynamic loads are based on wave action, etc? If my memory is right, DNV and Noble Denton standards usually provided guidance on calculating rigging loads, and I am guessing that's where you got the DAF...

The only way I'd entertain the idea were if the DAF were some dynamic factor applied to a quasi-static land-based lifting scenario. In my past work in the specialized lifting field, I regularly saw unnecessary factors being applied where they ought not to be by pretend-gineers with tight sphincters. In short, your static load only matters if the situation is... static! Otherwise, I'd be designing to the dynamic load, and taking care to ensure that the lifting equipment has undergone recent NDT to ensure that other dynamic loading hasn't caused fatigue damage.

 

[human909]

NOTE Terminology code requirements vary between regions. So you really need to go to your local code. That said:

To my ROUGH knowledge WLL/SWL is generally a static load or mass. There is normally a very significant safety margin over the breaking load limit. This safety margin allows for dynamic factors in normal lifting and moving as well as strength reduction due to material variability and other strength reduction factors.

In my past work in the specialized lifting field,... In short, your static load only matters if the situation is... static! Otherwise, I'd be designing to the dynamic load, and taking care to ensure that the lifting equipment has undergone recent NDT to ensure that other dynamic loading hasn't caused fatigue damage.

Your latter comment surprises me. A load being lifted is not static by definition. Yet as far as I'm aware in basic lifting a dynamic factor is not normally applied to your load.

That said you no doubt have more experience in the field so I defer to your expertise.

 

[escapizm]

This is indeed an offshore lift in the North sea, I am proposing to our analysis dept some further consideration (as no one here can give me a definitive yes or no either) they may well defines a smaller DAF and impose limiting sea-states etc for the lift, I will update with there input.

tks for your time folks.

 

[12345abc6ttyui67]

Refer to the new Eurocode 19901-6 Chapter 18 (I think). It's by far the most comprehensive guide I have come across for what factors to include in what calculation.

The only thing it doesn't cover it test loads...

 

[Lomarandil]

Any crane operator worth his salt is able to perform typical lifts on land without any significant dynamic acceleration.

Marine lifts, especially in open water, are a different animal. I'd lean toward keeping the dynamic load within SWL (and limiting operation as needed) in most cases, although I'm sure there's some room to improve on that in limited circumstances.

----
just call me Lo.

 

[Ussuri]

Short answer, maybe, maybe not.

Is this the crane hook or something like an eye hook? If its rigging compenents like shackles and UK legislation doesn't apply then the static load is compared with the WLL, the dynamic load is compared against the MBL/factor. But if you are covered by LOLER then you cannot exceed the WLL.

Another common reference is DNVGL-ST-N001 (which replaced the DNV Marine Ops, and the VMO Standard), which states:

16.5.2.6 The shackle dynamic load (considering all relevant factors in [16.3.4.1] and including DAF) shall
not be greater than the least of the following:
a) WLL stated on the certificate x DAF
b) Shackle MBL/3.0
c) Documented proof load value for the shackle (see [16.12.3.1] for proof load test documentation
requirements).
The above requirements are applicable subject to the following conditions:
— The lift is an engineered lift taking in to account all the applicable factors and requirements of this
standard.
— The MBL is derived using the correct factor of safety (manufacturers have different factors of safety).
This is particularly important if a shackle is changed out during the course of a project.
Guidance note:
Where local or national regulations are different to those contained in this standard, then those regulations shall be considered
governing if this provides a higher level of safety or serviceability than this standard.
Where other requirements are different to those contained in this standard (e.g. client or lifting contractor), then these may be used
providing they give a higher level of safety or serviceability than this standard.
---e-n-d---of---g-u-i-d-a-n-c-e---n-o-t-e---

However, if this is covered by LOLER, the ACOP states:

Overload
282 A load greater than the SWL or rated capacity should not be lifted except
where, for the purposes of thorough examination or testing, the competent
person requires it.

 

[Craig_H]

human909, as Lo mentions, controlled lifts with land-based cranes are quasi-static scenarios. A smooth operator can keep dynamic effects to a negligible amount. I've observed this directly with load cell monitoring on the hook block. Worst case scenarios only resulted in hook loads varying ~5%, which is pretty small potatoes when your rigging has a safety factor on breaking strength of 5.0. When the crane is no longer resting on a stationary object, then we get into significant dynamic effects, which are indeed a whole different animal. In such cases, all components supporting the load (the crane, rigging, hook, hoist lines, etc) need to be able to handle the dynamic loads caused by the inevitable motion of the crane base and the load relative to each other.

I only once applied a dynamic factor to a land-based lift, and that was because we were lifting with strandjacks. Those impose stop-start loads every stroke of the jack, which do result in amplification of the dead load being lifted.

 

[human909]

Thanks Craig.

 

[dhengr]

Escapism:
I would have designed the original lifting equipment and components for the intended SWL (safe working load), times any code and client required safety factors (FoS) and DAF (dynamic amplification factors). Thus, my equipment design load is much higher than the SWL and relates to material yield strength, buckling of components and the like. The high FoS of 5 relates to ultimate or breaking strengths of components, and should never even be approached in normal usage. So, in that respect, the SWL shown on the equipment already includes/contemplates normal FoS and the DAF which were spec’ed. at the time of design and manufacture. And, as mentioned above by Craig_H, the DAF does not have to be added to the weight of the load to be lifted a second time, with this new total staying below the SWL.

Also, as mentioned above, there may be some exceptions or circumstances where a new, higher DAF is appropriate for the local conditions. These determinations are the responsibility of the engineer managing the particular lift, and are left to his/her engineering judgement of the current situation. They can also shut the job down under adverse conditions. Just as important as an understanding of the above design and engineering philosophy, is that the equipment be maintained and inspected regularly, I think most codes imply/say…, ‘inspect before every use.’ The relatively high FoS are, in part, because this equipment is used by different people each time, is abused in its use and handling, and sits around for long periods of time btwn. short periods of intensive use, many times under less than ideal storage conditions.

 

[escapizm]

I have subsequently increase the WLL of the rigging so the DAF loads is below WLL.

Tks for your input.