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The particularities of offshore cranes

*Article for Crane Brasil magazine – Edition 57/2018

Source: OOS International

The cranes used in lifting activities on offshore platforms, whether fixed or floating, are generally of the “crane on pedestal” or “pedestal crane” type, where the superstructure is fixed on a steel tube welded to the hull or to the surface. platform structure.

This geometry differentiates the offshore crane from the land crane in terms of overturning stability, ensuring greater robustness to the former and obviously freeing it from problems of support base repression, as can happen with land cranes.

When loading tables, there are very important differences, the main addition being the parameter of significant wave height (Hs), which is the average of the one third of the highest wave heights in a period of time, and is used to estimate the load. maximum lifting force that can occur during an operation due to the movement of the platform, the crane, the support vessel and the load. The higher the wave height, or Hs, the more force the crane must withstand, lowering its maximum working load.

As for operational risks, offshore cranes are susceptible to overload due to the hook being caught in the support boat and, when it descends on the wave, it can even pull the superstructure off the pedestal. To reduce this risk, electronic overload suppression devices can be used (European approach) or increased structural robustness (American approach).

Another operational difference is that offshore cranes, at least the most modern ones, are certified to lift people for transshipment, which is not allowed by land crane manufacturers, including mandatory safety devices. This feature is important, as the main international standards for offshore lifting provide for the lifting of people, including the text of the future NR-38, for work on offshore platforms.

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