Article for Crane Brasil Magazine – Edition 58/2018
One of the most significant differences between onshore and offshore lifting operations is the movement of the crane’s support base. While on land there is a practically fixed base, at sea, mainly on floating platforms, the crane base moves in all directions, combining with rotational movements, generally occurring at the same time.
The consequence of these movements is the amplification of the forces in the load, in the slings, in the cable and in the crane itself. There is also amplification of the movement of the load, with increased speed and range of motion. In addition, due to the wave effect, there is the relative movement of the load and the point where it will be placed or removed.
In air and water lifting operations, that is, where a load is going to be lifted in the air and introduced into the water, or vice versa, as is the case with subsea equipment, the risk increases, because in addition to the movements already described, now acts the hydrodynamic force of water and waves, demanding even more of the resistance of the components and expertise of the operators.
To reduce the dynamic effect on the load and the crane, as well as to slow it down or keep it almost static in relation to a point, there are special equipment called heave compensators, which compensate for the relative vertical movement between the load and the crane, being basically of two types: passive (passiveheavecompensation) and active (activeheavecompensation).
The passive compensator is composed of a hydraulic and mechanical system that accumulates or releases energy, extending or retracting a cylinder that supports the load, reducing its vertical movement.
The active compensator has a computerized system that calculates the movement of the crane and releases or retracts the cable to keep the load in the same vertical position regardless of the movement of the crane.
Special devices ensure efficiency and safety by reducing the effects of crane support base movements at sea.
Special devices ensure efficiency and safety by reducing the effects of crane support base movements at sea.
The growing increase in technology and the consolidation of offshore lifting engineering has allowed for the successful completion of increasingly complex operations, maintaining a satisfactory level of safety, preserving properties, the environment and, above all, lives.
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