engleski

Use of aged tankers as offshore and port oil storages

Demolition of aged ships is an important strategy for balancing the global ship fleet capacity and is influenced by the ship obsolescence, technical developments and environmental regulations on ship demolition, operational costs as well as by the state of the shipping market in general. Instead submitting aged tankers to usual recycling process, which is nowadays subject of different policies, their cargo modules can be sometimes used to increase storage capacities in ports, if there is economic justifiability. It is, however, necessary to care about ship hull integrity both for the sake of human safety during their operation and potential environmental issues. This work brings a procedure for strength assessment of a ship structure partially immersed in mud and is motivated by a practical problem of structural integrity evaluation of an aged single-bottom tanker which was grounded in mud and used as oil storage in order to increase the port capacities. The ship is supported in part by the mud and in the other part by the surrounding sea water. In the first step, a mathematical model of the ship static equilibrium is formulated, consistently taking into account ship, cargo and ballast weights, the supporting mud reaction and the surrounding water buoyancy. Secondly, the developed physically consistent mathematical model is used as a basis for load determination within a detailed 3D FEM analysis. The thickness measurement campaign was conducted in order to directly account for the corrosion effect and 3D FEM model is updated with the exact thickness values. Conclusions on ship suitability to safely serve as port oil storage are drawn based on the FEM results and allowable stress levels prescribed by the class society. The developed procedure can be also used for assessment of ship residual strength in the salvaging procedure after stranding, when the distribution of sea bottom reaction should be defined.

tanker, oil storage, ageing effect

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