Strength assessment of an aged single hull tanker grounded in mud and used as port oil storage
This paper deals with a practical problem of structural integrity evaluation of a single hull tanker which, after its regular service, was grounded in mud and used as port oil storage. The fore and the aft part of the ship were removed, whereas its middle module was kept to be used as a liquid cargo storage and a permanent ballast that ensures the ship continuous contact with the sea bottom. Therefore, the ship can be considered as supported in part by the mud and in the other part by the surrounding water. Although the ship is classed as a stationary object, the reliable strength assessment is still necessary to check its structural integrity in order to avoid potential environmental issues. The analysis was done in two steps. At first, the mathematical model of ship static equilibrium has been formulated, consistently taking into account the supporting mud reaction and buoyancy. Secondly, the developed physically consistent mathematical model is used as a basis for a detailed 3D FEM analysis, where the 3D FEM model is generated based on the available technical documentation and thickness measurements of the whole ship structure, which was performed in order to directly account for the effect of ageing (corrosion). Representative stresses in all structural elements are determined and compared with the permissible ones. Conclusions on ship suitability to serve as port oil storage are drawn.