Numerical Stability Analysis of an Underwater Spherical Oil Storage Tank

Abstract

The most important and promising direction in the Russian oil and gas industry is the development of the Arctic shelf, the largest in the world. Today, in the case of the development of oil and gas deposits remote from the coast, the use of underwater pipelines is not only unprofitable, but also technically unfeasible due to the short summer navigation. A problem arises when mastering the delivery of energy carriers to the industrial regions of Russia, as well as for export. One of the ways to solve this problem is the use of underwater reservoirs as a means of temporary accumulation of the product. During the operation of underwater oil storage facilities, situations may arise that lead to dome deformation. To prevent such negative consequences, a reliable prediction of the stress-strain state is required. In this paper, the authors considered the modeling of the stress-strain state of the welded joint of the wall-to-bottom of the tank, as well as the zone of monolithic steel dome of the body in concrete. The depth of 100 m for the installation of an underwater storage was chosen due to the presence of hummocks in the seas of the Russian Arctic, which can affect the seabed to a depth of 15–40 m, as well as icebergs — up to 80 m. The authors developed a numerical axisymmetric finite element model of an underwater storage section, which allows to determine the stress distribution in the domed part of the tank, as well as in the foundation, in accordance with all the features of the underwater tank. The calculations showed that for the considered operating conditions of the deposits, the use of sheets of high-strength steel D690W with a thickness of 50 mm is not enough to ensure the stability of the structure, since stresses arise in the weld that exceed the yield strength of the selected steel. Therefore, it is required either to reduce the immersion depth of the storage, or to provide for a greater thickness of the domed part of the body with the use of ribs that increase the rigidity and stability of the structure.