Abstract
Up to 60% of storage tanks in operation have uneven settlement of the outer bottom contour, which often leads to accidents. Russian and foreign regulatory documents have different requirements for strain limits of metal structures. There is an increasing need for harmonizing regulatory documents. The aim of this study is to theoretically justify and to assess the possibility of applying the U.S. standards for specifying the allowable settlement of storage tanks used in Russia. The allowable uneven settlement was calculated for a vertical steel tank (VST-20000) according to API-653, a standard of the American Petroleum Institute. The calculated allowable settlement levels were compared with those established by Russian standards. Based on the finite element method, the uneven settlement development process of a storage tank was modeled. Stress-strain state parameters of tank structures were obtained at the critical levels established in API-653. Relationships of maximum equivalent stresses in VST metal structures to the vertical settlement component for settlement zones of 6 to 72 m in length were determined. When the uneven settlement zone is 6 m in length, the limit state is found to be caused by 30-mm vertical settlement, while stresses in the wall exceed 330 MPa. When the uneven settlement zone is 36 m in length, stresses reach the yield point only at 100-mm vertical settlement.
Highlights
Uneven settlement is one of the causes that give rise to limit states in metal structures of vertical steel tanks (VST), which often lead to accidents [1,2,3]
Despite accumulated research findings and long-term experience in tank construction, researcher have failed to resolve a number of issues related to assessing the stress-strain state of VST, which is subject to uneven foundation settlement [7]
The comparison of the allowable settlement levels according to [12] with those specified in Russian standards [13] shows that the settlement tolerances established in Russian documents are much more stringent than the U.S ones (Fig. 1)
Summary
Uneven settlement is one of the causes that give rise to limit states in metal structures of vertical steel tanks (VST), which often lead to accidents [1,2,3]. Effects of uneven foundation settlement on the stress-strain state of storage tanks were studied by Russian scientists, such as V. P. Borodavkin and others, as well as by foreign scientists — J. Despite accumulated research findings and long-term experience in tank construction, researcher have failed to resolve a number of issues related to assessing the stress-strain state of VST, which is subject to uneven foundation settlement [7]. For non-axisymmetric strains of a tank shell, it is not always possible to determine high-stress zones in metal structures [8]
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