Typical damage in steel storage tanks in operation

The safe and long service life of structures could be assured only when adequate design and construction are combined with a proper and regular maintenance. The principal objective of this paper is to identify the most common failures that may occur in above ground cylindrical steel storage tanks in operation, to suggest better design decisions, possible solutions for repair and provide guidelines for appropriate care and maintenance of this type of structures. A group of specialists was assigned the task to conduct a site inspection and provide a statement for the operational condition of 7 new and 13 steel storage tanks in service, owned by State agency “State reserve and war-time stocks”. The facilities contain different oil products – petrol, diesel and mixed fuel stored at ambient temperature and atmospheric pressure. The anchorage conditions vary. Some of the examined storage tanks were built in the 1970s, others – in the period 2009 - 2014. The audit was carried out in accordance with the Agency’s internal directive and standards API 650, API 653, EN 1993-4-2, EN 14015. Based on this representative study and the practical design experience of the authors, this paper classifies the most frequently reported damage in different elements of tanks in operation – foundations, anchorage (if present), annular plates, tank bottom, shell, roof (fixed or floating), attached accessories and systems. Illustrative examples are presented, along with explanations for the critical aspects of adequate maintenance. Finally, some conclusions are drawn in the form of guidelines for failure prevention and if the damage already exists - possible ways for restoration of the facility to its proper operational state.