Peculiar Issues of Evaluation of Strength, Reliability, and Accident Risk of Isothermal Tanks to Store Liquefied Gases

It is not possible to design completely reliable and flawless structures and facilities. Although precisely designed, accurately manufactured and assembled, such structures and facilities can have defects that are permissible on the condition of compliance with the established loading modes unless certain parameters are reached. The most critical issue among the threats to the safe operation of isothermal tanks to store liquefied gases is the violation of operating conditions, namely the increase in internal pressure of the gaseous phase. It is associated with the fundamental inability of a defect-free, fully serviceable thin-walled shell with a flat bottom and a conical or domed roof to withstand an emergency increase in internal gas pressure. A few accidents in isothermal tanks that occurred earlier in the world are associated with the emergency increase in internal pressure. The hazards identified when assessing the risk of accident in an isothermal tank are listed in descending order of their importance. The excess of scheduled values by structure parameters or liquefied gas storage process is prioritized as the first criticality. These are primarily the increase in internal gas pressure, then defects of structure, random impacts, etc. The algorithm for evaluating the frequency of accidental leakage in an isothermal tank remaining in operation upon the expiration of the designed lifetime is proposed.