On the Issue of Choosing Criteria of Standardization of Minimum Safe Distances for Cryogenic Semi-Isothermal Liquefied Natural Gas Tanks

Currently, the industry of small- and medium tonnage liquefied natural gas is actively developing in the Russian Federation. One of the most crucial issues is the development of the appropriate regulatory and methodological framework based on the contemporary standard and legal regulation of safety in industry. Today, there is a qualitative difference in values of minimum permissible distances for semi-isothermal tanks of liquefied natural gas as adopted in Russian and international documentations (for the Russian documentation, significantly longer distances are adopted), which clearly indicates differences in accident scenarios adopted for consideration. The study analyzes the specific conditions of the destruction of ground-based single-wall cylindrical tanks used for drainage-free storage of liquefied hydrocarbon gases under an extreme external impact accompanied by explosive boiling of a thermodynalically superheated liquid and fireball generation. Materials and technologies, quality control methods and protection systems as well as the operating conditions applied for manufacturing of semi-isothermal cryogenic tanks actually exclude a possibility of a significant spontaneous breach of leak-tightness of the internal self-supporting container, which is proved by a complete absence of incidents for a more than 50-year period of their active use both in Russia and abroad. It has been demonstrated that, unlike single-wall tanks for typical cryogenic semi-isothermal tanks of liquefied natural gas with powder-vacuum or multilayered screen-vacuum thermal insulation, in normal operation modes the conditions of thermodynamic overheating of liquefied gas cannot be reached. Therefore, when minimum safe distances from stationary ground-based cylindrical thermally insulated tanks of liquefied natural gas are standardized, the scenario of a spontaneous breach of a leak-tightness of the internal container and a spill of full volume of stored product and BLEVE effect with the generation of a fireball must be prevented.