Design of Low Temperature Storage Tank Outer Tank and Metal Magnetic Memory Testing

[1] The design standard for the outer tank of LNG storage tanks for low-temperature storage tanks is API620. The outer tank of a single capacity tank only accommodates cold insulation materials and evaporated gases, and does not require the loading of low-temperature liquids. Therefore, the design requirements of the outer tank are similar to those of a regular room temperature storage tank. 1、 The low soil temperature, soil freezing, formation of ice layer in the soil (mainly for drilling soil), and thickening of the ice layer at the lower part of the LNG storage tank foundation can cause huge expansion forces. The lifting force generated by these expansion forces can harm the storage tank and its components, such as the storage tank with the pump suction port connected to the bottom of the tank. To prevent such hazards, the foundation of the storage tank generally adopts a foundation with a heating system or an elevated concrete pedestal. Due to the small total weight of the 20000m ³ low-temperature storage tank, the foundation of the natural growth gas storage tank adopts an elevated concrete pedestal, which is convenient for production operation and maintenance, and saves construction investment. 2、 The design of the outer tank should consider various aspects including construction, testing, replacement pre cooling, normal operation, and maintenance. The main external loads include: (1) internal pressure and vacuum partial pressure caused by operation; (2) The weight of the storage tank body and specified medium from an empty tank to a tank filled with high gas pressure; (3) Partial and complete support systems, as well as anticipated impacts from foundational conditions; (4) Additional loads generated by platform and ladder supports, as well as climate conditions such as excessive snow; (5) Wind load or specified seismic load; (6) Load caused by pipeline connection; (7) The weight of all insulation materials. [2] The metal magnetic memory testing technology for LNG storage tanks was proposed by Professor Dubov of Russia in the early 1990s and developed in the late 1990s as a new non-destructive testing and diagnostic method for detecting material stress concentration and fatigue damage. It is a non-destructive testing method that records and analyzes the distribution of the self leakage magnetic field generated in the stress concentration zone of the parts and equipment. Metal magnetic memory testing does not require specialized magnetization and demagnetization of the tested object, but utilizes the self magnetization of the component in the geomagnetic field, without the need for specialized cleaning of the component surface. The lifting effect of the probe has little effect and does not require coupling, making it particularly suitable for on-site use. It has suitable speed, excellent performance, and good detection sensitivity. This technology can not only detect stress concentration areas in natural growth gas storage tanks at a suitable speed to identify defects, but also determine the cause of damage development based on actual stress deformation information. It is a non-destructive detection method for early detection and diagnosis of defects in LNG storage tanks. However, due to the fact that metal magnetic memory detection technology is a new type of detection technology, many problems still need to be solved in terms of instrument use and practical applications.