Optimum Design And Study Of Large Scale LNG Tank

Because of large volume, quality, complex structure, higher security requirements and investment, large scale LNG tank has no any specific design standard in domestic. An inner tank material selection, design standard discussion and structure optimization of a large scale LNG tank are studied in the thesis. According to low temperature properties of LNG, Ni9 steel is selected as a suitable inner tank material. The thesis summarizes chemical composition, mechanical properties and capacity of Ni9 steel at home and abroad and analyzes its weld abilities. Based on design codes related to a large scale storage tank, such as EN 14620, API 620/650, JIS B8501 and.etc, the thesis gives calculation methods of wall thickness, design methods of tank bottom annular plate, sketch plate and tank roof. In addition, the wall thickness of 1.0×104, 5.0×104,1.0×105and 1.5×105m3 LNG tank are calculated and plotted into curves using software ORIGN. By comparing analysis, calculation results of EN 14620 are the most economy therefore a design code that suits for our country is specified referring to the standards. Three kinds of calculation wall thickness methods are compiled into programs using VC++. Compared simulation results with calculation results, error is very small and programming correctness is verified. A pre-stressed concrete structure is a major development tendency of a large scale LNG storage tank and an external tank is studied. The height and diameter of an inner tank are optimized and D/H=8/3 is conducted somewhat reasonably. Take a 160,000 m3 LNG tank in Fujian as example, structural and thermal stress are analyzed by software ANSYS. The results show that a large angle welded seam and different lap siding joints exist stress concentration phenomenon. Using ANSYS a structure and parameter optimization of wall plate lap joints are done and some useful conclusions are drawn that stress concentration factor is minimum when tapered segment length L is 50mm and cone angleαis 78.667°and also used in other large scale cryogenic storage tanks. The thesis has some reference value for domestic design and research of a large LNG tank.