Rational Structure Design And Finite Element Analysis Of A Vertical Cryogenic Storage Tank With A Large Opening

In this thesis, the numerical analysis was carried out on a vertical cryogenic storage tank with a large opening. In order to eliminate convective heat transfer, the vertical cryogenic storage tank was constructed as jacket structure in which vacuum was produced between inner and outer cylinder shells. Thus, strength failure and external pressure instability are the main failure modes. At the same time, due to the process requirement, a large opening is arranged at the top of the inner and outer cylinders, and also designed as a double shell structure. In addition, both the inner and outer cylinders are strengthened with reinforcing ribs. Because of the complex structure, general calculation or design by rules cannot provide accurate design of the structure. Therefore, in this thesis, finite element models of the vertical cryogenic storage tank with different opening structures were established with ANSYS software. The structure strength under the internal pressure and stability under the external pressure together with the reinforcement effects of ribs were investigated and assessed conforming to JB4732-1995 Steel pressure vessels —Design by analysis. The following are the main work and conclusions:(1)When the large opening is eccentrically arranged without any reinforcing ribs, very large stress concentration occurs at the connection area between heads and the large opening tube. Strength assessment finds that the local stress is much larger than the allowable stress. Meanwhile, the inner cylinder deforms biasly as a result of the asymmetric structure and unbalance of pressure in the jacket produced by the eccentric opening.(2) When the large opening is eccentrically arranged with reinforcing ribs on the heads, the general stress intensities and deformations are significantly reduced, meaning that the reinforcing ribs do have large reinforcement effects. However, it is found that after categorization, the local stress still cannot meet the strength requirements based on JB4732-1995 Steel pressure vessels —Design by analysis regardless of the forms and size of the reinforcing ribs. The reason is that when the large opening is eccentrically arranged, the high stress area caused by the opening overlaps with the high stress area at the head knuckle region and thus yields a very large local stress, and as at the knuckle region, effective reinforcement is hard to carried out. In addition, as the structure is asymmetric because of the large opening, the inner cylinder deforms biasly upon forming vacuum in the jacket, which accentuates the stress concentration at the tube connection area.(3) When the large opening is eccentrically arranged, although it may be convenient to operate, the local stress is too large. To ensure safety operation, the large opening should be relocated. It turns out that when the opening is centrically located with arranging some reinforcing ribs, the whole equipment meets the strength requirements according to JB4732-1995 Steel pressure vessels —Design by analysis. This result should be considered in the design of the vertical cryogenic storage tank with a large opening.(4) Stability analysis was also performed on the outer cylinder of the tank when the large opening is centrically located, including general calculation with design by rules and numerical simulation with eigenvalue analysis. The allowable external pressure was obtained and assessment results show that the equipment will not buckle under the normal external pressure.