Stress Analysis And Structural Optimization Of A Typical Cryogenic Pressure Vessel Pipes

The cryogenic vessel pipes are usually installed at room temperature and works at low temperature, the difference of the two temperatures could be over 200℃, which can lead to a large temperature stress.Without a proper design or manufacture,higher stress in the pipes may be caused which would affect the normal operation of the vessel. According to the current design codes of cryogenic vessels, no accurate methods and guides about the design of pipes could be used. Based on this, a typical cryogenic vessel which is used in a company was acted as the research object; numerical analysis was adopted to analyze the stress distribution of the top and the bottom inlet pipes and the improper design of the pipes was found. Optimization method which was used to reduce the pipe stress was proposed.It was concluded that with proper design of the π compensator, the stress which is caused by the connection of the pipes and vessels could be reduced and the safety of cryogenic vessels be improved.Main research contents and achievements of this work are as follows:(l)With finite element method, stress distribution in the top and bottom inlet pipes of the typical vertical cryogenic vessel were studied. The research indicated that local stress in the top and bottom inlet pipes were excessive due to the improper pipeline arrangement, therefore the inlet pipes’structure optimization was required.(2)The top and bottom inlet pipes of a vertical cryogenic vessel structure optimization design method was researched.The similar π compensator accorded with cryogenic vessel structure was proposed. Influence of the size parameters for the similar π compensator structure on stress distribution in pipes was studied with finite element method. Proper structure dimension of the similar π compensator was provided to reduce stress level in top longer and bottom shorted inlet pipes effectively.(3)The stress distribution of the connecting region between the head and the top pipe before and after the optimization was studied. It was concluded that the stress level of the connecting region of the head and the top inlet pipes obviously decrease after the optimization of the pipe structure. According to the path analysis at the place of maximum stress intensity, the membrane stress of the head under the top inlet pipe after optimization was 31% lower than that before optimization, and the membrane stress+bending stress was reduced by 40%.