Thermal Stress Analysis Of LNG Storage Tank During Pre-cooling Process

The pre-cooling process is an operation step that must be carried out before the LNG storage tank is put into production.Improper operation in the pre-cooling process may lead to the structural damage of the LNG storage tank.This paper takes a 2×10⁴m3bimetallic full-containment LNG storage tank as an example,uses ANSYS workbench software to establish a three-dimensional solid model,simulates and calculates the thermal stress of the tank during the pre-cooling process,analyzes the effects of different temperature drop rates and temperature gradients on the thermal stress and deformation of the inner tank wall,inner tank bottom,anchor belt and outer tank,summarizes the relationship between temperature gradient and thermal stress distribution,and determines the location of thermal stress concentration during the pre-cooling process;analyzes the thermal stress and deformation of the connection between the inlet pipe and the tank top under different pre-cooling process schemes,and checks its safety.The calculation results show that:The temperature drop rate has little effect on the maximum thermal stress of the inner tank,while the temperature gradient is the main factor;The greater the temperature gradient at the lower part of the tank wall,the greater the thermal stress of the tank wall,when the temperature gradient in the0-2m area of the lower part of the tank wall reaches 30°C,the thermal stress of the tank wall reaches 93.18MPa;The greater the temperature gradient at the edge of the tank bottom,the greater the maximum thermal stress of the tank,when the temperature gradient in the area with 12-19m radius of the tank bottom reaches 30°C,the maximum thermal stress of the tank wall reaches 123.89MPa;When there is no temperature gradient,the thermal stress of the inner tank wall is concentrated at the welding position between the tank wall and the anchor belt,when there is a temperature gradient in the inner tank,the thermal stress of the tank wall is concentrated at the height of 45mm at the lower part of the tank wall;Under the two pre-cooling schemes of LN₂ pre-cooling and LNG pre-cooling,the maximum thermal stress of the connection structure between the inlet pipe and the tank top is concentrated at the connection between the rib plate and the ring plate at the upper end of the annular tube,which are 96.79MPa and84.29MPa respectively.According to the actual pre-cooling data,the thermal stress and deformation of the storage tank are analyzed,and the optimization suggestions for the worksite pre-cooling operation are put forward according to the thermal stress analysis results.