Thermal–mechanical investigation of steel tanks for molten salt thermal energy storage

Molten salts play an important role in the renewable energy transition, serving as a thermal storage medium for concentrated solar power. This study presents a numerical investigation into the thermal and mechanical performance of a steel tank, of commercial size and setup, for molten salt storage. A 2D axisymmetric sequential thermal-stress model is developed. Input parameters are validated from the data of the Solar Two and Andasol plants. Thermal-mechanical stress analysis is performed considering the yield criterion and directionality. A sensitivity analysis is performed for inventory level, thermal gradient, friction coefficient, inventory temperature, and foundation stiffness. The transient operating condition with cyclic thermal and mechanical loads is simulated. Elastic–plastic analysis is performed to predict the damage location and residual stress during an operation cycle. From the stress analysis, mechanical stress as high as 268 MPa develops at the tank floor edge, which reduces to 197 MPa with the salt thermal load. At the center, a maximum stress of 157 MPa is generated, but only due to thermal loads. The temperature gradient and higher friction between the tank floor and foundation exacerbate the stress levels. These stresses exceed the yield strength limit of steel. During a cyclic transient operation, radial stress of 260 MPa develops at the floor edge where the elastic–plastic damage occurs. Residual stress of 82 MPa and 35 MPa is generated in radial and circumferential directions. The floor deforms plastically every operation cycle and can eventually crack. This study offers a comprehensive analysis of the tank’s thermal-mechanical behavior and offers insights to mitigate potential failures and optimize design. • Developed and validated a thermal-stress model of a commercial-size molten salt tank. • Analyzed stress on the tank floor, considering the yield criterion and directionality. • Studied stress on the tank floor under varying physical and operational parameters. • Simulated the tank’s transient operating condition. • Predicted elastic–plastic damage location and residual stress during a cyclic operation.