Modeling weld-induced residual stress and distortion in large-scale 347H stainless steel molten salt storage tank floors

Weld-induced residual stress and distortion in 347H stainless steel molten salt storage tank floor can significantly compromise structural reliability. This study developed a full-scale thermo-elastic–plastic shell element framework to evaluate distributions of residual stresses and distortions within tank floors as a function of diameter, ranging from 24 m to 39.6 m with a 7 mm plate thickness. A three-step modeling methodology was implemented: (1) a small-scale high-fidelity solid element model, (2) heat source simplification and calibration for shell element model, and (3) the full-scale shell element model. The material database was previously validated using neutron diffraction measurements. Comparative analysis suggests that the shell-element approach with a simplified one-pass weld is a computationally efficient and suitable methodology for full-scale floor welding simulation. However, for investigations requiring high-resolution through-thickness gradients and localized multi-axial stress states, the solid model remains necessary. Results show that peak longitudinal stresses consistently occur within the long-edge welds, increasing from 641 MPa in the 24 m floor to 687 MPa in the 39.6 m diameter assembly. Both the tank size and weld plate layout along with constraint design were found to play a critical role in distortion. Maximum displacements up to 158.5 mm in the normal direction were developed in the floor of these large tanks.