Thermo-mechanical behavior of stainless-clad bimetallic steel-concrete thermal energy storage unit during initial charging

Concrete cracking induced by significant thermal expansion mismatch between encased stainless steel pipes and surrounding concrete remains a critical barrier limiting the application of concrete-based Thermal Energy Storage (TES) systems in high-temperature scenarios. To address this issue, this study proposes a novel TES unit design utilizing Stainless-Clad (SC) bimetallic steel heat-exchanger pipes, where an inner stainless steel cladding provides corrosion resistance against solar salt and an outer alloy steel substrate provides load-carrying capacity and mitigates pipe-concrete thermal expansion mismatch. Numerical simulations were performed to evaluate the thermo-mechanical behavior and feasibility of the TES unit during initial charging. Results showed that the concrete cracking induced by pipe-concrete thermal expansion mismatch could be effectively mitigated by adopting SC bimetallic steel pipes, although cracks caused by concrete internal temperature gradients persist. Meanwhile, the cladding in the SC pipe satisfied the conservative shakedown criteria, while the substrate exceeded the limit. The interfacial shear stress between the two layers consistently remained below the shear strength. The incorporation of an outer steel jacket provided a pronounced confinement effect that effectively restrained concrete cracking, with the degree of confinement increasing as the jacket thickness and the friction coefficient increased. Compared with a conventional concrete-based TES unit, the proposed design reduced the unit energy storage cost by 42.2%, demonstrating its favorable economic performance.