Evaluation of Alternative Base Materials for Mitigation of Stress Relaxation Cracking in Thermal Energy Storage Tanks

Concentrating solar power (CSP) plants with thermal energy storage (TES) face challenges related to stress relaxation cracking (SRC) in molten hot salt tanks. While alloy 347H stainless steel (SS) is commonly employed due to its stress corrosion cracking (SCC) resistance and sufficient mechanical properties, it suffers from SRC in the weld region. This study explores alloy 1.4910 as a potential alternative, known for its superior creep strength and molten salt corrosion resistance. Thermomechanical testing using a Gleeble® 3500 physical simulator reveals promising results for alloy 1.4910 heat affected zone (HAZ) and 16-8-2 filler (ER16.8.2) fusion zone (FZ), with no cracking observed within a 22-hour test period at elevated temperatures ranging from 600 to 800°C and initial true stress conditions of 650 MPa (0.174 strain) for HAZ and 460 MPa (yield strength) for FZ. In contrast, alloy 347H HAZ and matching filler FZ experienced cracking within a few hours at 800°C. Metallurgical characterization and fractography are additionally conducted on cross welded 1.4910 samples with 16-8-2 filler and thermomechanical Gleeble® samples.