Testing and evaluating of structural materials for CSP applications

The next generation of Concentrated Solar Power (CSP) plants are expected to operate at higher temperatures than those currently in use, for improved efficiency and reduced cost of power generation. Degradation mechanisms that threaten structural alloys at elevated temperatures include thermal fatigue and creep as general threats to all sections of the system. In addition, specific degradation mechanisms caused by liquid sodium as the preferred heat transfer fluid material, eutectic salts or metals as Phase Change Material (PCM) in the storage and supercritical CO2 Brayton cycle in the generator threaten the plant. These threatening mechanisms have been discussed in this paper with some ideas for testing and evaluation specific to each condition

Corrosion of stainless steel 316 in eutectic molten salts for thermal energy storage

Stainless steel 316 was examined for compatibility with the eutectic mixtures of NaCl + Na2CO3 and NaCl + Na2SO4 at 700 °C and Li2CO3 + K2CO3 + Na2CO3 at 450 °C in air for thermal energy storage. Electrochemical measurements combined with advanced microscopy and microanalysis techniques were employed. NaCl + Na2CO3 was found as the most aggressive salt at 700 °C. The attack morphology on the surface was uniform corrosion with no localized degradation at 450 °C. Microscopy observations showed grain boundary oxidative attack as the primary corrosion mechanism at 700 °C with depletion of alloying elements from grain boundaries