Testing and Evaluating of Structural Materials for CSP Applications
Authors: Sarvghad Madjid , Will Geoffrey , Steinberg Theodore A 
Published: February 2020

The next generation of Concentrated Solar Power (CSP) plants are expected to operate at higher temperatures than those currently in use for improved efficiency [1]. A prerequisite for this is an improved compatibility between the materials used to construct the plant with environmental conditions. CSP systems use combinations of mirrors to concentrate the sun's light energy onto a receiver, which captures the energy and converts it into heat to generate electrical power [2, 3]. The cycle starts when the sunbeam is reflected onto the central receiver tower. The Heat Transfer Fluid (HTF) absorbs the thermal energy and carries it to the heat storage system. The thermal energy is then transferred through a heat exchanger (HE) to a superheated CO2 Brayton Cycle. The sCO2 then flows through a turbine which generates electricity. The cycle continues by recycling the sCO2 to the HE.
This study provides a brief review on evaluating degradation mechanisms that threaten structural alloys at elevated temperatures, Figure. 1. A comprehensive evaluation should consist of thermal fatigue and creep measurement. Corrosion as a result of the dissolution of alloying elements in the alloy by liquid sodium, as HTF material, and carburization or decarburization of the material need investigation [4, 5]. Liquid metal embrittlement (LME) caused by the penetration of sodium through grain boundaries and erosion due to the movement of liquid sodium in the system are also interesting to be studied [6, 7].
Eutectic salts or metals used as Phase Change Materials (PCM) in the storage are responsible for significant corrosion damage in the storage system. Mechanisms leading to corrosion by PCMs including oxidation, fluxing, de-alloying, impurities, thermal gradient and thermal cycling need more investigation [8-10]. Erosion due to the phase transformation from liquid to solid and vice versa is also important [11]. The susceptibility of sCO2 Brayton cycle to corrosion damage and erosion due to the flow of compressed hot gas in the system could be also considered for evaluation [12-14].
Figure captions

Figure.
1
Diagram showing common issues threatening structural materials at high temperatures in a CSP plant.

References
[1] Australian solar thermal research initiative (ASTRI), in, http://www.astri.org.au/ (accessed 6 June 2017).
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[3] K. Lovegrove, W.S. Csiro, 1 - Introduction to concentrating solar power (CSP) technology, in: K. Lovegrove, W. Stein (Eds.) Concentrating Solar Power Technology, Woodhead Publishing, 2012, pp. 3-15.
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[10] M. Sarvghad, G. Will, T.A. Steinberg, Corrosion of Inconel 601 in molten salts for thermal energy storage, Solar Energy Materials and Solar Cells, 172 (2017) 220-229.
[11] P.D. Myers, D.Y. Goswami, Thermal energy storage using chloride salts and their eutectics, Applied Thermal Engineering, 109 (2016) 889-900.
[12] F. Rouillard, F. Charton, G. Moine, Corrosion behavior of different metallic materials in supercritical carbon dioxide at 550°C and 250 bars, Corrosion, 67 (2011) 1-7.
[13] D.D. Fleming, A.M. Kruizenga, Identified corrosion and erosion mechanisms in SCO2 Brayton cycles, in, Sandia National Laboratories, 2014.
[14] D.D. Fleming, Corrosion and Erosion behavior in Supercritical CO2 power cycles, Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States), 2014.

Figure 1