Thermomechanical testing under operating conditions of A516Gr70 used for CSP storage tanks

Abstract

Thermal energy storage (TES) in molten salts is the storage dominating technology in solar power applications today. In two-tank molten salt storage systems energy density ranges from 30 to 70 kW h/m3 are achievable. The salt material used is a binary system, composed of 60% NaNO3 and 40% KNO3. In the 8 MWhth pilot plant built and tested by Abengoa, the storage tanks were made of steel A516Gr.70 using the Appendix M of code API 650 for their design. A specific testing device was developed to evaluate thermo-mechanical properties, and a study was conducted in order to evaluate tensile properties of A516Gr.70 specimens under operation conditions for the hot tank at the pilot plant that is in contact with molten salts at 380 °C. Results confirmed the outcomes of the work: the reduction of the yield limit, elongation before fracture, and Young modulus at 380 °C after having been 5 min immersed in molten salts. Moreover, after a creep-test simulating operating 7 days conditions during, an additional reduction of the yield limit was measured.

The research leading to these results has received funding from Spanish government (Fondo tecnológico IDI-20090393, ConSOLida CENIT 2008-1005). The work is partially funded by the Spanish government (ENE2011-28269-C03-02, ENE2011-22722, ENE2015-64117-C5-1-R, and ENE2015-64117-C5-2-R). The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° PIRSES-GA-2013-610692 (INNOSTORAGE) and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The authors would like to thank the Catalan Government for the quality accreditation given to their research groups GREA (2014 SGR 123) and research group DIOPMA (2014 SGR 1543). Dr. Camila Barreneche would like to thank Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva FJCI-2014-22886.