Browsing by Author "Navas, M."
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- High-temperature corrosion performance of austenitic stainless steels type AISI 316L and AISI 321H, in molten solar saltPublication . Gomes, A.; Navas, M.; Uranga, N.; Paiva Luís, Teresa; Vasques, I. F.; Cunha Diamantino, TeresaABSTRACT: The corrosion rates of AISI 316L and AISI 321H austenitic stainless steel, immersed in a stagnant isothermal mixture of 60% NaNO3 and 40% KNO3 molten salt at 550 degrees C in atmospheric air are 8.6 and 9.0 mu m/yr, respectively. The corrosion mechanism was proposed by recording the weight changes of the steel coupons at different time intervals up to 3000 h, and by the characterization of multilayer oxide scales formed on the steel surface. Multilayers made of different oxides, mainly Fe2O3 and Fe3O4, are the principal scale products. At 3000 h, the thickness of the scale layer formed on AISI 321H (7.5 +/- 2.9 mu m) is slightly higher than the one formed at the AISI 316L (6.9 +/- 2.1 mu m). This small difference might reflect the partial spallation of the corrosion layer on AISI 321H, which is seen for times longer than 1000 h. A minimal change of the composition of the molten nitrate salt is observed in time and is predominantly due to the appearance of soluble chromate products and nitrite compounds (0.004 wt% and 1.4 wt% at 3000 h, respectively). The observed corrosion behaviour of these alloys shows that they are good candidate for usage as containers of molten nitrate salts in the thermal energy storage (TES) system for a CSP plant.
- Methodologies for assessing corrosion under dynamic conditions with molten salts in CSP/CST applications [Resumo]Publication . Cunha Diamantino, Teresa; Pedrosa, Fátima; Paiva Luís, Teresa; Figueira Vasques, Isabel; Gil, Mafalda; Navas, M.; Veca, E.ABSTRACT: Renewable energy implementation represents a key point in reversing global warming and climate change. In recent years, there has been an investment in Concentrated Solar Power (CSP) with Energy Storage (TES). Solar Salt is the most energy storage fluid optimized with a melting point of 223 °C and thermally stable up to about 550 °C. One of the most relevant problems in the use of fluids as thermal energy storage is their compatibility with construction materials (pipes, valves and tanks). This fact, combined with high temperatures (300-550 °C) makes the materials more susceptible to corrosion. Static immersion experiments are suited to screen and compare different candidate materials for molten salt applications (Fernández et al., 2019; Gomes et al. 2019), but corrosion rates derived from these experiments might differ significantly from the rates experienced in a real operating environment of a solar plant (Florian et al. 2021). There are currently no specific procedures for evaluating corrosion in molten salts under dynamic conditions, so it is important to develop more practical application conditions to validate methodologies and facilities. The main purpose of this work is to identify the suitable procedures to make a reproducible experimental dynamic corrosion test using an experimental set-up that can vary the velocity of molten salts over a wide range.