# Dynamic Corrosion Test Using LiNO3 Containing Molten Salt for CSP Applications
## 1 Introduction  
According to the International Energy Agency (IEA) [1], concentrated solar power (CSP) plant capacity is expected to grow 87% (4.3 GW) over the forecast period of 2018-2023, which is a 32% increase compared to 2012-2017. China leads the production with 1.9 GW, followed by 1 GW from projects that receive multilateral development bank support in Morocco and South Africa, 1 GW in the Middle East, and 300 MW each in Australia and Chile. Spain and the United States, the two countries with the most installed capacity, are not expected to commission projects over the forecast period. Therefore, China is expected to overtake the United States to have the second-largest CSP capacity installed by 2023. Recent auction results indicate significant cost-reduction potential. But technology risk, restricted access to financing, long project lead-time, and market designs that do not value thermal energy storage (TES) continue to challenge CSP deployment [1]. The cost reduction in CSP technology has been one of the main objectives, especially in the storage block. In this direction, different additives have been proposed in order to improve the thermal properties in the solar salt (60 wt.% NaNO3 + 40 wt.% KNO3), as NaNO2, Ca(NO3)2 and LiNO3 [2; 3; 4; 5; 6]. Table 1 shows the main thermal properties obtained with these additions compared to solar salt. Since NaNO\({}_{2}\) needs to use an inert atmosphere to avoid the oxidation of NaNO\({}_{2}\) to NaNO\({}_{3}\) as well as the early thermal decomposition of Ca(NO\({}_{3}\))\({}_{2}\) mixture beyond 520 \({}^{\circ}\)C [7], LiNO\({}_{3}\) has been proposed as one of the main interesting additives to TES materials based on nitrate salts. As shown in Table 1, the addition of LiNO\({}_{3}\) could reduce the melting points of these molten salt mixtures to 130 \({}^{\circ}\)C obtaining a work temperature range around 465 \({}^{\circ}\)C [6]. This reduction in the melting point temperature can improve the parasitic consumption due to freezing protection systems, also in addition to the effect of increasing the current field temperature limitation and the impact on plant capacity factor, therefore, an interesting cost reduction could be obtained in the CSP plant economic balance related with the storage block. The thermal properties obtained by adding LiNO\({}_{3}\) to solar salt have been studied by several researchers [3; 8; 9; 10], including also the corrosive behavior of these mixtures in commercial alloys at the storage target temperatures in parabolic trough and central tower power plants, 390 \({}^{\circ}\)C and 550 \({}^{\circ}\)C, respectively. Table 2 shows the main results obtained in carbon and stainless steels. The selection of the materials for tanks, piping and other components is made taking into account the potential corrosion and the operation temperature. In general, stainless steel (AISI 347) is selected for zones where the salt temperature could exceed 400 \({}^{\circ}\)C, whereas the rest of pipes and tanks are made of carbon steel (A516). Nevertheless, there is a lack of knowledge about the compatibility of molten salts with common container materials under dynamic conditions. Corrosion is expected to be enhanced in dynamic conditions, due to continuous renewal of the molten salt layer in contact with the metal surface, or the erosion of the passivating oxide layer. In this direction, [PERSON] et al. [14] reported the higher corrosion rate comparing dynamic and static set ups, using a molten salt pilot plant with a LiNO\({}_{3}\) ternary molten salt in contact with AISI 316, using the composition proposed in this study. The major corrosion test reported in the literature are focused on the study of the effect of the chloride content as well as the impurity influence in this process, using the binary solar salt (60 wt.% NaNO\({}_{3}\) + 40 wt.% KNO\({}_{3}\)). [PERSON] et al.