When a system for thermal energy storage (TES) is designed, many factors must be considered: storage time, dimensions, material to store heat, etc. Usually, molten salts are selected as TES materials because of their great thermal properties at high temperatures. When the whole TES system is going to be built, the material to be used for containing the thermal storage material becomes an important issue. It must have proper mechanical properties, withstand high temperatures and, above all, resist corrosion due to storage material, being in most of the cases, highly corrosive molten salt mixtures. To determine the corrosion on a metal plate, ASTM Standard-G1-03 procedure is usually applied, in which the corroded metal sample is submitted to several cycles including: attack by a chemical solution, washing, cleaning, drying, and weighing. In order to minimise the handling of the sample, a new methodology (Dynamic Gravimetric Analysis, DGA) has been developed and used to determine the corrosion produced in carbon steel A516Gr70 samples induced by different salt mixtures commonly used as molten salts containing different amounts of chloride, at working temperatures conditions. The results show that the higher is the content of chloride in molten salts the greater is the steel loss produced by corrosion and makes the corrosive kinetics to be highly increased when it is overtaken. The research leading to these results has received funding from Spanish government (Cdti-Fondo tecnológico IDI-20090393, ConSOLida Cdti-CENIT 2008-1005). The work is partially funded by the Spanish government (ENE2011-22722). The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under Grant agreement no 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 the research group DIOPMA (2014 SGR 1543). Dr. Camila Barreneche would like to thank Ministerio de Economía y Competitividad de España for her Grant Juan de la Cierva FJCI-2014-22886.