Study of corrosion by Dynamic Gravimetric Analysis (DGA) methodology. Influence of chloride content in solar salt

Abstract

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 minimize 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.

Dynamic corrosion tests comparison: Dynamic reactor vs high temperature pilot plant scale setup for Chilean LiNO3 containing molten salt

“…In order to minimise the handling of the sample, a new methodology (Dynamic Gravimetric Analysis, DGA) has been developed at University of Barcelona [11]. The samples are hung on a platinum wire and fully submerged into a glass beaker containing the chemical cleaning solution for 2 h, thus allowing the rust to be cleaned during this time.…”

A eutectic salt high temperature phase change material: Thermal stability and corrosion of SS316 with respect to thermal cycling

“…The effect of corrosion was determined by measuring the amount of corrosion products formed on the surface of the SS316 sample, by using the dynamic gravimetric analysis (DGA) [8]. The traditional methods proposed by the ASTM Standard G1-03 [25] requires intensive sample manipulation, while the DGA technique reduces human handling when determining the corrosion rate, and improves the accuracy of results.…”

“…Sulphuric acid at low concentrations also makes the oxide layer become less compact and thus facilitates the oxide descaling process without removing the corrosion layer itself. Following this procedure [8], the coupon was then hung from an analytical balance (Ohaus Explorer) with an accuracy of ± 0.1 mg and submerged in the cleaning solution, allowing the dissolution of the formed scales. The balance was connected to a computer (software RealTerm: Serial Capture Programme 2.0.0.43) which recorded the weight of the coupon every second, providing a real-time weight loss of the descaling process.…”

“…Corrosion mechanisms in molten salt are complex and highly dependent upon impurities, temperature, alloying elements and oxidant availability. Corrosion in molten salts generally proceeds in five steps: (1) oxidant dissolving into melt, (2) oxidant transport in melt, (3) corrosion reactions at salt/metal surface, (4) oxide scale dissolution into melt, and (5) preferential dissolution of soluble products [7].The majority of high temperature corrosion tests have focused on steel in the presence of molten nitrate salt and the effect of impurities under isothermal conditions [8][9][10].…”

The Role of Innovation in Industry Product Deployment: Developing Thermal Energy Storage for Concentrated Solar Power

“…• The second stage was the testing at pilot plant at the University of Lleida, where a 0.3 MWht pilot plant was built to carry out a deep characterisation of the molten salt properties [38]. At the same time research was carried out at the University of Barcelona, where thermomechanical testing under operating conditions of container materials such as A516Gr70 were developed [39], and at Inasmet, where corrosion tests were performed [40].…”