Molten Salt Corrosion
General Considerations
Molten salts, commonly used as heat transfer fluids in solar power plants, are essentially eutectic mixtures of sodium-potassium nitrates and the nature of these bonds provides strong ionic conditions and good chemical stability of the thermal solution against metal corrosion.
However, they are very hygroscopic and highly reactive with water molecules, which combined with its tend of thermal dissociation to form NOx, can produce high concentrated nitric acid and lead the system to a quite extreme acid attack.
The corrosion phenomenon can occur within a few hours and the effects are shown in the following photo. Make sure to dry the system after the pressure test and nitrogen purge is a must. We really mean it.
