Corrosion Behavior of 347H Stainless Steel in NaCl-KCl-MgCl2 Molten Salt: Vapor, Liquid, and Interface Comparison

TL;DR

This study examines how 347H stainless steel corrodes in different parts of a molten chloride salt system, finding that vapor exposure causes the most damage.

Contribution

The paper identifies distinct corrosion mechanisms in vapor, liquid, and interface conditions of molten salt for 347H stainless steel.

Findings

Corrosion was most severe in molten salt vapor due to HCl steam reacting with Fe and Cr.

At the interface, liquid Mg reduced corrosion by depositing Fe and Cr onto the metal surface.

Molten salt immersion caused minimal damage due to Mg's purification effect.

Abstract

The suitability of 347H stainless steel (SS347H) for chloride salt environments is critical in selecting materials for next-generation concentrated solar power (CSP) systems. This study investigated the corrosion behavior of SS347H in a ton-scale purification system with continuously flowing chloride salt under three conditions: exposure to NaCl-KCl-MgCl2 molten salt vapor, immersion in molten salt, and at the molten salt surface interface. Results revealed that corrosion was most severe in the molten salt vapor, where HCl steam facilitated Cl− reactions with Fe and Cr in the metal, causing dissolution and forming deep corrosion pits. At the interface, liquid Mg triggered displacement reactions with Fe2+/Cr2+ ions in the salt, depositing Fe and Cr onto the surface, which reduced corrosion intensity. Within the molten salt, Mg’s purification effect minimized impurity-induced corrosion, resulting in the least damage. In all cases, the primary corrosion mechanism involves the dissolution of Fe and Cr, with the formation of minor MgO. These insights provide valuable guidance for applying 347H stainless steel in chloride salt environments.

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