Liquid-metal corrosion loop tests

The mechanism of temperature-gradient mass transfer is illustrated in Figure 1. This type of corrosion may be studied in a thermal-convection loop test (Figure 2). Because the solubility of most container materials in a particular liquid metal is temperature-dependent, solution in the hot section and subsequent deposition in a cooler section may occur. The results of this type of corrosion may be seen in Figures 3 and 4. 

Because forced-convection loops are costly to construct, it is now the usual practice to operate the loops as permanent testing facilities, with corrosion specimens cycled in and out of the facility. Test specimens of various materials are generally placed in the hot leg, and the effect of the flowing liquid on the specimens is determined from changes in weight, dimensions, composition, mechanical properties, and microstructure. Such an approach yields data on maximum corrosion rates as a function of temperature and liquid metal flow rate. Any attempt to elucidate corrosion mechanisms, however, is hampered by the inability to interrelate dissolution and deposition processes. 

It should be noted that, since the leading concept of the fusion power-plant system with V-alloys uses liquid Li as coolant and tritium-breeder, the majority of the corrosion and compatibility studies have been oriented to those with liquid Li. Although V is susceptible to oxidation at high temperature, oxidation is not an issue in liquid Li because of high O affinity of Li. A corrosion test using a mono-metallic thermal convection Li loop made of V-4Cr-4Ti pipes, conducted at 700°C for 2355 h, showed the corrosion loss rate corresponded to only <1 pm/year [26]. 

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