Liquid sodium corrosion testing

Because sodium, which is liquid between about 100°C and 881°C, has excellent properties as a heat-transfer medium, with a viscosity comparable with that of water and superior heat conductivity , much attention has been paid to liquid sodium corrosion testing of metal and alloys. Indeed, ASTM have issued a Standard Practice which can be used for determination... 

Test method for determining the susceptibility to intergranular corrosion of 5XXX series aluminium alloys by mass loss after exposure to nitric acid (NAMLT test) Practice for liquid sodium corrosion testing of metals and alloys... 

In liquid metal corrosion testing, aU of these variables should be recognized and addressed. It is not possible in this chapter to provide a full account of the ramifications of each of them. Instead, one or two of the more important ones have been selected for illustrative purposes in some cases, these illustrations are presented as specific examples of behavior in liquid sodium or liquid lithium. Numerous references are cited from the literature for information on the variables not described in detail. 

Sodium, potassium and sodium-potassium alloys Liquid sodium, potassium or alloys of these elements have little effect on niobium at temperatures up to 1 000°but oxygen contamination of sodium causes an increase in corrosionSodium does not alloy with niobium . In mass transfer tests, niobium exposed to sodium at 600°C exhibited a corrosion rate of approximately 1 mgcm d . However, in hot trapped sodium at 550°C no change of any kind was observed after 1 070 h . 

The effect of carbon on the corrosion of stainless steels in liquid sodium depends upon the test conditions and the composition of the steels . Stabilised stainless steels tend to pick up carbon from sodium, leading to a degree of carburisation which corresponds to the carbon activity in the liquid metal. Conversely, unstabilised stainless steels suffer slight decarburisation when exposed to very pure sodium. The decarburisation may promote corrosion in the surface region of the material and, under creep rupture conditions, can lead to cavity formation at the grain boundaries and decreased strength. 

Vanadium is resistant to attack by hydrochloric or dilute sulfuric acid and to alkali solutions. It is also quite resistant to corrosion by seawater but is reactive toward nitric, hydrofluoric, or concentrated sulfuric acids. Galvanic corrosion tests mn in simulated seawater indicate that vanadium is anodic with respect to stainless steel and copper but cathodic to aluminum and magnesium. Vanadium exhibits corrosion resistance to liquid metals, eg, bismuth and low oxygen sodium. 

The DOT test differs from the FHSA test principally in that the exposure period is 4 hours instead of 24 hours, and dry substances are tested dry - they are not moistened with saline solution. Consequently, this test is less sensitive to small differences in the activity of compounds, but it provides a more realistic model of accidental human exposure. The data in Table VI. indicates that the breakpoint between irritant and corrosive liquid sodium silicates occurs between 1.6 and 1.8 ratio, but it is also probably influenced by the concentration of the solutions. 

J-L. Courouau, F. Balbaud-Celerier, V. Lorentz, Th. Dufienoy, Corrosion by liquid sodium of materials for sodium fast reactors the CORRONa testing device. Proceedings of ICAPP ll, Paper 11152, Nice, France, May 2-5, 2011. 

For the sake of understanding and prediction, some laboratory corrosion tests of 316L(N) in liquid sodium are reported in Refs. [24,37]. In a dedicated device [38], the steel was exposed to static sodium at 550°C with about 40 ppm oxygen up to 5000 h. This oxygen content is much higher than the SFR requirement it is only aimed at scanning the different corrosion mechanisms at the laboratory scale. The observations of the corroded specimens permit to identify several phenomena (Fig. 17.13) ... 

Finally, for these temperatures and oxygen contents, there is a low dissolution of the steel, confirmed by the analysis of the liquid sodium of the loop showing a slight increase in the metaUic fractions. Longer tests need to be carried out to precisely measure the corrosion kinetics in these laboratory conditions. 

The corrosion resistance of various metals and alloys in high-temperature liquid lithium is shown in Figure 11. Unfortunately, lithium is much more corrosive than sodium. Consequently, it will be impossible to take full advantage of its many attractive heat-transfer properties until a satisfactory container material is found. The most corrosion-resistant pure metals in a static isothermal system are molybdenum, niobium, tantalum, tungsten, and iron. Of the commercially available structural materials, no alloys tested to date have had satisfacto corrosion resistance at a temperature above 1400 F. for extended time periods in systems where temperature differentials exist. Even though iron has good resistance in static isothermal lithium, iron and iron-base alloys suffer from mass trans-... 

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