Liquid-metal corrosion tests

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. 

Testing procedures for liquid-metal corrosion are given in Chapter 19. 

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 contrast to aqueous corrosion typically involving loss of electrons from the dissolving metal, liquid metal corrosion is generally considered to proceed by simple solution mechanisms. The principal variables affecting corrosion in a liquid metal system are temperature or temperature range or cycling, elements present, area-to-volume ratio, purity, flow velocity, surface condition, and microstructure. In reactor applications, the neutron flux may be an additional factor. In combination, these variables produce enough complexity so that in the present state of the art, it is rarely possible to make confident predictions about the performance of a previously untried systan. Empirical tests are usually required. 

Section V on Testing in Environments (H. Hack, Section Editor) includes chapters on outdoor and indoor atmospheres, seawater, fresh water, soils, concrete, industrial waters, industrial chemical, petroleum, high-temperature gases, organic liquids, molten salts, liquid metals, corrosion inhibitors, in-vivo, and microbiological effects. Each chapter provides a descriptive overview of the environment and factors and variables affecting corrosion rates and mechanisms. 

Corrosion of metals corrosion testing in liquids under laboratory conditions without mechanical stress) (in German) Beuth Verlag GmbH, Berlin... 

Corrosion testing in liquid metals and fused salts 19 84... 

Corrosion Testing in Liquid Metals and Fused Salts ... 

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. 

Static test results may be evaluated by measurement of change of mass or section thickness, but metallographic and X-ray examination to determine the nature and extent of attack are of greater value because difficulty can be encountered in removing adherent layers of solidified corrodent from the surface of the specimen on completion of the exposure, particularly where irregular attack has occurred. Changes in the corrodent, ascertained by chemical analysis, are often of considerable value also. In view of the low solubility of many construction materials in liquid metals and salts, changes in mass or section thickness should be evaluated cautiously. A limited volume of liquid metal could become saturated early in the test and the reaction would thus be stifled when only a small corrosion loss... 

Shipment and Storage. The weight per gallon is 5.6 kg. MSG is shipped and stored in 55-gallon (0.208 m3) steel drums or 5-gallon (0.02 m3) steel pails with a polyethylene liner. Anhydrous MSC is also corrosive toward titanium, titanium—palladium, and zirconium as measured in metal strip tests at 50°C. It is classified as a corrosive liquid. 

Some cadmium-plated bolts and nuts were purchased and installed as a test in the plant. More bolts were purchased and eventually some of the cadmium-plated bolts were installed on the outlet piping flanges of a cracking furnace. The high temperature outlet flanges on the furnace started to weep a bit. An experienced, intelligent pipefitter attempted to snug up a few bolts and the nuts crumbled. (The cause of the failure was later determined to be due to corrosion phenomena called liquid metal embrittlement. )... 

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 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. 

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