Corrosion tests carried out in Pb-17Li in both capsules and a convection loop (hot leg temperature 768 K, cold leg temperature 748 K, flow rate 10 mm/s) have shown that Type 316 stainless steel undergoes almost complete loss of Ni and Mn, and extensive loss of Cr to form a porous ferritic zone. Ferritic zone depths measured on the loop samples exposed between 1000 and 4000 h were in good agreement with previous data. Some evidence was found for the interaction of chromium with oxygen dissolved in Pb-17Li. Examination of the cold leg samples revealed deposition products of iron and chromium but no deposits containing nickels were observed. These observations were rationalised in terms of recent measurements of the solubilities of metals in Pb-17Li.
Corrosion tests carried out in Pb-17Li, with and without added oxygen, have shown that oxygen enhances the corrosion of 316 steel by increasing the depth of the ferritic corrosion layer and the extent of chromium depletion within the layer. Tests using Pb-Li alloys with compositions between Pb-17Li and Pb-11Li and in pure Pb showed no change in the depth of the ferritic zone with composition of the alloys but a significant increase for pure Pb. Measurements of the solubility of nickel in Pb-17Li and Pb-10Li showed the solubility to be similar for both compositions and to be much less than that previously measured in pure Pb. The solubility may be expressed by the equations: log10S(wppm) = 4.832−981,2/T(K) for Pb-17Li, log10S(wppm) = 5.148−1162/T(K) for Pb-10Li.
The results of corrosion studies on 316 stainless steel in liquid lithium, carried out in both static capsules and thermal convection loops, are reported. The penetration of 316 steel by lithium is shown to be directly related to the nitrogen content of the lithium in capsule tests. Data on the nitrogen level in lithium required for the formation of Li9CrN5 is given. The deposition of nickel and the formation of carbides from lithium of high carbon level have been studied in loop tests. Manganese depletion and deposition is thought to take place by a solution mechanism, rather than by the formation of a ternary nitride.
