Corrosion and Creep of Pressurized Stainless-Steel Tubes in Liquid Sodium at 873 and 973 K

Corrosion and creep behavior of tubes fabricated of three German stainless steels have been studied in a 10 000-h test in a sodium loop at 873 and 973 K. The measured weight losses depend on the temperature and the oxygen content of the sodium. The results of metallographic examinations with respect to the formation of ferritic surface layers are in agreement with element concentration profiles obtained by analytical techniques. The stabilized stainless steels pick up carbon from the sodium even at 973 K although the carbon content of the liquid metal is in the range of 0.1 to 0.2 ppm. The measured carburization corresponds to the thermochemical data of both the steels and the liquid alkali metal. The creep rates of two of the steels are not influenced by the sodium, and the third material in the cold-worked condition shows an acceleration of the creep by a factor of 5. The different behavior cannot be explained by structural or chemical changes in the materials due to the action of sodium. Future examinations will clarify the different effects of sodium on the behavior of the slightly different materials.