Wastage characteristics of welds of high-chrome steel heat transfer tube of steam generator; Micro-Leak and small leak sodium-mater reactions

Shimoyama, Kazuhito ; not registered; Usami, Masayuki; Tanabe, Hiromi; Yoshida, Eiichi; not registered

For the development of a once-through unit type steam generator for an FBR, materials having a high mechanical strength at elevated temperatures and high resistivity against stress corrosion cracking (scc) are needed as its heat transfer tubes. High-chrome ferritic steels such as Mod.9Cr-1Mo, 9cr-2Mo, and 9Cr-1Mo-Nb-V steel are considered to meet these requirements. As previously reported, there was not large difference of resistivity among these materials and it was confirmed that high-chrome ferritic steels were more wastage -resistant than the 2.25Cr-1Mo steel which is a representative ferritic steel as tube materials. Since wastage data of weld portion at which the initial leak is apt to occur had been insufficient in order to totally evaluate the wastage resistivity of the high-chrome ferritic steels wastage tests in the micro-leak and small leak ranges were conducted for the tube-tube weld point of Mod.9Cr-1Mo steel. Major results are as follows : (1)In the micro-leak tests, there are not large differences in the self-wastage resistivity between the weld and the base metal. And the wastage resistivity is independant of the location of the leak starting point (a weld metal, a bond of weld, or a heat affected zone). (2)In the small leak tests, there are not large differences in the wastage resistivity between the weld and the base material. In the results, the empirical formula of wastage rate that derived from the base materials of the high-chrome ferritic steel can also be applied to the heat transfer tubes including the weld materials.