Alloy Optimization for PWR Steam Generator Heat-Transfer Tubing

摘要

Several materials have been used for heat-transfer tubing in light water reactor steam generators, including Type316 stainless steel (a few early units in the late 1960s), Alloy 600MA (mill annealed), Alloy 600TT (thermally treated), Alloy 800Mod, and the current preference, Alloy 690TT. The susceptibility of Alloy 600MA (Ni-16Cr-9Fe) to stress-corrosion cracking led to extensive corrosion studies to select and qualify a new material. Alloy 690TT (Ni-30Cr-10Fe) was chosen in the mid-1980s as the best heat-transfer tubing material, although Alloy 800Mod (Fe-33Ni-22Cr) remains an alternate choice. The basis for selecting Alloy 690TT is briefly summarized, along with a description of efforts to optimize tube manufacturing practices for corrosion resistance. Efforts at further optimization are described, including preconditioning of the tubing by some form of inner-diameter surface passivation in order to minimize corrosion product release rates upon initial service.