Corrosion Fatigue Behavior of 316LN Stainless Steel Hollow Specimen in High-Temperature Pressurized Water

Environmentally assisted fatigue is an important factor in the design, safety review, and life management of key components used in nuclear power plants. Piping systems, valves, and small-bore pipes are sensitive to fatigue damage in nuclear power plants. In this work, a kind of hollow specimen for fatigue testing was designed. High-temperature pressurized water flows through the inside of the specimen, and the outside of the specimen is exposed to air. The corrosion fatigue behavior of 316LN stainless steel was investigated in high-temperature pressurized water using the hollow specimens. The experimental results show that the fatigue strength of 316LN stainless steel was reduced in a high-temperature pressurized water environment, and its fatigue life decreased with decreasing strain rate. The fatigue lives obtained by hollow and standard round bar specimens were comparable, which indicate that it is reasonable and feasible to use the hollow specimen to study the environmentally assisted fatigue performance of nuclear-grade structural materials in a high-temperature pressurized water environment. At low strain rate conditions, the fatigue crack initiation region is a typical fan-shaped pattern with quasi-cleavage cracking characteristics. The fatigue crack growth region is characterized by fatigue striation, and the environmental effects are highly significant in the stage of fatigue crack initiation. The fatigue damage mechanism of 316LN stainless steel in a high-temperature pressurized water environment is also discussed.