Effect of Grain Size on Corrosion Fatigue Behaviors of Primary Coolant Pipes of Nuclear Power Plants

Abstract

Corrosion fatigue is one of the most important failure modes of primary coolant pipe used in nuclear power plant, due to the thermal cyclic stress caused by a variety of start-up and shutdown as well as transients when severed in the high temperature and pressure water environment. And 316LN stainless steel is one of the main materials used in pressurized water reactor in nuclear power plant. The mechanisms of fatigue crack initiation and propagation were elucidated by investigating the composition properties of oxide films formed in simulated service environment. The effects of grain size on the fatigue life and crack initiation mechanism of 316LN stainless steel in 320°C water environment were also investigated. The results indicated that the specimens with fine grains (30μm) own the longest fatigue lives than those with intermediate (80μm) and coarse grains (210μm). The fatigue stress amplitudes of the specimens increased with the grain refinement, although the fatigue lives of the specimens with intermediate and coarse grains were close. Fatigue cracks were often initiated at the persistent slip bands on the surfaces of the specimens with intermediate and coarse grains, while it was not easy to be initiated on the fine grain specimens. Finally, combined with the experimental results and the actual production of industry, a suggestion for the production of the primary coolant pipe is put forward.