Fatigue Crack Growth Curve for Austenitic Stainless Steels in BWR Environment

Abstract

Fatigue crack growth data obtained in the simulated BWR water environment were analyzed to establish a formula for reference fatigue crack growth rate (FCGR) of austenitic stainless steels in BWR water. The effects of material, mechanical and environmental factors were taken into the reference curve, which was expressed as: da/dN=8.17×10−12⋅Tr0.5⋅ΔK3.0/(1−R)2.12(1≦ΔK≦50 MPam) where da/dN is fatigue crack growth rate in m/cycle, Tr is load rising time in seconds, ΔK is range (double amplitude) of K–value in MPam, and R is stress ratio. Tr=1 s if Tr<1 s, and Tr=1000 s if Tr cannot be defined. ΔK=Kmax−Kmin if R≧0.ΔK=Kmax if R<0.R=Kmin/Kmax. The proposed formula provides conservative FCGR at low stress ratio. Although only a few data show higher FCGR than that by proposed formula at high R, these data are located in a wide scatter range of FCGR and are regarded to be invalid. The proposed formula is going to be introduced in the Japanese Plant Operation and Maintenance Standard.