Effect of surface hemispherical dent depth on the microstructure evolution and stress corrosion cracking of heat transfer tubes in steam generator

The deformation mechanism and SCC behavior of alloy 690TT with dents are investigated. Dents lead to stress concentration and microstructure changes, increasing stress corrosion cracking (SCC) sensitivity. The deformation mechanism at dents is slip and twinning. The dent shoulder zone experiences oxidation due to the residual tensile stress, whereas the dent bottom zone induces SCC due to the stress concentration, exhibiting a symmetrical distribution of "splayed character". There is a critical threshold exists for dent depth that induces SCC, and the length of SCC cracks is positively correlated with dent depth in a power function.