Effects of Cl^- and Cu²⁺ on Stress Corrosion Cracking of Alloy 690

The effects of Cl^- and Cu²⁺ on the stress corrosion cracking（SCC） of Alloy 690 made in China were investigated using the slow strain rate tensile（SSRT） test. The surface and cross section morphologies of tested specimens, as well as the fractographs, were observed by 3D measuring laser microscope and SEM, respectively. It is found that the SCC resistance of Alloy 690 decreases evidently in the solutions containing 100mg/L Cl^- and 1000mg/L Cu²⁺. Many corrosion pits appear in the surface of the specimens and there are SCC initiations on the bottom of the pits. Moreover, SEM fractographs show that it is typical intergranular fracture. The observations of texted specimens are consistent with SSRT results, indicating that, it is the combined effect of both Cl^- and Cu²⁺ that brings about SCC of Alloy 690. The mechanism of combined effect is discussed briefly.