Microstructure and stress corrosion cracking behavior of Alloy 690TT steam generator tubes with internal bulge defect

Abstract

Alloy 690TT tube samples with different sizes of internal bulge defect (IBD) are prepared by actual hydraulic tube expansion in field and their microstructure and stress corrosion cracking (SCC) behavior are studied in detail. The hardening level and residual strain increase as moving from the original area of the tube to the bulged area, and so as for the increasing of deformation sizes. Corrosion test with a duration of 2000 h shows that the IBD area has higher SCC sensitivity than the original tube. In addition, IBD with larger size is more sensitive to SCC.