The effect of dissolved oxygen on fatigue behavior of Alloy 690 steam generator tubes in borated and lithiated high temperature water

• Boat-shaped sample was used to study fatigue behavior of Alloy 690 tubes.
• Fatigue life of Alloy 690 tubes was longer at 5500 ppb dissolved oxygen than at <5 ppb dissolved oxygen.
• Persistent slip bands facilitated rupture of oxide film on Alloy 690 tubes.
• High oxide film growth rate at 5500 ppb dissolved oxygen prevents fatigue crack initiation.

Corrosion fatigue behavior of Alloy 690 tubes used for actual steam generator (SG) was investigated in borated and lithiated high temperature water containing <5 ppb (by weight) and 5500 ppb dissolved oxygen (DO) using boat-shaped specimens. It was found that the fatigue life at 5500 ppb DO was longer than at <5 ppb DO. The surface cracks and fracture characteristics of the specimens after fatigue tests were carefully examined. The effects of DO concentration on fatigue crack initiation and propagation of Alloy 690 tubes in high temperature water are discussed.