Magnetite-accelerated stress corrosion cracking of alloy 600 in water containing 100 ppm lead oxide at 315 °C

Abstract

The purpose of this work is to verify the effect of magnetite coupled with Alloy 600 on stress corrosion cracking (SCC) behavior in water containing 100 ppm PbO at 315 °C. SCC tests were conducted using U-bend specimens partially covered with magnetite, simulating a condition wherein magnetite was deposited on steam generator tubes. The maximum crack depths of the Alloy 600 specimens coupled with magnetite were 20–68% greater than those of the uncoupled specimens for a given test time. The coupling of magnetite to Alloy 600 led to the fast growth of oxide films, resulting in the formation of relatively Cr-depleted inner oxides with defects. The corrosion potential of Alloy 600 was 90 mV lower than that of magnetite at 80 °C, indicating that the corrosion of Alloy 600 could be stimulated by galvanic coupling with magnetite. The accelerated stress corrosion and altered film properties were discussed from the viewpoint of a galvanic coupling effect.