The effect of axial stress to hoop stress ratio on the susceptibility of unirradiated Zircaloy-4 to iodine stress corrosion cracking

Abstract

Specimens of stress relieved Zircaloy-4 tubing were internally pressurized at 633 K with helium containing a nominal concentration of 60 g iodine per square meter of Zircaloy surface. The ratio of applied axial stress (σa) to applied hoop stress (σh) was varied between zero and infinity by axially loading the pressurized specimens. The susceptibility to stress corrosion cracking (SCC) varied in a complex manner with stress ratio (σa)(σh) in the range 0 <(σa)(σh) < 1 and was substantially greater under hoop tension (σa)/(σh) = 0) than under axial tension (σa)/(σh) = ∞). It is concluded that the influence of stress ratio in the range 0 < (σa)/(σh) < 1 most likely arises through its effect on the circumferential strain rate. On the other hand, the difference between the SCC susceptibilities under axial and hoop loading is probably attributable to fabrication-induced anisotropy of the grain orientation and shape.