The authors applied a constant tensile force to a range of small circumferentially notched and fatigue cracked specimens taken from an aluminium extrusion, subject of a number of industrial failures. Both specimens and failed pressure vessel components were manufactured from the same batch of 6351-T6 aluminium alloy extrusion. Each specimen was subjected to a different magnitude of constant load at room temperature; the initial applied K1 being less than K1c. It was found that the specimens broke after a period of time; relationships between the initial applied K1 and the time to failure, and crack growth rate emerged. SEM studies of the fracture surfaces indicated plane strain brittle fracture.