Burst Test on the Steam Generator Tube With Multiple Part-Through-Wall Flaws

Abstract

This study carried out burst tests on steam generator (SG) tube specimens containing multiple axial part-through-wall (PTW) flaws at room temperature (RT). The specimens were machined from SG tube of Alloy 690TT with an outer diameter of 19.05mm and a thickness of 1.067mm. The flaws were made by electro-discharge machining (EDM) method on the outer surface of specimen. In the experiment, six types of multiple PTW flaws with a constant depth of 50% of wall thickness and single flaw with four different lengths were considered. The results showed that the interaction effect for collinear axial PTW flaws diminished with increasing ligament length between flaws. The ligament length had less influence on the interaction effect for longer flaws than shorter flaws. For non-aligned axial PTW flaws, however, the interaction effect was increased and remained with increase in circumferential ligament length. For parallel axial PTW flaws, the positive interaction effect appeared when the ligament between flaws was less than 2mm. However, the failure pressure decreased with increasing circumferential ligament length between flaws and reached the minimum when they were separated by about 90-degree in circumferential direction. Interaction effect was enhanced as number of flaws for collinear and non-aligned axial PTW flaws increased. Regardless of flaw configurations and ligament lengths, multiple PTW flaws of shorter length were failed by rupture at bottom of flaws followed by coalescence and unstable tearing. But, the flaws of length longer than 25.4mm were failed by rupture at bottom of one of multiple axial flaws.