Study on local failure conditions of nuclear containment steels

Abstract

Tensile tests were performed for notched round-bar and plate specimens to acquire the local failure characteristics of SGV480 and SPV490 steels for nuclear containment structures. The notched round-bar specimens were sampled from base metals, weld joints including heat affected zone (HAZ), and simulated-HAZ materials. The simulated-HAZ materials were made using multiple heating and cooling processes with induction heating and forced air cooling. The limit strain was calculated using the Bridgman’s solution with the notch cross-sectional dimensions of the specimens, which were continuously measured with a profile projector. All notched round-bar specimens caused the tensile type ductile fracture, and there was no significant difference in the limit strains among the base metal, HAZ, and simulated-HAZ material. The limit strains were higher than the ASME VIII-2 design curve, and showed conservative results. Tensile tests using the full or partial width notched plate specimens were performed for the base metals of the two steels. In the cases of small curvature notched specimens of both full and partial widths, cracks occurred on the surface of the notch bottom and propagated into the depth of the material, until the specimens finally fractured. The limit strain plots were concentrated in a low strain and stress triaxiality position. In the cases of large curvature notched specimens of both types, no cracks occurred, and the specimens would suddenly fracture in shear after a slight shrinking of thickness. The limit strains of the notched plate specimens were lower than those of the notched round-bar specimens.