Characteristic Fracture Behavior of 9% Nickel Steel Weldment

Abstract

The available data on the brittle fracture initiation properties, of 9% Ni steel weldments bear out their satisfactorily high toughness at low temperatures, but have a'little ambiguity that arises in connection with the pop-in fractures and the tendency of HAZ cracks to deviate, into the lower, strength ductile weld metal which are observed when conducting fracture toughness tests on 9% Ni steel. weldments at low temperatures. However, no basic concept by which to assess. the significance of such fracture. behavior has been established yet.
With this fact in mind, and investigation was undertaken in order to arrive at a more precise interpretation of the correlation between a such fracture behavior and structural intergity of 9% Ni steel LNG storage tanks. Three-point bending COD tests using coil-spring loading equipment and wide plate tests were performed on 9% Ni steel weldments made using the austenitic Ni-based and matching ferritic fillers. In these tests the pop-in behavior was also observed to some extent at -196°C, and the tendency for elimination of pop-ins by precipitating complete failure was predominantly observed at the same level off stress intensity in COD terms. It was nevertheless shown that 9% Ni steel weld-HAZs had no doubt satisfactory toughness at the LNG temperature(-162°C).