Full-Thickness Crack Arrest Fracture Toughness of 9-Percent Ni (ASTM 553, Type 1) Steels

Measurements were made of the full-thickness crack arrest fracture toughness (FTCAT) of three 9-percent Ni steels having the range of thicknesses and Charpy V-notch toughnesses of plates now in LNG storage tank service. Unlike the plates used in large pressure vessels, these thinner plates do not crack under a condition of plane strain, so that test method ASTM E1221 “Standard Test Method for Determining Plane-Strain Crack-Arrest Fracture Toughness, K_la, of Ferritic Steels,” was modified for these tests. The toughness of all three steels was measured at liquid nitrogen temperature (−196C), but two of the three were too tough to be measured at LNG storage temperature (−162C). Even the least tough plate had a high enough toughness to arrest long cracks in LNG storage service.