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, K1a, 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.