Fracture Mechanics Aspects of the Structural Integrity Technology of Spherical Aluminum Containment Vessels for LNG Tankers

The Kvaerner-Moss spherical tank design offers significant economic advantage for the shipboard transport of liquefied natural gas. An analytical and experimental approach based on fracture mechanics concepts was used to assist the designer in providing answers to the following basic questions: (1) Might a discontinuity smaller than detectable by nondestructive inspection lead to catastrophic fracture; (2) How fast would such a discontinuity grow under fatigue loading likely to occur during the lifetime of the tank; (3) Could a fatigue crack growing part way through the tank wall precipitate catastrophic fracture before it grows through the wall and is detected as a leak; and (4) If leakage develops, how much time is available to get the ship safely to port for discharge and repair? Both “critical” locations in the tank, i.e., the highest stressed region of the membrane and the equatorial ring, are examined. Available data indicating the safety of spherical tanks fabricated of aluminum alloy 5083-0 is documented.