[chris]

The Norwegian semi-submersible drilling rig Alexander L. Kielland capsized while operating in the Ekofisk oil field in March 1980. The disaster killed 123 people.

A March 1981 investigation concluded that the rig collapsed after a fatigue crack developed in bracing D-6, one of six braces connecting the D-leg to the rest of the structure. The crack was traced to a 6 mm fillet weld joining a non-load-bearing flange plate for a sonar device to the bracing.