The Alexander L Kielland was a semi-submersible mobile rig built between 1973 and 1976 in France for an American operator. Although it was designed as a drilling rig, it was only ever operated as an accommodation platform during its four years in service. On the 27th of March, 1980, during a storm in the North Sea, the floating drill platform "Alexander Kielland" suffered a catastrophic failure that caused it to capsize. The platform was being used as crew quarters for a nearby rig at the time of the incident. 123 crewman died.
Exponent investigated the capsizing, performing numerous analyses including a simulation of the wave/structure interaction over the life of the rig, a fatigue and crack-growth analysis of the failed structural member, a calculation of the dynamic response of the damaged structure, and a flood analysis.
During the storm, one cross-brace securing the columns fractured. Loss of this brace overloaded a main column attachment, which fractured and separated one column and pontoon completely from the platform. This immediately caused the platform to list some 12 degrees. Within 14 minutes, as water surged through open windows and other openings, listing increased to 20 degrees, at which point the platform became unstable and capsized.
Detailed evaluation of the recovered platform revealed that the brace fracture had resulted because a small weld crack was left in a hydrophone attachment during fabrication; this crack propagated gradually by fatigue under wave loadings during many months of normal service. Before the accident storm, the brace already contained a huge crack that extended almost completely around the brace.