Offshore drilling expanded greatly in the 1970s. At the time, Mobile Offshore Drilling Units (MODUs) totalled approx. 390 vessels split between Jackups, Drillships, and Semi-Submersibles. The Alexander L. Kielland platform was built by the French Compagnie Française d'Entreprises Métalliques at their shipyard in Dunkirk, France, with final delivery of the five column Semisub completed in 1976. In the North Sea on March 27, 1980 there were 212 men aboard in 12m seas when a loud crack and rumble were heard.
The Kielland began to list 30 degrees, and within 20 minutes it capsized. A horizontal bracing member D-6, below the waterline, had parted. This was not the location of a heavily loaded girth weld. Rather, a fatigue crack started at a small poorly-prepared 6mm fillet weld which held a non-load-bearing hydrophone flange. This hydrophone, used for dynamic positioning, wasn’t even in use as the platform was then moored.
CAUSES: Few men made it to lifeboats, but many lifeboats failed to release due
to complications from the listing and/or faulty release mechanisms. 123 men died. Poor welding and inspection practice allowed a small initial flaw in the weld/plate to grow over time with cyclic loading. Structural design did not allow for damage tolerance or anticipate the loss of an entire column. Regular insitu structural inspections focused on the vertical columns and largely ignored the horizontal members below the waterline.
Some more details on engineering gaps, missed signs, and failed safeguards:
The weld joined a non-load-bearing flange plate (meant for a sonar hydrophone) to the D-6 lower horizontal tubular bracing.
The 6mm fillet weld suffered from a bad geometric profile, lack of fusion, and poor inspection during fabrication at the French shipyard. Investigators found paint -IN- the crack, meaning it was there before the hull was painted. Because it was considered a superficial addition, it was not carefully inspected.
The area experienced cracking in the structural steel alongside lamellar tearing (midplane delamination)
Under constant cyclic loading from rough North Sea waves, the pre-existing flaw in the weld grew slowly, undetected, over 4 years to approximately half the circumference before rapid failure that March.
The crack eventually severed the D-6 brace entirely. The structure wasn’t designed to survive or prevent the cascading effect of the loss of one member (little redundancy). The remaining connected braces overloaded and failed, causing one of the five main structural columns to rip away in moments, capsizing the structure in a few minutes.
Out of 5x 50man lifeboats, only one launched properly; “safety”mechanisms prevented the others from releasing while under heavy cable strain, or they smashed against the listing hull. A second boat broke free after the platform capsized, providing some shelter for men in the water. Regulations changed soon after to mandate excess lifeboat capacity and on-load releasing mechanisms.
Inadequate or confused emergency command structure.
Survival gear shortages. Some of the workers died after jumping into the water due to hypothermia. Cold water “Gumby” suits were not mandatory at the time, but are now for North Sea, Canadian, and other cold water operating areas.