The Sleipner A platform sank in 1991 — a $700M engineering failure

The Sleipner A platform was a Condeep-type concrete offshore gas platform being built for Statoil in the North Sea. On 23 August 1991, during a controlled ballasting operation in Gandsfjord, Norway, the gravity-base structure suddenly flooded and sank in 65 meters of water. The hull was a total loss. No one was injured because the platform was evacuated before the operation.

An investigation traced the failure to a design flaw in the cell walls of the concrete structure. The finite element analysis, run on the NASTRAN software package, had underestimated the shear forces by 47 percent. The concrete walls were designed too thin for the hydrostatic pressure they would face at depth. The analysis had used an unconservative concrete code and had failed to model the proper boundary conditions.

The hull was eventually redesigned and rebuilt at a cost of roughly $700 million, and the Sleipner A platform began gas production in 1993. The case became a standard textbook example of how finite element analysis must be validated against physical testing. The collapse remains one of the most expensive engineering design failures in history.