The gravity base structure (GBS) of the Sleipner A platform, Fig. 1, suffered a serious leakage and sank during a controlled ballast test operation in the Gandsfjord outside Stavanger early in the morning, Friday 23. August 1991. The 14 people onboard the platform were all rescued by boats lying nearby. There were thus no casualties or injuries. At the very same day Norwegian Contractors" (NC) management established an internal Investigation Committee with the aim to determine the facts, conditions and circumstances related to the accident, establish the probable cause, analyse consequences for installed platforms and propose improvements for future platforms. To assist in this work a"group of internationally highly recognized experts and companies served as consultants to the Committee. None of them had ever before been involved in the Sleipner project. These consultants were:
Ove Arup & Partners, London
Dr. Ing. AAas-Jakobsen, Oslo
Professor Bruno Thurlimann, Zurich
Danish Hydraulic Institute, Copenhagen
Germanische Lloyds, Hamburg
Scandpower, Kjeller
Technica, London
The NC Committee worked in parallel with a corresponding committee established by Statoil, the operator for the Sleipner field. THE SLEIPNER A GBS The Sleipner A platform was the twelth in a series of Condeep GBS-platforms designed and built by NC for use in exploitation of hydrocarbons in the North Sea. The platform was going to operate in 82 m 01 water and had 24 caisson cells of which four extended upwards to form the deck supporting shafts. The four 110m high shafts were:
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two conductor shafts, B3 and D3, with (12 + 16) 26"conductors and (8 + 8) 16" and 12" J-tubes,
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one riser shaft, C1
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one utility shaft, C6 A view of the D3-shaft with mechanical outfitting is given in Fig. 2.
