Sleipner A offshore platform
Encyclopedia
Sleipner A is a combined accommodations, production and processing offshore platform at the Sleipner East gas field
in the Norwegian sector of the North Sea
. It is a Condeep
-type oil platform
, built in Norway
by the company Norwegian Contractors
for Statoil
.
It is known for its catastrophic failure on 23 August 1991, due to a design flaw, that resulted from an error caused by unconservative concrete codes and inaccurate Finite element analysis modelling of the tricell, which formed part of the ballasting/flotation system.
. In addition, the Sleipner T carbon dioxide
treatment platform is linked physically to the Sleipner A platform by a bridge.
The original hull was a gravity base made up of support pilings and concrete ballast chambers from which three or four shafts rise and upon which the deck sits. Once fully ballasted, the hull was to sit on the sea floor. There were 24 chambers, of which four formed the 'legs' supporting the facility on top in the case of the Sleipner A oil rig.
The hull was redesigned after the accident and the Sleipner A Platform was successfully completed in June 1993.
where it was to be lowered in the water in a controlled ballasting operation at a rate of 1 meter per 20 minutes. This was necessary for the fitment of the deck platform to the hull. As the hull was lowered to the 65 metres (213.3 ft) mark, rumbling noises were heard followed by the sound of water pouring into the unit. A cell wall had failed and a serious crack had developed, and sea water poured in at a rate that was too great for the deballasting pump
s to deal with. Within a few minutes the hull began sinking at a rate of 1 meter per minute. As the structure sank deeper into the 210 metres (689 ft) fjord, the buoyancy chambers imploded and the rubble struck the floor of the fjord, creating a Richter magnitude scale
3 earthquake.
Later analysis showed that the failure would occur at 62 metres (203.4 ft)
No one was injured during the accident.
in Norway discovered that the root cause of the failure resulted from inaccurate NASTRAN
calculations in the design of the structure. Stress
es on the ballast chambers were underestimated by 47% and some concrete walls were designed too thin to resist foreseeable hydrostatic pressure when submerged. As the pressure increased, the walls failed and cracked, allowing sea water to enter the tank at an uncontrolled rate, eventually sinking the hull.
After the accident, the project leaders from Norwegian Contractors were brought before the Statoil board, and were expecting severe repercussions. But the director instead asked the famous question "Can you make a new one before schedule?" to which the contractors replied "Yes we can". The new hull was completed before schedule.
Sleipner gas field
The Sleipner gas field is a natural gas field in the North Sea, about west of Stavanger, Norway. Two parts of the field are in production, Sleipner West , and Sleipner East . The field produces natural gas and light oil condensates from sandstone structures about below sea level. It is operated...
in the Norwegian sector of the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
. It is a Condeep
Condeep
Condeep refers to a make of gravity base structure for oil platforms developed and fabricated by Norwegian Contractors in Stavanger, Norway. A Condeep usually consists of a base of concrete oil storage tanks from which one, three or four concrete shafts rise...
-type oil platform
Oil platform
An oil platform, also referred to as an offshore platform or, somewhat incorrectly, oil rig, is a lаrge structure with facilities to drill wells, to extract and process oil and natural gas, and to temporarily store product until it can be brought to shore for refining and marketing...
, built in Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
by the company Norwegian Contractors
Norwegian Contractors
Norwegian Contractors AS was the world leading turnkey concrete gravity base structure supplierin the period of 1974 to 1994. Aker Marine Contractors AS was established in 1995 and is a continuance of the marine activities in Norwegian Contractors AS.Norwegian Contractors AS have worked on...
for Statoil
Statoil
Statoil ASA is a Norwegian petroleum company established in 1972. It merged with Norsk Hydro in 2007 and was known as StatoilHydro until 2009, when the name was changed back to Statoil ASA. The brand Statoil was retained as a chain of fuel stations owned by StatoilHydro...
.
It is known for its catastrophic failure on 23 August 1991, due to a design flaw, that resulted from an error caused by unconservative concrete codes and inaccurate Finite element analysis modelling of the tricell, which formed part of the ballasting/flotation system.
Location
Sleipner A is located on the Sleipner East gas field on the North Sea. Also six satellite fields–Gungne, Loke, Alpha North, Sigyn, Volve and Volve South–are tied-back to Sleipner A. In addition to its own operations, the platform is used as a remote operation center for the Sleipner B wellhead platform. The Sleipner B is operated from the Sleipner A via an umbilical cableUmbilical cable
An umbilical cable or umbilical is a cable which supplies required consumables to an apparatus. It is named by analogy with an umbilical cord...
. In addition, the Sleipner T carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
treatment platform is linked physically to the Sleipner A platform by a bridge.
Design
The platform is designed to accommodate roughly 160 people. The platform deck is 60 by with height of 210 metres (689 ft).The original hull was a gravity base made up of support pilings and concrete ballast chambers from which three or four shafts rise and upon which the deck sits. Once fully ballasted, the hull was to sit on the sea floor. There were 24 chambers, of which four formed the 'legs' supporting the facility on top in the case of the Sleipner A oil rig.
The hull was redesigned after the accident and the Sleipner A Platform was successfully completed in June 1993.
Collapse
The original hull collapsed during the final construction because of a design flaw. It was towed into GandsfjordGandsfjord
Gandsfjord is a fjord in Rogaland, Norway. Gandsfjord is an arm of Boknafjorden which is adjacent to the cities Stavanger and Sandnes. The entire west side of Gandsfjord is highly developed. The east side of the fjord has many mountains and peaks. In the outer parts of the fjord there are several...
where it was to be lowered in the water in a controlled ballasting operation at a rate of 1 meter per 20 minutes. This was necessary for the fitment of the deck platform to the hull. As the hull was lowered to the 65 metres (213.3 ft) mark, rumbling noises were heard followed by the sound of water pouring into the unit. A cell wall had failed and a serious crack had developed, and sea water poured in at a rate that was too great for the deballasting pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s to deal with. Within a few minutes the hull began sinking at a rate of 1 meter per minute. As the structure sank deeper into the 210 metres (689 ft) fjord, the buoyancy chambers imploded and the rubble struck the floor of the fjord, creating a Richter magnitude scale
Richter magnitude scale
The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....
3 earthquake.
Later analysis showed that the failure would occur at 62 metres (203.4 ft)
No one was injured during the accident.
Investigation
The post-accident investigation by SINTEFSINTEF
SINTEF , headquartered in Trondheim, Norway, is the largest independent research organisation in Scandinavia. Every year, SINTEF supports research and development at 2,000 or so Norwegian and overseas companies via its research and development activity....
in Norway discovered that the root cause of the failure resulted from inaccurate NASTRAN
Nastran
NASTRAN is a finite element analysis program that was originally developed for NASA in the late 1960s under United States government funding for the Aerospace industry. The MacNeal-Schwendler Corporation was one of the principal and original developers of the public domain NASTRAN code...
calculations in the design of the structure. Stress
Stress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
es on the ballast chambers were underestimated by 47% and some concrete walls were designed too thin to resist foreseeable hydrostatic pressure when submerged. As the pressure increased, the walls failed and cracked, allowing sea water to enter the tank at an uncontrolled rate, eventually sinking the hull.
After the accident, the project leaders from Norwegian Contractors were brought before the Statoil board, and were expecting severe repercussions. But the director instead asked the famous question "Can you make a new one before schedule?" to which the contractors replied "Yes we can". The new hull was completed before schedule.