Edda 2/7C and Alexander L. Kielland (right) |
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| Career | |
|---|---|
| Name: | Alexander L. Kielland |
| Fate: | capsized / sunk at |
| General characteristics | |
| Length: | 103 m (338 ft) |
| Beam: | 99 m (325 ft) |
Alexander L. Kielland was a Norwegian semi-submersible drilling rig that capsized whilst working in the Ekofisk oil field in March 1980 killing 123 people.
The capsize was the worst disaster in Norwegian waters since World War II. The rig, located approximately 320 km east from Dundee, Scotland, was owned by the Stavanger Drilling Company of Norway and was on hire to the U.S. company Phillips Petroleum at the time of the disaster. The rig was named after the Norwegian writer Alexander Lange Kielland.
The rig was built as a mobile drilling unit at a French shipyard, and delivered to Stavanger Drilling in July 1976. The floating drill rig was not however used for drilling purposes but served as a semi-submersible 'flotel' providing living quarters for offshore workers. By 1978 additional accommodation blocks had been added to the platform, so that up to 386 persons could be accommodated.[1]
In 1980 the platform was working in the Norwegian north sea providing offshore accommodation for the production platform Edda 2/7C.
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In driving rain and mist, early in the evening of 27 March 1980 more than 200 men were off duty in the accommodation on Alexander L. Kielland. The wind was gusting to 40 knots (74 km/h) with waves up to 12 m high. The rig had just been winched away from the Edda production platform.
Minutes before 18:30 those on board felt a 'sharp crack' followed by 'some kind of trembling'. Suddenly the rig heeled over 30° and then stabilised. Five of the six anchor cables had broken, the one remaining cable preventing the rig from capsizing. The list continued to increase and at 18.53 the remaining anchor cable snapped and the rig turned upside down.
130 men were in the mess hall and the cinema. The rig had seven 50-man lifeboats and twenty 20-man rafts. Four lifeboats were launched, but only one managed to release from the lowering cables. (A safety device did not allow release until the strain was removed from the cables.) A fifth lifeboat came adrift and surfaced upside down; its occupants righted it and gathered 19 men from the water. Two of Kielland's rafts were detached, three men being rescued from them. Two 12-man rafts were thrown from Edda and rescued 13 survivors. Seven men were taken from the sea by supply boats and seven swam to Edda.
No-one was rescued by the standby vessel which took an hour to reach the scene.
Of the 212 people aboard 123 were killed, making it the worst disaster in Norwegian offshore history since WWII. Most of the workers were from Rogaland.
A year later in March 1981, the investigative report concluded that the rig collapsed owing to a fatigue crack in one of its six bracings (bracing D-6), which connected the collapsed D-leg to the rest of the rig.[2] This was traced to a small 6mm fillet weld which joined a non-load-bearing flange plate to this D-6 bracing. This flange plate held a sonar device used during drilling operations. The poor profile of the fillet weld contributed to a reduction in its fatigue strength. Further, the investigation found considerable amounts of lamellar tearing in the flange plate and cold cracks in the butt weld. Cold cracks in the welds, increased stress concentrations due to the weakened flange plate, the poor weld profile, and cyclical stresses (which would be common in the North Sea), seemed to collectively play a role in the rig's collapse.
The rig was recovered in 1983 at the third attempt. It was scuttled later that year after a search for missing bodies had been completed, as well as several tests to determine the cause of the disaster. The fatigue crack had grown over time from a hydrophone port in the bracing tube. Judging by paint on part of the fractured surface the crack was probably due to improper labour at the plant in Dunkerque, France where the rig was built in 1976.
Other major structural elements then failed in sequence, destabilising the entire structure. The design of the rig was flawed owing to the absence of structural redundancy.
(Dave Myles B.E.M. of J.R.C. in Aberdeen, Scotland, designed the charges to fit around the legs and carried out the demolition/scuttling of the rig in the Nedstrand Fjord)
A consequence of the Alexander L. Kielland disaster was the tightening of command organization on offshore installations in the North Sea so that there was a clear source of authority for ordering abandonment in crises. The 14 minutes between initial failure of the leg and the rig's eventual capsize left a window in which most of the personnel on board could have escaped, given a more effective command structure. But it would seem that no one took charge on the night. These revised command structures (more akin to conventional shipping command structures) are now frequently put into use when vessels lose anchorage in storm conditions or when fixed installations are threatened by out-of-control vessels.
Not long after Alexander L. Kielland capsized, her sister rig, Henrik Ibsen, suffered a jammed ballast valve causing her to list twenty degrees, but it was later righted again.[3]
Approximately 18 months later Ocean Ranger capsized in similar weather conditions off the Newfoundland coast. An investigation into the causes of the Ocean Ranger disaster by the US Coast Guard established that structural failure was not a factor.