Investigation of the Alexander L. Kielland Failure - Metallurgical and Fracture Analysis
Authors: Naess Almar Almar , Haagensen Per J. , Lian Bjøm , Moan Torgeir , Simonsen Tor 
Published: October 2008

At about 6.30 p.m., on March 27, 1980 one of the five legs of the hotel platform Alexander L Kielland separated from the rest of the structure in a storm on the Ekofisk field in the North Sea. Approximately 20 minutes later the platform capsized, resulting in a loss of 123 lives; 89 persons were rescued. The failure started with the fatigue fracture of one of the lower tubular bracings attached to a vertical column (leg D). In rapid succession the remaining five bracings connecting leg D to the platform failed by overloading. The fatigue crack started from a double fillet weld joining a 0.325 m diameter tube to bracing D6 through a wall penetration. The tube served as a hydrophone mount. The fillet welds were partially cracked in the early history of the platform due to low mechanical strength in the thickness direction of the hydrophone mounting tube combined with poor welding and high residual stresses.

The fracture surface of the D6 bracing exhibited distinct beach mark patterns along the first 60-100 mm from each of two initiation sites. In later stages unstable ductile crack propagation by tearing alternated with slower growth by fatigue until final rupture took place. Fractographic studies by electron microscope revealed patches of striations near the initiation points.

The striation spacing was compared with macroscopic crack growth rates obtained from test specimen cut from the failed D6 brace. Cumulative damage calculations indicated that the design fatigue life of the hydrophone fillet weld was inadequate.

Introduction

Shortly after the Alexander L Kielland disaster a Commission of Inquiry was appointed through a Royal Decree to investigate the failure of the platform. The authors were requested by the Commission to make, firstly, a preliminary examination of the then available fractured members and secondly, to provide technical advice and assistance concerning recovery of other fractures and to plan and carry out an extensive program of metallurgical studies, materials testing and failure Analysis.

Platform Design And History

Alexander L Kielland was one of eleven semi-submersibles of the Pentagon design that were built from 1969 through 1977. The platform design was developed in France during the late 1960s by the Institute Francis du Petrol and Forex Neptune S.A. Alexander L Kielland was one of seven rigs built by CFEM (Companies Franchise Enterprises Metalliques); it was the ninth Pentagon rig. Sections for the rig were fabricated in several French and German yards by subcontractors, final assembly tool place in CFEM's Dunkirk yard. The rig was delivered to its Norwegian owners in 1976.

Although Alexander L Kielland was designed and built as a drilling platform it never was used as such. Instead, the accommodation capacity of 80 was increased to 348 through three modifications that involved the installation of temporary accommodation modules in the pipe rack area. The 200 t, 40 m high drilling derrick was left in place.

The main dimensions of the Alexander L Kielland platform which was registered at 10,105 t, are 103 × 99 m in plan and the depth is 40.5 m from top of deck to base of pontoon (see Figure 1).