Derailment of freight train no 9914 at Malmbanan, Norrbotten County

Summary in English

On 17 December 2023, a loaded train operated by LKAB Malmtrafik AB derailed with one wheel near Tornehamn on the Malmbanan line between Kiruna and Narvik. The wheel and subsequently both wheels, derailed over a distance of 15 km causing extensive damage to the track. At Vassijaure station, the derailment worsened, with several vehicles derailing and inflicting further damage to the infrastructure. The derailment caused no injuries.

The investigation revealed that the wheel fractured from the running surface to the hub of the wheel axle, losing its press fit at the hub. This allowed the wheel to move inwards along the axle and derail inside the right rail in the direction of travel. The fracture initiated from a fatigue crack at the back of the wheel flange and progressed as a rapid brittle fracture along the entire length of the crack to the hub.

Technical investigations confirmed that the wheel met applicable requirements and standards. Additionally, no deviations in the maintenance of the wheel axle were identified.

The wheel damage was likely caused by a combination of unfavourable and interacting factors that had not previously been assessed in relation to the risks of fatigue cracks in the flange and brittle fracture in to the hub. Simulations and calculations of various load cases indicate that tensile stresses and fatigue cracks can occur in the flange. For more comprehensive insights that could lead to revised design and maintenance criteria, further studies and detailed analyses are required.

Causes of the accident

The direct cause of the derailment was a wheel moving along its axle.

The cause of the wheel moving was a fracture resulting from a fatigue crack in the flange, extending to the hub, which led to the wheel losing its press fit on the axle.

The load cases and factors that contributed to the fatigue crack and subsequent fracture likely interacted negatively and approached strength limits.

The load cases and factors that initiate and propagate fatigue cracks in the flange have not been part of normal design or maintenance criteria for railway wheels.

Safety recommendations

In light of the measures that have been taken or will be taken by
LKAB Malmtrafik AB and Chalmers University of Technology, SHK refrains from issuing any safety recommendations.