 On 17 June 2000 , a Class 73 train derailed at Nelaug Station on the Sørland Line . The train was traveling at slow speed and no @-@ one was injured , but had the derailment happened at full speed , it could have been fatal . The derailment was caused by a fatigue failure in the front axle of the train . All Class 71 and 73 trains were immediately grounded , and were investigated by maintenance crews . The derailed train had recently had its axle checked for fatigue , but no cracks had been found . On 19 June , NSB stated that they had made insufficient tests during the 100 @,@ 000 @-@ kilometer ( 62 @,@ 000 mi ) controls . Class 71 had been through ultrasonic testing and were therefore allowed to resume operation the day after the accident . A DNV report from late August concluded with that the cracks had been caused by rust , which was again caused by water being sealed in by the corrosion @-@ protective layer . 
