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2021/05

Class investigation of axle bearing failures on 7 November 2019 and 27 March 2020

This class investigation report looks into two derailments (on 7 November 2019 and 27 March 2020) involving the same type of two-axle freight wagon (Lgns). In both incidents, the failure of an axle bearing caused overheating and deformation of the wagon's axle bearing and wheel axle, which, in turn, caused the wheel to lose its position and derail.

In both incidents, the components were largely destroyed and deformed by heat and heavy loads. Because this made it difficult to interpret what lay behind the damage, the Norwegian Safety Investigation Authority (NSIA) chose to review the most common faults that cause overheating with a view to assess their relevance to the two incidents. That review, together with a review of work processes for maintenance of axle bearings, brought to light several factors that, in the NSIA's opinion, leave room for improvement. Several of these factors concern the need for documentation of all parts of the work process, including those that are exclusively based on established practice or discretionary assessment. As a consequence, CargoNet AS has updated their requirements to Mantena AS, the maintenance contractor. Though none of the above findings can be seen to have had any direct links to the incidents in question, improvements on this point can help reduce the likelihood of axle bearings becoming overheated.

A railway undertaking is responsible for ensuring that its rolling stock is in good running order, including after having undergone maintenance. The undertaking placing the maintenance order, may set specific requirements on how to maintain their rolling stock. Even so, the NSIA deems it a demanding task to examine and understand the grounds for the individual work descriptions of a certified entity in charge of maintenance (ECM). Good cooperation between the various parties involved is therefore important.

Current leakage erosion was observed in connection with a detailed examination of axle bearings under a microscope. This had not previously been considered a major problem in freight wagons with this type of axle bearing. It has not been part of the scope for this safety investigation to study the type of situations that give rise to such erosion. This is considered to be a very extensive task. The NSIA is of the opinion that there is a need for collaboration between several of the parties involved in order to gain more knowledge about current leakage erosion in axle bearings. 

No monitoring systems were in place for advance detection of signs of overheating in the two axle bearings that failed. In the NSIA's opinion, Bane NOR SF should examine the effectiveness of today's network for detecting faulty rolling stock, and, at the same time, assess the future needs for detector data in connection with condition-based maintenance.

The Norwegian Safety Investigation Authority submits three safety recommendations following this class investigation:
1. In order to build more knowledge, the maintenance contractor should register and document the types of damage found in discarded axle bearings. 
2. A collaboration of several parties should be set up to register the causes, scope and severity of current leakage erosion in axle bearings in this type of rolling stock.
3. The infrastructure manager, in collaboration with relevant parties, should examine the effectiveness of today's system for monitoring faults in rolling stock, and assess future needs.


Photo: NSIA


Photo: FOLAT

Published 06.05.2021

Safety recommendation

Safety recommendation Rail no 2021/12T

In 2019 and 2020, two derailments were caused by bearing failure in the same type of freight wagon from CargoNet AS, within the space of only five months. The investigation has shown that Mantena AS, the maintenance contractor, does not keep an overview of the type of damage found in bearings that are discarded during inspections. In accordance with the ECM Regulation (Commission Regulation (EU) No 445/2011), a railway undertaking may request such information when developing maintenance specifications, with a view to determining causes of damage.

The Norwegian Safety Investigation Authority recommends that the Norwegian Railway Authority request CargoNet AS to cooperate with Mantena AS to document the types of damage found in discarded axle bearings.

Safety recommendation Rail no 2021/13T

In 2019 and 2020, two derailments were caused by bearing failure in the same type of freight wagon from CargoNet AS, within the space of only five months. The investigation has shown that current leakage erosion is found in a large proportion of the axle bearings used in CargoNet AS's ordinary operations. Such damage generally arises as a result of interaction with the infrastructure. How this occurs, whether the cause lies in the infrastructure and whether the same problem is experienced by railway undertakings other than Cargo Net AS are matters that should be further investigated.

The Norwegian Safety Investigation Authority recommends that the Norwegian Railway Authority request Bane NOR SF to coordinate collaboration between relevant players in order to register the causes, scope and severity of current leakage erosion in axle bearings.

Safety recommendation Rail no 2021/14T

In 2019 and 2020, two derailments were caused by bearing failure in the same type of freight wagon from CargoNet AS, within the space of only five months. The faults in the axle bearings were not detected before the incidents occurred. By means of condition monitoring along the track, it is possible to detect different fault conditions in rolling stock before they become critical, but such systems are hardly used in Norway.

The Norwegian Safety Investigation Authority recommends that the Norwegian Railway Authority request Bane NOR SF to collaborate with relevant parties to examine the effectiveness of today's system and future needs for monitoring faults in rolling stock.

Facts

Location Bergen central station and Bergseng station
Occurrence date 07.11.2019
Train No Axle bearing failures
Type of Transportation Freight train
Type of occurrence Class investigation
Rolling Stock Freight wagon

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