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1148 views
03:02 Aug-07-2008

Rolf Diederichs

Director, Editor, Publisher, Internet, PHP MySQL
NDT.net,
Germany,
Joined Nov 1998
602
Expert voices doubt on the Safety of ICE Train Wheel Axles

In Germany happened in July at Cologne's railway station an incidence which released a strong debate on Deutsche Bahn's safety management. A defective axle caused one of the high-speed trains to derail. Prosecutors suspect that the train travelled with a defect wheel or axle along the high-speed line between Frankfurt and Cologne, with speeds of up to 300 kilometers per hour (186 mph). A fracture and derailment just minutes before Cologne under high speed could cause a disaster like in Eschede (killing 101 people). An expert believes that a crack already existed and the incident could be prevented by better inspections. I summarized a critical assessment in the article "Expert voices doubt on the Safety of ICE Train Wheel Axles"
http://www.ndt.net/search/docs.php3?id=6808&content=1

I would like to hear opinions about this debate, especially what about "Ultrasonics is now expected to save the day"?
The wheel-set axle is a complex geometry which is difficult to test with ultrasonic testing. Is thesystem which is used at Deutsche Bahn enough reliable? In NDT.net Database we can find articles which describe wheel-sets hollow axle testing, also from Deutsche Bahn, but what system is in operation? What about set-up errors or operator errors? Human error is a part of the reliability of detection. If the axle tends to fatigue crack is ultrasonic testing the right solution to allow the risk in operation? Does this case indicate proper risk management or is the risk too high in order to save money?



 
02:34 Aug-12-2008

Hermann Wuestenberg

R & D
BAM Berlin,
Germany,
Joined Nov 1998
26
Railway axle inspection The event reported concerning a broken axle at the German high-speed train ICE3 in Cologne in July rises some critical questions about the safety management of the german railway society DB AG. Even the poor reliable informations given until to day to the public by the concerned bodies (DB AG, EBA – Eisenbahn-Bundesamt, a surveillance and licensing authority ) are evoking the suspicion, that behind this event are some severe problems with the general risk management of the wheel set. It seems to me, that one should discuss the possible backgrounds of this event despite the traditional information policy of the official bodies, to say nothing with the hint to an ongoing prosecutor activity.

What information do we have? An axle has been broken and there are pictures indicating that this happened probably at the end of the journal. The reason for the fracture is not yet confirmed, but the hastily introduced reduction of the inspection intervals from 300000 km (about 6 month) to 60000 km (about 6 weeks)is a useful measure only in case of a fatigue crack phenomenon. So we have to deal with a fatigue damaging mechanism, which apparently has been underestimated. And there are always three factors to be considered, the mechanical strength of the structure, the collective of loads and the non-destructive inspection strategy based on a clearly defined knowledge about the crack growth to be expected. Those influences are the mayor ingredients of what is called a Risk Informed Inspection, a concept discussed and applied e.g. in the nuclear industry for the inservice inspection of pressurized components (see also ASME Section XI).

Since the DB AG has after the Eschede accident heavily invested in modernized NDT inspection techniques also for axles – e.g. mechanized ultrasonic inspection of axles with and without inner boreholes – one has to ask what has been wrong with the broken axle, in a situation, where a modern and hopefully also reliable NDT technique has been available. First remark to be made is, that even new and modern inspection techniques have to demonstrate their performance as e.g. described in the Appendix VIII of ASME Section XI or in the European ENIQ document. It is not sufficient to demonstrate with the help of a reference axle with test reflectors the correct sensitivity setting. A performance demonstration should deliver a kind of POD (probability of detection) estimate for cracks with different depth under the realistic surface condition of an axle in service. Only with such an information the contribution of the NDT to a general risk management can be evaluated. Are there any efforts made by the DB AG to assure the NDT performance according to the above mentioned concepts?

If the NDT and its performance is not involved in the Cologne axle fracture, one has to ask for the reasons of a fatigue underestimate. This evokes a similarity with the Eschede accident, where also a neglected fatigue process has been the main reason, but in this case without an useful NDT surveillance. We all hope that this is not indicating an established bad practice introduced under money saving pressure. Remains the question concerning a risk informed inspection concept. Is there an intention to go into this direction?

Hermann Wuestenberg

----------- Start Original Message -----------
: In Germany happened in July at Cologne's railway station an incidence which released a strong debate on Deutsche Bahn's safety management. A defective axle caused one of the high-speed trains to derail. Prosecutors suspect that the train travelled with a defect wheel or axle along the high-speed line between Frankfurt and Cologne, with speeds of up to 300 kilometers per hour (186 mph). A fracture and derailment just minutes before Cologne under high speed could cause a disaster like in Eschede (killing 101 people). An expert believes that a crack already existed and the incident could be prevented by better inspections. I summarized a critical assessment in the article "Expert voices doubt on the Safety of ICE Train Wheel Axles"
: http://www.ndt.net/search/docs.php3?id=6808&content=1
: I would like to hear opinions about this debate, especially what about "Ultrasonics is now expected to save the day"?
: The wheel-set axle is a complex geometry which is difficult to test with ultrasonic testing. Is the system which is used at Deutsche Bahn enough reliable? In NDT.net Database we can find articles which describe wheel-sets hollow axle testing, also from Deutsche Bahn, but what system is in operation? What about set-up errors or operator errors? Human error is a part of the reliability of detection. If the axle tends to fatigue crack is ultrasonic testing the right solution to allow the risk in operation? Does this case indicate proper risk management or is the risk too high in order to save money?
------------ End Original Message ------------




 


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