|Rolf Diederichs, NDT.net
The exact cause of an incident that saw a high-speed ICE train jump the rails when leaving Cologne station at low speed on 9 July 2008 is still not determined. It seems clear that a wheel-set axle on one of the first carriages of the ICE train was broken. Such wheel-sets are allowed to remain in service after 300.000 kilometer providing they pass ultrasonic inspection. Over the past few years this limit has been gradually increased step by step.
None of the train's 250 passengers were injured in the accident in Cologne. The train had only travelled a few meters and passengers were able to evacuate via a normal platform. An earlier generation of ICE trains was involved in the world's worst-ever high-speed rail disaster in 1998. An ICE train derailed near the city of Eschede, killing 101 people and injuring 88. A broken wheel rim caused that deadly train crash.
Rail operator Deutsche Bahn consequently has ordered the third generation of its ICE trains back to their depots to check their wheel-set axles for technical failures. Deutsche Bahn AG carried out ultrasound tests on the axles of 61 ICE-3 trains, the newest version of the high-speed InterCityExpress.
The Cologne prosecutors' office said it was investigating the incident to determine whether the axle was damaged during the train's high-speed journey from Frankfurt airport to Cologne, following reports that passengers heard unusual noises.
German magazine Der Spiegel reported on its website that Cologne's district attorney has launched an investigation into the incident. The Spiegel: "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). The line, which is Germany's fastest, is considered a national prestige project and a crucial link in the European Union's high-speed rail network."
Tracks and their dynamical impact on the axles
We have to be aware that in Germany the high speed ICE operates on the same rail infrastructure as all other trains including cargo trains. This causes critical loads for the wheel-set. It would be like making Formula 1 automobiles with heavier suspension so they could race on logging roads. In other countries like France the high speed trains travel on its own special rails.
In another article Der Spiegel publishes critical statements of Dr. Vatroslav Grubisic . More than 40 years Grubisic was specialist in "für betriebssichere Bemessung von Fahrzeugbauteilen" at Fraunhofer-Institute in Darmstadt. Because of his experience in this field he was called "Wheel Pop".
The expert criticizes that the lifetime of wheel-sets was estimated too high and warns that signs have been ignored over years. But the Deutsche Bahn has confidence in the wheel-sets. It was just luck that the wheel axle was broken at low speed, but under high speed this derailment could cause a disaster like in Eschede, said Vatroslav Grubisic. The expert believes that a crack already existed and the incident could be prevented by better inspections.
Accordingly to Grubisic opinion, Deutsch Bahn should have had knowledge about the problem with the lifetime and fatigue cracks. Early measurements showed that the wheel-sets of the ICE-3 series where designed too weak for this high operational load. This caused fatigue cracks which later resulted in a fatal error.
Already, in 2006 an article was published by the professor together with the scientific Gerhard Fischer; "Versagen von Radsatzwellen und dessen Ursachen". The most recent article about this subject was published in April 2008 in Magazin "ZEV Rail", Bahn-Vorstand, Karl-Friedrich Rausch is co-publisher of this magazine.
Ultrasonic testing is now carried out each 60.000 kilometer,
but ultrasonic testing can find the small cracks?
Grubisics agrees with the decision of Deutsche Bahn now to order the wheel-set inspection after 60.000 kilometer instead of 300.000 kilometer, this is absolutely necessary but he believes this does not mean that periodic ultrasonic testing will find the small cracks.
Hollow axle testing
ICE3 high-speed trains are equiped with wheel sets on hollow axles. These have to be inspected periodically by ultrasonic testing to find possible defects at an early stage, for example every 300.000 km. An angled beam scan from a rotating probe in the bore is used. This
inspection is mechanised.
The primary difficulty and skill required for the inspections is
discriminating between geometrical echoes and crack signals. For time safing reasons the ultrasonic inspection has to be performed on train. 
Ultrasonics is now expected to save the day
Ultrasonic testing principle of hollow axles.
DIN 27 201-7 "Zustand der Eisenbahnfahrzeuge - Grundlagen und Fertigungstechnologien - Teil 7 Zerstörungsfreie Prüfung"
State of railway vehicles - Basic principles and production technology - Part 7: Non-destructive test
(Anhang A) / Appendix A
Rahmenbedingungen für Prüfanweisungen zur Prüfung von Radsatzwellen und Rädern.
Important Statement in DIN 27 201-7:
....Radsatzwellen und Räder sind nach festgelegten Prüfzyklen einer zerstörungsfreien Prüfung zu unterziehen.
Das Verfahren, die Prüfzyklen und der Umfang der Prüfung ist vom Hersteller bzw. vom Halter EVU festzulegen ..." 
The Method, the inspection period and the scope of inspection has to be decided by manufacturer or operation company!
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?
- 5. Fachtagung ZfP im Eisenbahnwesen 2008 DGZfP, March, Wittenberg Germany
- Mechanisierte Radsatzwellenprüfung mit HPS - angepasste Lösungen für die Hersteller und Instandhalter Thomas Oelschlägel, Deutsche Bahn AG
- Experte zweifelt an Sicherheit von ICE-Radsatzwellen, Der Spiegel 19.7.2008
- Geltende Normen bei Radsatzwellen unzureichend?, Junge Welt 25.7.2008
- Der Kölner Zugunfall war »Vorbote« für weitere ICE-3-Radwellenbrüche, Junge Welt 25.7.2008
- Sicherheitsmängel bei der Bahn? , Neues Deutschland 19.7.2008
- Bruch einer Antriebsachse des ICE 3 gibt weiter Rätsel auf, VDI-nachrichten 18.7.2008
- Kölner ICE-Unfall - Anzeige gegen den Bahnvorstand, Rheinische Post 5.8.2008
- Kostendruck lässt Achsen brechen, Bahn für Alle
- Erneut Riss in Achswelle / Verdacht der fehlenden Dauerfestigkeit erhärtet sich, Eisenbahnkurier 2005/2004
"An dem Fahrzeug 612 089 wurden bei einer Ultraschallprüfung eine Rissbildung festgestellt, bei der bereits 1/3 der gesamten Querschnittsfläche gerissen war. Es ist davon auszugehen, dass ein Radsatzwellenbruch unmittelbar bevorstand."
Die Norm DIN 27201-7 "Zustand der Eisenbahnfahrzeuge - Grundlagen und Fertigungstechnologien - Teil 7: Zerstörungsfreie Prüfung",
3. Fachseminar Verfahrens- und Produktnormen in der ZfP, DGZfP 2007
- DGZfP Fachausschuss Zerstörungsfreie Prüfung im Eisenbahnwesen