Problems With Crack Detection In High-Speed ICE Wheels
The Deutsche Bahn AG (DB) knew about the problems with the crack detection technique used on the railroad wheels of the high-speed ICE. "The DB knew that wheels must be tested" said Prof. Hermann Wüstenberg, chairman of the ultrasonic testing committee of the German Society for Nondestructive Testing (DGZfP) to NDTnet.
When ICE was first developed, the DB followed a testing procedure which gave clear results for wheels with low running time. However, in May 1996, recognizing the weaknesses of this system, the DB began to develop a new procedure.
Before, wheels with short running time had been be tested with the "ultrasonic surface wave method" only. With this method it is possible to test the complete circumference of the wheel in "one shot." However, this surface wave method delivers uncertain results when small surface disturbances are present, e.g., water drops, oil film. Results are especially affected after long running times; in other words, the method is weakest just where it needs to be strongest. With increasing running time the results of crack detection are more and more imprecise.
The new test systems which had been discussed in May 1996 involved a much better ultrasonic method in addition to an eddy current method. It is unclear why until today this only been partially implemented in new trials; specifically the eddy current method had not been put into practice.
Because the DB had knowledge of the problems that existed with the testing methods they used, they must answer the question: Why was safety not accorded a higher priority? (NDTnet)