Assessment of safe life inspection intervals or forged axles/rotors: the influence of in-service NDT reliability (POD curve)

A new scientific approach for the assessment of safe life in service inspection intervals now takes into account both fracture mechanics parameters, in service loadings and NDT reliability. The driving application has been the increasing demand for the reliability assessment of railways components, especially for high speed trains applications. This leads to a new definition of safety factor that can be determined by a “defect tolerant” approach and by the evaluation of “safe life” inspection intervals as a function of materials characteristics, propagation models and NDT inspections. The present paper deals with the influence on inspection intervals of railways axles given by different POD curves of different NDT techniques. Initially, the POD curve of an innovative bore probe has been derived by means of dedicated experimental UT measurements and the CIVA® 8.1 software. This curve has then been exploited together with the crack propagation behaviour of the reference material in order to define inspection intervals of high speed railway axles.The results have been compared to more traditional end scan UT techniques. This approach is suitable for all kinds of rotors employed in power generation fields, aeronautics and navy fields.