Problems of High-Speed Rail Flaw Detection

Abstract

The main factors that reduce the quality of non-destructive testing of rails during high-speed scanning are considered. The most significant factors are the quality and volume of obtaining primary information about the condition of the monitored rails. It is shown that, at high-speed (up to 120 km/h) control, the compression of the defect location zone is clearly manifested and the length of the areas with acoustic contact violations increases. Analysis of real flaw diagrams of diagnostic complexes shows that with an increase in the scanning speed, the length of the location zone even from such large reflectors in the rails, such as bolt holes, significantly decreases. The average length of the instability zone of the bottom signal over the welded joints of the rails also increases significantly. The compression of the location zones of the reflectors can be compensated by expanding the aperture of the ultrasonic transducers. Improving the quality of the acoustic contact requires further improvement of the design of the search system and the systems for supplying the contacting liquid to the transducers, depending on the scanning speed. The Magnetic Flux Leakage(MFL) method can effectively detect defects in the rail head up to 20 mm deep at high speeds. Mathematical modeling of the magnetic flux in the controlled rails is performed. This allows us to start creating a new rail magnetization system with an increased interpole distance for high speeds. The introduction of modern methods for processing a significant flow of flaw detection information using neural networks requires the formation of a large sample base of training signals from real defects in different sections of rails. This is a complex task in its own right. For the first time, the issues of checking the operability of flaw detection devices in real control conditions are raised. Testing of ultrasonic equipment at high speeds is proposed to be carried out with the help of special electronic-acoustic simulators of defects. They are installed on different surfaces of the rails on which the diagnostic complexes pass. Operational quality control of ultrasonic rail inspection can be evaluated by statistical analysis of signal parameters from structural elements (bolt holes). The choice between the monitoring performance and the required reliability of detecting rail defects must be made based on the results of real passes of diagnostic complexes at operating scanning speeds.

Application of Model Data for Training the Classifier of Defects in Rail Bolt Holes in Ultrasonic Diagnostics

“…Currently, the problem of searching for and recognizing defects is entirely assigned to the flaw detector operator [1,[3][4][5][6]. As a result of this, the human factor influences the quality and speed of the defectogram analysis.…”

“…As a result of this, the human factor influences the quality and speed of the defectogram analysis. The small size of graphical images of defects, against the background of a significant length of the entire defectogram, measured in tens of kilometers of the railway track, significantly increases the psycho-emotional load on the flaw detector operator and increases the likelihood of missing defects [1,3,[7][8][9][10], which increases the risk of accidents in railway transport. Therefore, an important direction is the creation of automatic defect recognition and expert systems.…”

“…The methods of automatic decryption of data used in commercial software products often use the amplitude criterion, applying the principles of statistics to data analysis. However, many years of experience in using this approach did not solve the problem of automating the decoding of defectograms [1,3,9,[11][12].…”

“…To test the proposed approach, a model was created describing the process of reflecting and recording ultrasonic waves from structural reflectors of rails in the form of bolt holes and their radial cracks. This defect is referred to in the literature as «Star Crack» and is detected by a flaw detector channel with a preferred central angle of ultrasound input in the range of 38°-45° [2][3]. In most cases, radial cracks develop in the bolt holes and run along the rail neck at an angle of 45° to the longitudinal axis of the rail (Figure 2).…”

“…In most cases, radial cracks develop in the bolt holes and run along the rail neck at an angle of 45° to the longitudinal axis of the rail (Figure 2). The orientation of fatigue cracks in the neck is determined by the variety of combinations of deviations in the sizes of pads and rails from the nominal value [3]. Despite the systematic introduction of a seamless track on the railway network, the diagnosis of bolt holes is an important task [3].…”