Using a magnetic flux leakage method to estimate railway track bolted joint gaps

The periodic estimation of the rail joint gap values allows evaluating the reliability of the continuous welded railway track and preventing its temperature deformations. The purpose of this study is to search for a simple and reliable way to evaluate the rail joint gap, which allows you to determine the desired values during high-speed inspection in automatic mode in a wide range of temperatures. A brief overview of existing techniques for evaluating rail joint gaps based on different physical principles is given. In the proposed technique, a magnetic flux leakage (MFL) method with the placement of electromagnets on the wheel axes of a car bogie is used. Such magnetization systems are applied recently on flaw-detector cars and provide a stable magnetic flux in the tested rails. Using a three-dimensional model of the rail segment with a bolt joint, we studied the characteristics of the magnetic flux leakage fields when changing the size of the rail gap in the entire practical range. The characteristics are selected that are most sensitive to a change in the gap and by which its value can be determined. With small values of the gaps the amplitude of the magnetic sensor signal is proposed as a main informative parameter, and with large gaps the estimation based on the distance between the signal extremums is more preferred. The results of computer modeling of the influence of the joint gap on the parameters of the magnetic signal qualitatively coincide with the results of field measurements made at inspection speeds up to 60 km/h.

magnetic flux leakage, MFL, rail NDT, rail break, bolted rail joint, rail joint gap, continuous welded track, magnetizer, magnetic sensors