Shaw.Din     Charles. Huang             TECLAB

In recent years, China's high-speed rail technology has made rapid progress and has frequently won large orders in the international market. Under heavy loads, railway tracks are prone to fatigue and even cracking in stress concentration areas due to repeated rolling and trampling by trains over the years, as well as temperature changes. In recent years, corresponding rail inspection technologies and methods have also undergone innovative development: from hammer tapping sound detection decades ago to ultrasonic A-scan manual detection, and now to fully automatic ultrasonic high-speed flaw detection vehicle online detection, domestic rail integrity and health testing is also advancing with the times and flourishing. This article introduces various current ultrasonic orbit detection technologies and future research directions.

1. Manual wheeled rail flaw detector

Wheeled rail flaw detectors generally come in two forms: dual wheel and single wheel. Dual wheel detectors can simultaneously detect two rails, with higher detection efficiency than single wheel detectors. Install more than ten MHz ultrasound probes into the wheel probe at different design angles. During the inspection, the ultrasonic signal is coupled by spraying water onto the contact area between the rail and the wheel probe. The ultrasonic signal is emitted from the ultrasonic probe head through the water path inside the wheel probe, and the water film on the rail surface is coupled into the rail for flaw detection. The test results are presented in B-scan format.

The manual wheeled rail flaw detector requires manual movement of the detector on the rail for inspection. The detection speed is limited by the walking speed of the person, generally not exceeding 5Km/h. Compared with traditional hammer listening and ultrasonic wave A-scan single point measurement technology, this equipment has greatly improved accuracy and efficiency. But for the rapidly developing railway industry, this detection efficiency is still far from meeting the current detection needs.

2. Wheeled rail online flaw detection vehicle

The online wheeled track flaw detection vehicle has been upgraded to speed up based on the manual wheeled flaw detector. Install the wheeled ultrasonic probe group onto a tram, car, or train. The number of probes can range from tens to dozens, and the ultrasonic detection unit adopts a parallel working mode with dozens of channels, increasing the detection speed from tens of kilometers per hour to nearly hundreds of kilometers per hour. The test results are still displayed in the form of ultrasonic B-scan. The test results can be saved to the computer for subsequent analysis. By analyzing the detection signal, it is possible to roughly determine the location, depth, and size equivalent of the defect. This ultrasonic wheel rail online inspection technology is currently the mainstream rail inspection method.

During the inspection of wheeled track inspection vehicles, ultrasound mainly propagates from the tread along the central axis of the rail, mainly detecting internal cracks, voids, and other defects in the rail head and waist. These areas are also the most prone to cracks and other faults in the rail.

The side and bottom of the rail head are relatively less prone to fatigue cracks, and ultrasonic guided wave technology is a feasible solution for detecting these areas.

3. Ultrasonic guided wave orbit detection system
  

Ultrasonic guided wave detection technology uses a pressure device to press the KHz ultrasonic array probe tightly against the rail, and generates guided waves on the surface of the rail for long-distance detection, with a detection length of tens of meters at a time. This technology is highly sensitive to cracks, corrosion, or local defects on the bottom and side of the rail head. However, due to the need for piezoelectric array probes to be attached to railway tracks, they are not suitable for online detection.

In order to apply this technology for online detection, it is possible to consider replacing the piezoelectric guided wave array probe with an EMAT electromagnetic coupling ultrasonic probe. EMAT can lift 1-4 mm away from the rail surface during detection without the need for coupling agents. Thus achieving high-speed online measurement. Further research is needed on related technologies.