During routine vehicle operation, rails are subjected to intense bending and shear stresses, plastic deformation and wear, leading to the degradation of their structural integrity over time. Defects form in the rail head, web or foot, but are most prevalent in the railhead. Defects caused by wheelslip, squats, shelling and rolling contact fatigue need to be identified.
One of the main problems in the current methods of inspecting railheads is the need for the sensing device to be in contact with the railhead itself, which inherently limits the speed of inspection. The current methods of eddy current inspection, alternating current field measurement, conventional ultrasonic testing and magnetic flux leakage have all proved inadequate for the envisaged resource efficient rail transport system of the future with their slow inspection speeds and limited defect detection.
Eddy current inspection, the most widely used method, and alternating current field measurement can only be applied at walking speed and are limited to detecting surface breaking defects only.
Ultrasonic testing is also a walking speed technology where the orientation of defects greatly affects the likelihood of detection and is unable to detect surface defects.
Magnetic flux leakage inspection does allow a faster inspection rate, up to 35 km/hr, but it cannot detect defects below 4mm in size.