17 December 2008
Corrosion in the foot of the rail is particularly difficult to identify. Despite this difficulty, rail networks need to assess the likelihood of rail damage by identifying the extent of any rail foot corrosion.
ULTRAWave is the ultrasonic rail flaw detection system developed by CATER over a decade in the Japanese rail inspection market. CATER, an established Australian RFD company, has enhanced ULTRAWave to identify corrosion in the foot of the rail under the web.
ULTRAWave uses rail height detection (RHD) to constantly measure the rail height. Significant changes to the rail height are shown as a RHD artefact in the ULTRAWave screen. The display of an RHD artefact (which can be corrosion) is done in a similar method to all other ultrasonic beams in ULTRAWave. The operator can simply identify this foot fault from clear C-scan graphics which aid the operator in understanding the ultrasonic signal.
The operator can specify what level of corrosion depth they want to alarm with (for example, 6mm deep then detect and show). Operator familiarity enhances the recognition of the corrosion. The operator can refine the signal for their particular rail situation and preference.
RIPWave is the CATER developed post-processing analysis software which is able to collate, synchronise and accept all forms of information, whether it be ultrasonic, visual, legacy or current. The corrosion is treated like any other artefact in the post analysis software analysis and can be filtered, searched, measured, reported and printed.
Backwall Echo is the return of the ultrasonic signal from the bottom of the foot of the rail. A line displayed on the screen represents when there has been a loss of signal. Corrosion of the foot under the web is represented as a series of dots showing the actual height.
Loss of Backwall Echo (LBWE; called loss of bottom in some markets) occurs independently whether corrosion is present or not. On its own, LBWE is not enough information to identify a foot corrosion problem. The RHD can occur without LBWE. The RHD is definitely a height fault with the rail and is a possible indicator of foot corrosion.