Health monitoring of draglines using ultrasonic waves

Abstract The Australian coal industry operates a large number of draglines, with more than 30 draglines by the BHPBilliton Mitsubishi Alliance alone. The average age of the fleet is ∼25 years. Although some of the machines have passed their design life, there is pressure to increase the duty and extend their operational life. Unfortunately several large mining structures have recently collapsed, due to fatigue related component failures. It is desirable that tools for assessing and monitoring the structural health of draglines be developed if they are to be managed safely and economically. The use of piezoceramics to produce Lamb waves for use in damage detection has been reported by numerous authors [SPIE, 3044 (1997), 186]. These devices are used to detect damage at the high end of the frequency spectrum, i.e. ∼1 MHz. Lamb waves can propagate over long distances, giving the possibility of inspecting several metres of structure in a single test. This paper will show that by using ultrasonic waves, and by studying both the diffraction pattern and the reflected waves, we can both detect and size cracking in a typical weld cluster. This technique has the advantage that it can be performed automatically without increased downtime or the need to continually access hard to reach regions.