Detection of Cut Notches and Corrosion on Anchor Bolts


The overhead catenary system (OCS) comprises of the pantograph which presses against the underside of the lowest overhead wire or the contact wire. Current collectors are electrically conductive and allow current to flow through to the train and back to the feeder station through the steel wheels on one or both running rails. With water seepage due to occurrence of monsoon rain and porosity of the cement material, the mineral rich rock structure can undergo much more rapid degradation under an electrochemical process due to the potential of the OCS. SEM images of the corroded bolts segment show high porosity surface with corroded voids. EDX study shows the presence of high oxide, chloride, and iron elements as indicative of a corroded bolt. The first backwall echo of the ultrasonic peak amplitude provides an understanding of the length of a bolt. Comparative study can provide a signature of the bolts which have been corroded with less fringe peaks due to the presence of bolts’ threads which tends to wear out with the duration of corrosion. Fatigue cracks are mimicked and modelled with cut notches of varying depths on bolts followed by immersion in corrosive peroxide solution for accelerated corrosion. A good clear distinction of the presence of such peak signal amplitudes due to cut notches with the referenced backwall echo peaks of the corroded bolts could be registered by the ultrasonic tests. The height of the signal peak amplitudes could give an indication of the depth of cut at the notch and the quantity of such peaks provide an indication of the number of cut notches. The ultrasonic test provides an effective means for non-destructive testing of such bolts which are embedded in concretized underground tunnel.
