Ultrasonic Inspection of Bolts using an Integrated Probe Attachment

Anchor bolt inspection for an overhead catenary system (OCS) in an underground tunnel has been a significant operational challenge. The existing method of visual testing gives an inadequate measure of the bolt’s integrity as the embedded section of the bolt cannot be inspected. Ultrasonic testing provides a more effective approach to inspect the entire bolt volume but there are difficulties in performing this manual inspection in the tunnel at an overhead position, at height and with inadequate lighting. With these challenging operating conditions, one major problem encountered is the inconsistency in the ultrasound signals acquired due to the inability to maintain good surface contact and sufficient pressure between the probe and the bolt. This paper proposes a novel design of an integrated ultrasound probe that is permanently attached to the anchor bolt and only requires the operator to connect the cable to the probe to function. Several inspection runs have been conducted to study the consistency of the ultrasonic testing results over a period of time for bolt specimens integrated with this probe attachment. Cuts of various depths were also fabricated to simulate defects on these specimens and it was found that repeatable results could be observed in detecting and quantifying these defects.