Development of three-channel HTS-SQUID inspection system for orthotropic steel decks of expressway bridges

We have developed a three-channel high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) eddy current testing (ECT) system for detection of a fatigue crack which occurs in a steel deck plate used in expressway bridges. To avoid physical interference between adjacent channels, a dipole coil with compact design is employed. A field test using the three channel ECT system was performed on an expressway bridge having an orthotropic steel deck structure under traffic lane restrictions. Although a signal corresponding to existence of a fatigue crack was not detected due to a low occurrence rate of fatigue crack, we could demonstrate a stable and long-time operation in an urban area during the daytime and acquisition of correct data corresponding to some structural features of the expressway bridge.