Development of an HTS-SQUID Based Nondestructive Evaluation System for Boiler Tubes On-Site Inspection in Thermal Power Plant

In ultra-supercritical (USC) thermal power plants, Super304H (KA-SUS304J1HTB, ASME code: 2328) is widely used in the superheater and reheater tubes in boilers because of its excellent creep rupture strength under high-temperature and -pressure conditions. Thus, a degradation diagnosis of these tubes after long-term operation should be conducted using a quick and easy inspection. In this study, in order to discover the degradation of the boiler tubes for early diagnose before they rupture, a high-temperature superconductor (HTS)–superconducting quantum interference device (SQUID) with high sensitivity was used. A SQUID-based nondestructive evaluation system for the on-site inspection of boiler tubes in an USC thermal power plant was developed. Our system comprises a movable eddy current testing (ECT) probe and HTS-SQUID gradiometer. Five LED markers were set on a manually operated ECT probe for position detection using a stereo camera. Customized software was used for data acquisition through a lock-in amplifier and data visualization on a PC with a connected smart glass. Thus, the system can be used for quick inspection by time-sequence signals and detailed scanning through a two-dimensional contour map projected on the smart glass. Therefore, this study successfully introduced an HTS-SQUID-based nondestructive evaluation system for the on-site inspection of boiler tubes.