Nondestructive Inspection Using an HTS SQUID for Copper Heat-exchanger Tubes

Abstract

A nondestructive inspection (NDI) system using an HTS SQUID for copper heat-exchanger tubes has been constructed. An eddy-current-based NDI method using an HTS SQUID gradiometer cooled using a cryocooler was employed for the detection of micro flaws in thin copper tubes 6.35 mm in diameter and 0.8 mm in thickness. With an excitation field of 1.6 μT at 5 kHz, a flaw in the tube, measuring 30 μm deep and 15 mm long, was successfully detected by the system with a high signal-noise ratio of at least 20. Numerical simulations were also conducted to determine how many sensors would be required for inspection around the circumference of an entire tube.