Cylinder-type magnetic cameras and their coverage performance evaluation for inspection of heat exchanger tubes

Abstract

Eddy current array (ECA) probes are recently used to inspect heat exchanger tubes in a nuclear power plant. The ECA probes are usually produced by arraying multiple exciting/sensing coils with a transmitting-receiving scan approach. This paper introduces an alternative solution with cylinder-type magnetic cameras, which use a single exciting bobbin coil and a multiple magnetic sensor matrix. Two cylinder-type magnetic probes with different diameters (13.3 mm and 17.2 mm) and numbers of Hall sensors (11 × 12 and 16 × 23) were fabricated to inspect heat exchanger tubes. We propose a procedure to investigate both the circumferential and axial coverage performances of the cylinder-type magnetic probe. The coverage performance in the circumferential direction shows a better result than that in the axial direction (e.g., 72% with 55.17%) even they have the same spatial resolution. And, the coverage performances of the two probes have averages value over 89%.