Nondestructive Testing of Ferromagnetic Tubes using a Bobbin-type Integrated Hall Sensor Array

A probe that can examine a ferromagnetic heat-exchanger finned tube with a curved part is proposed in this paper. The distortion in the electromagnetic field due to the existence of flaws and tube support plate (TSP) was measured using an active-type excitation coil, a bobbin-type Hall sensor array, and a passive-type pick-up coil. The active-type excitation coil could recognize the existence and location of flaws. The Hall sensor array could recognize the existence, location, and distribution of flaws. The passive-type pick-up coil could recognize the position of TSP, which was used as a landmark. The effectiveness and TSP-recognition ability of the proposed probe were verified using a finned-tube specimen made of STS 439 with various types of artificial defects.