Affiliations: [a] Department of Control and Instrumentation Engineering, Chosun University, Gwangju, Korea | [b] Department of Mechanical and Automotive Engineering, Chonnam National University, Gwangju, Korea | [c] KEPCO Plant Service and Engineering Co., Ltd., Busan, Korea
Correspondence:
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Corresponding author: Jungmin Kim, Department of Control and Instrumentation Engineering, Chosun University, Gwangju 501-759, Korea. Tel.: +82 62 230 7101; E-mail:jm.kim@chosun.kr
Abstract: This paper proposes an encircling-type magnetic camera
for inspecting the damage to control rods. The magnetic source and sensors
in the magnetic camera were separated from each other, which minimized the
electromagnetic interference of adjacent sensors and improved the spatial
resolution. An induced current (IC) appears on a control rod whenever a
time-varying current is applied to the magnetic source, i.e., an encircling
coil. The IC flows along the circumferential direction (θ -direction)
of the rod, and generates a time-varying magnetic field in the radial
direction (r-direction) around the defect. Bobbin-type integrated Hall
sensors are arrayed inside the encircling coil, and therefore the
r-direction magnetic field around the defect is measured. Seventeen Hall
sensors were arrayed at a 21° angle with respect to 1.85-mm resolution
to measure the electromagnetic field distribution on a stainless-steel small
bore piping system, which had an external diameter of 10 mm and a thickness
of 0.5 mm. The 40% (1-mm diameter) and 20% (3-mm diameter) depths of
the hole-type wears were inspected using the proposed system. In addition,
slit-type cracks with a length of 3 mm, depth of 0.2 mm, and width of 0.1 mm
in both axial and circumferential directions could be inspected.
Keywords: Control rod, encircling coil, eddy current, sensor array, small bore piping system, magnetic camera, imaging
