Magnetic NDE system for detection of crack in steel deck with high lift-off using secondary differential detection coil

Recently, the aging of buildings and infrastructure facilities is becoming a social problem. In the steel structure, the nondestructive evaluation with high lift-off is required to inspect the steel material under the asphalt or concrete, such as the steel floor slabs of roads. Under the high lift-off condition, the influence of the magnetic noise and applied magnetic field should be reduced because the signal from the crack is small. In order to reduce the influence of the magnetic noise, in this study, the detection of crack signal by eddy current testing was examined using a detection coil of a differential coil. This differential coil is a secondary differential coil combining two differential coils aiming for improving the signal to noise ratio (SNR) by reducing the influence of the magnetic noise and applied magnetic field. Using this secondary differential coil, the crack with high liftoff of 80 mm was detected, and it is expected to detect the cracks in steel structures located under the asphalt or concrete.