Abstract
We developed a non-contacting ultrasonic guided wave testing technique using magnetostrictive effects and high-temperature superconductor (HTS) SQUID for STPG370 steel pipes. A pair of C-shaped electromagnets was used to magnetize the STPG370 pipe while rotating the pipe, in order to give uniform remnant fields as bias fields. Conditions to give larger remnant field in the pipe were investigated using an electromagnetic field simulation. The simulation results indicated that C-shaped pb permalloy iron cores with an aperture angle of 20 degree and a diameter of 20 mm should be utilized for the magnetization. An excitation coil was wound around one of the magnetized parts, which is used as a transmitter. One cycle sine current of 9 App at 50 kHz was repeatedly supplied to the coil to generate T(0,1) mode guided waves in the pipe. The other magnetized part, which was used as a receiver, was combined with the HTS-SQUID gradiometer, which was located above the pipe with a lift-off of 4 mm. In measurements, the pipe was rotated to perform all-round measurements. A contour map of the time-series signal distribution of T(0, 1) mode guided wave was obtained around the pipe.
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