All-Round Inspection of a Pipe Based on Ultrasonic Guided Wave Testing Utilizing Magnetostrictive Method and HTS-SQUID Gradiometer

We developed an ultrasonic guided wave testing system for pipes utilizing magnetostrictive method and hightemperature superconductor (HTS) superconducting quantum interference device (SQUID) gradiometer. Two pre-magnetized nickel thin plates were adhered on an aluminium pipe. One of them with a field coil was used as a magnetostriction-based T (0, 1) mode guided wave transmitter, while the other was used as a receiver. Allround inspections of the pipe without and with a circumference slit were conducted by measuring the T (0,1) mode guide waves around circumference of the pipe using the HTS-SQUID-based guided wave testing system. The optimum experimental setup about excitation frequency and input current to the transmitter was investigated using ez-SQUID electronics. By applying a sine burst current of 0.2 A at 50 kHz with single cycle to the transmitter and rotating the pipe stepwise at 30°, “B-scan” images of the guided wave propagating on the pipe without and with slit were measured. An axisymmetric distribution of a reflected wave from the slit was well detected. We analyzed distribution of incident waves and reflected waves from the end of the pipe based on magnetization in the nickel plates using an electromagnetic simulator and proposed a new transducer.