Experimental Research On NDT Of Steel Tubes Using Magnetostrictive Guided Waves

Guided waves technology has much potentiality in testing of pipe works for its advantages of high efficiency and low costs compared to traditional methods. Non-destructive testing of steel tubes using magnetostrictive device was experimentally studied.An experimental system prototype was firstly developed,which consists sensors, transmitters and receivers. A personal computer in cooperation with a single-chip processor was used to automate the experimental procedure. The signal generating circuit is implemented by gating the continuous sinusoidal wave for several cycles. The signal-to-noise ratio was improved through two measures of connecting the electrical ground of the conditioning circuits to the steel tubes tested and averaging the detected signal. The software based on the ADlink card and Windows operating system was developed for data acquiring, recording, and displaying. The experimental results show that the system can be employed to low frequency magnetostrictive guided wave test.Secondly, the wave propagation experiments are made on two different steel tubes in good condition. The excited wave modes and their dispersion were analyzed by time and time-frequency domain signal processing methods. Effects of different parameters, i.e. number of gated cycles and density of magnetic field, on guided waves transmitting are evaluated. The comb sensor, circumferential array sensor and radial sensor were designed and discussed with experimental results and theoretical predictions.Finally, two different artificial defects of different sizes were manually made and detected using L(0,2) mode. Reflected signals by defects can be recognized for holes of 3.5mm in diameter and notches of 1.5mm in depth, respectively. The results may provide reference for practical applications.