Inductive coil is used as the nondestructive testing sensor of a wire rope or a pipe, because of its low cost and high durability. However, the winding structure is complex and difficult to design during the field test. Hundreds or even thousands of turns are needed to improve the signal to noise ratio (SNR) and the data processing is cumbersome. In this paper, based on the theoretical analysis and 3D transient magnetic field simulation, a kind of iron core is presented as coil winding skeleton for the wire rope nondestructive testing. Additional iron core plays a role of magnetism concentration, where the magnetic flux leakage (MFL) path is changed and the MFL of the defect is converged to the core. Therefore, the SNR of the coil which is wound on the iron core is improved, and the coil winding skeleton is simplified with the iron core structure optimization. Meanwhile, the influence of the coil cross-section area on the test result analysis is eliminated, and the influence of the lift-off distance between coil and wire rope on the detection result is also reduced. Finally, it is proved by experiment that the SNR of coil with the iron core proposed in this paper is increased almost six times, which makes it easier for defect analysis.

Improve the signal to noise ratio and installation convenience of the inductive coil for wire rope nondestructive testing

The pipeline in-service needs to be inspected in a certain period to master its structural health status. An ultrasonic guided wave, which can propagate along pipelines with less energy loss, provides an efficient method for long-term in situ inspection. The guided waves can detect both corrosion and cracks existing in structures. To overcome the problem of huge amounts of data and to maintain defect identification accuracy, the compressed sensing method for guided wave inspection is proposed. The compression process is essentially a scheme of analog to information conversion to compress the signal. It is accomplished by random demodulation and the equivalent sampling rate below the Nyquist rate helps to save most of the storage. Compressed data are recovered to the sparse spatial domain based on the constructed dictionary from a guided wave propagation model. To verify the effectiveness of the proposed method, both numerical simulations and experimental investigations are conducted. The results indicate the availability of compression and high accuracy of defect location after recovery. The influences of different compression schemes and compression ratios are further analyzed. In addition, the comparisons with direct recovery without compression and traditional analysis methods demonstrate the advantageous performance of the proposed method.

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Compressed Sensing Method for Health Monitoring of Pipelines Based on Guided Wave Inspection

Ultrasonic guided wave-based nondestructive testing systems are widely used in various fields of industry where the structural integrity of components is of vital importance. Signal interpretation in these systems might become challenging due to multimodal and dispersive response of the interrogated structure. These phenomena degrade the signal-to-noise ratio and also lower the spatial/temporal resolution. This paper compares the use of Maximal Length Sequences and linear chirp excitation signals to develop a novel signal processing technique using dispersion compensation and cross-correlation. The technique is applied to both simulated and experimental multimodal signals from an aluminium rod for performance assessment. It is quantitatively validated that the technique noticeably improves the signal-to-noise ratio of the guided wave response and is able to acquire an accurate time of flight of the individual wave modes, and hence, the propagation distance. The technique is compared for both linear chirp and maximal length sequences excitation signals. Noise analysis for these excitation signals is also presented.

Coded Waveform Excitation for High-Resolution Ultrasonic Guided Wave Response

Ultrasonic guided wave testing method is very effective in safety monitoring of complex structures, such as large-scale tank floor and industrial metal plate. The fundamental shear horizontal (SH) wave mode with the Lorentz force mechanism has the advantage that the propagation velocity does not change with the frequency. However, it is hard to recognize the dispersed ultrasonic signal accurately due to the bidirectional propagation characteristics of the SH guided wave. Therefore, a new transducer structure with a fan-shaped periodic permanent magnet (PPM) and centripetal conductor has been designed to achieve guided wave focusing and signal enhancement. Compared with the traditional transducers, the new-designed transducer has been proved to be more effective in energy focusing on the simulation and experimental verification. For the new structure of the transducer, the aperture angle, focusing radius, and coil rotation angle are studied in detail in this paper. The results show that, as the aperture angle and the coil rotation angle decrease, the signal intensity becomes higher at the focusing position. Moreover, as the focal radius increases, the amplitude of the ultrasonic signals on the focusing side and the divergent side will decrease, while the difference between the two sides will increase exponentially. In the defect detection in this paper, the reflected signal intensity of the new-designed fan-shaped PPM focusing coils electromagnetic acoustic transducer (EMAT) is approximately two times that of the traditional parallel PPM parallel coils EMAT. Therefore, the newly designed EMAT is of great significance for the signal enhancement.

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Point-Focusing of Shear-Horizontal Wave Using Fan-Shaped Periodic Permanent Magnet Focusing Coils EMAT for Plate Inspection

Detection of magnetic flux leakage (MFL) is widely used in nondestructive testing (NDT) of wire rope. We built and tested an MFL measuring device based on unsaturated magnetic excitation to address...

Quantitative nondestructive testing of wire rope based on pseudo-color image enhancement technology

As a rapid, noncontact, and nondestructive technology, magnetostrictive guided waves have been widely used for the quality inspection of pipes and stay cables. Traditionally, a single-frequency signal with a high amplitude and a long pulse duration is used to increase the excitation energy and detection distance. However, the longer the pulse duration of a single-frequency signal is, the lower the resolution of adjacent defects and the accuracy of defect location will be. A novel method of addressing this problem is proposed in this paper. An encoded multifrequency excitation signal, whose frequency range is selected from a calculated dispersion curve, is used to excite the guided wave. After passing through the signal-conditioning board, the detected defect signals are sampled, averaged, and then filtered using a matched filter. In this manner, the pulse width of echoes can be greatly compressed. Our experimental results demonstrate that our proposed method can improve the resolution of adjacent defects and the accuracy of defect location in the propagation direction of the magnetostrictive guided wave.

A Magnetostrictive Guided-Wave Nondestructive Testing Method With Multifrequency Excitation Pulse Signal

The invention discloses a detecting device based on magnetostrictive guide waves. The detecting device comprises a signal generator, power amplifier connected to the signal generator, a excitation sensor connected with the power amplifier, a detection sensor, a signal conditioner connected with the detection sensor, a signal collector connected with the signal conditioner, a PC (personal computer) connected with the signal collector and a power device for powering the devices above. Guide wave signals are excited and detected on part of areas of the outer surface of a pipeline, and the problem that sensors surrounding the pipeline cannot by mounted due to the space between the pipeline and periphery objects is small is solved. Encoding signals are used as excitation signals, time width of the excitation signals is increased, frequency variation range of the encoding signals is set between 1kHz and 200kHz, high-pulse-compression-ratio signals are obtained through sampling signal processing and analyzing, high adjacent flaw resolution along the length direction of a to-be-detected object is achieved, and large guide wave detection range is obtained.

Detecting device and method based on magnetostrictive guide waves

The invention discloses a transverse wave detecting device based on magnetostrictive guide waves. The detecting device comprises a signal generator, power amplifier connected to the signal generator, a excitation sensor connected with the power amplifier, a detection sensor, a signal conditioner connected with the detection sensor, a signal collection storage connected with the signal conditioner, a PC (personal computer) connected with the signal collection storage and a power device for powering the devices above. The signal generator is further connected with the signal collection storage. The excitation sensor comprises a permanent magnet and excitation coils circumferentially winding on a to-be-detected object. The detection sensor comprises a permanent magnet and detection coils circumferentially winding on a to-be-detected object. Multiple layers excitation coils are nested to excite guide waves higher in energy, and effective detecting range of the guide waves is enlarged. Multiple layers of detection coils are serially connected layer by layer, amplitude of guide wave echo signals is increased, high detection signal to noise ratio is obtained, and detection flexibility is increased.

Transverse wave detecting device and method based on magnetostrictive guide waves

Because of loss of cross-sectional area of pipes and ropes caused by corrosion and mechanical damage, the maximum stress and structural strength of material will be greatly reduced. In order to avoid structural failure, it is important to intelligently measure the loss rate of cross-sectional area of material. The traditional methods of measuring the residual material thickness are based on contact measurement method, so the measuring efficiency is low and it is not suitable for long time intelligently health monitoring of structure. This paper proposes a novel method to solve this problem. Magnetostrictive sensors are used to excite guided wave and detect the signals reflected from defects. And then, the cross-sectional loss of the defects can be intelligently calculated by using the detected signals by monitoring computer. The calculated results will be helpful for structural health measurement. The experimental results demonstrate that our proposed method can realize long range and non-contact intelligent measurement of cross-sectional loss of material.

Jinping Sun

Papers

A Magnetostrictive Guided-Wave Nondestructive Testing Method With Multifrequency Excitation Pulse Signal

Detecting device and method based on magnetostrictive guide waves

Transverse wave detecting device and method based on magnetostrictive guide waves

Intelligent magnetostrictive measurement technology for loss rate of cross-sectional area of rectangular notch