Guided Wave Inspection Research Articles

1201 超音波ガイド波捏傷のためのメッシユレス弾性波動解析方法の開発

1201 超音波ガイド波捏傷のためのメッシユレス弾性波動解析方法の開発

J041021 圧電フィルムを用いたガイド波の多点計測([J041-02]超音波計測・解析法の新展開(2))

The guided wave is a kind of an ultrasonic wave and is used for the non-destructive test of huge structures, such as a pipeline. When defects exist in the structure, such as a slit and thinning, the propagation behavior of the guided wave is very complicated. Therefore, development of the interpretation of the measured guided wave is necessary in the on-site inspection. The authors have studied the guided wave measurement using PVDF. Then, the combination of the magnetostrictive transducer and the PVDF sensor will be applicable for sophisticated interpretation of the guided wave inspection. In this paper, the guided wave of a test specimen with a defect is measured using the combination, and the results are discussed.

Material hardness and ageing measurement using guided ultrasonic waves

Elastic properties of materials can be easily determined from the ultrasonic wave velocity measurement. However, material hardness cannot be obtained from the ultrasonic wave speed. Heat treatment and ageing affect the microstructure of many materials changing their hardness and strength. It has been already established that ultrasonic attenuation and dispersion are also affected by the material microstructure. It is investigated in this paper if the attenuation of ultrasonic guided waves can be correlated with the material ageing or duration of heat treatment and material hardness. To this aim six identical aluminum 2024 alloy plate specimens were subjected to different durations of heat treatment at 150°C and were inspected nondestructively propagating Lamb waves through the specimens. Attenuation of the Lamb wave was found to be inversely related to the hardness. Rockwell hardness test was performed to corroborate the ultrasonic observations. In comparison to the Rockwell hardness test the ultrasonic inspection was found to be more sensitive to the heat treatment duration and material ageing. From these results it is concluded that guided wave inspection method is a reliable and probably more desirable alternative for characterizing the hardness and microstructure of heat treated materials. Earlier investigations correlated the bulk wave attenuation with the material ageing while this work is the first attempt to correlate the guided wave attenuation to the material hardness and ageing.

Extracting Quantitative Information on Pipe Wall Damage in Absence of Clear Signals From Defect

It has been well established that guided waves are sensitive to structural damages encountered on their path of propagation and for this reason this technique is very efficient for distinguishing defective structural components from defect-free ones. Although the guided wave technique can identify a specimen having a distribution of defects, detecting and quantifying a small defect on its path from a long distance, as required for structural health monitoring (SHM) applications, is not an easy task for the guided wave inspection technique even today, especially when the transducers cannot come in direct contact with the pipe wall. The current technological challenges for pipe inspection by generating guided waves using noncontact transducers are to detect a small defect on the pipe wall and estimate its location and size from a long distance when the reflected signal from the defect cannot be clearly identified as is the case for low frequency guided waves that can propagate long distances. Electro-magnetic acoustic transducers (EMATs) are used here to generate guided waves in the pipe by the noncontact technique. This paper shows how small a defect in a pipe wall can be detected and its location and dimension can be estimated using relatively low frequency guided waves generated and received by EMATs even when the defect signal is not clearly visible in the time history plot because various wave modes reflected from the defect and pipe ends overlap.

자기자화자왜센서를 이용한 설비 off-line Health Monitoring 시스템 개발

본 논문은 석유화학 플랜트 등의 결함을 자기자왜센서기술을 활용하여 주기적으로 검사하는 오프라인 모니터링이 가능한 'Health Monitoring System'의 개발과 그 활용성에 대해 확인하였다. 기존의 유도파 검사 방식은 용접부위 검사에는 적용할 수 없고, 일반적인 부위에서도 노이즈 및 반사파 등으로 검사의 정밀도에 한계를 갖고 있다. 본 기술은 주기적인 모니터링을 통해 결함의 진전에 따른 변위정보를 활용할 수 있음으로서, 더 정밀한 검사가 가능하기 때문에 석유화학 플랜트에서 매우 유용하게 활용될 수 있을 것으로 사료된다. This thesis examines the development and application of 'Health Monitoring System' which monitors periodically the state of a pipe of petrochemical plant by using magnetostrictive sensor technology. The existing guided-wave inspection methods cannot be applied to welding part inspection in pipe, and has a limit of precision when applied to general parts because of noise, reflected waves, and so on. This technology uses the information on displacement of a defect through periodic monitoring, which makes more precise inspection, and can be utilized very usefully in a petrochemical plant.

Guided Wave Inspection and Monitoring of Railway Track

Cost-effective NDE of the vast length of aging railway track around the world remains a challenge for the community. Continuously welded rail is installed in tension but temperature changes can result in rail buckling if the initial tension is insufficient or fatigue cracks and ultimately rail breaks if the initial tension is excessive. The NDE challenge therefore includes both the detection of defects and the measurement of axial stress. Since continuously welded railway lines may be thought of as one-dimensional elastic waveguides, they are natural candidates for guided wave ultrasound, which offers the potential to interrogate a large length of rail from a single position. Guided waves have been proposed as a means of detecting the axial stress in rails to prevent buckling and also as a means of detecting complete breakage and cracks prior to breakage. This paper reviews the approaches used and the modeling methods available to support the development of nondestructive inspection and monitoring systems. Possibilities for future systems are also discussed.

Defect Imaging Using Time Reversal Guided Waves in Pipes

In order to realize defect imaging for guided waves inspection in a pipe, a time reversal method based on baseline subtraction method was introduced. In this method, baseline signals were prepared by detection on undamaged pipe. After that residual signals were obtained by executing subtraction between inspection signals and baseline signals. At last, without using the rectangular window for signal interception, time reversals signals are produced by time reversing the whole residual signals. Experiment and numerical simulation results show that this method simplifies the existing time reversal defect imaging method for guided wave inspection in pipes. Especially, a relatively whole defect’s passive wave field captured by this method will help us to achieve better imaging effect.

Torsional guided wave attenuation in piping from coating, temperature, and large-area corrosion

Guided wave inspection is a recently commercialized approach for assessing the integrity of pipeline structures. It involves propagating a guided wave along a length of pipe and any abrupt change in the cross-section reflects a portion of the energy, indicating both the location and severity of damage from the detected signal. While not having the sensitivity of other inspection strategies, the technology is advantageous given its potential to rapidly inspect relatively long distances from a single sensor installation. One challenge with guided wave inspections is that general corrosion occurring over a large surface area, which is a common problem in many industries, may not reflect enough energy to be detected given the lack of an abrupt change in the cross section of the pipe. A potential solution for detecting and characterizing large-area corrosion is to measure the attenuation of the guided wave. Experiments were performed to measure the attenuation of the fundamental torsional guided wave over a 10–140kHz frequency range for varying degrees of corrosion. Additionally, guided wave attenuation was measured on pipes with three different corrosion-protection coatings over a 10–60kHz frequency range as a function of ambient temperature. By understanding the degree of attenuation as a function of both frequency and temperature in common pipeline configurations (coated and uncoated), it should be possible to approximate the degree of corrosion of in-service pipeline.

Non-Contact Guided Waves Tomographic Imaging of Plate-Like Structures Using a Probabilistic Algorithm

A non-contact testing with laser generated ultrasonic transmitter and an air-coupled transducer is very attractive technique in guided wave inspection. It can be used for online inspection and structural health monitoring (SHM) where contact method with embedded sparse sensors can not be applied such as the case of high temperature application. In this paper, tomography based on probabilistic algorithm was employed in conjunction with the hybrid non-contact method. This present approach can be successfully used for detecting, locating and imaging multi-defect in plates. This algorithm is based on the use of signal difference coefficient of guided waves acquired for good and faulty conditions. The simplicity of this algorithm makes it suitable to be implemented to non-contact based online inspection scheme. [doi:10.2320/matertrans.I-M2011853]

Study and comparison of different EMAT configurations for SH wave inspection

Guided wave inspection has proven to be a very effective method for the rapid inspection of large structures. The fundamental shear horizontal (SH) wave mode in plates and the torsional mode in pipe-like structures are especially useful because of their non-dispersive character. Guided waves can be generated by either piezoelectric transducers or electro- magnetic acoustic transducers (EMATs), and EMATs can be based on either the Lorentz force or magnetostriction. Several EMAT configurations can be used to produce SH waves, the most common being Lorentz-force periodic permanent magnet and magnetostrictive EMATs, the latter being directly applied on the sample or with a bonded strip of highly magnetostrictive material on the plate. This paper compares the performance of these solutions on steel structures. To quantitatively assess the wave amplitude produced by different probes, a finite element model of the elementary transducers has been developed. The results of the model are experimentally validated and the simulations are further used to study the dependence of ultrasonic wave amplitude on key design parameters. The analysis shows that magnetostrictive EMATs directly applied on mild steel plates have comparatively poor performance that is dependent on the precise magneto-mechanical properties of the test object. Periodic permanent magnet EMATs generate intermediate wave amplitudes and are noncontact and insensitive to the variations in properties seen across typical steels. Large signal amplitudes can be achieved with magnetostrictive EMATs with a layer of highly magnetostrictive material attached between the transducer and the plate, but this compromises the noncontact nature of the transducer.

Application of Ultrasonic Guided Waves Testing Method in Coiled Springs

In this paper,application of defect detection by ultrasonic guided waves in springs has been studied in three aspects,which are theoretical calculation, simulation modeling and experiments.For the springs structure is helix and it can not be directly described easily,less work has been done on theoretical calculation of elastic wave propagation in the springs.The elastic wave equation of the spiral structure is established and calculated numerically here,considering the theoretical calculation helps to quantitative analyze the law of elastic wave propagation in the springs.Then guided waves dispersion relations corresponding is achieved.The experimental results of spring field testing agree well with the theoretical calculations and simulations,indicating the effectiveness of ultrasonic guided waves inspection in springs.

Experimental Study of High Frequency Guided Wave Inspection of Anchored Bolts

High frequency longitudinal guided waves were used to inspect the anchored rock bolts. Experiments were conducted to find the optimal frequencies for the bolt testing. A broad-band signal was excited at the top end of the bolt, and the power spectral density(PSD) analysis of the bolt end reflected waves was made. Base on that the frequency component of the bolt end reflected waves could be obtain, and the frequencies with higher power spectral density values are the optimal ones. At optimal frequencies, the guided wave attenuates more slightly than it is at other frequencies and the bolt end reflected waves can be clearly acquisitioned. Experimental results show that the optimal frequencies of guided wave in a free bolt and in an anchored bolt are quite the same, and they are mainly affected by the bolt instead of the anchor media. Conclusions can be drawn that the propagation velocities of guided wave at optimal frequencies in a free bolt are close to those in the embedded section of the bolt. As a result, the bolt length and the position of flaw in the anchored bolt can be determined by the guided wave velocity in a free bolt and the reflected wave from the bolt end and from the flaw, respectively.

Guided Waves Tomography and Image Fusion for Damage Identification in Pipes

The detection of localized defects such as cracks and corrosion in pipes using guided waves has been shown to be an effective nondestructive evaluation technique for structural health monitoring (SHM). Cross borehole tomography in seismology is introduced into the guided wave inspection of a pipe when the pipe is considered as an unwrapped plate. Guided waves propagating in pipe with a crack defect are simulated using the finite element model and the arrival times for the fastest modes are extracted and sent to the tomographic algorithm. The tomographic reconstruction is based on the simultaneous iterative reconstruction technique (SIRT). For some cylindrical shell geometries such as stacked storage tanks, access to the entire circumference of the structure could be impractical or even impossible, three different image fusion techniques are used to enhance the image equality reconstructed from the incomplete datasets. The results show that the defect is more pronounced after imaging fusion.

An Analysis for Effect Factors of Ultrasonic Guided Wave Tomography in Structural Health Monitoring

Localized flaws such as corrosions in petroleum pipelines often cause fragility, impairing integrity and shortening service lifetime of the structures. There has been much interest recently in monitoring the integrity of the pipe structures. Ultrasonic guided waves provide a highly efficient technique for rapid pipe inspection because they can be made to propagate significant distances in pitch-catch configurations. Crosshole tomographic geometry is formed in such pitch-catch configurations when transmits and receivers are respectively laid along two parallel circumferential belts around the pipe. Considering the pipe as an unwrapped plate, we investigate the adapation of the tomographic reconstruction in seismology to the guided wave inspection of a pipe. Various effects such as transducer arrangement, mesh precision, sampling interval and iterative algorithm on tomographic reconstruction are analyzed. The results provide a theoretical basis for quantitative detection of pipeline flaw using guided wave tomography.

Double-channel, frequency-steered acoustic transducer with 2-D imaging capabilities

A frequency-steerable acoustic transducer (FSAT) is employed for imaging of damage in plates through guided wave inspection. The FSAT is a shaped array with a spatial distribution that defines a spiral in wavenumber space. Its resulting frequency-dependent directional properties allow beam steering to be performed by a single two-channel device, which can be used for the imaging of a two-dimensional half-plane. Ad hoc signal processing algorithms are developed and applied to the localization of acoustic sources and scatterers when FSAT arrays are used as part of pitch-catch and pulse-echo configurations. Localization schemes rely on the spectrogram analysis of received signals upon dispersion compensation through frequency warping and the application of the frequency-angle map characteristic of FSAT. The effectiveness of FSAT designs and associated imaging schemes are demonstrated through numerical simulations and experiments. Preliminary experimental validation is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The presented results demonstrate the frequency-dependent directionality of the spiral FSAT and suggest its application for frequency-selective acoustic sensors, for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health.

An analytical model for guided wave inspection optimization for prismatic structures of any cross section

This paper presents an analytical modeling technique for the simulation of long-range ultrasonic guided waves in structures. The model may be used to predict the displacement field in a prismatic structure arising from any excitation arrangement and may therefore be used as a tool to design new inspection systems. It is computationally efficient and relatively simple to implement, yet gives accuracy similar to finite element analysis and semi-analytical finite element analysis methods. The model has many potential applications; one example is the optimization of part-circumferential arrays where access to the full circumference of the pipe is restricted. The model has been successfully validated by comparison with finite element solutions. Experimental validation has also been carried out using an array of piezoelectric transducer elements to measure the displacement field arising from a single transducer element in an 88.9-mm-diameter pipe. Good agreement has been obtained between the two models and the experimental data.

J042024 複数の周波数のガイド波を用いた減肉形状の推定([J04202]超音波計測・解析法の新展開(2))

J042024 複数の周波数のガイド波を用いた減肉形状の推定([J04202]超音波計測・解析法の新展開(2))

A Time Reversal Guided Wave Inspection Method Based on One Signal Generator Tunnel

Aiming at the multi-channel problem for the time reversal guided wave inspection,a new signal incited method is proposed based on the investigation of the relationship between the detection signals and the locations of transducers.In this method,different time reversal signals are re-incited one by one by different transducers with different time intervals which will be compensated by the intervals between different transducers.According to this,a time reversal guided wave defect inspection method based on one signal generator channel can be realized on reasonable transducer locations,interception window width and L(0,2) mode used for forcing defect guided wave source.The result of numerical simulation show that the interception window width and the quantity of transducers are important factors influencing inspection capability of the time reversal guided wave.

Long-Range Testing of Welded Elbow Pipe Using the T(0,1) Mode Ultrasonic Guided Wave

An experimental investigation of sensitivity in defect detection in welded elbow pipes using the T(0, 1) mode guided wave was carried out. A piezoelectric ring-shaped sensor system was cramped on one of the two straight parts in the straight-elbow-straight setting. An artificial defect was introduced into the other straight part. To evaluate the sensitivities, the depth of the artificial defect was gradually increased to 2.0 mm by 0.05 mm increments. The following are the obtained experimental results. (1) Spurious signals due to the two welds, which could be markedly changed by varying the welding conditions were found. (2) These spurious signals interfered with and masked the defect signal, but changes in signal amplitude owing to the incremental defect could be sufficiently detected. (3) Sensitivities of defect detection in welded elbow pipes were approximately 1/4–1/5 that in a straight pipe. At the end of the paper, the characteristics of the observed waveform in the welded elbow pipes are discussed for use in the guided wave inspection.

Detection and Mode Identification of Axial Cracks in the Steam Generator Tube of the Nuclear Power Plant Using Ultrasonic Guided Wave

For those people who are involved in NDE, there is a growing concern regarding the significant traveling distance of a guided wave in a structure, which ensures the inspection of a large area of the structure from a single location. A significant number of studies on the guided wave have therefore been made to apply the foregoing to a nondestructive evaluation in many different industries and resulted in an increase in the efficiency of practical guided wave inspection. Unlike the previous studies based mainly on the detection of circumferential flaws, this study is focused on the axial flaw detection in the steam generator tubes of Korean standard nuclear power plants by generating the guided wave by changing frequency and selecting the applicable mode from the dispersion curve for the steam generator tube calculated in this study, where the dispersion-based short-time Fourier transform (D-STFT) algorithm is used to enhance mode identification. In conclusion, the L (0,1) mode at 2.25MHz is found to be most sensitive in detecting axial flaws in a steam generator tube.