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The use of guided waves is now widespread in industrial NDT for locating metal loss in pipelines, that manifests as pitting, corrosion and general wall thinning. In this paper, a screening technique is assessed in terms of defect detection and defect sizing capability. Shear Horizontal (SH) guided waves propagate circumferentially around the pipe whilst the scanner is moved axially along the length. This type of tool is preferable to other methods, being applied to the exterior of the pipe, without requiring full circumferential access, and is able to operate through thin coatings (up to 1 mm thick). It is designed to provide a pipe screening tool for petrochemical pipelines both topside and subsea, particularly for detecting defects at pipe support areas. The system's efficacy in terms of detection and sizing of defects is considered via experimental measurements on artificially induced defects and in service corrosion patches, with results compared to finite element modelling of the interaction of the guided waves with artificial defects. Finite element modelling has been used to better understand the behaviour of different wave modes when they interact with defects, focusing on the mode conversions and reflections that occur. 相似文献
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The reflection of guided waves from notches in pipes: a guide for interpreting corrosion measurements 总被引:7,自引:0,他引:7
A. Demma P. Cawley M. Lowe A. G. Roosenbrand B. Pavlakovic 《NDT & E International》2004,37(3):167-180
Ultrasonic guided waves are used for the rapid screening of pipelines in service and simple, standard testing procedures are already defined. The implementation of the method enables the localization of the defects along the length of the pipe and offers a rough estimate of defect size. In this article we present a systematic analysis of the effect of pipe size, defect size, guided wave mode and frequency on the reflection from notches. The maximum and minimum value of the reflection coefficient at varying axial extent are identified and used for the purpose of defect sizing. Maps of reflection coefficient as a function of the circumferential extent and depth of the defect are presented for a 3 in. schedule 40 steel pipe. An approximate formula, which allows these results to be extrapolated to other pipe sizes, is proposed and evaluated. 相似文献
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There is an increasing interest in high frequency short range guided waves to screen or monitor for corrosion. This contrasts with long range guided waves (LRGWs) which screen pipes for large patches of corrosion and have been successfully used in corrosion management for the past twenty years. The fundamental setup described in this paper uses circumferential guided waves, which are excited at a single location on a pipe and travel around the pipe wall and are detected at the same location. The study uses a finite element model assisted method to evaluate the detection capability of two short range circumferential guided wave setups which use both the reflected and transmitted signals. The setups themselves consist of either an axial array of transducers, for monitoring, or a single transducer which axially scans a pipe. Both setups have an array or scan pitch between either adjacent transducers or measurements. The detection capability of the fundamental Lamb wave modes (A0 and S0) in both reflection and transmission have been compared, as well as a hybrid shear horizontal wave setup, which uses the SH0 mode in reflection and the SH1 mode in transmission. A sensitivity analysis was conducted using two separate methods to determine the probability of detection (POD) for either the reflection or transmission signals. Both methods determine a POD for a specific defect, noise level, and array or scan pitch. Probability images are produced which map the POD for a range of defect sizes. For the parameters investigated in this study, it was found that in transmission large diameter defects have a higher detectability, whereas deep, narrow diameter defects are more detectable in reflection. A generalised overview of the sensitivity of short range guided waves is presented by combining both the reflection and transmission PODs. The data fused sensitivity of the S0 and SH hybrid modes are given as 0.6% and 0.75% cross sectional area (CSA) respectively, allowing for the comparison with LRGWs. The A0 mode was excluded from the POD analysis because it was much less sensitive than the other two modes. 相似文献
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Local wall thinning of pipes, resulting from corrosion, is the major cause of accidents in nuclear power plants. In order to assure the integrity of pipes, a variety of NDE techniques have been proposed. It is well recognized that the utilization of guided waves to detect flaws in pipes has been a very effective tool for long-range inspection in NDE. Since most conventional research on guided waves has focused on long-range inspection, it is difficult to evaluate a defect in a local area. An objective of this study is to develop a non-contact inspection technique for the quantitative evaluation of defects on a local area in a cylindrical tube. Therefore, the purpose of this study is to introduce an advanced inspection system and a new signal processing method for the evaluation of defects such as corrosion in a pipe. In this study, an advanced non-contact method for pipe inspection is proposed, which generates the ultrasonic guided wave by laser and receives it by a dual air-coupled transducer. Information on each directional defect location and length is obtained by using a line scan along a circumferential and longitudinal direction. Received signals are analyzed by using the peak-to-peak amplitude of waveform and the maximum center frequency magnitude of the frequency spectrum. The optimal mode selection of guided waves based on a dispersion curve is also discussed. The experimental results using the proposed method show that the location and the size of the defect could be evaluated successfully in the 2-dimensional scanning images. 相似文献
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根据铜管中轴对称纵向模式导波的频散曲线及L(0,2)模式导波的位移分布曲线,选择频率0.49MHz的L(0,2)模式导波,对带有不同缺陷的铜管进行检测试验。结果表明,L(0,2)模式导波对铜管中各种缺陷均有良好检出能力,缺陷的反射波幅主要取决于缺陷径向和周向尺寸,而缺陷的轴向尺寸对反射波幅基本没有影响。 相似文献
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The investigation addresses the scope of rapidly quenched Fe80Si8B12 ribbons as magnetostrictive sensor (MsS) material to generate guided waves in galvanised iron pipe and evaluation of defects with different geometries and dimensions. Enhancement in the effective defect size (EDS) of transverse and pit type defects increased the MsS signal. However, the backwall echo showed opposing trend (transverse: reduced and pit: increased) with increase in dimensions of these defects. Such behaviour of backwall intensities has been correlated to different type of guided wave strain field distributions around these defects and reflection coefficients. 相似文献
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超声水平剪切(shear horizontal, SH)导波换能器在对焊接板结构进行缺陷检测时具有重要的应用价值. 为了研制换能器以对焊接结构进行多帧满秩成像检测, 运用导波半波长理论对超声SH导波的激发和换能器内部多重散射回波进行了分析.根据多重散射理论推导了匹配层介质颗粒密度与衰减的关系, 确定匹配层的组分. 提出3种V型斜楔结构, 对平面型前楔结构换能器和非平面型前楔结构换能器内部的多重散射回波进行对比试验. 结果表明,正交前楔结构换能器内部二重以上散射回波幅值减小了45%以上. 对正交前楔结构换能器进行性能测试, 其所激发的SH导波对焊接结构板中尺寸当量为?12 mm的缺陷回波信号信噪比达到了14.5 dB,具有较为优异的检测能力. 试验验证了理论分析的有效性, 所研制的正交前楔结构超声SH导波换能器可对焊接结构板中与波长尺寸当量的缺陷进行多帧满秩成像检测. 相似文献
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A quantitative study of the interaction of the T(0,1) torsional mode with axial and oblique defects in a pipe is presented in this paper. A mode decomposition technique employing the chirplet transform is used to separate the multimodal signals reflected from the defects. Reflection signals are obtained from experiments on a carbon steel pipe. The influence of the crack length and inclination angle on the reflection is investigated. Reflection from an axial defect is found to consist of a series of the wave pulses with gradually decaying amplitude. Results show that the reflection coefficient of the axial crack initially increases with the crack length, but finally reaches an oscillating regime. Furthermore, it is revealed that for an oblique crack, the reflection coefficient is linearly dependent on the equivalent circumferential extent of the defect and is independent of the axial length. In addition, it is shown that the coefficients for a steep defect are greater than those for a gentle defect. 相似文献
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Point-focusing electromagnetic-acoustic transducers (PF-EMATs) for shear-vertical (SV) waves were developed for crack inspection of stainless-steel pipes. The transducer has improved defect detectability by accumulating SV waves generated by concentric line sources at a focal point in phase. An optimum frequency for defect detection was found to be 2 MHz, with which a crack of 0.5 mm depth near a weld was clearly detected. The EMAT exhibited defect detectability comparable to that of a conventional phased-array piezoelectric transducer, indicating that this new EMAT is highly practical for the non-contacting evaluation of stress-corrosion cracking in stainless steels. 相似文献
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In recent investigations, the application of the transducers used in plates has been extended to pipe inspection with circumferential arrays because of the similar particle displacement patterns of some modes between plate and pipe, such as SH and torsional modes. Motivated by the configuration of magnetostrictive patch transducer (MPT), in which a planar solenoid array (PSA) coil was adopted to generate SH waves in plates, we proposed a MPTs array employing a modified planar solenoid array (MPSA) coil, i.e. MPSA coil-MPTs array, for generating and receiving the torsional mode in pipes. The configuration of the MPSA coil modified from PSA coil is suitable to be arranged on the pipe surface and can generate high-power waves. In the suggested configuration of MPT, because the direction of the actuating dynamic magnetic field produced by the MPSA coil is orthogonal to the direction of the static magnetic field produced by the permanent magnets in the magnetostrictive patch, the shear deformation induced by the magnetostriction in the patch will be delivered to the pipe, thus generating the torsional mode. First, it was experimentally verified that the fundamental torsional mode, T(0,1), could be effectively generated and received in pipes with the developed MPSA coil-MPTs array. Then, we studied the relationship between the frequency response characteristic of the developed MPSA coil-MPTs array and the interval defined by the distance of adjacent solenoids in the MPSA coil. Simultaneously, the circumferential crack defects in pipe were successfully identified. Finally, the performance of the MPSA coil-MPTs array was compared with that of previous meander coil-MPTs array. The comparison results demonstrated that the developed MPSA coil-MPTs array could enhance the power of the torsional mode. 相似文献
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板中水平剪切导波可用于焊接结构板材远距离成像检测,超声SH导波换能器的性能对较大尺度焊接结构板材超声导波成像检测至关重要.对板中SH导波进行了动力学分析,并结合半波长条件设计了合理的斜楔角度、压电晶片频率及尺寸等导波换能器的重要参数,通过加前背衬、取消后背衬、楔块前沿设置锯齿槽等措施,简化了换能器的工艺结构,减小了换能器内部回波干扰,提高了检测灵敏度.结果表明,设计研发的SH导波换能器激发的导波有较强的检测能力,可用于对较为复杂的T形一对焊焊接结构板材进行成像检测,能够有效表征焊接结构板材中与导波波长尺寸量级相当的缺陷,其性能指标达到了较大尺度焊接结构板材成像检测的要求.为开展较大尺度焊接结构超声导波成像检测奠定了基础. 相似文献
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Localised corrosion is a major concern in the petrochemical industry, and often occurs as clusters of pits. A study of the reflection from two and three small circular holes in pipes with the fundamental torsional guided wave incident is presented. FE analyses with both part and through thickness holes at different relative positions are presented, and are a step towards estimation of the scattering behaviour of multiple and random defects. The validity of employing the superposition technique in estimating reflection coefficients is assessed. Results show that the reflection coefficient for the T(0,1) mode is dependent on absolute frequency and axial separation, and independent of circumferential position. Employing superposition is found to be valid down to defect centre to centre separation distances of two diameters in the worst case, with improved validity with shallower defects. Results from the FE analyses are validated experimentally. 相似文献
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This work presents a method of characterising pipeline defects using a small number of radiographs taken at different angles around the pipe. The method relies on knowledge of the setup geometry and use of multiple images, and does not require calibration objects to be included in the setup. It is aimed at use in situations where access is difficult such as in subsea pipeline inspections. Given a set of radiographs, a background subtraction method is used to extract defects in the images. Using a ray tracing algorithm and knowledge of the experimental setup, the range of possible locations of the defect in 3D space is then calculated. Constraints are applied on potential defect shapes and positions to further refine the defect range. The method is tested on simulated and experimental flat bottomed hole defects and simulated corrosion patch defects with lateral and axial sizes ranging from 12.5 to 33.8 mm and thickness between 3 mm and 16 mm. Results demonstrate a good, consistent ability to calculate lateral and axial defect dimensions to within ±3 mm of the true size. Defect thickness calculations are more difficult and as such errors are more significant. In most cases defect thickness is calculated to within 4 mm of the actual value, often closer. Errors in thickness are due to overestimation, meaning the calculation could be used to place a maximum limit on potential defect size rather than as an actual estimate of the thickness. This would still be useful, for example in deciding whether a defect requires further investigation. 相似文献
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Recently, a magnetostrictive patch transducer (MPT) by means of the highly magnetostrictive (such as nickel or iron–cobalt alloy) patch attached on the specimen has been applied in nondestructive ultrasonic testing in waveguides. In the study, we proposed a new MPTs array employing a multi-splitting meander coil (MSMC) for generating and receiving longitudinal guided waves in pipes. In the suggested configuration, the directions of the static magnetic field produced by the permanent magnets and the dynamic magnetic field produced by the MSMC are in the axial direction of the pipe. Two finite element models were established to simulate the distribution of the static and dynamic magnetic fields in the patch, respectively. The proposed MSMC was made of flexible printed circuit (FPC), so it could be easily installed on pipe surface. The performance of the proposed MPTs array was experimentally studied. Firstly, it was experimentally verified that the axisymmetric longitudinal guided wave mode, L(0,2), could be effectively generated and received in pipes with the developed MSMC-MPTs array. Secondly, the frequency response characteristics of the developed MSMC-MPTs array were related to D (the distance between adjacent belts of the MSMC). Thirdly, we demonstrated the ability of the developed MSMC-MPTs array for the identification and location of a crack defect in pipes. Finally, we compared the performances of the MSMC-MPTs array and conventional meander coil-MPTs and proved that the signals of the longitudinal guided wave mode could be enhanced by using the developed MSMC-MPTs array. 相似文献
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To Kang Dong-Hoon Lee Sung-Jin Song Hak-Joon Kim Young-Do Jo Hyun-Joon Cho 《NDT & E International》2011,44(2):178-187
Ultrasonic guided waves have been widely utilized for long range inspection of structures such as oil and petrochemical pipes. However, weldments, support, insulation, and attenuation make it difficult to examine pipe-like structures. In order to overcome such difficulties, it is desired to focus ultrasonic guided wave at the area under interrogation. In this paper, we discuss two focusing techniques: angular profile tuning and signal based focusing. The angular profile tuning approach relies on a theoretical prediction of pressure field of ultrasonic guided wave produced by an ultrasonic transducer mounted on the pipe. And, the signal based focusing is focusing ultrasonic guided waves using cross-correlation analysis. To compare the performance of these two techniques, non-axisymmetric guided waves are focused to abnormalities such as a through-wall hole and a circumferential notch, using an ultrasonic guided wave array system that has been specially fabricated for this purpose. The advantages and limitations of these two focusing techniques are addressed. 相似文献