共查询到19条相似文献,搜索用时 801 毫秒
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为解决应用超声导波检出油气对焊弯管缺陷的难题,分析了弯头及环焊缝对L(0,2)模态、T(0,1)模态导波的传播影响,发现环焊缝会使导波产生反射,弯头及环焊缝会使导波产生衰减和模态转换,而导致油气对焊弯管缺陷难以检出;提出了基于B扫描成像的超声导波检测方法,通过B扫描图像辅助识别弯管缺陷信号;最后加工了2根带缺陷的油气对焊弯管,采用上述方法进行检测试验。试验结果表明,基于B扫描成像的超声导波检测方法能够有效检测并定位出弯头及过弯头后直管上的缺陷。 相似文献
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《无损检测》2019,(12)
超声导波在弯管中的传播较在直管中人传播更为复杂,而在实际工程现场,弯管弯头部位的检测尤为重要。利用磁致伸缩超声导波激励出扭转模态T(0,1),研究了超声导波在弯管中典型部位的缺陷检测问题及不同检测频率对弯管缺陷识别的影响。试验结果表明:检测频率低会导致超声导波反射信号在拱背外侧缺陷和弯头焊缝处发生频散而难以分离;检测频率高,得到的弯头拱背内侧缺陷与拱背外侧缺陷的信号幅值都很小。因此选择合适的检测频率,才能更好地对弯头缺陷进行有效识别。T(0,1)模态导波经过弯头时,能量会在拱背外侧产生聚焦,在拱背内侧出现发散,拱背外侧缺陷比拱背内侧缺陷更容易检出;信号经过弯头后,能量衰减严重,衰减后的能量约为原来的一半。 相似文献
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实验研究了基于磁致伸缩效应的超声导波技术在实际管道检测中的检测能力。在实验过程中传感器与管道之间采用机械干耦合方式,控制传感器单向激励低频T(0,1)模态超声导波。对一根长9.6m的管道试样进行实验,激励的T(0,1)模态超声导波在管道中传播153.6m后,管道端面回波信号仍然具有高信噪比。对两段现场蒸汽管道的检测实验,得出单向激励64kHz,T(0,1)模态超声导波能够检测到13m管道长度内的焊缝、支架、弯头等管道典型结构并且位置误差小于150mm。 相似文献
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使用超声导波进行无损检测是实现结构健康监测的重要手段,但是其多模态特性会增加损伤信号提取难度,因此需要在激发时尽可能激励单一模态。使用粘贴于结构表面的压电晶片激发和接收超声导波,通过多种尺寸晶片在不同结构厚度下的导波试验,对导波各模态的激发特性进行了研究。结果表明附着于结构表面的压电晶片不但可激发S0模态,同时也可激发出A0模态;为了有效抑制A0模态的幅值,激发晶片的直径需要大于A0模态的波长。 相似文献
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天然气集输站场管道缺陷检测在天然气生产管理及安全环保上扮演着重要角色。近年来,国际上发展出以超声波入射在管壁中形成导波传播来对管道进行长距离全面快速检测的方法,既可有效检测管道中存在的缺陷,大大降低管道设备风险指数,又可减少管道检测成本。对超声导波检测技术在天然气集输站场的管道检测中遇到的一些情况进行了分析总结。 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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We developed a pitch-catch system based on electromagnetic acoustic transducers (EMATs) for pipe inspection, which moves inside the pipe in the axial direction. The first higher mode, T(0,2), of the torsional guided wave is transmitted and detected, and variations of amplitude and phase are measured while moving the EMATs. Several aluminum pipes containing dish-shaped defects are inspected, and the amplitude and phase show enough detection sensitivity. It is found that the phase measurement has better potential as a tool for quantitative inspection. The applicability of the technique for steel pipe is also confirmed. 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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时频重排方法在管道导波信号处理中的应用 总被引:1,自引:0,他引:1
针对超声导波的多模态和频散特性会导致信号波包在结构中传播发生展宽的现象,研究了400kHz时的管道导波时域信号。指出了用时频分析方法可以直观地描述导波信号在传播过程中的能量分布,准确反映主要模态信息和各模态群速度变化趋势,建立与导波频散曲线间的对应关系,并且利用时频重排的方法可以进一步提高分析结果的可读性。 相似文献
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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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