钢板缺陷的脉冲漏磁检测系统设计及试验

基于脉冲漏磁检测技术检测钢板缺陷,实现钢板表面和背面缺陷的区分。利用设计的钢板脉冲漏磁检测系统,提取了钢板表面和背面缺陷的信号,分析在脉冲信号激励下的缺陷漏磁信号特征。根据信号电压峰值和电压谷值同步曲线区分缺陷,编写了基于Labview的检测程序,实现了钢板表面和背面缺陷检测和区分。在实验室条件下,通过设计的脉冲漏磁检测系统,对刻有矩形槽的钢板进行了检测。试验结果表明,基于脉冲漏磁检测技术,利用电压信号峰值和谷值同步采样曲线,可对钢板表面和背面缺陷进行检测和区分。     

电磁超声和涡流组合检测方法

两栖装甲车工作环境恶劣,车体尤其是底部容易破损。提出了一种电磁超声和涡流组合检测的快速方法,利用电磁超声的激励信号在被测金属表面感应的涡流,实现表面和近表面缺陷的涡流检测,无须额外增加专门的涡流线圈及其激励电路。设计了组合检测系统和探头,对带有表面缺陷和内部缺陷的装甲钢试块进行了检测试验。结果表明,该方法可以实现装甲钢试块内部缺陷和表面裂纹的检测,比单一的电磁超声检测或涡流检测能获取更全面的有用信号。     

基于电磁超声的钢板自动检测方法探讨

分析了钢板制造方法及可能存在的缺陷,应用电磁超声技术对钢板进行自动检测,主要从电磁超声检测基本原理与声波产生、换能器波型选择与排列、对比试板及其人工缺陷设计、检测闸门设置及检测结果显示与记录等方面进行研究。结果表明：电磁超声自动检测可以对钢板进行全覆盖非接触扫查,实现高速、高温检测,满足大管径、壁厚和高压油气输送用钢板检测要求,对于研究钢板电磁超声自动检测方法具有参考价值,且对制定相关钢板电磁超声自动检测标准具有借鉴作用。     

基于电磁超声的钢板裂纹检测系统

设计了一种基于磁致伸缩原理的电磁超声裂纹检测系统。该系统由脉冲电源激励换能器线圈,进而在钢板中激发超声波,接收信号经过放大滤波后输入计算机进行处理。利用此系统进行钢板裂纹检测试验,裂纹定位误差〈1％。系统运行稳定可靠,可以用来检测钢板裂纹缺陷。     

基于脉冲涡流/电磁超声复合检测方法的复杂缺陷检测

相比于电磁超声检测方法,脉冲涡流检测方法对于近表面缺陷具有较高检测灵敏度。而电磁超声信号本身包含脉冲涡流信号部分,基于此特点,开发了电磁超声/脉冲涡流的复合无损检测方法。首先,基于有限元理论开发了电磁超声/脉冲涡流复合信号的数值模拟方法;其次,提出了基于频谱分析、滤波等策略对混合检出信号进行信号分离提取的方法,并结合试验验证了所提方法的有效性;最后,基于复合检测方法对铝板中的三种类型缺陷(表面缺陷、底部减薄缺陷、复合缺陷)同时成功地进行了检测,验证了所开发复合检测方法的优越性。     

曲折线圈折线角度对EMAT换能效率的影响

针对曲折线圈型电磁超声换能器的换能效率,分析了不同折线角度曲折线圈对EMAT(电磁超声换能器)换能效率的影响。根据声束指向原理,通过改变载流导线的角度,设计了0°、30°、60°、90°曲折线圈激励产生电磁超声导波,并采用收发分离式换能器结构在钢板上进行检测试验。结果表明,曲折线圈载流导线角度为0°时,EMAT激发的声波能量集中,方向性好,回波信号幅值强,为钢板的长距离检测提供了可能;曲折线圈载流导线角度增加为30°、60°、90°时,EMAT激发的声波信号纯净,简化了模态分析,对工程中钢板检测的信号简化处理具有重要意义。     

基于电磁超声的管道裂纹检测法实验研究

设计了电磁超声传感器线圈和测试电路,对22.5mm厚钢板不同深度的裂纹类缺陷进行测试,以确定电磁超声裂纹检测的性能。通过分析电磁超声传感器(EMAT)所接收的导波信号,就可以准确判断裂纹的位置,用适当的数据分析可对裂纹缺陷尺寸进行量化,从而验证了使用电磁超声技术检测管道应力腐蚀裂纹(SCC)是一种切实可行的检测方法。     

空心抽油杆的超声导波检测

利用超声纵向导波对抽油杆缺陷进行检测。将空心抽油杆简化为一管状波导,利用管道中的导波频散曲线,并结合抽油杆的缺陷检测要求,设计出适合抽油杆缺陷检测的传感器,选择合适的导波模态对抽油杆表面上宽1 mm、深1 mm的周向槽进行检测,试验结果表明将抽油杆简化为管状波导是可行的,利用设计的环状传感器激发出纵向轴对称L(0,2)导波模态,有效检出了抽油杆表面的缺陷。     

不锈钢储液罐的涡流检测

介绍了涡流检测的基本原理,运用该方法对自制不锈钢刻槽试块进行了涡流检测,得到了人工刻槽及晃动信号的阻抗示意图。采用该工艺对11台不锈钢储液罐焊缝进行了涡流检测,发现了一位置阻抗示意图信号与试块刻槽阻抗示意图信号相似,经宏观检查确认两位置存在3条表面裂纹缺陷,从而证实了涡流方法检测不锈钢焊缝表面裂纹的可行性。     

脉冲涡流检测信号的同步采样方法

为了有效利用脉冲涡流信号的低频成分检测钢板内部裂纹缺陷,提出了脉冲涡流同步采样方法。介绍了该方法的工作原理;采用在钢板上加工不同规格矩形槽的方法模拟钢板的裂纹缺陷;设计了由激励线圈和检测线圈构成的传感器,实现脉冲涡流信号的提取;采用数据采集卡采集信号,以Labview为平台,实现同步采样方法的软件设计。对钢板缺陷的检测和试验数据的分析,证明了脉冲涡流同步采样方法在钢板内部裂纹缺陷检测中具有较高的灵敏度,可以有效识别钢板内部裂纹缺陷。     

电磁超声技术在焊缝检测中的应用

电磁超声技术利用洛伦兹力或磁致伸缩原理在金属或磁性材料中激发出超声波,它是一种超声无损检测新技术。相对于其他无损检测技术而言,电磁超声具有所有的超声检测的优势。声波的激发发生在材料的表面而不是在传感器内部。所以它与传统的基于压电换能器的超声检测相比,具有无需耦合剂、可非接触、可适用于超低温或超高温环境、有利于工业自动化以及可方便有效地实现横波检测及导波检测等优势。Innerspec Technologies公司致力于电磁超声技术的研发和应用,在近十几年中开发了150多台工业在线电磁超声检测系统,广泛应用于钢铁、汽车制造、石油天然气管道和压力容器等领域。作为一种超声波技术,电磁超声可以应用于各种厚度测量、缺陷检测以及材料表征。举例讨论了电磁超声在焊缝检测中的应用。第一个应用是利用导波对激光拼焊板的检测。第二个应用是电阻焊钢管的在线检测。利用沿着周向传播的超声导波对焊缝进行检测,克服了由于焊缝位置偏转对传统超声焊缝检测设备带来的困难。第三个应用是水平横波以及多通道电磁超声相控阵技术实现奥氏体不锈钢焊缝的检测。     

Enhancement of ultrasonic signal using a new design of Rayleigh-wave electromagnetic acoustic transducer

The main disadvantage of electromagnetic acoustic transducers (EMATs) is their inefficiency in generating ultrasound. A new design of Rayleigh-wave EMAT is proposed with improved ultrasonic generation efficiency on non-ferromagnetic materials. The new EMAT's magnet is narrower than the meander-line coil used in the transducer and the coil itself has an uneven distribution of conductors. The principle of the new design is informed by finite element simulations, which show that the EMAT generates Rayleigh waves more efficiently by taking advantage of both horizontal and vertical magnetic fields of the magnet simultaneously. Experimental measurements verify that the maximum amplitude of the ultrasonic signal generated by the new design of EMAT working under a pulse-echo configuration has been enhanced by 90%, when compared to conventional designs.     

Efficient detection of delamination in multilayered structures using ultrasonic guided wave EMATs

This paper presents an efficient method for the detection of delamination using a combined technology of ultrasonic guided wave and electromagnetic acoustic transducer (EMAT). The material for inspection studied in this paper is a three-layered brass/copper/brass metal composite for coin stocks. We first observed a cyclic behavior of wave sensitivity to delamination width in the experiment. This observation is then confirmed with finite element simulation. We found out that the cyclic behavior is related to the phase velocity of the converted wave modes in the two subsystems after delamination. To compensate for the cyclic behavior, two wave modes are used in an industrial inspection system to ensure effective detection of delamination in the composite sample. The inspection speed achieved with this EMAT inspection system is 1.8 m²/s.     

Enhancement of signal amplitude of surface wave EMATs based on 3-D simulation analysis and orthogonal test method

The amplitude of an ultrasonic signal generated by electromagnetic acoustic transducers (EMATs) is typically low when compared to those generated by contacting transducers, which restricts the application of EMATs in the fields of nondestructive testing and nondestructive evaluation. The transmission process of a surface wave EMAT is studied, based on a previously established 3-D model, with the aim of enhancing the amplitude of ultrasonic waves generated by the EMAT. The effect of changing various EMAT parameters on the surface wave is investigated, by utilizing the orthogonal test method. Results indicate that after optimization, the signal amplitude of the EMAT has increased by 25.2%.     

电磁超声的数值模拟方法

电磁超声检测技术由于无需媒介以及与被测物体非接触,不但可提高检测效率,而且可将超声检测技术的应用扩展到高温、高速和在线检测。根据电磁超声传感器的工作原理,建立了基于有限元的电磁超声无损检测数值分析方法,开发了相应的计算程序,验证了其有效性。应用开发的电磁超声数值模拟程序,研究了不同激励方式对电磁超声波的影响,得到了相应超声波在均匀各向同性金属介质中的传播过程。该计算方法和程序为实际电磁超声检测中缺陷的定量和探头优化提供了手段。     

电磁超声高温测厚原理及应用案例

电磁超声是超声波无损检测的一个分支。该技术利用电磁场的相互作用,在被测材料表面产生超声波。因此,电磁超声无损检测过程无需使用耦合剂,并且支持非接触检测。不停工情况下的在役管道以及其他压力容器的剩余壁厚测量是当今无损检测领域的一个研究热点。在常温管道测量方面,使用传统的压电超声可以比较精确地测量管道的剩余壁厚。但是,在高温管道测量方面,目前高温耦合剂还是存在易于挥发、效果不稳定的缺点,而且价格昂贵,不利于实际应用。文章介绍了电磁超声测厚的基本原理、电磁超声厚度测量的仪器设备、探头及其使用范围。结合高温管道测厚的实际应用案例,对电磁超声测厚应用进行了阐述、分析和总结。最后得出,电磁超声由于无需接触、不需要耦合剂等特点,对材料的高温测厚具有独特的优势。     

A hybrid nondestructive testing method of pulsed eddy current testing and electromagnetic acoustic transducer techniques for simultaneous surface and volumetric defects inspection

In this paper, a hybrid nondestructive testing (NDT) method combining with the pulsed eddy current testing (PECT) method and the electromagnetic acoustic transducer (EMAT) method has been proposed and validated through numerical simulations and experiments. First, a numerical code is developed for the simulation of hybrid EMAT/PECT signals based on the developed EMAT and PECT code. Second, based on the numerical simulation, the influences of the eddy current induced by the excitation coil and the eddy current due to the velocity effect of the ultrasonic wave are compared and analyzed. In addition, the features of the EMAT and the PECT signals are analyzed respectively. Third, several signal separation and extraction methods are proposed on the basis of the spectral analysis and filtering strategies for extracting EMAT and PECT signals from the mixed signals of the hybrid EMAT/PECT method and their validity are evaluated through experiments. Finally, hybrid EMAT/PECT experiments are conducted and three types of defects (surface defects, bottom thinning defects, composite defects) in an aluminum plate and a SUS304 plate are successfully detected at the same time using the proposed hybrid NDT method and the signal feature parameters. Based on the numerical and experimental results, the proposed hybrid PECT/EMAT NDT method is demonstrated both high detectability and high efficiency for detecting surface and volumetric defects at the same time.     

用于无损检测的电磁超声换能器研究进展

电磁超声换能器(EMAT)是一种通过电磁耦合方法产生和接收超声波的换能器。由于EMAT具有非接触性、无需耦合剂等优点,受到广大无损检测与评估工作者的广泛关注。从物理原理出发,介绍了EMAT过程数学建模、装置设计以及工程应用等方面的研究现状,并对其发展趋势作出了展望。     

In-situ monitoring of ultrasonic attenuation during rotating bending fatigue of carbon steel with electromagnetic acoustic resonance

Using electromagnetic acoustic resonance (EMAR), we studied the evolution of the surface-shear-wave attenuation and phase velocity during rotating bending fatigue of a 0.45% C steel. In the EMAR method, we used a magnetostrictively-coupled electromagnetic acoustic transducer (EMAT) for the contactless measurements of the axial shear wave that is a surface-shear wave, propagating in a cylinder-specimen circumference direction with the axial polarization. The attenuation coefficient always showed sharp peaks around 90% of the fatigue life, independent of the fatigue-stress amplitude. In addition to the ultrasonic measurements, we made crack-growth observations using replicas and measured recovery of attenuation and velocity after stopping the cyclic loading just before and after the peak. From these results, we concluded that the evolution of the ultrasonic properties is caused by a drastic change in dislocation mobility being accompanied by the crack growth.     

一种优化激发电磁超声Lamb波的方法

超声Lamb波的频散特性和多模式特性导致回波信号复杂难于分辨。为了解决该问题,结合电磁超声换能器(EMAT)的主要设计参数和Lamb波的特征方程,推导电磁超声Lamb波的激发方程和激发曲线。通过选取电磁超声Lamb波在激发曲线上的工作点以削弱多模式和频散现象,进而提出了一种优化激发电磁超声Lamb波的方法。采用该方法分析了零模式Lamb波在工程应用中的有效性,并进行了试验验证。