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ERW管焊缝缺陷漏磁检测方法可行性分析 总被引:1,自引:0,他引:1
介绍了现有由轴向磁化和周向磁化检测技术组合构成的相对螺旋扫查式钢管漏磁检测方法,分析了该方法对ERW管焊缝缺陷检测的困难所在:相对螺旋扫查方式所形成的周期性焊缝信号掩盖了其上的缺陷信号,并且在漏磁叠加场的根源上难以区分.针对此问题,提出一种单一轴向磁化下的轴向直线扫查式ERW管焊缝漏磁检测方法,并通过实验和有限元法对其可行性进行了论证分析,在发现单一轴向磁化下钢管纵向伤可形成漏磁场并被观察出的基础上,对ERW管焊缝上最难以检出的人工纵向伤进行检测试验,最终表明:ERW管焊缝缺陷在单一轴向磁化下的漏磁检测方法具有可行性. 相似文献
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针对传统的基于最小二乘法板形信号模式识别方法抗千扰能力差、精度低,神经网络识别方法在实际应用中效果不佳的问题,通过对板形信号和板形识别数学模型的分析,首先将板形信号模式识别过程转化为函数的优化问题。为提高板形信号识别的精度和速度,以勒让德正交多项式作为板形缺陷的基模式,用模糊识别理论与混沌优化方法对该函数进行优化求解。采用模糊理论作为初步识别,用以降低混沌优化的求解维数和缩小搜索空间,借助梯度下降法的思想对混沌优化的局部搜索能力进行改善,从而进一步提高了混沌优化对板形信号模式识别的识别速度和精度。 相似文献
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提出基于3/2维谱分析的螺栓松动非线性检测及定位方法,用多尺度法分析螺栓松动产生非线性相位耦合的机理,研究3/2维谱分析处理信号的过程并分析其识别非线性二次谐波原理,以铝板上螺栓结构为实验对象,利用粘贴在铝板表面的压电作动/传感元件进行实验,对结构响应信号进行3/2谱分析,有效判断螺栓的连接状态;为实现松动螺栓的定位,定义螺栓松动的非线性指标,引入径向基插值函数,实验获得粘贴在铝板上压电列阵响应信号的非线性指标,利用径向基插值函数拟合损伤定位图像。实验结果表明,该方法能有效检测螺栓松动非线性,实现松动螺栓定位。 相似文献
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In high-speed magnetic flux leakage (MFL) testing, the tested workpieces pass rapidly through magnetizers. Thus, the magnetization time for workpieces is short. Because of the eddy current effect, the magnetic field inside the workpieces cannot instantly reach equilibrium, and if the magnetizing time is insufficient for the field to reach equilibrium, the MFL signals will be changed because of incomplete magnetization. In this article, the magnetization time lag caused by eddy currents and the influence of this lag on high-speed MFL testing is investigated. The time required for magnetic field to reach equilibrium in specimens, including steel bars and pipes, is obtained by theoretical calculations, finite element simulations, and experiments. The results indicate that the time required for a magnetic field inside a specimen to reach equilibrium is in the range of 50–100 ms. Using conventional magnetizers, the defect signals at testing speed of 10 m/s change because the workpiece reaches the detection zone before the magnetic field inside reaches the stable state. A simple solution is to increase the axial length of the magnetizing coil. After this procedure, signals obtained at 0.1 m/s and 10 m/s are almost identical. 相似文献
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Simulation and Analysis of 3-D Magnetic Flux Leakage 总被引:1,自引:0,他引:1
《IEEE transactions on magnetics》2009,45(4):1966-1972
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ABSTRACTTo improve the accuracy of the magnetic flux leakage (MFL) nondestructive testing in practical applications, it is very significant and key to deal with the detected MFL signals. As for the de-noising process of the MFL signals, a multilevel filtering approach based on wavelet de-noising combined with median filtering is proposed. By analyzing and comparing the de-noising properties of three wavelet families, i.e., Daubechies wavelet, Coiflets wavelet, and Symlets wavelet, two wavelet bases with the best de-noising performance are recognized and selected, namely sym6 and sym8 (the Symlets wavelet functions of order 6 and 8). Then, a new cascaded filter is constructed by combining sym6 and sym8 wavelets and cascading the median filtering method. An experimental platform is established to carry out the MFL testing, through the de-noising process for the measured MFL signals, and the results indicate that the proposed improved algorithm integrates with the merits of wavelet de-noising and median filtering. Compared with the traditional wavelet de-noising, the improved algorithm can not only improve the signal-to-noise ratio (SNR), but also reduce the de-noising error, resulting in enhancing signal quality to facilitate subsequent defect recognition. 相似文献
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ABSTRACTIt has been widely accepted that the magnetic flux leakage (MFL) testing system can be applied only to the inspection of ferromagnetic materials. The possibility of using the MFL testing apparatus to inspect nonferromagnetic metals is discussed in this article. According to Faraday’s law of induction, eddy current rises in the conductor passing through the MFL magnetizer. The perturbation of eddy current and its corresponding magnetic field caused by defects are theoretically analyzed. Then, the finite element method is carried out to verify the theoretical analyses and extract the perturbed magnetic field signals. Furthermore, the influences of specimen conductivity and moving velocity on the detection signal amplitude are also simulated. The results show that the nonferromagnetic conductors are possible to be inspected by the MFL apparatus, and higher conductivity or inspection speed will facilitate the inspection. 相似文献
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Gas transmission pipelines in the United States are primarily inspected using the magnetic flux leakage (MFL) nondestructive
evaluation (NDE) technique. However, accurate analysis of the NDE signals in terms of the underlying defects requires a thorough
knowledge of various operational parameters such as B-H characteristics of the pipe wall, the velocity of the scanning tool,
etc. In certain situations, information about such operational parameters is either absent or hard to obtain. Appropriate
signal processing techniques can be applied to the raw MFL signals to ensure that defect characterization is possible in spite
of local variations in the test situation. This paper presents two such signal processing methods—one, to compensate the MFL
signal for variations in pipe-material grade, and the other to remove the effects of signal distortion that occur due to the
velocity of the scanning device. 相似文献
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Abstract Gas transmission pipelines in the United States are primarily inspected using the magnetic flux leakage (MFL) nondestructive evaluation (NDE) technique. However, accurate analysis of the NDE signals in terms of the underlying defects requires a thorough knowledge of various operational parameters such as B-H characteristics of the pipe wall, the velocity of the scanning tool, etc. In certain situations, information about such operational parameters is either absent or hard to obtain. Appropriate signal processing techniques can be applied to the raw MFL signals to ensure that defect characterization is possible in spite of local variations in the test situation. This paper presents two such signal processing methods–one, to compensate the MFL signal for variations in pipe-material grade, and the other to remove the effects of signal distortion that occur due to the velocity of the scanning device. 相似文献
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The application of magnetic sensors in the traditional magnetic flux leakage (MFL) technique has a significant influence on the detection results. The sensor is typically used to directly measure the amplitude of the magnetic leakage flux intensity as the detection signal. In view of noise effects on the detection result and the subsequent misinterpretation of defect signals, a new non-destructive testing method is proposed. The proposed method intends to measure the magnetic flux change rate using two sensors. A mathematical model is first established to present the principle of the change rate measurement. Based on the magnetic dipole theory, it is inferred that the new method is applicable and sensitive to the detection and location of defects. Moreover, this method is advantageous as it inhibits the interference of MFL noises such as the distension noise, background noise, and vibration noise. The model predictions are then verified by a series of simulations. Finally, an experimental platform is set up to practically detect the defect of a steel plate, and the results agree with the demonstrations and simulations. 相似文献
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In the magnetic flux leakage (MFL) method of nondestructive testing commonly used to inspect ferromagnetic materials, a crucial problem is signal inversion, wherein the defect profiles must be recovered from measured signals. This paper proposes a neural-network-based inversion algorithm to solve the problem. Neural networks (radial-basis function and wavelet-basis function) are first trained to approximate the mapping from the signal to the defect space. The trained networks are then used iteratively in the algorithm to estimate the profile, given the measurement signal. The paper presents the results of applying the algorithm to simulated MFL data. 相似文献
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T. W. Krause R. W. Little R. Barnes R. M. Donaldson B. Ma D. L. Atherton 《Research in Nondestructive Evaluation》1996,8(2):83-100
Stress-dependent magnetic flux leakage (MFL) signals of the normal surface component (radial) MFL signal from blind-hole defects
in pipeline steel were investigated. Three different stress rigs with uniaxial stress and field configurations were used.
A double-peak feature in the MFL signal was defined quantitatively by a saddle amplitude, which was taken as the difference
between the average of the double peaks and the corresponding saddle point. Results indicated that the saddle amplitude increased
linearly with increasing tensile surface stress and decreased, or did not exist, for increasing compressive surface stress.
Finite-element calculations indicated that stress concentration also increased with increasing defect depth. The measurements
and analysis demonstrate that the stress-dependent saddle amplitude behavior in the radial MFL signal is associated with surface-stress
concentrations near the blind-hole defects. 相似文献
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In-line inspection of ferromagnetic gas or oil pipe lines having pipe wall defects is typically accomplished using magnetic flux leakage (MFL) technique. An efficient modelling and computational scheme for forward model, during the process of solving inverse problems in magnetostatic non-destructive evaluation using finite-element method is presented. The shape, size and place of defect are determined considering the nonlinearity of the pipe material using genetic algorithm as the optimisation technique. It is shown that the reduced model improves the FE computations significantly. The methodology for construction of defect shapes from particular MFL signals has been explained 相似文献