面向超声导波检测的管道腐蚀建模及仿真实现

超声导波技术被大量应用于管道腐蚀的检测与评估。腐蚀是实际管道中的主要缺陷形式,管道腐蚀缺陷形貌多样且复杂,针对管道腐蚀导波检测的很多研究是通过仿真手段开展的。常用的缺陷简化模型不能充分反映实际腐蚀缺陷的复杂程度,有可能造成分析结果的偏差。本文在分析腐蚀特点基础上提出了基于W-M分形函数的腐蚀仿真模型,研究了管道腐蚀缺陷的有限元自动建模仿真方法,并通过分析讨论超声导波检测不同腐蚀缺陷的仿真结果对模型的有效性进行了验证,结果证明基于本文提出的腐蚀模型所得缺陷回波可提供更丰富的缺陷信息,有利于揭示管道腐蚀特征与导波信号之间的量化关系。本文的研究成果可为进一步分析管道腐蚀缺陷的检测评估建立理论基础。     

Ultrasonic defect detection of a petroleum pipeline in a viscoelastic medium

During detection of the defects in the inner wall of a petroleum pipeline via an ultrasonic nondestructive evaluation method, the defect echo and the inner-wall echo often overlap. It is difficult to identify the arriving time of the defect echo. When an ultrasonic wave propagates in a viscoelastic medium, the stress relaxation and creep deformation result in a signal characterized by frequency. The wave speed and attenuation rate are dependent on the frequency; thus, the ultrasonic signal has different shapes along the wave propagation path. Sometimes the wave shape is wry. The empirical mode decomposition technology used for separating the overlapping echo signals has been presented in this paper. With such technology, the original ultrasonic signal can be decomposed and then some intrinsic mode functions (IMFs) and a residue can be obtained. Different IMFs contain different echo signals. Some useful IMFs are selected to reconstruct the ultrasonic signal. The peaks of the reconstructed ultrasonic signal envelope indicate the arriving time of the echo signals. The experimental results show that this method is effective for detection of the defects in the inner wall of a petroleum pipeline. The text was submitted by the authors in English.     

管道壁缺陷超声波在役检测的量化分析研究

介绍了管道壁缺陷超声波在役检测原理和技术性能，指出超声波在役检测技术具有直接测量和量化的特点，特别适用于管道壁腐蚀减薄缺陷和其它减薄缺陷的在役检测，对管道壁厚度的检测精度高。介绍了管道壁缺陷的超声波在役检测方法，给出了四种典型的管道壁缺陷型式，指出建立并完善管道壁缺陷超声波在役检测的量化分析模型，对于提高检测精度具有十分重要的意义。在对四种典型管道壁缺陷型分析的基础上，通过对四次反射回波时间和相对幅值的分析识别，建立了管道壁缺陷超声波在役检测的量化分析模型，并给出了计算框图。最后，对四种典型管道壁缺陷型式进行了模拟试验分析。     

An effective defect identification scheme in pipeline ultrasonic testing

The identification of a defect from its pulse-echo ultrasonic signal is a difficult task but greatly significant for defect evaluation in pipeline ultrasonic testing. In this work, an effective defect identification scheme, which uses the deconvolution technique, is developed to identify the ultrasonic signals from simulated defects with two different shapes (a notch and a transverse cylindrical cavity) on a pipeline specimen. A DSF (Defect Similarity Function) defined as a deconvolution of a target signal by a reference signal is used to classify the defects. Experimental results indicate that the DSFs for the same type of defect-reference signals are narrow impulselike patterns with larger amplitudes, while those for the different types of defect-reference signals are broad impulselike patterns with relatively smaller amplitudes. Furthermore, the DSF is sensitive to defect shapes but non-sensitive to the measuring distance and defect size. Therefore, the defects can be identified from the pattern of the DSF. The proposed technique shows great potential for the identification of defects via ultrasonic signals in the pipeline inspection. This text was submitted by the authors in English.     

Failure probability of corrosion pipeline with varying boundary condition

This paper presents the effect of external corrosion, material properties, operation condition and design thickness in pipeline on failure prediction using a failure probability model. The predicted failure assessment for the simulated corrosion defects discovered in corroded pipeline is compared with that determined by ANSI/ASME B31G code and a modified B31G method. The effects of environmental, operational, and random design variables such as defect depth, pipe diameter, defect length, fluid pressure, corrosion rate, material yield stress and pipe thickness on the failure probability are systematically studied using a failure probability model for the corrosion pipeline.     

基于CCD成像的轴承滚柱表面缺陷智能检测的研究

提出了一种基于CCD成像的轴承滚柱表面缺陷非接触检测技术。CCD将目标转换为视频信号并输送到图像采集卡,图像采集卡对视频信号进行解析、数字化后输送给专用的图像处理系统,对图像进行处理,再用LabVIEW软件编程。     

Multi-range sensors for the measurement of liquid film thickness distributions based on electrical conductance

The paper presents an approach toward an enhancement of the measuring range of high-speed sensors for the measurement of liquid film thickness distributions based on electrical conductance. This type of sensors consists of electrodes mounted flush to the wall. The sampling of the current generated between a pair of neighboring electrode is used as a measure of the film thickness. Such sensors have a limited measuring range, which is proportional to the lateral distance between the electrodes. The range is therefore coupled to the spatial resolution. The proposed new design allows an extension of the film thickness range by combining electrode matrices of different resolution in one and the same sensor. In this way, a high spatial resolution is reached with a small thickness range, whereas a film thickness that exceeds the range of the high resolution measurement can still be acquired even though on the costs of a lower spatial resolution. A simultaneous signal acquisition with a sampling frequency of 3.2 kHz combines three measuring ranges for the characterization of a two-dimensional film thickness distribution: (1) thickness range 0–600 µm, lateral resolution 2×2 mm², (2) thickness range 400–1300 µm, lateral resolution 4×4 mm², and (3) thickness range 1000–3500 µm, lateral resolution 12×12 mm². The functionality of this concept sensor is demonstrated by tests in a horizontal wavy stratified air–water flow at ambient conditions. Using flexible printed circuit board technology to manufacture the sensor makes it possible to place the sensor at the inner surface of a circular pipe.     

An equivalent electrical circuit design for pipeline corrosion monitoring based on piezoelectric elements

Underground pipelines are important infrastructure for transporting energy resources, particularly water and oil. Due to the high risk of damage and possible consequences, close monitoring of pipelines is a serious challenge for researchers and decision makers. Piezoelectric sensors/actuators are being used to monitor the physical characteristics of pipelines, including corrosion and crack. Piezoelectric ceramics as transmitters and/or receivers are connected to data concentrators in order to monitor the defects in pipelines. The performance and accuracy of this system highly depends on the accurate interpretation of the received electrical signals due to changing mechanical fields. However, due to the existence of two different fields, namely, electrical and mechanical, in this problem, simulation and interpretation of the damages occurring in pipelines is a consistent challenge. This paper proposes an equivalent electrical circuit model for a complete monitoring system which contains piezoelectric ceramics and a pipeline equivalent electrical circuit with corrosion defects and cracks through the pipeline. The pipeline is integrated with PZT sensor and actuator, in which PZT actuator generates waves along the thickness of the pipeline and its response is received by a PZT sensor. The proposed model approximates the electrical signal achieved by the PZT sensor to a complete health monitoring system. As the sensing signals in the present model are in one single field (i.e. electrical instead of mechanical and electrical), analysis and signal processing are more efficient, and the results are better understood. Numerical examples and, where applicable, simple tests have been presented to show the functionality and performance of the system.     

腐蚀管道的剩余强度评定及ANSYS二次开发

针对腐蚀管道对工作承压能力的影响,利用ANSYS软件建模仿真,通过与真实材料拉伸试验的数据对比,验证了有限元方法有较高的可靠性。进一步研究了内腐蚀缺陷尺寸对管道剩余强度的影响,并重点研究了相邻腐蚀缺陷相互作用和群腐蚀管道的评价方法。研究结果表明,管道的剩余强度会随着缺陷尺寸的增大而减小,相邻腐蚀缺陷在轴向和环向距离一定范围内会随着间距增大而相互影响减小。利用相邻腐蚀缺陷相互作用准则建立了等效简化群腐蚀的方法。为了解决ANSYS评定管道剩余强度操作的复杂性,开发了针对单个腐蚀和复杂腐蚀的评估软件。     

基于平衡电磁技术的管道裂纹全角度检测方法

针对管道表面裂纹缺陷方向各异的问题,提出一种基于平衡电磁技术的裂纹全角度检测方法。通过麦克斯韦方程分析了时谐电磁场下管道内表面的电磁分布,根据磁通与感应电流的畸变分析了管道表面各方向裂纹的检测机理与检测信号规律,并证明了平衡电磁技术对管道裂纹全角度检测的有效性。利用有限元方法计算分析了裂纹与检测方向成七种不同角度时管道内表面的电磁畸变程度,并通过仿真得到相应的感应电压信号,根据仿真结果进行有效性试验,结果表明,平衡电磁检测技术能够对管道表面裂纹实现全角度检测,检测信号特征以检测方向与裂纹成30°夹角为分界,0°～30°信号特征为先波谷后波峰,检测信号幅度随着角度增加逐渐减小,峰谷间距快速变小;30°～90°信号特征为先波峰后波谷,检测信号幅度随着角度增加逐渐增大,峰谷间距缓慢变小;当检测方向与裂纹成30°时,感应电压信号为双峰谷特征,且峰峰值最小。该方法为管道表面裂纹角度的量化研究提供了理论依据和实验基础。     

Digital beam control for fast differential voltage contrast

A new method for voltage contrast enhancement by image subtraction is presented. It is based on a modification of a commercial column automation system that digitizes beam positions and intensity signals in a scanning electron microscope (SEM). The new modulus performs via hardware all the operations of bias control and signal differentiation at each image point, resulting in a minimum acquisition time of 4 μs per point, that is less than 0.3 seconds to obtain a 256 × 256 pixels image with 8 bit gray resolution. The digital handling of intensity data, gives high precision differential images and the control of beam position prevents spatial differentiation effects, enabling noise reduction by time integration of intensity data in each point.     

DSP技术在线阵CCD测量系统中的应用

本文介绍数字信号处理器DSP在线阵CCD信号实时采集与处理系统中的应用。测量系统采用CCD传感器光采样与ADC数据采集、DSP数据处理三级流水线结构。结合AD采样技术， 充分发挥DSP处理器片内存储器容量大，快速灵活运算能力的特点，使用DSP片内双数据缓冲区交替对CCD进行信号采集和数据处理；在进行数据处理过程中，DSP以中断方式读取AD采样结果。文章还介绍了DSP的线阵CCD系统在LAMOST光纤定位单元定位精度检测装置中的应用。     

管道对接焊缝超声检测爬行器的研制

介绍了一种用于管道对接焊缝内部缺陷检测的自动检测爬行器的工作原理、系统结构和工作特点。该系统在PC机的控制下相对焊缝运动，实现了超声检测的自动化。试验结果表明，该系统在灵活性和易于使用等方面取得了较满意的结果，具有较广泛的适用性。     

Flow around a pipeline and its stability in subsea trench

Offshore subsea pipelines must be stable against external loadings, which are mostly due to waves and currents. To determine the stability of a subsea pipeline on the seabed, the Morrison equation has been applied with prediction of inertia and drag forces. When the pipeline is placed in a trench, the force acting on it is reduced considerably. Therefore, to consider the stability of a pipeline in a trench, one must employ reduction factors. To investigate the stability of various trenches, we numerically simulated flows over various trenches and compared them with experimental data from PIV (Particle Image Velocimetry) measurements. The present results were produced at Reynolds numbers ranging from 6×10³ to 3×10⁵ based on the diameter of the cylinder. Quasi-periodic flow patterns computed by large-eddy simulation were compared with experimental data in terms of mean flow characteristics for typical trench configurations (W/H=1 and H/D=3, 4). The stability for various trench conditions was addressed in terms of mean amplitudes of oscillating lift and drag, and the reduction factor for each case was suggested for pipeline design.     

Estimation of the state of rod structural elements based on recording of deformation responses to serial impact excitations

Based on the example of welded and one-piece-cut steel (Steel 10) frame triangular elements (4 × 8 × 245 mm) using the methods of thermal unloading up to the temperature T _max = 625°C, serial impact testing of parent (stressed) and unloaded elements, and comparative analysis of Fourier images of deformation responses with respect to unloaded elements, it was found that a nonlinear region of the Fourier image degenerates into a linear one and the maximum of the linear regions of the Fourier image shifts up to 2 Hz. The dynamic deformation responses of the elements were recorded using superbroadband (from 10⁻² to 10⁸ Hz) ferroelectric microsensors based on thin Pb(Zr_0.53Ti_0.47)O₃ films with a thickness of ∼2.0 μm with a 0.8 mm² contact pad. The results can provide a the signal for distinguishing stressed states of structures and their elements.     

超声导波对不同类型管道腐蚀检测的适用性研究

以超声导波检测技术理论为基础,结合压力管道实际腐蚀类型,对腐蚀检测进行了理论分析;介绍对一段压力管道进行超声导波检测试验情况,并对结果进行了分析。总结并用试验验证了超声导波检测技术适用的压力管道腐蚀类型。     

基于TOFD周向扫查图像特征的管道缺陷超声检测

利用超声衍射时差法(Time-of-flight diffraction,TOFD)对管道进行周向扫查检测时,直达纵波传播路径与管道表面不平行,需分别对直达纵波上下区域内缺陷进行识别和定位检测。特别地,管道结构导致TOFD近表面盲区增大,缺陷衍射波与直达纵波发生混叠。针对上述问题,理论分析极坐标系下的管道TOFD周向扫查图像中缺陷衍射波特征,借此确定缺陷与直达纵波的相对位置。在此基础上,对盲区外缺陷进行定位检测,并结合自回归谱外推方法计算盲区内缺陷深度。试验结果显示,对于外壁半径100.0 mm,壁厚30.0 mm碳钢管道,在5 MHz中心频率和不同探头中心距(Probe center separation,PCS)的检测条件下,埋深4.0 mm的上表面开口槽与埋深16.0 mm的下表面开口槽均可检出,且定位误差不超过0.36 mm。缺陷衍射波特征与PCS直接相关,对管道进行周向扫查检测时应合理调整参数。     

机械密封润滑膜分布的超声检测技术

针对机械密封润滑膜分布检测问题,利用超声原理建立了机械密封润滑膜分布的多点测量模型。构建了由信号发生、超声发射-接收、数据采集及数据存储-显示等模块组成的润滑膜分布测量系统,并配备了模拟测量装置。在模拟测量装置上对厚度为5 μm、10 μm和20 μm的润滑膜进行了检测。结果表明：采用超声原理可对润滑膜分布进行精确测量,单点测量误差范围为0.2～1.1 μm,膜厚5 μm的检测精度最高。     

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4___0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 Bin. Residual stresses attributed to 7-A1203 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2~u method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667_＋20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.     

Optimization of excitation frequency and guided wave mode in acoustic wavenumber spectroscopy for shallow wall-thinning defect detection

In plate-like structures, wall-thinning defects resulting from corrosion may not be accompanied by any indication of damage on the surface. Thus, inspections are required to ensure that wall-thinning defects are within allowable limits. However, conventional ultrasonic techniques require physical contact to the structure. Alternatively, acoustic wavenumber spectroscopy (AWS) may be used for detecting, locating, and characterizing defects. This paper describes the performance of AWS in the estimation of a wall-thinning defect size in thinplate structures using finite element analysis (FEA). Through a series of FEAs, the structure’s steady-state response to a single-tone ultrasonic excitation is simulated, and the wall-thinning defect-size effect on the wavenumber-estimation accuracy is investigated. In general, the A0 guided wave mode is widely used to visualize defects because of the nature of the wave speed variation in relation to the plate thickness. However, it is not appropriate for the detection of relatively shallow wall-thinning defects, because the rate of change in wave speed with the thickness decreases with increasing plate thickness. To overcome this limitation, we propose a method to optimize excitation frequency and effective guided wave mode instead of utilizing the A0 mode. The results can be used to determine the size of shallow wall-thinning defects in plate-like structures.