磁记忆技术在管件裂纹检测中的应用

基于金属磁记忆效应的原理，本文研究了利用磁记忆技术检测管件裂纹，虚拟仪器系统和漏磁传感器是检测系统的核心。试验表明，运用该技术检测管件裂纹是完全可和和有效的。     

基于小波理论的漏磁检测的噪声消除

利用噪声信号和测试信号对各个尺度上的波谱的不同表现,应用小波理论对漏磁法检测海底管道的腐蚀和缺损情况中的信号噪声进行消除,根据相应的实验得出了一些海底管道缺陷检测的具体特征。     

提高漏磁法检测抽油杆疲劳裂纹灵敏度的新方法

采用漏磁法可检测抽油杆表面存在的各种缺陷,但对于在现场检测的抽油杆表面却存在油污(虽然经过清洗)、表面粗糙及直线度低(虽然经过矫直)等问题,使得检测过程中的检测探头与被检测的抽油杆接触不严密,造成对微小缺陷特别是疲劳裂纹的检测信号不敏感.研制了拉伸式管/杆漏磁无损检测实验台,对拉伸实验杆预制疲劳裂纹并对其进行了检测试验,结果采集到了更大的疲劳裂纹信号,因此用该方法提高了漏磁法检测抽油杆疲劳裂纹的灵敏度.     

用电导磁法无损检测40Cr钢连杆螺栓裂纹

利用钢铁零件的成分、组织结构、力学性能与其磁性能之间的关系和电磁无损检测仪的工作原理,通过两个实例阐明了在微型空压机生产中的快速电磁无损检测仪在生产中的具体应用经验.     

钢坯表面裂纹的检测技术

表面裂纹的检测是生产高质量钢材的重要保证。目前,冶金企业已经开始应用一些检测技术对钢坯表面裂纹进行在线检测或离线检测。介绍了目前常用的几种钢坯表面裂纹检测技术的原理、特点、应用实例及其检测效果,这些技术包括涡流检测法、漏磁检测法、红外检测法和机器视觉检测法。在此基础上,总结了钢坯表面裂纹缺陷检测技术的发展方向。     

石化储罐缺陷的漏磁检测系统

首先分析了漏磁检测的原理和漏磁检测技术的适用范围,然后探讨了石化储罐漏磁检测系统总体结构及其漏磁检测程序,并对其广阔前景进行了展望。     

基于面阵霍尔传感器的漏磁检测

传统漏磁检测中,单探头检测面积小,且采用永磁体励磁时,移动装置不灵活,检测效率较低.因此,本文采用交流励磁,设计48个面阵传感器检测模块,单次有效覆盖面积(36 ×36)mm.电路设计采用多路复用技术,用DG508作为多路模拟开关,myR1O1900数据采集卡分时控制采集;上位机软件中对原始数据采用自平衡技术;数据处理过程采用阈值增强技术,提高缺陷图像显示效果.实验表明:该设计可检测厚度2mm保护层下的人工刻槽.     

管道焊缝裂纹扩展的流固磁耦合表征

本工作利用虚拟裂纹闭合技术(Virtual crack closure technique,VCCT)提出一种单裂纹和多裂纹扩展通用的流固磁耦合方法,研究了流体压力的动态施加、流体-管道焊缝结构-磁场耦合作用下管道焊缝裂纹的扩展问题。该流固磁耦合方法每递增一次流体压力载荷,则完成一次裂纹增量扩展,更新裂纹几何形状,并重构网格,循环进行裂纹扩展计算和磁场分析,实现铁磁性管道焊缝裂纹扩展的流固磁耦合。以管道焊缝不同环向位置分布的单裂纹、多裂纹等六种工况为数值模拟算例,根据扩展结果中描述裂纹扩展的裂纹张开距离、裂纹扩展长度、磁感应强度水平分量峰值、磁感应强度垂直分量峰值等特征值,衡量裂纹所在位置的危险等级,判断管道焊缝损伤部位与损伤程度,识别多裂纹与单裂纹。该方法的实现可为在役管道焊缝裂纹的漏磁检测与评价、管道再制造修复等提供理论基础。     

漏磁检测技术在管道检测中的应用

为了检测埋地管道的腐蚀状态,开发了管道漏磁检测技术。该检测技术通过对管道局部磁化,检测磁化管段的磁场分布,识别记录缺陷位置磁场的畸变来判断腐蚀缺陷。该检测技术在多条管线上进行应用,其检测结果准确可靠,根据检测结果可以及时修复损伤严重的部位,保证管道安全运行。根据管道修复情况可以确定管道下次检测日期。分析检测结果的误差产生的原因,确定了设备分辨率、调试状态、管道自身特性等若干影响检测结果因素,并对今后的改进工作指出了切入点。     

海底管道缺陷漏磁检测器数据采集系统研发

针对海底管道内可利用空间小、运行工况恶劣的实际情况,研发一款海底管道缺陷漏磁检测器数据采集系统.该系统选用ARM实现对各功能单元的控制,并以FPGA结合A/D采样芯片进行多路漏磁检测信号的并行采集;通过对各功能单元的一体化和集成设计,在确保能准确有效采集和存储缺陷漏磁信号数据的前提下,实现系统结构的整合及简化.牵拉试验和检测工程应用结果表明:该数据采集系统运行稳定,采集、处理缺陷漏磁检测数据质量高,达到设计要求,完全满足海底油气管道缺陷漏磁检测工程应用的技术要求.     

A Dynamics Study of a Magnetic Flux Leakage （MFL） Signal and its Application to Defect Location Discrimination in Steel Pipes MFL Testing Equipment

Difference processing was used to the direct current magnetic flux leakage(DC-MFL) signal,emanating from the defects machined artificially on the internal and external surfaces of a steel pipe.Consequently,the location discriminating index δ was provided to identify the defect whether it is on the internal surface or the external one.Three characteristics,shape,depth and orientation of the defect,were discussed through a series of experiments on the artificial defects,such as transverse notches,oblique notc...     

Modeling and Experimental Studies on 3D-Magnetic Flux Leakage Testing for Enhanced Flaw Detection in Carbon Steel Plates

ABSTRACT

For enhanced detection of flaws in engineering components using magnetic flux leakage (MFL) technique, measurement of the leakage magnetic field components along the three perpendicular directions is beneficial. This article presents the three dimensional-magnetic flux leakage (3D-MFL) modeling and experimental studies carried out on carbon steel plates. Magnetic dipole model has been used for the prediction of MFL signals and images. Sensitivity of the MFL signals peak amplitudes of tangential (H_X), circumferential (H_Y), and normal (H_Z) components with respect to flaw length, width, depth and lift-off have been studied. A 3D-GMR sensor has been used for simultaneous measurement of all the three components of leakage magnetic fields from surface flaws in 12 mm thick carbon steel plates. The experimental MFL images have been compared with the model predicted MFL images. The sensor has shown the capability to detect and image 0.9 mm deep surface flaws with a signal to noise ratio of 8 dB. Principal component analysis (PCA)-based image fusion has been performed for fusion of the 3D-MFL images to obtain a geometrical profile of the flaws. Study reveals that 3D-GMR enhances the capability for detection of flaws having irregular geometries.     

基于脉冲漏磁理论的管道腐蚀缺陷宽度定量技术

在带保温层管道腐蚀缺陷的定量检测中,缺陷的宽度定量是一项重要内容.提出了采用脉冲漏磁技术对带保温层管道的腐蚀缺陷进行检测.通过提取传感器峰值扫描波形中极值点的位置差△D作为特征量,分析了无保温层和带保温层情况下,△D随管壁腐蚀缺陷宽度的变化规律,从而得出了对管道腐蚀缺陷进行宽度定量的方法.实验结果证明了所采用方法的正确性和有效性.     

Modeling the Effects of Pit Corner Geometry on Magnetic Flux Leakage Signals

Three-dimensional magnetic finite element analysis (FEA) has been used to simulate the effects of different pit corner geometries on magnetic flux leakage (MFL) signals. The pit corner geometries studied fall into three main categories: right angle, smooth triangular, and smooth round. These geometries are simulated using rectangular grooves and circular pits in steel plate. The axial and radial components of the MFL signal are obtained on the topside as well as the underside of the steel plate. Both the peak position and the peak height/depth of the MFL signal were found to be influenced by the sharpness of the pit corner. In general, the underside axial MFL peaks shifted toward the center of the pit, and their height increased with decreasing sharpness of the corner. For the underside radial MFL peaks, there was an appreciable peak shift; however, the change in peak height was insignificant. However, the peak height depends strongly on pit depth. The topside results were only slightly different from the underside. Despite some changes in MFL signal position and form, it was concluded that in practical inspection situations these changes would be relatively small and difficult to quantify.     

Residual Magnetic Flux Leakage: A Possible Tool for Studying Pipeline Defects

Simulated defects of different shapes and sizes were created in a section of API X70 steel line pipe and were investigated using a residual magnetic flux leakage (MFL) technique. The MFL patterns reflected the actual shape and size of the defects, although there was a slight shift in their position. The defect features were apparent even at high stresses of 220 MPa when the samples were magnetized at those particular stresses. However, unlike the active flux technique, the residual MFL needs a sensitive flux detector to detect the comparatively weaker flux signals.     

Magnetization Time Lag Caused by Eddy Currents and Its Influence on High-Speed Magnetic Flux Leakage Testing

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.     

钢管漏磁在线检测技术的研究

介绍了钢管漏磁检测的基本原理,对钢管在线漏磁检测系统进行总体设计。分析了漏磁场理论模型和讨论了影响缺陷漏磁信号的一些因素及补偿方法,针对该系统的特点设计了高速数据采集板,借助Windows系统平台,在所研制硬件的基础上,采用多线编程和虚拟设备驱动技术编制了数据采集、分析、状态显示、实时控制等面向对象、多功能模块化的软件,详细叙述了漏磁信号数据分析的方法和过程。这种系统具有检测速度快、数据吞吐量大、效率高、钢管缺陷分辨率高等特点。     

Factors Affecting Magnetic Flux Leakage Inspection of Tailor-Welded Blanks

The development of a laboratory-based tailor-welded blank (TWB) inspection system using the principles of magnetic flux leakage (MFL) is presented. The effects of variations in inspection system operating parameters are quantified to allow for optimized system performance. The parameters examined include the applied magnetic field strength, inspection scanning velocity, spatial resolution of acquired signals, specimen end effects, and pole piece liftoff. The results indicate that this inspection method is relatively insensitive to operating parameters and is therefore robust.     

Three-Dimensional Localization of Defects in Stay Cables Using Magnetic Flux Leakage Methods

The application of magnetic flux leakage (MFL) methods to the nondestructive evaluation (NDE) of metal parts has been known for several decades. The inspection of large-diameter cables (Ø 100 mm), such as bridge stay cables, is a new field of application for the MFL method. The large cross-section of the cables requires the generation of strong magnetic fields in order to obtain the induction fields necessary for an accurate inspection of the cables. A new device for the inspection of stay cables has been developed in order to meet the requirements given by the size of the cables. Measurements performed with the developed device on full-scale specimens in the laboratory and first calculations confirm the validity of the MFL approach to the inspection of bridge stay cables. The equipment was used satisfactorily in 2001 for the NDE inspection of the 68 locked coil stay cables (121 mm < Ø < 167 mm) of a bridge in Southeast Asia. For such cables, no exact localization within the cross section was performed. Thus far, an accurate indication of the position of the detected flaws along the length of the cables could be given. A qualitative statement about position and size of the flaws within the cross section of the cable could also be made. Given the large steel cross-section of the cables, no other nondestructive method to confirm the findings could be applied to assess the exact size and position of the detected flaws. The proposed analytical method presented in this paper makes it possible to increase the amount of information that can be extracted from the measured MFL data with regard to the exact location of the detected flaws within a cross section of a stay cable.