Three-axis magnetic flux leakage in-line inspection simulation based on finite-element analysis

With the increase of pipelines, corrosion leakage accidents happen frequently. Therefore, nondestructive testing technology is important for ensuring the safe operation of the pipelines and energy mining. In this paper, the structure and principle of magnetic flux leakage （MFL） in-line inspection system is introduced first. Besides, a mathematic model of the system according to the ampere circuit rule, flux continuity theorem, and column coordinate transform is built, and the magnetic flux density in every point of space is calculated based on the theory of finite element analysis. Then we analyze and design the disposition of measurement section probes and sensors combining both three-axis MFL in-line inspection and multi-sensor fusion technology. Its advantage is that the three-axis changes of magnetic flux leakage field are measured by the multi-probes at the same time, so we can determine various defects accurately. Finally, the theory of finite element analysis is used to build a finite element simulation model, and the relationship between defects and MFL inspection signals is studied. Simulation and experiment results verify that the method not only enhances the detection ability to different types of defects but also improves the precision and reliability of the inspection system.

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 loea-tion discriminating index 8 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 notches and pits on the steel pipe. The approach has been verified effective to address the defect location identifying problem, albeit the limits on the accuracy assessment to those natural defects on steel pipes in service.

Advances in magnetic flux leakage testing technology

Magnetic flux leakage(MFL)testing technology has the advantages of simple principle,easy engineering implementation and low requirements on the surface of the detected workpiece.Therefore,it has been one of the research hotspots in the field of non-destructive testing(NDT)and widely used for testing long distance pipelines.This paper presents the development of MFL tesing technology from the aspects of basic theory,influencing factors,magnetization technology,signal processing,etc.The problems to be solved and the future development are summarized,which can provide reference for the research and system development of MFL testing technology.

Evaluation of Surface Cracks Using Magnetic Flux LeakageTesting

The magnetic field distribution characteristics of surface cracks with various widths are discussed based on finite element (FEM) results. The crack depth was 0.20 mm, the width range was from 0.02 to 1.00 mm. The results showed that crack width and lift-off (the distance between surface and sensor) will influence signals. Discussed in this paper is the influence of various lift-off parameters on the peak to peak values of the normal component in magnetic flux leakage testing. The effects can be applied to evaluate surface breaking cracks of different widths and depths. An idea is presented to smooth narrow, sharp crack tips using alternating current (AC) field magnetization.

Magnetic Flux Leakage Course of Inner Defects and Its Detectable Depth

As a promising non-destructive testing(NDT)method,magnetic flux leakage(MFL)testing has been widely used for steel structure inspection.However,MFL testing still faces a great challenge to detect inner defects.Existing MFL course researches mainly focus on surface-breaking defects while that of inner defects is overlooked.In the paper,MFL course of inner defects is investigated by building magnetic circuit models,performing numerical simulations,and conducting MFL experiments.It is found that the near-surface wall has an enhancing effect on the MFL course due to higher permeability of steel than that of air.Further,a high-sensitivity MFL testing method consisting of Helmholtz coil magnetization and induction coil with a high permeability core is proposed to increase the detectable depth of inner defects.Experimental results show that inner defects with buried depth up to 80.0 mm can be detected,suggesting that the proposed MFL method has the potential to detect deeply-buried defects and has a promising future in the field of NDT.

Composite excitation multi-extension direction defect magnetic flux leakage detection technology

In the traditional pipeline magnetic flux leakage(MFL)detection technology,circumferential or axial excitation is mainly used to excite the magnetic field of defects.However,the domestic and foreign pipeline detection devices currently in operation are mainly axial excitation MFL detection tools,in which circumferential cracks can be clearly identified,but the detection sensitivity of axial cracks is not high,thus forming a detection blind zone.Therefore,a composite excitation multi-extension direction defect MFL detection method is proposed,which can realize the simultaneous detection of axial and circumferential defects.On the basis of the electromagnetic theory Maxwell equation and Biot Savart law,a mathematical model of circumferential and axial magnetization is firstly established.Then finite element simulation software is used to establish a model of a new type of magnetic flux leakage detection device,and a simulation analysis of crack detection in multiple extension directions is carried out.Finally,under the conditions of the relationship model between the change rate of leakage magnetic field and external excitation intensity under unsaturated magnetization and the multi-stage coil magnetization model,the sample vehicle towing experiment is carried out.The paper aims to analyze the feasibility and effectiveness of the new magnetic flux leakage detection device for detecting defects in different extension directions.Based on the final experimental results,the new composite excitation multi extension direction leakage magnetic field detector has a good detection effect for defects in the axial and circumferential extension directions.

Research on Magnetic Flux Leakage Detection Method for Subsea Pipeline

The intelligent pig based on the (MFL) is frequently used for in-line inspection of transportation pipelines. The article discusses the key technology of an MFL tool that includes the sensors structure, the constitution of tool hardware, software and the analysis method of MFL signal.

Wavelet domain adaptive filtering algorithm for removing the seamless pipe noise contained in the magnetic flux leakage data

With the widespread application and fast development of gas and oil pipeline network in China, the pipeline inspection technology has been used more extensively. The magnetic flux leakage （MFL） method has established itself as the most widely used in-line inspection technique for the evaluation of gas and oil pipelines. The MFL data obtained from seamless pipeline inspection is usually contaminated by the seamless pipe noise （SPN）. SPN can in some cases completely mask MFL signals from certain type of defects, and therefore considerably reduces the detectability of the defect signals. In this paper, a new de-noising algorithm called wavelet domain adaptive filtering is proposed for removing the SPN contained in the MFL data. The new algorithm results from combining the wavelet transform with the adaptive filtering technique. Results from application of the proposed algorithm to the MFL data from field tests show that the proposed algorithm has good performance and considerably improves the detectability of the defect signals in the MFL data.

Quantitative Interpretation for the Magnetic Flux Leakage Testing Data Based on Neural Network

In order to interpret the magnetic flux leakage (MFL) testing data quantitatively and size the defects accurately, some defect profiles inversion methods from the MFL signals are studied on the basis of the neural network.Because the wavelet ba- sis function neural network (WBFNN) has good accuracy in the forward calculation and the radial basis function neural network (RBFNN) has reliable precision in the inversion modeling respectively,a new neural network scheme combining WBFNN and RBFNN is presented to solve the nonlinear inversion problem for the MFL data and reconstruct the defect shapes.And such details as the choice of wavelet basis function,the initialization of the weight value and the input normalization are analyzed,the train- ing and testing algorithm for the network are also studied.The inversion results demonstrate that the proposed network scheme has good reliability to interpret the MFL data for some defects.

Influence of Slot Defect Length on Magnetic Flux Leakage

A key issue, which influences the applications of magnetic flux leakage testing, is defect quantification. There have been many research on the relationship between width, depth and magnetic flux leakage of slot defect. However, the length factor is often ignored. The relationship between characteristics of defect leakage field and defect length was investigated. The magnetic flux leakages of a series of plate specimens with the same width, same depth and different length slot defects were tested under the same magnetizing conditions. Testing results show that defect length is an important parameter needed to consider in quantifying defects.

Coefficients de-noising with wavelet transform for magnetic flux leakage data obtained from oil pipeline

This paper considers the problem of noise cancellation for the magnetic flux leakage (MFL) data obtained from the inspection of oil pipelines. MFL data is contaminated by various sources of noise, and the noise can considerably reduce the detectability of flaw signals in MFL data. This paper presents a new de-noising approach for removing the system noise contained in the MFL data by using the coefficients de-noising with wavelet transform. Experimental results are presented to demonstrate the advantages of this de-noising approach over the conventional wavelet de-noising method.

Speed Measurement Feasibility by Eddy Current Effect in the High-Speed MFL Testing

It is known that eddy current effect has a great influence on magnetic flux leakage testing(MFL).Usually,contacttype encoder wheels are used to measure MFL testing speed to evaluate the effect and further compensate testing signals.This speed measurement method is complicated,and inevitable abrasion and occasional slippage will reduce the measurement accuracy.In order to solve this problem,based on eddy current effect due to the relative movement,a speed measurement method is proposed,which is contactless and simple.In the high-speed MFL testing,eddy current induced in the specimen will cause an obvious modification to the applied field.This modified field,which is measured by Hall sensor,can be utilized to reflect the moving speed.Firstly,the measurement principle is illustrated based on Faraday’s law.Then,dynamic finite element simulations are conducted to investigate the modified magnetic field distribution.Finally,laboratory experiments are performed to validate the feasibility of the proposed method.The results show that Bmz(r1)and Bmx(r2)have a linear relation with moving speed,which could be used as an alternative measurement parameter.

长输油气管道内检测技术

管道内检测技术是长输油气管道内检测最有效的方法之一,是长输油气管道缺陷检测、评估与完整性评价的重要手段。随着我国能源行业的高速发展,管道成为能源输送的最有效载体,这对管道内检测技术提出了新的挑战,应运而生多种新的检测方法与解决方案。梳理了长输油气管道内检测技术的发展过程,阐述了长输油气管道内检测技术的国内外研究现状,针对长输油气管道内检测现存在的问题,对新技术、新方法的原理、应用情况进行归纳总结,并提出管道内检测行业的未来展望。

铁磁性腐蚀产物对管道漏磁内检测的影响分析

漏磁内检测是一种高效识别长输管道本体缺陷的检测方法,但某些腐蚀点(如杂散电流腐蚀)含有大量铁磁性腐蚀产物,会影响缺陷处漏磁场的溢出,导致检测的数据评价偏小,甚至出现漏检。从漏磁内检测的基本原理出发,阐述了缺陷处漏磁场产生的原因,结合牵拉试验和实际工程案例,说明了铁磁性腐蚀产物对腐蚀缺陷处漏磁场的溢出具有一定的阻碍作用,为今后加强该类型缺陷的识别,提高管道漏磁内检测的检测效果提供技术支撑。

管道内检测技术在山区高含硫气田的应用研究

山区高含硫气田集输管道因输送原料气成分及输送环境复杂,导致管道内壁发生电化学腐蚀,存在泄漏风险,因此对酸气管道开展内检测非常重要。漏磁检测技术是在高含硫气田应用比较成熟的内检测技术。近几年又新起了电磁涡流内检测,具有通过性好,对小尺寸缺陷识别度高,更适应于小管径低流速管道。本文结合某高含硫气田漏磁和涡流检测技术的应用成果,对检测技术的现场适应性、优点以及局限性进行分析,并提出改进建议,为今后同类型气田在检测技术选择上提供一定的技术支撑。

基于局部椭圆变形的长输管道内检测的实践应用

论述了基于局部椭圆变形的长输管道,在无法实施局部换管的特定条件下如何实施内检测工作的应用实践。通过对漏磁检测设备的连接臂、皮碗法兰和探头进行改造,提升了检测设备在3D(内径)弯管处的通过能力,实现了不发生卡球事故的安全目标。通过对现场实测数据和内检测报告数据的分析比对,验证了内检测数据量化精度达到Rosen公司标准。为今后在长输管道局部椭圆变形及其他变形的特定条件下,实施内检测工作积累了实践经验,为类似管道的内检测、技术管理和安全运营提供了一定的借鉴作用。

低压输气管道水驱漏磁内检测可行性研究

本文以解决低压输气管道漏磁内检测时检测器速度过快为目的,提出了以气驱改为水驱的方式进行漏磁内检测的方法,本文首先阐述了漏磁内检测原理及局限、低压输气管道漏磁内检测难点及策略,然后从前期准备、漏磁检测及流程恢复三方面展开阐述了低压输气管道气驱改为水驱漏磁内检测的关键环节,并通过实际工程案例验证了低压输气管道水驱漏磁内检测流程的可靠性,为低压输气管道漏磁内检测提供了一种新思路。

运载火箭电磁阀漏磁特性量化研究与极性检测系统设计

传统的运载火箭电磁阀极性测试往往通过“耳听手摸”的方式,故存在漏检误检、测试记录不可量化及数据追溯、无法精准判读、测试效率低等问题;因此对运载火箭典型姿控电磁阀开展了漏磁性能的测量与量化分析,掌握阀体各部位漏磁场分布规律、漏磁场随距离衰减变化规律、电磁阀之间漏磁场相互影响情况,并提出了一种非接触式的可视化电磁阀极性检测系统设计方法,采用三冗余敏感探头采编设计保证极性检测准确性,经试验测试验证,实现了无需精确安装即可100%检测电磁阀动作及时序动作精准判读,提升了电磁阀极性检测能力和测试效率;该系统已成功应用于大型运载火箭的总装测试流程中,对于提升运载火箭自动化测试水平具有重要意义。

泄流板在管道漏磁检测器中的应用

为适应大口径天然气管道介质流速快的特点,需要在管道漏磁检测器上安装速度控制系统来实现对检测器运行速度的主动调控,但对于已经服役的管道漏磁检测器,不具备安装速度控制系统的空间。对于一定流速的天然气管道,可以利用泄流板调节检测器的运行速度。由于泄流板开设固定面积的泄流孔,检测器发送过程中的起动压差至关重要。利用牵拉试验获取了检测器起动所需压差,利用带固定泄流孔的检测器起动压差方程验证检测器能否正常起动,利用建立的固定泄流孔局部阻力系数方程得出泄流后检测器的运行速度。经过4次工业应用,验证了上述方程和计算流程的可靠性。

基于漏磁内检测的管道特征信号分析

管道作为1种能源运输方式,由于内部复杂介质的作用经常会发生腐蚀现象,开展管道漏磁内检测工作是评价管道运行状况有效方法。此研究项目以管道漏磁内检测为基础,采用有限元分析方法,开展管道缺陷、焊缝、法兰、补板和接管漏磁场空间分布特性的研究,提取缺陷漏磁场关键特征参数,分析缺陷漏磁场空间分布规律,为缺陷信号的识别提供理论基础。