Pulse-modulation eddy current inspection of subsurface corrosion in conductive structures

Due to corrosive and hostile environment, in-service conductive structures are prone to subsurface corrosion which has posed a severe threat to structural integrity and safety. Although Pulsed eddy current testing (PEC) has been found advantageous over other Electromagnetic Non-destructive Evaluation (ENDE) techniques particularly in detection and characterisation of subsurface defects in conductive structures, it is subject to technical drawbacks. In light of this, in this paper, Pulse-modulation eddy current technique (PMEC) is proposed in an effort to enhance the inspection sensitivity to subsurface corrosion and quality of corrosion imaging. Closed-form expressions of PMEC responses to subsurface corrosion are formulated via the Extended Truncated Region Eigenfunction Expansion (ETREE) modelling. A series of simulations are subsequently conducted to analyse the characteristics of PMEC signals and inspection sensitivity. Following this, experiments of PMEC for evaluation and imaging of subsurface corrosion are carried out. Through theoretical and experimental investigation, it has been found that PMEC is advantageous over PEC in terms of evaluation sensitivity and quality of corrosion imaging.     

基于暂态磁场梯度信号的脉冲涡流无损检测和定量评估技术

脉冲涡流检测技术是目前对多层金属结构实施有效检测和定量评估的无损检测方法之一。传统脉冲涡流检测技术基于电磁感应原理,采用感应线圈或磁场传感器采集暂态磁场信号,以实现对多层金属结构内部缺陷的定位、识别以及量化评估。文章提出一种新型脉冲涡流检测技术,该技术主要基于已在核磁共振成像(MRI)领域得到应用的磁场梯度测量技术,将磁场梯度信号测量与脉冲涡流检测相结合,以实现对多层金属结构脉冲涡流检测灵敏度的提高。基于ETREE解析法,建立了所提方法的理论模型,推导了脉冲涡流检测磁场梯度信号理论表达式。通过仿真和试验,证明了该方法在多层金属结构亚表面材质劣化检测中的优势。     

Defect edge identification with rectangular pulsed eddy current sensor based on transient response signals

The Pulsed Eddy Current (PEC) testing is an increasingly emerging nondestructive testing & evaluation (NDT&E) technique. The main purpose of this study is to improve the performance of defect edge identification of C-scan imaging technique utilizing the rectangular PEC sensor. When sensor scans along the defect, peak waves of response signals always present a crest and a trough in direction of magnetic induction flux, while present different shapes in direction of exciting current. The maximum and minimum values of peak waves in direction of magnetic induction flux are corresponding to the moment of sensor entering and leaving the length edge of defect, which provides us a way to evaluate the length edge of defect. To evaluate the width edge of defect, we obtain and analyze the C-scan imaging results in direction of magnetic induction flux. For improving the identification of width edge of defect, we proposed news features from response signals and differential response signals. Experiment results have shown that the width edge of defects on surface can be identified effectively by selecting and normalizing the appropriate features in time domain. Therefore, both length edge and width edge of defect can be evaluated effectively in direction of magnetic induction flux. The rectangular PEC sensor is helpful for C-scan imaging inspection technique and has a good prospect in field of nondestructive testing & evaluation.     

Pulsed eddy current imaging and frequency spectrum analysis for hidden defect nondestructive testing and evaluation

Hidden defect characterisation in some complex structures is difficult. Pulsed Eddy Current (PEC) imaging based on rectangular excitation coil is investigated in this paper and hidden defect nondestructive testing and evaluation (detection, classification, and quantification) is carried out based on the various C-scan images. Experimental results have illustrated that hidden defects can be identified effectively by particular character in C-scan imaging results and sub-surface defects can be discriminated to correct class by selecting the rising time from response in time domain. The quantification information of hidden defects is preliminarily obtained based on the contour and 3D images. In addition, PEC imaging and frequency spectrum analysis are effective to detect, classify, and evaluate the sub-surface defects under the influence of edge effect of specimen. To sum up, PEC imaging is an effective approach to characterise hidden defects and sub-surface defects.     

基于脉冲涡流差分信号提离交汇点的亚表面层材质劣化检测技术理论研究

多层金属结构广泛应用于石油、化工、航天和能源等工业领域的大型、复杂装备中。由于服役工况一般较为恶劣,该结构亚表面层材质性能会出现劣化,直接威胁到大型、复杂装备的安全运转。通过脉冲涡流检测理论仿真,发现了一种基于脉冲涡流差分信号的新型提离交汇点。通过对该交汇点的特性研究,提出了一种能够对多层结构亚表面层材质劣化进行检测和评估的方法。由于当前的脉冲涡流检测技术主要针对金属结构表面层材质劣化进行检测,所以该方法的提出拓展了脉冲涡流检测技术的应用领域。通过数值仿真,所提方法的正确性及实用性得到了验证。     

脉冲涡流技术对飞机结构内层裂纹缺陷的检测识别

如何检测老龄化飞机多层结构中的裂纹缺陷一直是无损检测领域的一个难点。脉冲涡流技术是一种可以对多层结构中缺陷进行有效检测的电磁无损检测技术。理论推导了脉冲涡流渗透深度的公式,得出适当的减小脉冲激励频率与增加占空比有利于检测深层缺陷。设计了实验系统与矩形传感器,对激励信号的频率与占空比进行了优化设计。对多层结构中的内层缺陷进行了实验,并对微弱的检测信号进行了必要的数据处理。实验结果证明脉冲涡流检测技术可以对内层裂纹缺陷进行有效的检测。脉冲涡流技术将会在航空无损检测领域发挥重大的作用。     

接收线圈位置对脉冲涡流检测灵敏度的影响

研究了对带包覆层管道的内部腐蚀进行脉冲涡流检测时,接收线圈的位置变化对检测灵敏度的影响,进行了探头置于激励线圈下不同位置的有限元仿真和试验研究。有限元仿真结果表明:在轴向和周向2个方向都是当检测线圈位于激励线圈边缘正下方时检测效果最好,其灵敏度分别为0.61、0.60。验证试验表明:在轴向和周向2个方向上,最佳检测位置都是位于激励线圈边缘正下方,其灵敏度分别为0.26、0.27。试验结果与仿真结果基本一致,表明接收线圈在激励线圈外边缘正下方附近时,检测灵敏度达到最大。研究结果有助于带包覆层管道腐蚀的脉冲涡流检测的传感器设计。     

Pulsed eddy current technique for defect detection in aircraft riveted structures

The Pulsed Eddy Current (PEC) technique is an effective method of quantifying defects in multi-layer structures. It is difficult to detect defects in riveted structures of aging aircraft. Based on theoretical analysis of PEC technique, three different probes, including a differential hall probe, a differential coil probe, and a two-stage differential coil probe are designed to detect this kind of defects. The averaging method and wavelet analysis method are used to de-noise the hall response signals. By selecting peak amplitude and zero-crossing time of response signal in time domain as key features, defects in riveted structures can be detected effectively. The experimental results indicated that the differential coil probe acted as effectively as the differential hall probe. The defects between third layer and fourth layer in riveted structures can be detected by utilizing the two-stage differential coil probe. The PEC technique has a promising application foreground in the field of aeronautical nondestructive testing.     

A feature extraction technique based on principal component analysis for pulsed Eddy current NDT

Pulsed Eddy current (PEC) is a new emerging NDT technique for sub-surface defect detection. The technique mainly uses the response peak value and arrival to detect and quantify the defects. This could suffer from noise and be not sufficient to extract more information about the defects, e.g. depth information of defects. This paper introduces the application of principal component analysis in extracting information from PEC responses. A comparative test carried out shows that the introduced technique has performed better than the conventional technique in the classification of defects.     

脉冲涡流和电磁声换能器双探头无损检测

在许多情况下，只应用一种NDT技术存在不足，这就迫使NDT操作人员使用一种以上的技术以保证检测出危害被检物使用寿命或功能的缺陷。但分别实施多种技术的检测，就会延长检验时间。介绍了一种新的NDT设施，采用两种不同的非接触无损检测技术进行互补，即电磁声换能器（EMAT）和脉冲涡流（PEC）探头。检测结果表明，脉冲涡流和电磁声换能器因是非接触，所以可应用于材料生产过程中的自动在线检验，也可用于在役检验。     

基于FSM无损检测的金属管道均匀腐蚀剩余寿命预测

目的预测均匀腐蚀下金属管道的剩余寿命。方法研究API579中对金属管道剩余寿命预测的方法,具体分析方法中存在的缺陷。采用场指纹法(FSM)对直径为750 mm、壁厚为10 mm的金属管道的腐蚀情况进行实时检测。检测时随机选择15个不同的位置,每隔3个月检测一次,通过检测各个位置电极对之间电压值的变化量计算出管壁厚度的变化值。结果根据对实验数据的分析,随着时间推移,金属管道壁厚值逐渐减小,且减小的速率越来越快。腐蚀速率与运输介质、含氧量、金属管道材料、运输介质中的杂质有着密切关系,全面分析实验数据可以得到金属管道腐蚀速率的规律。加入腐蚀速率影响因素的影响因子K,运用数理统计的方法探索性地提出了一种均匀腐蚀下金属管道剩余寿命Rlife预测的数学模型。结论在工程实际中,可以运用数理统计的方法对大量实时数据及运行过程中已经记录的数据进行分析,从而找到金属管道在特定环境下的腐蚀规律,再通过该数学模型可对均匀腐蚀的金属管道进行寿命预测。     

带包覆层铁磁性管道腐蚀脉冲涡流检测技术

应用脉冲涡流检测技术,对带包覆层的铁磁性管道腐蚀进行了检测。对不同厚度的包覆层、不同面积和深度的腐蚀缺陷进行了试验,分析检测灵敏度的变化。试验结果表明,对于较大面积的腐蚀缺陷,即使包覆层较厚,在合适的检测参数下,脉冲涡流也具有很好的检测能力。     

磁应力检测技术在双金属复合管检测上的实践

在高腐蚀性油气输送管道中,已经使用双金属复合管,其中内层是较薄的耐蚀合金内衬层,起到防腐蚀的作用,外层是较厚的普通钢质输送管用作结构支撑增加管材强度。内衬耐蚀合金层与钢质管材结合处的缺陷,以及管线焊接施工中造成的焊缝处的缺陷,通常会造成外层钢管内壁腐蚀的加速,引发管道腐蚀穿孔而发生泄漏,影响油气输送管道的安全运行。针对常规内、外检测方法难于适用在役双金属复合管线的检测与评价,采取非接触磁应力检测与评价技术,在国内某油田集输管道进行了现场的检测实践,取得了较好的效果。     

Mehrfrequenz-Wirbelstrom-Prüfung geschichteter Strukturen aus Aluminium zum Nachweis und zur Quantifizierung verdeckter Korrosion

Multifrequency eddy current inspection of layered aluminium aircraft structures to detect and quantify hidden corrosion The paper lines out the potential of the Eddy Current method to detect and evaluate corrosion-induced damage (attenuation of wall thickness) in deeper layers of aircraft structures (adhesioned aluminium plates). This task will be solved by the use of the eddy current inspection instrument (MFEC3-1) developed by the Institute of Nondestructive Testing (IZFP), suitable choise of system parameters and convenient design of the evaluation algorithm respectively. Information about quantitative extenion and amount of residual wall thickness caused by corrosion will be read out.     

基于CR技术的钢管壁厚测量工艺研究

本研究给出一种基于CR成像系统评价钢管壁厚的工艺方法。首先利用钢阶梯试块进行试验分析,研究CR成像系统对比度响应特性随射线能量的变化关系,以确定其用于厚度测量的线性响应范围,然后针对3个不同壁厚的钢管,按特种设备标准规定的检测技术等级分别对数字图像质量进行评价,以优化曝光参数,将最佳曝光参数下测量并拟合的厚度－灰度线性方程用于计算管壁厚度,计算结果与实际厚度的误差均不超过3%。研究结果表明CR测量特种设备管道管壁厚度的可行性,为管壁腐蚀监测提供一种辅助方法。     

Investigation of thermal imaging sampling frequency for eddy current pulsed thermography

Eddy Current Pulsed Thermography (ECPT) is an integrative Non-Destructive Testing and Evaluation (NDT&E) technique that has been applied for defect and material characterization of conductive material and components. Thermal transient images provide rich information for decision making. However, high sampling rates of a thermal camera creates high cost and will generate a large of amount of data which is difficult for remote monitoring in terms of computational efficiency and data communication. This paper investigates the impact of thermal image sampling rates versus feature extraction for defect characterization. After introduction of Eddy Current Pulsed Thermography (ECPT), different sampling rates of thermal images are applied for different characterization. Based on the feature robustness versus different sampling rates, appropriate sampling rates are reported. The impact of using high end and low end thermal cameras for ECPT non-destructive evaluation are discussed.     

Current deflection NDE for the inspection and monitoring of pipes

Routine inspection of oil and gas pipes for time dependent degradation is essential. Pipelines are most commonly inspected using In-Line Inspection (ILI), however restrictions from pipe geometry, features or flow rate can prevent its use. Facility pipework rarely facilitates ILI, and external inspection often warrants the undesirable removal of the pipe insulation and cladding. This work investigates the applicability of a current deflection non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly focusing on corrosion. Magnetic sensors are used to monitor variations in the spatial distribution of the induced magnetic flux density outside a pipe that arise from deflection of an injected electric current around inner or outer wall defects. An array of orthogonal magnetoresistive sensors has been used to measure the magnetic flux density surrounding six-inch schedule 40 seamless and welded carbon steel and austenitic steel pipes. The measurements were stable and repeatable to the order of 100 pT which suggests that the defect detection or growth monitoring of corrosion-type defects may be possible with a few amps of injected current when measurements are taken at around 50 mm lift-off. The sensitivity of the technique is dependent on factors including defect geometry, sensor lift-off, bends, variations in nominal pipe geometry or material properties, and the presence of ferromagnetic objects, each of which were investigated using either experiment or a validated finite element model.     

塔河油田苛刻环境下集输管线腐蚀防治技术应用

目的提升苛刻环境下油气集输管线的腐蚀防护能力,降低腐蚀速率,降低腐蚀穿孔造成的环境污染和人员伤害风险。方法针对塔河油田高H_2S、高CO_2、高H_2O、高Cl~-、高矿化度、低p H值的苛刻内腐蚀环境,通过科研攻关,揭示腐蚀机理,明确腐蚀规律特征,在借鉴国内外防腐技术的基础上,研发出集输管线内挂片法腐蚀监测装置,建立数据、形貌、位置的点腐蚀定量评价方法,以提高腐蚀监测的准确率与评价精度。结果研发出针对H_2O-H_2S-CO_2-Cl~-共存腐蚀环境体系的BX245-1Cr耐蚀钢种管材,其力学性能优异,耐蚀性好,现场试验中点腐蚀速率降低了37.8%,均匀腐蚀速率降低了11.0%。优化改进了非金属管材结构,提升了其耐强冲刷腐蚀性能,并通过添加碳黑与玻璃纤维同缠绕制管消除静电腐蚀。含高H_2S和高CO_2伴生气集输管线采用"预膜+连续加注+批处理"缓蚀剂防护技术,控制均匀腐蚀速率为0.001 mm/a,点腐蚀速率为0.0299 mm/a。含水原油集输管线采用涂层风送挤涂施工进行内涂层防护,解决了60 mm≤DN≤100 mm小口径管线内涂层补口的难题;应用PE管内穿插修复、涂层风送挤涂修复技术对腐蚀集输管线进行治理。结论形成了安全可靠、经济高效、节能降耗且实用的腐蚀防治关键技术系列,现场应用效果显著,为国内油田的腐蚀防治提供了技术借鉴与应用经验。     

带钢制保护套管的钢管腐蚀缺陷的脉冲涡流检测方法研究

流体输运钢管外部加一层保护性钢套管,会使从外部检测内管腐蚀更加困难。本研究基于脉冲涡流检测技术,设计一种扁平U型结构传感器,可在双层钢管间隙中检测内管腐蚀情况而不受套管影响,且该检测方法一次扫查可同时获得内管的内壁和外壁减薄信息。使用圆柱型探头和U型探头检测试件3处缺陷,同时将钢管间隙减小到25、35 mm,与不加套管时的检测缺陷结果进行对比。结果表明:和传统同轴式圆柱形探头相比,U型传感器对外部保护钢管有着较强的抗干扰的能力,对衰减曲线影响较小,在间隙间检测内管腐蚀缺陷有较高的灵敏度,能够满足工业现场要求。     

油气管道腐蚀与防护研究进展

随着管网的复杂化和管道腐蚀的多样化,管道老化问题日益显著,管道失效事故发生率上升,造成巨大的经济损失。分析了油管腐蚀的影响因素,管外土壤、管内输送介质及管杆腐蚀磨损是引起油管腐蚀的重要因素。归纳了油管腐蚀的一般特征,油管腐蚀是多种介质综合作用的结果,系统性总结了H_2S、CO_2腐蚀机理。H_2S腐蚀速率与其浓度呈正比关系,在浓度一定时,H_2S腐蚀速率主要取决于材料的硬度和强度。CO2腐蚀速率主要受温度、压力、介质流速以及pH值的影响。通过比较分析多种油管防护方法的优缺点,指出爆炸复合油管防护性能强且有效期长,是一种最适合油气井长效防护的方法。对管道施加外防护层和内壁检测是油管防护的有效手段,有益于降低油管事故率和提高油田综合效益。