Feature guided wave inspection of bond line defects between a stiffener and a composite plate

Adhesive bonding is widely used in aerospace composite structures. A continuous well-cured bond can offer good joint strength and improved fatigue and impact resistance, and is therefore crucial to the performance of the entire structure. This paper explores the feasibility of using feature guided waves (FGW) for rapid screening of the bond line between a stiffener and a carbon fiber reinforced polymer (CFRP) composite panel. Such FGWs are capable of focusing the wave energy along the stiffener and the bond layer, with limited radiation to the adjacent plate. The Semi-Analytical Finite Element (SAFE) approach is employed to understand the modal properties of FGWs that exist in the structure, and criteria are suggested to choose proper mode-frequency combination that is sensitive to adhesive defects. A shear horizontal type FGW mode is identified to be well suited, as it is easy to excite, and propagates with little dispersion and relatively low attenuation, while it retains sufficient energy around the bond layer. Both 3D Finite Element (FE) simulations and experiments are performed to study the interaction of the selected FGW mode with defects in the adhesive bond, and the results show excellent agreement. The reflection behavior and the wave-defect resonance phenomenon are investigated, which demonstrate the capability of the FGW for the bond line inspection.     

EMAT pipe inspection technique using higher mode torsional guided wave T(0,2)

We developed a pitch-catch system based on electromagnetic acoustic transducers (EMATs) for pipe inspection, which moves inside the pipe in the axial direction. The first higher mode, T(0,2), of the torsional guided wave is transmitted and detected, and variations of amplitude and phase are measured while moving the EMATs. Several aluminum pipes containing dish-shaped defects are inspected, and the amplitude and phase show enough detection sensitivity. It is found that the phase measurement has better potential as a tool for quantitative inspection. The applicability of the technique for steel pipe is also confirmed.     

Ultrasonic guided wave inspection of Inconel 625 brazed lap joints: Simulation and experimentation

The aerospace industry has been investigating the use of structural brazed joints. As a result of this effort, there is now a need for a rapid, robust, and cost-effective non-destructive testing method to evaluate the structural integrity of the joints. The mechanical strength of brazed joints is known to depend on the microstructural quantity of brittle phases. Ultrasonic guided waves offer the possibility of detecting brittle phases in joints using spatio-temporal measurements. This study focused on the development of a technique based on ultrasonic guided waves for the inspection of Inconel 625 lap joints brazed with BNi-2 filler metal. A finite element model of a lap joint was used to optimize the inspection parameters and assess the feasibility of detecting the quantity of brittle phases in the joint. A finite element parametric study simulating the input signal shape, the center frequency, and the excitation direction was performed. The simulations showed that the ultrasonic guided wave energy transmitted through, and reflected from, the joints was proportional to the amount of brittle phases in the joint. Experimental validations were then performed on three distinctive samples with variable amount of brittle phases in the joint. The samples had three different brazing times (1, 60 and 180 min). Finally, experimental results were in accordance with simulations and demonstrate the potential of the inspection method to estimate the quantity of brittle phases in a lap joint.     

蒸汽发生器管板与管孔密封焊缝的渗透检测

介绍了蒸汽发生器管板与管孔密封焊缝的渗透检测工艺及操作,对常见的密封焊缝渗透检测的缺陷进行了分析,可为国内核岛主设备管板与管孔密封焊缝的渗透检测及质量控制提供经验,供同行参考.     

核电主蒸汽超级管道管嘴成形有限元分析

针对核电主蒸汽超级管道管嘴的成形工艺难点:加热工艺、管嘴挤压成形工艺,采用有限元软件ABAQUS分析了影响核电主蒸汽超级管道管嘴成形的主要因素:凸模形状、凸模高度、接触摩擦力和材料温降等。分析结果表明,凸模轮廓直接影响材料的等效塑性应变和管嘴成形尺寸;凸模高度、表面摩擦条件影响管嘴壁厚和高度变化。优化这些影响因素后,进行管嘴一次挤压成形试验,试验结果表明,采用凸形凸模、调整凸模高度、增加润滑条件和降低坯料温降,可以成形出合格的管嘴零件。     

Circumferential higher order guided wave modes for the detection and sizing of cracks and pinholes in pipe support regions

The non-dispersive propagation of ultrasonic guided wave higher order modes cluster (HOMC) traveling along the circumferential direction in a hollow cylinder and its interaction with defects in pipe support regions is reported. These circumferential guided waves were generated in mild steel (MS) pipe specimens containing artificially created axial notches (simulating axial cracks) and pinholes (simulating pinhole-like defects) of different sizes in order to simulate conditions such as cracking and corrosion under pipe supports. The characteristics of these guided waves were also studied as a function of parameters related to how they were generated; namely, using: (a) 2.25 MHz linear phased array transducer, (b) 2.25 MHz conventional circular transducer and (c) 1 MHz conventional circular transducer. These higher frequency modes were explored for their ability to detect and size defects. Because of access limitations to the pipe support region in actual field testing, the transducer was always placed at a fixed circumferential position and moved axially along the length of the pipe. The defect position along the circumference was ascertained from the time of flight while the defect size was estimated using the amplitude data. The signals obtained for all three transducer configurations are compared for their ability to locate, detect and size the above-mentioned defects. It was shown that at these relatively higher frequencies, the guided wave modes exhibit small dispersion and have the ability to provide improved imaging of small size defects throughout the cross-section of the pipe.     

AP1000蒸汽发生器环焊缝局部热处理对U形管局部损伤的分析及预防

AP1000蒸汽发生器总装环缝局部消除应力热处理过程中,由于U形管的壁厚较薄,与支撑板间隙很小,支撑板暂时倾斜可能会在管子的局部形成永久性的塑性变形(压痕). 采用有限元方法,对蒸汽发生器管板和下封头环缝局部热处理过程进行分析,获得在局部消除应力热处理过程二次侧空气温度的分布情况,及各组件的温度变化及变形规律. 设计用于平衡内部温度的加热和冷却系统. 结果表明,分析能够模拟实际热处理过程中各组件的变形趋势,冷却和加热系统能够有效的预防管子局部形成永久性的塑性变形.     

An NDT guided wave technique for the identification of corrosion defects at support locations

Due to the large number of pipe supports over a piping run, a rapid reliable NDT system is needed to identify hidden corrosion defects at a pipe-support interface. To accomplish this, a system using Periodic Permanent Magnet (PPM) Electromagnetic Acoustic Transducers (EMAT׳s) to generate dispersive SH1 guided waves is implemented. For this study, both the effect of the support contact and a corrosion type defect are evaluated independently through finite element models and experiments utilizing a flat plate approximation. It was found that utilizing the SH1 plate wave near the inflection point or ‘knee’ of the dispersion curve yields a high sensitivity to gradual wall loss defects while experiencing a minimal effect from the support contact.     

Localization of defects in steam generator tubes using a multi-coil eddy current probe dedicated to high speed inspection

Steam generator (SG) tubing of pressurized water reactor in nuclear plants must be rapidly and accurately checked in order to detect defects in their early stages. In this paper, the authors present a multi-coil eddy current (EC) probe allowing both high speed inspection and circumferential localization of defects in the tube wall. A method of multi-coil EC signal processing, based on a continuous wavelet transform combined with a maximum likelihood diagnosis, is elaborated in order to enhance the detection performances and to provide automatic localization of defects. The inspection of SG tube samples shows good localization performances for defects as small as 10% deep, 15 mm long and 100 μm wide outer diameter notches, of both circumferential and axial orientations.     

小型堆直流蒸汽发生器传热管工艺研究及质量控制

针对小型堆直流蒸汽发生器,分析了其传热管的工艺过程.冷轧时,优化了冷轧工模具孔型的开口设计、孔型曲线设计及与之匹配的顶头变形段及定径段设计;TT处理时,控制温度在715 ℃、保温时间为5h以上,以提高抗晶间腐蚀的能力;弯制时,采用反变形法和特殊的模具设计,确定模具的开槽高度为9.91 mm、反变形量为0.09 mm,以...     

堆焊层缺陷对百万千瓦级蒸汽发生器管板封口焊质量的影响分析及处理

介绍了百万千瓦级蒸汽发生器管板堆焊层缺陷形成的原因,针对某制造厂发生的管板堆焊层的质量问题,采用分析和试验的方法确定该缺陷对后续管子管板封口焊缝质量的影响,并提出了该质量问题的处理方案,为处理和提高管板镍基堆焊层的质量问题提供参考。     

The reflection of guided waves from notches in pipes: a guide for interpreting corrosion measurements

Ultrasonic guided waves are used for the rapid screening of pipelines in service and simple, standard testing procedures are already defined. The implementation of the method enables the localization of the defects along the length of the pipe and offers a rough estimate of defect size. In this article we present a systematic analysis of the effect of pipe size, defect size, guided wave mode and frequency on the reflection from notches. The maximum and minimum value of the reflection coefficient at varying axial extent are identified and used for the purpose of defect sizing. Maps of reflection coefficient as a function of the circumferential extent and depth of the defect are presented for a 3 in. schedule 40 steel pipe. An approximate formula, which allows these results to be extrapolated to other pipe sizes, is proposed and evaluated.     

Circumferential guided wave EMAT system for pipeline screening using shear horizontal ultrasound

The use of guided waves is now widespread in industrial NDT for locating metal loss in pipelines, that manifests as pitting, corrosion and general wall thinning. In this paper, a screening technique is assessed in terms of defect detection and defect sizing capability. Shear Horizontal (SH) guided waves propagate circumferentially around the pipe whilst the scanner is moved axially along the length. This type of tool is preferable to other methods, being applied to the exterior of the pipe, without requiring full circumferential access, and is able to operate through thin coatings (up to 1 mm thick). It is designed to provide a pipe screening tool for petrochemical pipelines both topside and subsea, particularly for detecting defects at pipe support areas. The system's efficacy in terms of detection and sizing of defects is considered via experimental measurements on artificially induced defects and in service corrosion patches, with results compared to finite element modelling of the interaction of the guided waves with artificial defects. Finite element modelling has been used to better understand the behaviour of different wave modes when they interact with defects, focusing on the mode conversions and reflections that occur.     

Design of a guided wave absorber for Structural Health Monitoring system development

The objective of this paper is to present and validate an efficient guided wave absorber for increased sensitivity of structural health monitoring systems based on guided wave, and especially for inspection close to structure boundaries. Such an absorber would also help with systematic characterization of guided waves interaction with defects in aerospace structures. A complete numerical parametric study is undertaken using the power flow in the structure to determine the reflection and transmission coefficients and thus the dissipated energy by the absorber. Starting with the determination of the geometry and dimensions using Finite Element Modelling (FEM), and following with an investigation on the influence of the absorber's mechanical properties, a practical and efficient absorber is identified. The dimensions of the developed absorber are minimized to provide optimal results for frequencies ranging from 50 kHz to 500 kHz for an incident A₀ mode. The resulting right triangle cross section absorber of Teflon has been machined and tested experimentally using a piezoelectric wave generator on one side of the absorber, and a tri-dimensional laser Doppler vibrometer (3D-LDV) to measure the transmitted wave on the other side. Using a spatial Fourier transform approach for the determination of the experimental reflection and transmission coefficients, the numerical results have been successfully validated.     

Shear horizontal piezoelectric fiber patch transducers (SH-PFP) for guided elastic wave applications

A new type of a lightweight piezoelectric transducer is proposed for selective excitation of horizontal polarized shear (SH) waves. Based on piezoelectric fibers the transducers are flexible, i.e. show structure conformity. The novel approach allows to introduce significant surface tractions by a transducer with double layer crossed fiber arrangement without the need of heavy seismic masses. The transducer operating principles are explained and the performance of a first transducer version is demonstrated by laser vibrometric measuring of the waves emitted into a plate. Numerical modeling of the identical arrangement shows nearly perfect agreement with measurements for the main features while differences in some details helps to understand how the first transducer version can be improved. The transducer exhibits, depending on its aspect ratio, a rather high directivity and a strong mode selectivity.     

Nondestructive technique for identification of the dished end of nuclear fuel pellets

Use of an infrared technique for identifying the dished/flat ends of nuclear fuel pellets for PHWR is suggested. The studies show that this method can be used for on-line checking of the orientation of the pellets.     

A novel feature extraction for eddy current testing of steam generator tubes

For defect characterization in steam generator tubes, feature extraction to interpret eddy current testing (ECT) signals has been recognized as an important step. In this paper, we propose a new feature extraction from ECT signals for defect classification and defect sizing. Using the extracted features as an input vector, a multi-layer perceptron (MLP) neural networks are used to classify defect types and to predict defect size. Although the proposed method requires relatively fewer features for the defect classification, it provides not only a high level of classification accuracy but also promising robustness to noise. Moreover, for the prediction of defect size, the proposed method yields a comparable prediction accuracy even though it needs fewer features than the previous result.     

一种管道中的导波频散计算方法

为了求得管道中导波的频散特性,提出了一种基于有限元的模式分析法来求解频散关系。以导波理论为基础,构建了Navier-stokes方程,采用分离变量法得到Helmholtz方程及泛函形式,并利用COMSOL软件对Helmholtz方程进行特征值的求解,计算结果与半解析有限元法所求得的结果基本吻合,并且能够求解出环状模态,证明了该方法的有效性及求解的全面性。同时,运用导波理论及铁木辛柯梁理论对低频的频散关系进行理论求解,通过对比,验证了模式分析法的精度良好。最后通过位移分量分析了模态的特征,为管道导波无损检测提供了依据。     

A neural network-based technique for quantitative wire rope inspection

The possibility of solving the problems encountered in the quantitative inspection of broken wires with a neural network is discussed and a new algorithm is presented. In comparison with conventional methods, the performance of inspection is much improved with the neural network-based technique.     

岭澳核电汽轮发电机外机座冷却器罩装焊工艺

东方电机股份有限公司为确保岭澳核电发电机外机座关键部件冷却器罩的合格生产,从合同要求出发,结合企业实际情况,低成本、高质量地完成了冷却器罩制造.冷却器罩尺寸大,精度要求高,按合同要求一次成型难度大.通过几种备料成型方案的对比,最终选择较为有效且经济的方案.同时制定合理的装焊工艺,确保成型尺寸,最终控制了焊接变形,确保合...