Prototype EMAT system for tube inspection with guided ultrasonic waves

A prototype system with full computer support for ultrasonic inspection of ferritic tubes using guided waves is described. The ultrasonic waves are launched and received with the aid of electromagnetic acoustic transducers which are layed out as linear phased arrays. The array structure provides a good axial directivity for the transducers so that the probe can be positioned anywhere along the tube length sequentially transmitting ultrasonic pulses in the foreward and backward directions. While the probe is fixed at one axial position during inspection the tube length is measured by the system and flaws are detected from returning ultrasonic echos. Results of the inspection of tubes with natural flaws are given and the wavelength-spectrum of the ultrasonic mode used for the inspection is discussed with respect to flaw depth sizing.     

核电厂BOSS焊缝在线堆焊修复相控阵超声检验技术

核电厂反应堆换料水池与乏燃料水池冷却和处理系统（PTR）及设备循环冷却系统（RRI）中含有大量管座接头（BOSS）焊缝,其安全性和可靠性直接影响所存储核燃料的安全状态,对其进行缺陷排查和在线修复是核电厂在役检查监督的重点和难点。本文针对BOSS焊缝在线堆焊修复的特殊要求和检验难点以及射线检验的局限性,设计了一套专用的相控阵超声探头和检验工艺,试验验证结果满足堆焊修复要求,并制订了核电厂BOSS焊缝堆焊修复无损检验的方法和在役检查监督的策略。     

Crack detection and sizing technique by ultrasonic and electromagnetic methods

Improvements in defect detection and sizing capabilities for non-destructive inspection techniques have been required in order to ensure the reliable operation and life extension of nuclear power plants. For the volumetric inspection, the phased array UT technique has superior capabilities for beam steering and focusing to objective regions, and real-time B-scan imaging without mechanical scanning. In contrast to the conventional UT method, high-speed inspection is realized by the unique feature of the phased array technique. A 256-channel array system has developed for the inspection of weldment of BWR internal components such as core shrouds. The TOFD crack sizing technique also can be applied using this system. For the surface inspection, potential drop techniques and eddy current techniques have been improved, which combined the theoretical analysis. These techniques have the crack sizing capability for surface breaking cracks to which UT method is difficult to apply. This paper provides the recent progress of these phased array and electromagnetic inspection techniques.     

Performance demonstration for an automated ultrasonic testing system for piping welds

This paper addresses the implementation of an automated ultrasonic testing (AUT) system qualification by performance demonstration (PD) as imposed by the ASME Boiler and Pressure Vessel Code Section XI. To improve the reliability of the ultrasonic testing results for nuclear power plant (NPP) components, almost all engineering codes related to NPP inspection require the ultrasonic inspection systems to be qualified by passing a PD examination. In this study, an AUT system developed to inspect pipe welding parts in NPPs is introduced. To acquire a Korean Performance Demonstration (KPD) qualification, the developed system had a KPD. System obtained the qualification for flaw detection, length, and depth sizing from KPD.     

A model for predicting vessel failure probabilities including the effects of service inspection and flaw sizing errors

A numerical approach has been developed to predict the probability that a fabrication flaw in a reactor pressure vessel will extend by fatigue crack growth mechanisms and become a through-wall flaw. The fracture mechanics model treats the size of the flaw, the location of the flaw, and the parameters governing the fatigue crack growth rates as stochastic variables that are described by histograms that represent their statistical distributions. A latin hypercube approach forms the basis for efficient numerical calculations of vessel failure probabilities, in particular for those cases having very low probabilities that are not readily calculated by use of more conventional Monte Carlo simulations. A second aspect of the vessel failure model evaluates the benefits of in-service inspections at prescribed inspection time intervals and with prescribed nondestructive examination capabilities (probability of detection as a function of flaw size). A third aspect of the paper evaluates flaw sizing accuracy, and the impacts of flaw acceptance criteria. For representative values of flaw detection probability, flaw sizing errors, and flaw acceptance criteria, detection capability is the most limiting factor with regard to the ability of the in-service inspections to reduce leak probabilities. However, gross sizing errors or significant relaxations of current flaw acceptance standards could negate the benefits of outstanding probability of detection capabilities.     

Wave propagation visualization in an experimental model for a control rod drive mechanism assembly

Nondestructive inspection techniques such as ultrasonic testing, eddy current testing, and visual testing are being developed to detect primary water stress corrosion cracks in control rod drive mechanism (CRDM) assemblies of nuclear power plants. A unit CRDM assembly consists of a reactor upper head including cladding, a penetration nozzle, and J-groove dissimilar metal welds with buttering. In this study, we fabricated a full-scale CRDM assembly mock-up. An ultrasonic propagation imaging (UPI) method using a scanning laser ultrasonic generator is proposed to visualize and simulate ultrasonic wave propagation around the thick and complex CRDM assembly. First, the proposed laser UPI system was validated for a simple aluminium plate by comparing the ultrasonic wave propagation movie (UWPM) obtained using the system with numerical simulation results reported in the literature. Lamb wave mode identification and damage detectability, depending on the ultrasonic frequency, were also included in the UWPM analysis. A CRDM assembly mock-up was fabricated in full-size and its vertical cross section was scanned using the laser UPI system to investigate the propagation characteristics of the longitudinal and Rayleigh waves in the complex structure. The ultrasonic source location and frequency were easily simulated by changing the sensor location and the band pass filtering zone, respectively. The ultrasonic propagation patterns before and after cracks in the weld and nozzle of the CRDM assembly were also analyzed. Since this visualization method is not limited in the flat cross section, it will be useful in developing ultrasound-based structural health monitoring technologies, advanced nondestructive methods, and numerical models. In addition, the proposed laser UPI system could be a useful tool in optimizing the receiver and transmitter locations, the ultrasonic path, and the ultrasonic frequency.     

Development of an ultrasonic inspection system using array transducers

A new ultrasonic inspection system was developed to obtain ultrasonic images of defects. This system adopts an electronic beam control method using array transducers. The beam control modes are a compound scanning mode and a linear scanning mode. Both modes are performed by timing control of ultrasonic wave transmission and reception at each transducer element.In the focal beam, the refraction of the ultrasonic wave at the boundary between water and metal in immersion testing is utilized to improve the lateral resolution of the ultrasonic beam. In steel, the improvement is a maximum of 25% for focal lengths from 5 to 35 mm as compared to lateral resolution not utilizing refraction.This system successfully imaged two side drilled holes in a steel block.     

Apparative developments for inservice inspections of reactor pressure vessels

Inservice inspections of primary circuit components are important preventive measures to guarantee nuclear power plant integrity, satisfying simultaneously reactor safety and economy in plant operation. Emphasizing pressurized water reactor pressure vessel (RPV) inspections, recent developments of new generations of automated and mechanized ultrasonic inspection equipment are presented. Starting from general equipment design and inservice implementation criteria, specific examples are given. Main attention is directed to equipment realization of phased array and ALOK inspection techniques, especially in their combination. Refined aspects of subsequent computer processing and evaluation of defect detection data are described. Analytical features and potential for further developments become evident. Remote controlled RPV inspections are stressed by describing a new generation of central mast manipulators, forming an integral part of total inservice inspection system.     

Improved ultrasonic testing by phased array technique and its application

The phased array ultrasonic testing method is available for beam steering and focusing, and then the focused beam divergence angle can be narrowed and the sound level can be intensified at the focused region. In the present study, two examples of phased array application which are the linear scanning mode operation and the sector scanning mode operation, were conducted in order to establish the availability of this technique as an actual NDT technique. As the result of the experiments, it was recognized that both types of scanning mode had the capability for defect detection and successful estimation of the defect size. Furthermore, it was well realized that the real time B-scope display without mechanical scanning was effective to reduce the operating time of inspection.     

Availability study of a phased array ultrasonic technique

A phased array ultrasonic testing method is expected to be applicable to nuclear power plants for electrical ultrasonic beam control and real time B-scope image display. The availability of the phased array ultrasonic technique has been investigated and it has been verified that the sound beam is electrically steered to the intended angle and is electrically focused at the intended position. From the results of experiments, the dynamic aperture sizing technique was established as a practical method and this technique was demonstrated for artificial flaws.     

反应堆压力容器超声波相控阵检测工艺研究

通过对反应堆压力容器（RPV）模拟体建模,研发相控阵（PA）超声波检测技术,以代替常规超声波检测技术,并对2种检测技术的检测能力和定量能力进行对比和评估。验证试验表明,PA超声波检测技术的检测和定量能力满足标准要求,且可大幅度缩减检测时间,具有可观的经济价值。      

核电厂一回路管座焊缝超声波检测仿真研究

小尺寸支管接头（BOSS）焊缝作为核电厂一回路压力边界的薄弱环节,对其有效监控是核电厂日常和在役大修的重点和难点。采用仿真技术、工艺试验和现场应用验证等方法,设计并验证了BOSS焊缝的超声波相控阵检测工艺,解决了核电厂日常和在役大修中BOSS焊缝的监督难点。并得到类似超声波相控阵检测工艺的设计和验证方法。      

Steam generator small bore piping socket weld inspection using the phased array ultrasonic technique

As nuclear power plants age, the likelihood of failures in the small bore piping used in those plants caused by exposure to mechanical vibrations during plant operations increases. While small bore piping failures rarely cause plant shutdown, the management of small piping has been a keen area of interest since their repair or maintenance requires a reactor trip. Steam generator (SG) drain pipe socket welds are small diameter piping connections (nominal pipe schedule 3–4 inches) susceptible to mechanical vibration. SG drain pipe socket weld failures have caused coolant leakage. Therefore, more reliable inspection technologies for small bore piping need to be developed to detect problems at an early stage and prevent pipe failures. This research aims to improve the reliability and accuracy of small bore piping inspections through the design, manufacture and application of a new phased array ultrasonic testing technique and inspection system for SG drain line socket welds.     

On-line neuro-expert monitoring system for Borssele Nuclear Power Plant

A new method for an on-line monitoring system for the nuclear power plants has been developed utilizing the neural networks and the expert system. The integration of them is expected to enhance a substantial potential of the functionality as operators support.

The recurrent neural network and the feed-forward neural network with adaptive learning are selected for the plant modeling and anomaly detection because of the high capability of modeling for dynamic behavior. The expert system is used as a decision agent, which works on the information space of both the neural networks and the human operators. The information of other sensory signals is also fed to the expert system, together with the outputs that the neural networks generate from the measured plant signals. The expert system can treat almost all known correlation between plant status patterns and operation modes as a priori set of rules.

From the off-line test at Borssele Nuclear Power Plant (PWR 480 MWe) in the Netherlands, it was shown that the neuro-expert system successfully monitored the plant status. The expert system worked satisfactorily in diagnosing the system status by using the outputs of the neural networks and a priori knowledge base from the PWR simulator. The electric power coefficient is simultaneously monitored from the measured reactive and active electric power signals.     

Development of an intelligent system for ultrasonic flaw classification in weldments

Even though ultrasonic pattern recognition is considered as the most effective and promising approach to flaw classification in weldments, its application to the realistic field inspection is still very limited due to the crucial barriers in cost, time and reliability. To reduce such barriers, previously we have proposed an intelligent system approach that consisted of the following four ingredients: (1) a PC-based ultrasonic testing (PC-UT) system; (2) an effective invariant ultrasonic flaw classification algorithm; (3) an intelligent flaw classification software; and (4) a database with abundant experimental flaw signals. In the present work, for performing the ultrasonic flaw classification in weldments in a real-time fashion in many real word situations, we develop an intelligent system, which is called the ‘Intelligent Ultrasonic Evaluation System (IUES)’ by the integration of the above four ingredients into a single, unified system. In addition, for the improvement of classification accuracy of flaws, especially slag inclusions, we expand the feature set by adding new informative features, and demonstrate the enhanced performance of the IUES with flaw signals in the database constructed previously. And then, to take care of the increased redundancy in the feature set due to the addition of features, we also propose two efficient schemes for feature selection: the forward selection with trial and error, and the forward selection with criteria of the error probability and the linear correlation coefficients of individual features.     

Improvement of SH-wave EMAT phased array inspection by new eight segment probes

This paper presents a newly developed electromagnetic acoustic transducers (EMAT) probe with eight transmitter and eight receiver segments aiming to improve performance of a phased array EMAT probe with four transmitter and four receiver segments. Results of tests on artificial flaws in HAZ in a 6 inch diameter austenitic mock-up pipe were shown for characterizing its performance. The UT result with a conventional Piezo transducer was also referred for comparison.     

Waveguide ultrasonic liquid level transducer for nuclear power plant steam generator

This paper deals with the development and utilization of a new acoustic method to control the level of the coolant in industrial power-generating equipment. The development research was carried out on the basis of the method of acoustic impedance, based on measuring attenuation of a longitudinal ultrasonic wave in a waveguide sensing element. Ultrasonic attenuation is determined by the degree of submergence of the sensing element in liquid. For this purpose waveguide ultrasonic transducers are used, made with specially designed technology (waveguide acoustic transducers—WAT-technology). The transducers are adapted for operation under extreme conditions in the water coolant with temperatures up to 350°C and pressure up to 20 MPa. The paper tackles: principle of operation of transducers, methods of testing under laboratory conditions, design and results of calibration in a thermophysical test facility, results of the operational trial of the level transducer at the nuclear power plant in Zaporozhye.     

反应堆压力容器接管与筒体焊缝超声轮廓二维成像算法研究

核电厂复杂几何形状焊缝的超声信号位置直观显示对缺陷判断具有重要参考价值。核电厂反应堆压力容器（RPV）接管内表面通常带有一定的倾斜角度,采用传统的矩形B扫描成像算法,接管与筒体焊缝超声B/C扫描成像显示存在显示不直观、缺陷定位不准确的突出问题。本文提出了直线与直线、圆弧与椭圆弧通过圆弧相切连接的算法,利用绘制直线、弧的库函数实现轮廓的绘制并将超声信号显示在轮廓之中,形成了带轮廓的B扫描图像。通过计算在轮廓中穿过闸门线的A扫描信号的阈值,形成马鞍面形状的C扫描图像。核电厂RPV接管与筒体焊缝现场超声扫查数据验证了该算法的有效性和实用性。      

反应堆控制棒组件超声检测探头的研制

为了检测核电站反应堆控制棒组件,保障核电站在役检查顺利实施、降低检测成本。对反应堆控制棒组件（RCCA）检测用超声探头进行自主研制,本文详细介绍了15MHz-Φ4mm-FP8 mm RCCA超声探头制作流程,通过对压电晶片、声透镜、背衬3方面详细介绍探头制作工艺。通过对超声探头进行性能测试,测试脉冲周期数为1.5周,频带宽度为105%,在高温环境下仍能保持优良性能。对超声探头进行模拟检验测试,缺陷测试结果清晰可见,满足检验需求,可完全实现国产化替代进口产品。       

Monitoring the filling level of the rpv using stationary emus-probes

The determination of the filling level and the initiation of growth of bubbles in vessels and pipes containing fluids is an essential component of monitoring during operation.The ultrasonic pulse-echo-method is a measuring procedure suited for this purpose and applicable from the outside. Piezoelectric ultrasonic transducers can be used in principle at a temperature of 300°C, but in practice these transducers are not preferred because of the expense and inconvenience in coupling them to the vessel wall.These problems are solved using lectro agnetic- ltrasonic-(EMUS-)transducers. Due to physical reasons a longitudinal wave is generated in the fluid by the refraction of a shear wave in the vessel-wall. The filling level is measured in a pitch and catch-technique by a mirror reflection of the longitudinal wave at a construction element inside the vessel. This paper reports on laboratory investigations concerning the applicability of the technique and first experiences with an EMUS-prototype system installed in a nuclear power plant.