The nondestructive testing of tubes and pipes for nuclear application

The directive of the Reactor Safety Commission demands for all materials which are provided for the pressure bearing enclosure of the refrigerant a nondestructive testing with sufficient sensibility. The specification 3201.1 for nuclear application as well as company-internal rules of important manufacturers regulate the requirements derived from the above direction for the NDT of tubes and pipes.For an objective and reproducible testing, equipments with defined characteristics are employed. based on internal specifications, testing equipments are fabricated and then checked with a special computerized test system. Moreover probes are controlled with regard to their acoustic and electric properties.The NDT of heat exchanger tubes and of pipes is given here as an example:Heat exchanger tubes: The tests include the inspection of longitudinal and transverse defects, wall thickness, dimension and tightness. In connection with the NDT, defect catalogues are set up. By this means the chosen test sensitivity is verified, and so the high quality of the tubes is assured. Specially developed eddy-current methods prove that such tested tubes are free of corrosion-causing phases.Pipes: The pipes are tested for longitudinal and transverse defects, for laminations and for wall thickness. To fulfil the demand for an objective and reproducible testing, there was developed and installed an automatic, computer-controlled ultrasonic equipment with 40 probes.Development trends: For the NDT of heat exchanger and boiler tubes an electrodynamic excited ultrasonic test system is evolved which is also able to test curved and installed tubes. The sophisticated testing technology is completed by a qualified education and training of NDT personnel.     

Non-destructive methods for the defect detection in the ITER high heat flux components

This paper discusses the application of non-destructive testing (NDT) by ultrasonic technique for the control of the joining interfaces of the ITER divertor vertical target plasma facing units. The defect detection capability has to be proved for both metal to metal and metal to carbon/carbon fibre composite (CFC) joints because these two types of joints have to be realized for the manufacturing of the high heat flux units. In this paper the UT results coming from the investigation performed during the manufacturing, but also after the thermal fatigue testing (up to 20 MW/m²) of six mock-ups manufactured using the Hot Radial Pressure technology (HRP) in ENEA labs are presented and compared with the evidences from the final destructive examination. Regarding the Cu/CFC joint, the effectiveness of the ultrasonic test has been deeply studied due to the high acoustic attenuation of CFC to ultrasonic waves. To investigate the possibility to use the ultrasonic technique for this type of joint, an ‘ad hoc’ flat Cu/CFC joint sample, that reproduces the actual annular joint interfaces, was manufactured. This flat sample has the advantage of being easily tested by probes with different geometry and frequency. UT results are compared with X-ray and eddy current testing of the same sample.     

核电站关键部件超声检测计算分析系统

针对核电站关键部件超声检测特点,基于瑞利积分、基尔霍夫近似、几何衍射和波恩近似等理论,建立了声场及声场与缺陷相互作用理论模型,开发出核电站关键部件超声检测计算分析系统(UT-CAS),并以安全端异种钢焊缝超声检测为例介绍了UT-CAS的应用.结果表明,UT-CAS能够快速、准确地模拟各种检测环境,实现工艺验证、辅助分析和人员培训等功能.     

宽频超声无损检测核燃料元件及复合结构技术研究

根据层状复合结构非均匀性、层薄、质量要求高等特点,讨论了超声检测的特殊性,介绍了宽频相幅超声检测结合质量原理及图象化超声检测技术。实验表明:本技术及检测系统设计合理;宽频超声系统具有盲区小,分辨率高、可靠性好和功能强等特点。已成功用于核反应堆元件、爆炸复合结构、电子元件和其他层状复合材料的自动化无损检测。     

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.     

Aging material evaluation and studies by non-destructive techniques (AMES-NDT) — a European network project

This paper presents results obtained in a round-robin action organized in a concerted action of ten partners in the EURATOM program of the European Community. The objective of the research was to document the state of the art of available non-destructive testing (NDT) techniques in order to characterize material aging phenomena based on a reduction of Charpy-V energy and a shift in the fracture appearance transition temperature. Therefore, samples from the Japanese nuclear reactor pressure vessel JRQ-steel (ASMT Standard A533-B Class 1) have been thermally treated at 700°C for 18 h with a subsequent water quenching. Besides micromagnetic and electromagnetic NDT, the positron annihilation technique, ultrasonic reverberation by using Laser ultrasonics and the thermo-electrical power have been applied to characterize the aged material states.     

The stage reached in the drafting of KTA-rules for the nondestructive testing of austenitic materials

At the end of 1972, the KTA (the Nuclear Commission) was called into being by the BMI (the Federal Ministry of the Interior) and by industry to draw up mandatory technical rules on dimensioning, manufacturing, design, and operating of nuclear facilities. The KTA-rules also lay down - where necessary - details of nondestructive testing. The procedure to be followed in the nondestructive testing of austenitic materials or weldings is the subject of ongoing discussion. In the following, consideration is given to the provisions of the KTA-rule 3201 currently in force and of proposed modifications or supplements concerning the NDT of austenitic materials or weldings on components in the coolant system for light water reactors. Final provisions especially for the ultrasonic examination of austenitic weld seams are still in preparation.     

Secondary side corrosion in steam generator tubes: lessons learned in France from the in-service inspection results

Non-destructive testing (NDT) has proved to be very important in the maintenance of steam generator tubing. This is particularly true in the case of secondary side corrosion, because this type of degradation leads to various morphologies which are often complex (intergrranular attack) (IGA), intergranular stress corrosion cracking (IGSCC), or a mixture of both. Their detection and characterization by the usual NDT techniques have been achieved through numerous laboratory studies, which were conducted in order to determine the performance and limitations of NDT. Pulled tube examination in a hot laboratory was very valuable, for both NDT and fracture mechanics aspects. The eddy current bobbin coil probe, used for multipurpose inspection of tubes, allows the detection of IGA-SCC at the tube support plate elevation. In France, the use of rotating probes is not required for that type of degradation, since the repair criterion is based on bobbin coil results only. The bobbin coil is also used for detection of IGSCC occurring in free spans, within sludge deposits. The eddy current rotating probe allows, in that case, characterization of main cracks. Concerning the outer diameter initiated circumferential cracks which occur at the top of the tube sheet, only the rotating probe is used. An ultrasonic (UT) inspection was performed several times, in order to obtain information on UT capabilities. The goal of tube inspection is obviously knowledge of the status of steam generators, but also to follow up degradations and to estimate their revolution, and to verify the beneficial effect of some corrective measures, e.g. boric acid injection.     

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.     

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.     

Measurements of the acoustic field on austenitic welds: a way to higher reliability in ultrasonic tests

In nuclear power plants many of the welds in austenitic tubes have to be inspected by means of ultrasonic techniques. If component-identical test pieces are available, they are used to qualify the ultrasonic test technology. Acoustic field measurements on such test blocks give information whether the beam of the ultrasonic transducer reaches all critical parts of the weld region and which transducer type is best suited. Acoustic fields have been measured at a bimetallic, a V-shaped and a narrow gap weld in test pieces of wall thickness 33, 25 and 17 mm, respectively. Compression wave transducers 45, 60 and 70° and 45° shear wave transducers have been included in the investigation. The results are presented: (1) as acoustic C-scans for one definite probe position, (2) as series of C-scans for the probe moving on a track perpendicular to the weld, (3) as scan along the weld and (4) as effective beam profile. The influence of the scanning electrodynamic probe is also discussed.     

Main control system verification and validation of NPP digital I&C system based on engineering simulator

Full-scope digital instrumentation and controls system (I&C) technique is being introduced in Chinese new constructed Nuclear Power Plant (NPP), which mainly includes three parts: control system, reactor protection system and engineered safety feature actuation system. For example, SIEMENS TELEPERM XP and XS distributed control system (DCS) have been used in Ling Ao Phase II NPP, which is located in Guangdong province, China. This is the first NPP project in China that Chinese engineers are fully responsible for all the configuration of actual analog and logic diagram, although experience in NPP full-scope digital I&C is very limited. For the safety, it has to be made sure that configuration is right and control functions can be accomplished before the phase of real plant testing on reactor. Therefore, primary verification and validation (V&V) of I&C needs to be carried out. Except the common and basic way, i.e. checking the diagram configuration one by one according to original design, NPP engineering simulator is applied as another effective approach of V&V. For this purpose, a virtual NPP thermal-hydraulic model is established as a basis according to Ling Ao Phase II NPP design, and the NPP simulation tools can provide plant operation parameters to DCS, accept control signal from I&C and give response. During the test, one set of data acquisition equipments are used to build a connection between the engineering simulator (software) and SIEMENS DCS I/O cabinet (hardware). In this emulation, original diagram configuration in DCS and field hardware structures are kept unchanged. In this way, firstly judging whether there are some problems by observing the input and output of DCS without knowing the internal configuration. Then secondly, problems can be found and corrected by understanding and checking the exact and complex configuration in detail. At last, the correctness and functionality of the control system are verified. This method is also very convenient for expansion to other type digital I&C V&V. This paper is mainly focused on V&V of closed-loop control systems in full-scope DCS and several detailed reactor control (RRC) systems, including pressurizer pressure and water level control, steam generator water level control. The V&V works were carried out by applying engineering simulator. This paper describes the structure and function of the simulator, V&V procedure, results analysis and problems identified. Through the actual on-line virtual closed-loop testing on Ling Ao Phase II NPP project, many problems of DCS configuration were found and solved. And it proved that V&V based on engineering simulator enables significant time saving, improves economics and safety in the phase of engineering debugging.     

蒸汽发生器换热管电磁超声纵向导波换能器设计与优化

高温气冷堆蒸汽发生器换热管特殊的螺旋结构导致传统外置型电磁超声导波换能器难以进行有效检测。本文针对蒸汽发生器不锈钢换热管的缺陷检测,开发了一种新型内置型电磁超声纵向导波换能器,建立了有限元多物理场耦合模型,研究了换能器铁磁结构的静态磁场分布,并对换能器激励出的纵向导波进行了时域仿真。结果表明：采用挤压聚磁的换能器结构可保证线圈附近的垂直方向磁场远大于水平方向磁场,能高效地在管道内部激励单一模式的纵向导波;优化后的探头可检测直径为5 mm的通孔缺陷和长×宽×深为20 mm×1.5 mm×1.2 mm的环向槽缺陷。因此,新型电磁超声纵向导波换能器可有效激励纵向导波,并有望应用于高温气冷堆蒸汽发生器换热管的在役缺陷检测。     

Development of Ultrasonic Testing Equipment Incorporating Electromagnetic Acoustic Transducer

An ultrasonic testing equipment for use in in-service inspection of nuclear power plant piping has been developed, which comprises an angle-beam electromagnetic acoustic transducer mounted on a vehicle for scanning the piping surface to be inspected. The transducer functions without direct contact with the piping surface through couplant, and the vehicle does not require a guide track installed on the piping surface, being equipped with magnetic wheels that adhere to the piping material, permitting it to travel along the circumferential weld joint of a carbon steel pipe. The equipment thus dispenses with the laborious manual work involved in preparing the piping for inspection, such as removal of protective coating, surface polishing and installation of guide track and thereby considerably reduces the duration of inspection. The functioning principle and structural features of the transducer and vehicle are described, together with the results of trial operation of a prototype unit, which proved a 1 mm deep notch cut on a test piece of 25 mm thick carbon steel plate to be locatable with an accuracy of ±2 mm.     

Pre-qualification of brazed plasma facing components of divertor target elements for ITER like tokamak application

Qualification of tungsten (W) and graphite (C) based brazed plasma facing components (PFCs) is an important R&D area in fusion research. Pre-qualification tests for brazed joints between W–CuCrZr and C–CuCrZr using NDT (IR thermography and ultrasonic test) and thermal fatigue test are attempted. Mockups having good quality brazed joints of W and C based PFCs were identified using NDT. Subsequently, thermal fatigue test was performed on the identified mockups. All brazed tiles of W based PFC mockups could withstand thermal fatigue test, however, few tiles of C based PFC mockup were found detached. Thermal analyses of mockups are performed using finite element analysis (ANSYS) software to simulate the thermal hydraulic condition with 10 MW/m² uniform heat flux. Details about experimental and computational work are presented here.     

Remove Welding Residual Stress for CFETR Vacuum Vessel by Trailing Ultrasonic Impact Treatment

The China fusion engineering test reactor (CFETR) vacuum vessel is welded by narrow gap TIG (NG-TIG) welding, and the welding residual stress of the CFETR vacuum vessel can be redistributed by trailing welding ultrasonic impact treatment. In order to investigate the feasibility of the residual stress removing scheme, and to obtain the optimal trailing ultrasonic impact treatment technological parameters in the process of removing welding residual stress, a welding model that similar to vacuum vessel welding seam is established by using ABAQUS software, a NG-TIG welding heat source subroutine which is written in FORTRAN language used to simulate NG-TIG welding. According to the welding simulation results, a trailing welding ultrasonic impact treatment model is established, and the effects of the impact pin number, the impact method, the impact pin diameter and the impact frequency on welding residual stress are studied. The results show that the longitudinal residual stress in welding seam and its adjacent area and the lateral residual stress in the whole region have been obviously decreased by different trailing welding ultrasonic impact processes, and have made the tensile stress in the welding seam and its adjacent area has been changed into compressive stress, which can provide theoretical guidance and reference for actual production.     

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.     

工业CT技术特点及应用实例

概述了工业CT技术的主要特点及其在无损检测中的应用,介绍了工业CT在缺陷检测、焊缝质量诊断、密度分布表征、结构分析及装配质量检测等方面的应用实例.     

Improvement in accuracy of the measurements of residual stresses due to circumferential welds in thin-walled pipe using Rayleigh wave method

To achieve an acceptable safety in many industrial applications such as nuclear power plants and power generation, it is extremely important to gain an understanding of the magnitudes and distributions of the residual stresses in a pipe formed by joining two sections with a girth butt weld. Most of the methods for high-accuracy measurement of residual stress are destructive. These destructive measurement methods cannot be applied to engineering systems and structures during actual operation. In this paper, we present a method based on the measurement of ultrasonic Rayleigh wave velocity variations versus the stress state for nondestructive evaluation of residual stress in dissimilar pipe welded joint. We show some residual stress profile obtained by this method. These are then compared with other profiles determined using a semi-destructive technique (hole-drilling) that makes it possible to check our results. According to the results, we also present a new method for adjusting the ultrasonic measurements to improve the agreement with the results obtained from other techniques.