Nondestructive Evaluation System Research Articles

증기발생기 전열관 외면 축균열 건전성 평가를 위한 비파괴검사 크기 측정 평가

최근 국내 증기발생기 Alloy 600HTMA 전열관의 관 지지판 부위 외면 축균열 결함의 생성이 지속적으로 증가하고 있다. 이로 인하여 증기발생기가 설계수명 이전에 조기 교체되었으며 또는 교체 예정이다. 전열관 외면 축균열은 건전성 관리에 가장 위협이 되는 요소이므로 정밀한 건전성 평가가 요구된다. 와전류검사(ECT, eddy currunt testing)는 주기적으로 수행되어 지며 이 결과는 건전성 평가 입력 자료로 활용된다. ECT 검사시스템의 신뢰성은 검사기술과 평가자 기량에 의존하며, NDE 시스템 성능을 보여주는 지수는 열화탐지와 크기 측정 오차이다. 본 연구에서는 국내 평가자 성능이 반영된 크기 측정 오차와 그리고 최적의 균열 크기 측정 방법을 제시하였다. 실험은 국내 각기 다른 5개 회사에서 10명의 평가자가 참여한 다자간 비교시험의 결과를 사용하여 이루어졌다. 실험 결과 분석은 파괴검사 결과값과 비파괴검사로 측정된 값의 상관관계를 회귀분석을 통하여 이루어졌다. Recently, the initiation of outside diameter stress corrosion cracking (ODSCC) at the tube support plate region of domestic steam generators (SG) with Alloy600 HTMA tubes has been increasing. As a result, SGs with Alloy600 HTMA tubes must be replaced early or are scheduled to be replaced prior to their designed lifetime. ODSCC is one of the biggest threats to the integrity of SG tubes. Therefore, the accurate evaluation of tube integrity to determine ODSCC is needed. Eddy current testing (ECT) is conducted periodically, and its results could be input as parameters for evaluating the integrity of SG tubes. The reliability of an ECT inspection system depends on the performance of the inspection technique and abilty of the analyst. The detection probability and ECT sizing error of degradation are considered to be the performance indices of a nondestructive evaluation (NDE) system. This paper introduces an optimized evaluation method for ECT, as well as the sizing error, including the analyst performance. This study was based on the results of a round robin program in which 10 inspection analysts from 5 different companies participated. The analysis of ECT sizing results was performed using a linear regression model relating the true defect size data to the measured ECT size data.

Development of Non-destructive Evaluation System Using an HTS-SQUID Gradiometer with an External Pickup Coil

We are developing a new eddy-current non-destructive evaluation (NDE) system using a high-temperature superconducting quantum interference device (HTS-SQUID) gradiometer with the aim of applying it to power plants. Electric power facilities such as ducts and vessels are generally untransportable because of their size, and thus it is difficult to apply a conventional SQUID NDE system. The new NDE system employs an external Cu pickup coil which is supposed to be driven flexibly by a robot arm at room temperature and an HTS-SQUID chip which is placed in a magnetically shielded vessel. In the present research, we investigated the performance of an HTS-SQUID sensor connected with external pickup coils before mounting them to a robot arm. By varying the Cu coil conditions such as their sizes, the number of turns, and the diameter of wire, we qualitatively evaluated the frequency dependence of the effective area and the cutoff frequency.

The aircraft structural elements corrosion study using strain gauge method and pulse video thermography

Simultaneous influence of corrosion, static and dynamic loads on the elements of aircraft structures influence to a large extent their mechanical properties and the foreseen length of their service. The paper presents the influence of corrosion on physical and mechanical properties of the test bars made from materials for a wide range of applications which are used in aircraft structural elements manufacturing. Study comprises laboratory testing of bars for the simultaneous influence of corrosive environment, static and dynamic load. The problems are pinpointed regarding the use of strain gauges for continuous monitoring of the condition in real time. In addition, this paper deals with a modern non-destructive testing and evaluation system (NDT&E), whose operation is based on thermal image processing. Thermographic method has been used to detect a hidden corrosion in the aircraft structure in real life. The study results have shown the possibility of NDT application in simple and quick detection of areas affected by corrosion that are visually invisible.

A Script-Based, Parameterized Finite Element Mesh for Design and NDE on a GPU

ABSTRACTFinite element mesh generators exist in the public domain, a few even based on a parametric device description. The typical mesh generator requires some man–machine interaction to define the points and boundary conditions, and does not work for non-stop optimization iterations for which we need a mesh dynamically evolving through the iterations with optimization variables as changing parameters. Such mesh generators as do exist are rare, commercial, and not easily available to researchers except at great cost and never with the code to modify them to suit individual needs. We take a regular open source mesh generator and write a script-based interface as open source to run non-stop for optimization. We then use it to create a non-destructive evaluation system for army ground vehicles’ defect characterization and use it equally for machine design. A simple scheme of averaging neighbour heights gives us a smooth geometry without having to use Bezier curves. The mesh runs on the central processing unit but finite element optimization is on the graphics processing unit for speed and practicable testing times.

Reflection and transmission of guided ultrasonic plate waves by vertical stiffeners.

Ultrasonic guided waves are very useful for structural health monitoring. They have the potential to interrogate and detect damage in a structure over a large area with few transducers. Guided plate modes (Lamb waves) are used and proposed for damage detection at a distance in semi-monococque structures such as airplane fuselages and spacecraft structures. The interaction of guided plate waves with stiffening members such as ribs, stringers, or the integral stiffeners used in spacecraft structures limits the distance over which structural health monitoring non-destructive evaluation systems can detect damage. This paper develops a simple explanatory model for the scattering of low-order ultrasonic Lamb waves crossing a stiffening device. The model illuminates the underlying mechanics of waves crossing a stiffener. The model shows that stop-bands for transmission of S(0) (longitudinal pressure) waves across a stiffener line up with flexural resonances of the stiffener. It also demonstrates why transmission of A(0) (flexural) waves is more complicated and harder to predict. The model is shown to agree well with both boundary element method calculations and experimental measurements.

Development of probability of detection functions for evaluating integrity of axial outside diameter stress corrosion cracks in steam generator

The reliability of an eddy current testing (ECT) inspection system depends upon the inspection technique and quality of analyst. In evaluating the integrity of a steam generator (SG) tube, degradation detection and sizing accuracy are considered performance measures of the nondestructive evaluation (NDE) system. A probability of detection (POD) model serves as a functional measure of the ability of an NDE system to detect degradation. It is one of the inputs in the operational assessment, and it is used to estimate the degradation during service via ECT of the SG tube. In this study, the POD functions of the inspection technique and analyst were obtained to quantitatively analyze the ECT bobbin probe for axial outside diameter stress corrosion cracks in SG tubes. This should serve to evaluate the integrity of the SG tubes. The depth and amplitude of defects were used as parameters of the POD model. Hit (detection) and miss (no detection) binary data obtained from destructive and nondestructive inspection of cracked tubes were also used.

Non-destructive evaluation system of metal materials according to thermal behaviours

The infrared thermography non-destructive inspection technique is a quality inspection and stability assessment method, which was used to diagnose the physical characteristics and defects by detecting the infrared ray radiated from the object without destructing it. The technique is being applied to diverse sectors. Its usage and importance increase with the development of the industrial areas that require high reliability and stability, including the semiconductor, nuclear power, defense, aerospace, and car industries. In this research, Ultrasound infrared thermography non-destructive evaluation system for metal materials according to thermal behaviours is established. To build ultrasound infrared thermography inspection system, infrared thermography test was performed by optimal design of the ultrasound excitation device and external energy control.

Electro-Mechanical Impedance (EMI)-Based Incipient Crack Monitoring and Critical Crack Identification of Beam Structures

Fatigue-induced damage is often progressive and gradual in nature. Fatigue is often deteriorated by corrosion in ageing structures, creating maintenance problems, and even causing catastrophic failure. This ushers the development of structural health monitoring (SHM) and nondestructive evaluation (NDE) systems. Recent advent of smart materials applicable in SHM alleviates the shortcomings of the conventional techniques. Autonomous, real-time, remote monitoring becomes possible with the use of smart piezoelectric transducers. For instance, the electro-mechanical impedance (EMI) technique, employing piezoelectric transducers as collocated actuators and sensors, is known for its ability in damage detection and characterization. This article presents a series of lab-scale experimental tests and analysis to investigate the feasibility of fatigue crack detection and characterization employing the EMI technique. This study extends the work by Lim and Soh [1] to incorporate the phases involving crack initiation and critical crack. It is suggested that the EMI technique is effective in characterizing fatigue induced cracking, even in its incipient stage. Micro-crack invisible to the naked eyes can be detected by the technique especially when employing the higher frequency range of 100–200 kHz. A quick and handy qualitative-based critical crack identification method is also suggested by visually inspecting the admittance frequency spectrum.

A new fiber-optic non-contact compact laser-ultrasound scanner for fast non-destructive testing and evaluation of aircraft composites.

Laser ultrasonic (LU) inspection represents an attractive, non-contact method to evaluate composite materials. Current non-contact systems, however, have relatively low sensitivity compared to contact piezoelectric detection. They are also difficult to adjust, very expensive, and strongly influenced by environmental noise. Here, we demonstrate that most of these drawbacks can be eliminated by combining a new generation of compact, inexpensive fiber lasers with new developments in fiber telecommunication optics and an optimally designed balanced probe scheme. In particular, a new type of a balanced fiber-optic Sagnac interferometer is presented as part of an all-optical LU pump-probe system for non-destructive testing and evaluation of aircraft composites. The performance of the LU system is demonstrated on a composite sample with known defects. Wide-band ultrasound probe signals are generated directly at the sample surface with a pulsed fiber laser delivering nanosecond laser pulses at a repetition rate up to 76 kHz rate with a pulse energy of 0.6 mJ. A balanced fiber-optic Sagnac interferometer is employed to detect pressure signals at the same point on the composite surface. A- and B-scans obtained with the Sagnac interferometer are compared to those made with a contact wide-band polyvinylidene fluoride transducer.

Development of HTS-SQUID Gradiometer with an External HTS Multiturn Thin Film Pickup Coil

Highly-sensitive HTS-SQUIDs are applied to various systems such as eddy-current non-destructive evaluation (NDE) and compact magnetometer systems. To avoid unstable operation of the SQUID due to an excitation field, a flux transformer made of normal Cu wire is used to separate the pickup coil and SQUID. However, the resistance of the flux transformer generates thermal noise and reduces the signal bandwidth at low frequencies. In this study, we investigate use of a superconducting flux transformer with resistive connections (SFTR). The SFTR consists of pickup and input coils made of HTS thin films. The two coils are connected by using an HTS coated conductor. The input coil is stacked on an HTS thin film gradiometer. From the measured results of resistances of the connections between each coil and the coated conductor, it was found that the resistance of bonding wire was a dominant component. The estimated resistance of the SFTR was 7.2 mΩ, corresponding to a lower cut-off frequency of 11.7Hz.

Study on Non-destructive Evaluation of Flaws in Multilayer Duct Using an HTS-SQUID Gradiometer

We have investigated the performance of an eddy-current non-destructive evaluation (NDE) system using an HTS Superconducting quantum interference device (SQUID) gradiometer with the aim of applying it to the equipment in power plants. Use of the SQUID-NDE technique has an advantage, because SQUID has a high sensitivity or low noise characteristics at low frequencies for detecting magnetic signals. In the present research, we have tried to detect flaws in test samples simulating a multilayer duct in a plant, which consists of multilayer aluminum and resin plates. In the test samples, resin plates were sandwiched by aluminum plates. The top aluminum plate and the bottom multilayer aluminum plates were assumed as outer and inner duct layers, and the resin plates were assumed as an insulation layer in a multilayer duct of the plant. A slit-shaped through hole was opened in the bottom layer, and was assumed as a flaw in the duct layer. By using a SQUID-ECT system, we could detect signals from flaws located at more than 10mm deep positions in the test samples.

Investigation of capacitively coupled ultrasonic transducer system for nondestructive evaluation

Capacitive coupling offers a simple solution to wirelessly probe ultrasonic transducers. This paper investigates the theory, feasibility, and optimization of such a capacitively coupled transducer system (CCTS) in the context of nondestructive evaluation (NDE) applications. The noncontact interface relies on an electric field formed between four metal plates-two plates are physically connected to the electrodes of a transducer, the other two are in a separate probing unit connected to the transmit/receive channel of the instrumentation. The complete system is modeled as an electric network with the measured impedance of a bonded piezoelectric ceramic disc representing a transducer attached to an arbitrary solid substrate. A transmission line model is developed which is a function of the physical parameters of the capacitively coupled system, such as the permittivity of the material between the plates, the size of the metal plates, and their relative positions. This model provides immediate prediction of electric input impedance, pulse-echo response, and the effect of plate misalignment. The model has been validated experimentally and has enabled optimization of the various parameters. It is shown that placing a tuning inductor and series resistor on the transmitting side of the circuit can significantly improve the system performance in terms of the signal-to-crosstalk ratio. Practically, bulk-wave CCTSs have been built and demonstrated for underwater and through-composite testing. It has been found that electrical conduction in the media between the plates limits their applications.

Mechatronic Systems Design for an Autonomous Robotic System for High-Efficiency Bridge Deck Inspection and Evaluation

The condition of bridges is critical for the safety of the traveling public. Bridges deteriorate with time as a result of material aging, excessive loading, environmental effects, and inadequate maintenance. The current practice of nondestructive evaluation (NDE) of bridge decks cannot meet the increasing demands for highly efficient, cost-effective, and safety-guaranteed inspection and evaluation. In this paper, a mechatronic systems design for an autonomous robotic system for highly efficient bridge deck inspection and evaluation is presented. An autonomous holonomic mobile robot is used as a platform to carry various NDE sensing systems for simultaneous and fast data collection. The robot's NDE sensor suite includes ground penetrating radar arrays, acoustic/seismic arrays, electrical resistivity sensors, and video cameras. Besides the NDE sensors, the robot is also equipped with various onboard navigation sensors such as global positioning system (GPS), inertial measurement units (IMU), laser scanner, etc. An integration scheme is presented to fuse the measurements from the GPS, the IMU and the wheel encoders for high-accuracy robot localization. The performance of the robotic NDE system development is demonstrated through extensive testing experiments and field deployments.

Investigation of inductively coupled ultrasonic transducer system for NDE.

Inductive coupling offers a simple solution to wirelessly probe ultrasonic transducers. This paper investigates the theory and feasibility of such an inductively coupled transducer system in the context of nondestructive evaluation (NDE) applications. The noncontact interface is based on electromagnetic coupling between three coils; one of the coils is physically connected to the transducer, the other two are in a separate probing unit, where they are connected to the transmit and receive channels of the instrumentation. The complete system is modeled as a three-port network with the measured impedance of a bonded piezoelectric ceramic disc representing a sensor attached to an arbitrary solid substrate. The developed transmission line model is a function of the physical parameters of the electromagnetic system, such as the number of turns and diameter of each coil, and their separation. This model provides immediate predictions of electrical input impedance and pulse-echo response. The model has been validated experimentally and a sensitivity analysis of the input parameters performed. This has enabled optimization of the various parameters. Inductively coupled transducer systems have been built for both bulk and guided wave examples. By using chirped excitation and baseline subtraction, inspection distance of up to 700 mm is achieved in single-shot, guided-wave pulse-echo mode measurements with a 5 mm separation between the probing coils and transducer coil on an aluminum plate structure. In the bulk wave example, a delamination in an 8.9-mm-thick carbon fiber composite specimen is successfully identified from the changes in the arrival time of a reflected pulse.

Full wave numerical modelling of terahertz systems for nondestructive evaluation of dielectric structures

PurposeThe purpose of this paper is to describe the full‐wave modelling of pulsed terahertz systems utilized in non‐destructive testing.Design/methodology/approachAt the outset, some basic information on the terahertz NDT are outlined and then, general remarks on its numerical modelling are presented. Frequency domain FEM and time domain FDTD analysis is carried out. Finally comparison of computed and measured signals is shown in order to prove numerical analysis correctness.FindingsIt is possible to model in a relatively simple way a terahertz system for nondestructive evaluation of dielectric materials. In contrast to other published work, the entire measuring setup is modelled, including photoconductive antenna with hemispherical lens, focusing lens and evaluated material with exemplary defect.Originality/valueThis paper gives a description of the terahertz non‐destructive testing system with comparison of simulated and measured results.

Safe product design – the role of the NDT reliability analysis

Abstract In line with the damage tolerance design principles, an adequate non-destructive inspection system is needed to ensure structural integrity. Yet, when pushed to the limits of their detection capability, non-destructive evaluation systems do not produce consistent hit/miss indications. Their capability of detecting flaws is therefore expressed as a probability of detection. In the conventional signal response reliability analysis, the probability of detection is expressed as a function of the flaw size. The adequacy of the inspection system is verified by comparing the size of the flaw that is reliably detected with the maximum allowable flaw size, which will not undermine the structural integrity. Analyses of modern structures show that other parameters also determine the severity of the flaw for the structure. Within the multi-parameter reliability analysis, the probability of detection can be expressed as a function of diverse influencing parameters. When determining the adequacy of the non-destructive evaluation system, the capability of detecting a flaw has to be expressed and checked against the critical value of exactly that parameter that determines flaw severity for the structure. Failing to do so can lead to a rejection of the healthy, or acceptance of the bad part. The principle is demonstrated on the transmit-receive longitudinal ultrasonic inspection data of the iron cast component with surface, semi-elliptical, crack-like flaws.

Development of a compact DC magnetometer using HTS-SQUID and a rotating sample

We developed a compact DC magnetometer using a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) to measure very weak magnetic signals from samples such as paramagnetic and diamagnetic materials. The samples were rotated in the DC magnetic field that was detected by a normal conductive pick-up coil. The detected signal was transferred to an input coil that was inductively coupled to the SQUID. To clarify the basic characteristics of this system, the magnetic signal from a magnetic material was measured by varying the sample position and rotation speed. Then, the magnetic signal from pure water was measured under the optimized condition and a very weak magnetic signal from pure water was successfully detected. Therefore, the developed system could be applied to various non-destructive evaluation systems.

Development of non-destructive evaluation system using an HTS-SQUID gradiometer for magnetized materials

We have developed a new eddy-current non-destructive evaluation (NDE) system using an HTS SQUID gradiometer with the aim of applying it to practical materials with magnetization. The new NDE system employs a LN2-cooled external Cu pickup coil and an HTS SQUID chip placed in a magnetic shield made of HTS material. The HTS SQUID chip consists of an HTS planar gradiometer manufactured by using a ramp-edge junction technology and a multi-turn HTS thin film input coil coupled with the flip-chip configuration. The first-order coaxial gradiometric Cu pickup coil with a diameter of 16 mm and the baseline of 5.6 mm was used in the present NDE experiments. By using this NDE system, we could observe defect-induced magnetic signals without an appreciable influence of magnetization up to 10 mT. We also examined the ability of detecting deep-lying defects and compared with the results obtained using our previous NDE system.

Recent Developments of High-Tc Electronic Devices with Multilayer Structures and Ramp-Edge Josephson Junctions

Recent developments of electronic devices containing Josephson junctions (JJ) with high-Tc superconductors (HTS) are reported. In particular, the fabrication process and the properties of superconducting quantum interference devices (SQUIDs) with a multilayer structure and ramp-edge-type JJs are described. The JJs were fabricated by re-crystallization of an artificially deposited Cu-poor precursory layer. The formation mechanism of the junction barrier is discussed. We have fabricated various types of gradiometers and magnetometers. They have been actually utilized for several application systems, such as a non-destructive evaluation (NDE) system for deep-lying defects in a metallic plate and a reel-to-reel testing system for striated HTS-coated conductors.

Performance Test of Pump Combination Between Normetex 15 Scroll and MB 601 Pumps

The tritium compatible pumps are applied to the transportation of the fuel gases in the nuclear fusion power plant. Based on the limitations to handle the tritium gas, the development of the tritium compatible pumps is restricted and the information of those is not well-known. Through Normetex scroll and metal bellows pumps, which are utilized in the tritium facility in the world, are famous tritium compatible pumps, the information has the limitations for the capability of those. It is needed to evaluate the performance of those experimentally.The non-destructive characteristics evaluation system for dry vacuum pump is utilized for the performance tests of the MB 601 HP and the combination of the Normetex 15 scroll and the MB 601 HP pumps. Nitrogen and helium gases are applied for the performance tests. In the case of the MB 601 HP, significant dependency is found on gas species: the test on the pumping speeds with using nitrogen shows the similar result with the catalogue data but the different behavior with using helium gas. In the case of the combination of the Normetex 15 scroll and the MB 601 HP pumps, however, it is observed that the effect of the species of gases is reduced.