NDT Applications Research Articles

Enhancing corrosion detection in pulsed eddy current testing systems through autoencoder-based unsupervised learning

Pulsed Eddy Current Testing (PECT) stands out as an advanced method in Non-Destructive Testing due to its extensive spectrum characteristics in comparison to traditional ECT techniques, making it exceptionally suitable for identifying corrosion. Nonetheless, the analysis of PECT signals for corrosion detection poses a challenge due to the transient nature of these signals and the impact of sensor lift-off effects. As a result, conventional methods are facing hurdles in dealing with corrosion signals of poor quality. In this study, the challenge is addressed by employing unsupervised learning methods utilizing an autoencoder neural network. This autoencoder integrates Long Short-Term Memory and 1D convolutional layers, acquiring the underlying features of normal PECT signals from non-corrosive regions. Significantly, the model is trained exclusively on this normal data, thereby obviating the necessity for pre-existing corrosion information. Through learning the inherent structure of normal signals, the model can detect anomalies in unseen data, potentially indicating corrosion. The unsupervised framework presents several advantages, such as reducing reliance on prior corrosion knowledge, mitigating inherent noise, and addressing sensor lift-off effects. Experimental results were conducted to compare with traditional methods like the lift-off of intersection and lift-off compensation methods. This approach resulted in a significant improvement in SNR, ranging from 100 % to 200 %, thus facilitating more robust NDT applications employing smart PECT sensors empowered by unsupervised learning techniques.

Analysis and NDT Applications of a Gas Discharge Electroacoustic Transducer

Analysis and NDT Applications of a Gas Discharge Electroacoustic Transducer

Digital Holographic Interferometry for Wholefield NDT Applications

Holographic interferometry is a non-contact whole field optical technique used as a powerful NDT tool. This technique is highly sensitive and maps the object surface deformation as holographic fringe pattern. Conventional holography technique has practical difficulties in recording and reconstructing holograms. With the development in imaging sensor technology and fast algorithms in image processing, digital holography has been established. Digital holography uses high-resolution digital camera for recording holograms and does reconstruction of holograms numerically using a computer. This has enhanced the scope and application of holography for NDT many fold. In this paper application of digital holography to non-destructive testing is presented. The basic principle of digital holography and digital holographic interferometry in obtaining double exposure hologram for NDT is described. The software developed in house for numerical reconstruction of holograms is also explained. The advantages of digital holography over conventional holography in NDT applications are highlighted. Extensive experiments were carried out to prove the detectability of defects in both metallic and non-metallic materials and the results are presented. It is shown that digital holography is able to identify defects in a wide range of materials with great ease because of its high sensitivity and whole field nature.

Combining radar and ultrasound imaging for surface echo compensation and augmented visibility of interior structures in NDT applications

Millimeter-wave radar imaging is a promising technique in non-destructive testing. When a small material defect is located closely to the test object’s surface, the strong reflection caused by the air-material interface can overlap with the defect’s weak reflection and mask it. If the image resolution is not sufficient, the defect cannot be resolved and will not be recognizable in the reconstruction image. To solve this problem, surface echo compensation techniques have been invented. However, these techniques are usually restricted to planar surfaces, which for most applications is not the case. This article presents a technique for surface echo compensation of arbitrarily shaped objects. We propose to combine radar and air-coupled ultrasound. Since aircoupled ultrasound is not able to penetrate solids, an air-coupled ultrasound imaging system is only able to detect the surface of a solid object. The idea of our proposed concept is to employ the ultrasound signal to compensate for the surface echo in the radar signal. The proposed method is based on the idea of using signals of equal wavelengths for both wave types and an amplitude calibration. Then, the resulting signals for radar and ultrasound are formally equal, which makes it possible to directly combine them numerically. That way, a modified radar image can be obtained which only contains the reflections from the inside and highlights interior defects.

Innovative NDT Technique, for a More Productive Surface Damage Inspection

The challenges faced by NDT service companies are becoming increasingly prominent. First, these issues take place in a market comprised of old, rapidly aging infrastructure, which causes an increased demand for inspection. Moreover, there is a shortage of skilled labor as well as the increased departures of retiring experienced technicians, which puts a lot of pressure on service companies to keep pace with projects and honor their contracts. One way or the other, productivity gains will need to be realized to answer the growing demand with less manpower. This article will discuss surface damage NDT applications resolved with a 3D scanner. 3D scanning solutions involve only a short learning curve and require fewer certifications than traditional techniques. They are also much faster than manual tools, offering rapid field deployment and instant reports that are directly accessible in the field. The file format of the inspection results generates metrology-grade accuracy, traceable data over time, as well as human-independent results that eliminate measurement variations and ambiguity in result interpretation. This article will also introduce this relatively new technique in terms of performance and limitations, then it will present an overview of the different applications available in all traditional NDT industries such as oil & gas, aerospace, power generation, and more.

Ultrasonic signal noise reduction based on convolutional autoencoders for NDT applications

One of the most challenging problems of ultrasonic non-destructive testing is the signal distortion caused by the presence of noise, yielding the sound wave corruption and thus degrading the ultrasonic imaging technology performance due to Time of flight methods’ loss of precision. Deep learning algorithms have proven their effectiveness in reducing noise on several types of signals in different domains. In this paper, we propose a one-dimensional convolutional autoencoder for ultrasonic signal denoising. The efficiency of the proposed architecture is compared to the wavelet decomposition method, collating the peak signal-to-noise ratio values on the denoised signals. Our method proved its potential for NDT applications in recovering temporal information even on very noisy signals, and improving the PSNR by about 30 dB.

On the use of differential permeability and magnetic Barkhausen Noise Measurements for Magnetic NDT Applications

Mapping microstructural to macroscopic magnetic properties is challenging yet necessary for the development of novel non-destructive testing techniques based on magnetic measurements. The macroscopic properties of a material reflect the underlying magnetization processes and the microstructural configuration as a result of the history of the material. Magnetic nondestructive evaluation techniques are needed for the health monitoring in critical structures and the quality monitoring of materials used in components, such as transformers and motors. In this work, we assess the usability of metrics related to AC magnetometry and magnetic Barkhausen Noise through measurements on several series of samples of various grain sizes and levels of plastic deformation. AC magnetometry is preferred to magnetic Barkhausen Noise as it provides more repeatable and reliable metrics than mBN which suffers from higher uncertainty. Also, differential permeability curves are preferred to hysteresis loops because they can be obtained directly through ac magnetometry and provide several types of information, such as the peak value, the coercivity, the overall shape, the emergence and location of multiple peaks which are related to stresses. In the case of stress-dependent magnetization processes, both differential permeability and mBN results are consistent, regardless of the way strain is applied, and corroborate results previously reported. However, permeability measurements are inconclusive on the effect of grain size on magnetization processes while the mBN voltage increases monotonically with decreasing grain size, in both types of samples. The mBN energy associated with each applied field step is proposed as a complementary measure for the assessment of the contribution of the irreversible processes in a material where the permeability measurements are inconclusive. Finally, the experimental observations have been used to set up micromagnetic calculations by modeling a plastically deformed material as a soft matrix with grains enclosed by boundaries with high transverse anisotropy which act as pinning centres and prevent further rotation of the magnetization and its alignment with the applied field thus reproducing the typical phenomenological features of plastically strained materials.

NDT application for detection of corrosion under insulation in Vietnam

: In the oil and gas Industry, insulation materials can be used widely for piping system, tank and vessel in either low or high temperature applications. CUI can cause equipment degradation, fluid leak, which lead to explosion or environmental pollution and the cost will very expensive. Therefore, CUI need to be detected early to prevent damage. Through experiment, Center for Non-Destructive Evaluation (NDE) studied on establishing and appliying 4 NDT procedures for CUI examination on typical petroleum piping using in Vietnam. A discussion is presented below

Augmented Ultrasonic Data for Machine Learning

Flaw detection in non-destructive testing, especially for complex signals like ultrasonic data, has thus far relied heavily on the expertise and judgement of trained human inspectors. While automated systems have been used for a long time, these have mostly been limited to using simple decision automation, such as signal amplitude threshold. The recent advances in various machine learning algorithms have solved many similarly difficult classification problems, that have previously been considered intractable. For non-destructive testing, encouraging results have already been reported in the open literature, but the use of machine learning is still very limited in NDT applications in the field. Key issue hindering their use, is the limited availability of representative flawed data-sets to be used for training. In the present paper, we develop modern, deep convolutional network to detect flaws from phased-array ultrasonic data. We make extensive use of data augmentation to enhance the initially limited raw data and to aid learning. The data augmentation utilizes virtual flaws—a technique, that has successfully been used in training human inspectors and is soon to be used in nuclear inspection qualification. The results from the machine learning classifier are compared to human performance. We show, that using sophisticated data augmentation, modern deep learning networks can be trained to achieve human-level performance.

A Fast Interface Reconstruction Method for Frequency-Domain Synthetic Aperture Focusing Technique Imaging of Two-Layered Systems with Non-planar Interface Based on Virtual Points Measuring

Frequency-domain synthetic aperture focusing technique (SAFT), such as non-stationary phase shift migration (NSPSM), plays an essential role in the ultrasonic imaging of two-layered systems with non-planar interfaces. However, with NSPSM fast imaging under blind test conditions is hard to realize due to a lack of interface information in practice. To overcome this difficulty, a fast interface reconstruction method for NSPSM imaging of non-planar two-layered systems is proposed based on virtual points measuring. In blind testing conditions, a series of virtual points (VP) were created at the non-planar interface of the two-layered system by the time-of-flight (TOF) of the first incoming echo. Then, the interface for the two-layered system was quickly established by the interpolation of the VP. Finally, the NSPSM imaging for the two-layered system with non-planar interfaces was realized by the borderline which is used to distinguish the velocities of the coupling medium and tested part in the same extrapolating depth. The imaging results showed that the position of side-drilled holes was located correctly and the efficiency of the algorithm was significantly improved. Hence, the VP-NSPSM method is expected to achieve fast or even real-time imaging of two-layered systems with non-planar interfaces in practical NDT applications.

Multi-frequency GPR data fusion and its application in NDT

Ground-penetrating radar (GPR) is a non-destructive technique that utilizes high-frequency electromagnetic waves to detect and locate subsurface objects and interfaces. Resolution can be improved with an increase of the source frequency; however, this will lead to decreased investigation depth due to the stronger attenuation of the high frequency signal. Thus, there is a trade-off between the resolution and the investigation depth in the single central frequency-based GPR system. To obtain both high resolution and deep penetrating ability simultaneously, we applied multi-frequency GPR data fusion with three algorithms: time-domain fusion with weights/without, frequency-domain fusion with weights. The fusion effect is qualitatively and quantitatively evaluated and compared by the fused radar profile and Laplacian operator, which is a second derivative gradient operator and commonly used in image edge detection by detecting the zero-crossings of image intensity. The results of the numerical simulation and field data showed that the fused profile was able not only to retain the high resolution in the shallow area from the high-frequency antenna but also take advantage of the significant investigation depth of the low-frequency antenna by merging the multi-frequency data into a single profile. Thus, the fused GPR data has the ability to create a single profile with more information and detailed characteristics.

X-ray imaging and computed tomography for engineering applications

Abstract After an incremental development which took place over four decades, X-ray imaging has become an important tool for non-destructive testing and evaluation. Computed Tomography (CT) in particular beholds the power of determining the location of flaws and inclusions (e. g. in castings and composites) in three-dimensional object coordinates. Therefore, and thanks to a speed-up of the measurement, CT is now routinely considered for in-line inspection of electronics, castings and composites. When precision and not speed is important, Micro-CT (μCT) can be employed for Dimensional Measurements (DM, e. g. quality assurance and shape verification), as well as for in situ testing, and for characterizing micro-structures in metals and composites. Using appropriate image processing and analysis μCT can determine the local fibre orientation in composites, the granular morphology of battery cathodes or the inter-connectivity of certain phases in casting alloys. Today, the large variety of X-ray instruments and methods poses an application problem which requires experience and a lot of knowledge for deciding which technique applies best to the task at hand. Application-specific guidelines exist for X-ray radiography testing (RT) only, whereas standardization has been applied to CT, unfortunately leaving out high resolution sub μ CT, and nano-CT. For the latter exist an equally high number of NDT applications, however these instruments still necessitate a profound expertise. The task is to identify key industrial applications and push CT from system standardization to application specific automation.

One-dimensional equivalent circuit for ultrasonic transducer arrays

Ultrasonic transducer arrays utilized in medical imaging and NDT applications are generally composed of several piezoelectric elements arranged in 1D or 2D ways. These structures are usually modeled by sophisticated 2D and 3D numerical methods. In this paper, a one-dimensional electromechanical circuit inspired from the Mason’s simplified one, is utilized to model a transducer array composed of seven piezoelectric elements made of PZ27. The validity and the limitations of the model are pointed out by comparing the computed electrical impedances and displacements to the ones obtained experimentally. The novelty of our approach is to offer a simple electrical method to analyze the physical behavior of piezoelectric transducer arrays. This one, allows the study of the mechanical crosstalk between array elements and does not need expensive experiments such as displacement measurements using a laser vibrometer. Finally, the electrical model is expected to be utilized in harmonic and transient domain in order the reduce the crosstalk phenomenon.

A fuzzy divergence approach for solving electrostatic identification problems for NDT applications

A fuzzy divergence approach for solving electrostatic identification problems for NDT applications

Eddy current modeling in linear and nonlinear multifilamentary composite materials

Abstract In this work, a numerical model is developed for a rapid computation of eddy currents in composite materials, adaptable for both carbon fiber reinforced polymers (CFRPs) for NDT applications and multifilamentary high temperature superconductive (HTS) tapes for AC loss evaluation. The proposed model is based on an integro-differential formulation in terms of the electric vector potential in the frequency domain. The high anisotropy and the nonlinearity of the considered materials are easily handled in the frequency domain.

Simulation of Translational Data Acquisition Scheme of X-Ray Computed Tomography for Application in NDT

The invention of computed tomography some few decades ago, coupled with its applications in the field of non-destructive testing for industrial objects inspection has revolutionized the way inspections were formerly done. Despite the conventional data acquisition scheme which is integrated with a rotational stage in between the source and the detector works perfectly for small and lighter objects, hence, it seems impossible to investigate complicated, bulky objects with interconnected unbalanced composites. Moreover, it will be very expensive to harnessed technologies into the rotational stage which can be incorporated into this conventional technique with an optimum degree of accuracy. Therefore, this paper will consider the translational data acquisition scheme which is proven mathematically as an alternative method to the conventional technique [1]. This translational scheme takes into account the variations and the magnification of both the source x-ray and the detector around the object and then proceeded by scans from different focal distances. Python packages with necessary plugins were used in implementing the reconstructive algorithm generated in simulating and modelling a suitable image of inspected object.

Development of neutron imaging beamline for NDT applications at Dhruva reactor, India

Thermal neutron imaging techniques such as radiography or tomography are very useful tool for various scientific investigations and industrial applications. Neutron radiography is complementary to X-ray radiography, as neutrons interact with nucleus as compared to X-ray interaction with orbital electrons. We present here design and development of a neutron imaging beamline at 100 MW Dhruva research reactor for neutron imaging applications such as radiography, tomography and phase contrast imaging. Combinations of sapphire and bismuth single crystals have been used as thermal neutron filter/gamma absorber at the input of a specially designed collimator to maximize thermal neutron to gamma ratio. The maximum beam size of neutrons has been restricted to ∼120 mm diameter at the sample position. A cadmium ratio of ∼250 with L∕D ratio of 160 and thermal neutron flux of ∼4×107 n/cm2 s at the sample position has been measured. In this paper, different aspects of the beamline design such as collimator, shielding, sample manipulator, digital imaging system are described. Nondestructive radiography/tomography experiments on hydrogen concentration in Zr-alloy, aluminium foam, ceramic metal seals etc. are also presented.

无损检测在增材制造技术中应用的研究进展

无损检测在增材制造技术中应用的研究进展

Periodic Solitary Wave Impulses in Finite-Length Granular Chains

The acoustic wave propagation in a chain of spheres was predicted based on the discrete dynamic equations of spheres. Generation of the strongly nonlinear solitary wave impulses with a harmonic input has been investigated in simulations. The size of spheres, the material properties of chain structure as well as the length of chain determine the intrinsic dynamics of the granular system and frequency bands. The forced responses of a chain under harmonic excitation with a given frequency reveal that the broad bandwidth solitary wave impulses with different periods can be created in a certain length chain with no or a small precompression force. The results exhibit great potential in biomedical ultrasound and NDT applications.

SAFE-PML approach for modal study of waveguides with arbitrary cross sections immersed in inviscid fluid

Ultrasonic guided wave is an important non-destructive tool for large area inspections of immersed structures as well as fluid characterizations. In this paper, a numerical tool is developed for the modal study of immersed waveguides with arbitrary cross sections, by coupling the Semi-Analytical Finite Element (SAFE) method with Perfectly Matched Layer (PML). The model is first validated on waveguides with regular cross sections with analytical solutions. It is then applied to immersed waveguides with rectangular cross sections and L-shaped cross sections, showing the potential of guided waves for NDT applications and fluid characterizations.