No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Infrared thermography based defect detection in ferromagnetic specimens using a low frequency alternating magnetic field
Abstract
A new active infrared thermography based technique is proposed for defect detection in ferromagnetic specimens using low frequency alternating magnetic field induced heating. The test specimens (four mild steel specimens with artificially made rectangular slots of 8.0, 5.0, 3.3 and 3.0 mm depths) are magnetized using the low frequency alternating magnetic field and using an infrared camera the surface temperature is remotely monitored in real time. The alternating magnetic field induces eddy current in the specimens which increases the specimen temperature due to Joule’s heating. The experimental results show a thermal contrast in the defective region that decays exponentially with defect depth. The observed thermal contrast is attributed to the reduction in induction heating due to the leakage of magnetic flux caused by magnetic permeability gradient in the defective region. The proposed technique is suitable for rapid non-contact wide area inspection of ferromagnetic materials and offers several advantages over the conventional active thermography techniques like fast direct heating, no frequency optimization, no dependence on the surface absorption coefficient and penetration depth.
... Whereas the lowest induction frequency reported in literature was 50 Hz [15], in this work, induction frequencies far below 50 Hz are used for the first time. In Section 2.1, the basic theory for electromagnetic and thermal wave propagation is discussed. ...
... Using (7), the static heating term in (15) can be written as The profiles resemble those of a thermal wave penetrating into the surface. The average of the oscillating term over one period is zero. ...
... Using (7), the static heating term in (15) can be written as ...
Featured Application
Induction thermography as a nondestructive technique for defect detection in electrically conducting materials.
Abstract
The one-dimensional propagation of electromagnetic waves and the propagation of the resulting thermal waves in conducting material are analysed in a coherent way. The heat release due to resistive losses has a static and an oscillating part. Both are considered as heat source terms for the thermal diffusion equation. The time dependence of the temperature is described by analytical solutions. Electrically and thermally conducting materials are classified by the ratio of thermal penetration depth to the skin depth. Experiments performed on ferritic steel, stainless steel and carbon-fibre-reinforced polymer show the time dependence of the thermal signal after heating begins, as described by the theory. At low induction frequencies, an oscillating part of the surface temperature at the double of the induction frequency is detected in accordance with the theory. The results point out new opportunities for induction thermography.
... The non-destructive testing enables detection of discontinuities (defects) without changing the properties of the investigated materials [1][2][3][4]. Thus, it provides the tool for the quality control of the construction parts, elements of machines as well as final products. ...
... The results obtained with the algorithm trained with HEAT&COOL dataset are depicted in Fig. 17. Table 2 The values of relative mean error of depth estimation in the defected area, calculated for the particular defect depth using formulas (3) and (5) Table 3 The values of relative mean error of depth estimation in the defected area. calculated for the particular defect depth using formulas (3) and (5) ...
... Table 2 The values of relative mean error of depth estimation in the defected area, calculated for the particular defect depth using formulas (3) and (5) Table 3 The values of relative mean error of depth estimation in the defected area. calculated for the particular defect depth using formulas (3) and (5) ...
In the paper a two-stage neural algorithm for defect detection and characterization is presented. In order to estimate the defect depth two neural networks trained on data obtained using an active thermography were employed. The first stage of the algorithm is developed to detect the defect by a classification neural network. Then the defects depth is estimated using a regressive neural network. In this work the results of experimental investigations and simulations are shown. Further, the sensitivity analysis of the presented algorithm was conducted and the impacts of emissivity error and the ambient temperature error on the depth estimation errors were studied. The results were obtained using a test sample made of material with a low thermal diffusivity.
... Recently, we have demonstrated a new active IRT based defect detection methodology for ferromagnetic specimens using low frequency (50 Hz) alternating magnetic field induced heating [14]. Our results indicated a temperature difference between the defect and defect-free regions that decayed exponentially with defect depth which was attributed to the reduction in the induction heating due to leakage of magnetic flux in the vicinity of the defect regions. ...
... In the present study, we investigate the effects of non-magnetic inclusions on thermal contrast (temperature difference between the defect and defect-free regions) and temperature decay rates during IRT based defect detection in mild steel specimens. In the previous study [14], the proposed methodology was validated for idealized defects under laboratory conditions. However, during on-site or shop-floor inspection, the components are often contaminated with inclusions, like clay or dirt inclusions in the defects for submerged oil and gas pipelines or slag inclusions in welded specimens. ...
... Similar results were obtained for the other specimens too. This observation is in contrast with the earlier observed results in defects without any inclusions [14], where the defect regions showed a higher surface temperature due to bending of the magnetic flux lines in the vicinity of the defects, which resulted in a higher localized eddy-current density in the defect regions and an increased surface temperature. On the contrary, in the present case, due to the non-metallic and non-magnetic nature of the inclusions, eddy current heating is limited to the parent metal itself and the inclusion acts as thermal insulator. ...
... New high-speed NDE equipment has recently been developed, including high-speed cameras [11], Alternating Current Field Measurement probes (ACFM) [12]- [14], Electromagnetic Acoustic Transducers (EMATs) [15]- [18], Field Gradient Imaging (FGI) [19], ultrasonic phased arrays [20], and long-range ultrasonic, laser ultrasonic and multi-frequency eddy current sensors [21], acoustic sensors and infrared thermography [22]. The reliability of inspection methods for detecting cracks utilizing high energy laser or ultrasonic pulses was estimated by probability of detection concept (POD) and POD curves were introduced to justify the authenticity of inspection methods [23]- [25]. ...
... However, the problems with in-homogeneous heating, limited heating area and blocking effect of coil [41], [44] in ECPT reflective mode still challenge the accurate material and quantitative characterization of defects. Lahiri [23] recorded low frequency alternating magnetic field with wide area for thermographic defect NDE. Jäckel [45] developed an external magnetic field electromagnet yokes to improve the contrast between crack detection by induction thermography. ...
... Recently, He et al. [40] proposed lateral heat conduction for detection of parallel and rail tread oblique cracks detection using ECPT. Lahiri et al. [41] reported on defect detection by combining MFL and infrared thermal imaging. Mahendran and Philip [42] proposed a direct visualization of defect in morphologies based on MFL. ...
... Com-pared with ECPT, the block area under the excitation coil is reduced accompany with uniform induction heating. Compared with Ref. [41], it will generate more induction heating rapidly and imaging MC damages with shorter time about 200 ms, rather than the 100 s in low frequency alternating magnetic field induced heating. Compared with Ref. [42], the sensor lift-off impact will be reduced without the major influence of leakage magnetic field. ...
... Detailed discussions about the various experimental procedures and data analysis techniques of IRT can be found elsewhere [11,12] . IRT is widely used in the field of non-destructive evaluation for defect detection [13,14] , condition monitoring [15,16] and plastic deformation under tensile loading [17,18] . IRT has also been extensively used for monitoring the temperature rise associated with deformation under fatigue cycling. ...
... In this regard, it should be noted that the average temperature rises (ΔT) over the gauge regions of the samples were considered here. This technique minimises experimental error as the temperatures of several pixels are simultaneously measured and the average value is used for further analysis [13] . By contrast, localised temperature hot-spots were subsequently used for studying crack propagation during fatigue loading. ...
Infrared thermography is employed for online temperature measurement during high-cycle fatigue testing of nickel aluminium bronze (NAB) samples with inherent casting defects. NAB is a widely-used material for marine applications due to its high corrosion resistance and good mechanical strength. It is observed that the temperature of the samples increased during fatigue cycling due to conversion of work done to heat. The crack initiation time is estimated from the variation of sample temperature as a function of the number of fatigue cycles and it is observed that for defect-free samples approximately 90% of the fatigue life is consumed in crack initiation, whereas for samples with large volumetric internal defects or smaller defects close to the surface, crack initiation occurs much earlier. The location of the fatigue crack is identified from the acquired infrared images and the zone surrounding the crack tip appears as a hot-spot due to the localised high temperature originating from intense plastic deformation at the crack tip. The crack propagation path is visually mapped from the infrared images by tracking changes in the hot-spot locations during progressive cyclic loading. The crack propagation rate and the stress intensity factor are evaluated from the infrared images and a linear increase in the rate of crack propagation with a change in the stress intensity factor is observed on a log-log scale during stage II stable crack growth, which is in accordance with the Paris Law. The results suggest that a priori identification of the probable zone of failure is possible using the infrared thermography technique.
... Recently, He et al. [40] proposed lateral heat conduction for detection of parallel and rail tread oblique cracks detection using ECPT. Lahiri et al. [41] reported on defect detection by combining MFL and infrared thermal imaging. Mahendran and Philip [42] proposed a direct visualization of defect in morphologies based on MFL. ...
... Com-pared with ECPT, the block area under the excitation coil is reduced accompany with uniform induction heating. Compared with Ref. [41], it will generate more induction heating rapidly and imaging MC damages with shorter time about 200 ms, rather than the 100 s in low frequency alternating magnetic field induced heating. Compared with Ref. [42], the sensor lift-off impact will be reduced without the major influence of leakage magnetic field. ...
This paper investigates two non-destructive evaluation methods, magnetic flux leakage (MFL) and eddy current pulsed thermography (ECPT), for both artificial and natural multiple cracks (MC) detection and visualization. The detection capability and characteristics of MC visualization are verified and compared through simulations and experiments. Results show that, MFL testing reflects the surface shapes and orientations of MC by 3D magnetic field imaging. However, it is unable to evaluate the depth of artificial MC and detailed surface shapes of natural MC due to limitations of sensor array spatial resolution. ECPT shows more capability in MC visualization in detail from thermal images. The obtained thermal image sequences from ECPT demonstrate rich transient and pattern information to evaluate MC geometrical features. After discussion of the two methods with the probability of detection (POD) analysis, a promising new sensing structure which potentially combines both advantages of them is proposed to enhance the NDE performance for MC evaluation.
... Radiance received by the camera is converted to an electrical signal in the infrared detector of the camera and the object temperature is determined using suitable calibration functions [19]. IRT has been widely used for non-destructive evaluation [19][20][21][22][23], condition monitoring [24] and bio-medical applications [25,26]. For bio-medical applications, in general, passive thermography is used without any additional heat sources. ...
... For estimation of temperature rise, the ear and cheek regions of the subjects were considered and the average temperature values over the regions of interest were used for further analyses. This technique reduces experimental error as temperature of several points within a region of interest are simultaneously used for determining the average temperature which minimizes surface temperature fluctuations [22]. ...
... ECPT, as a new NDT method combining PEC and induction thermography, is undergoing significant development and is opening up new opportunities for defect characterization and material property evaluation. Tian et al. (2011), Lahiri et al. (2014 and other several studies proposed the ECPT technique for imaging multiple cracks using infrared (IR) camera based on inductive heating and heat diffusion. A comparison of the ECPT technique with different excitation configurations, namely, Helmholtz coils and ferrite-yoke-based excitation, for the characterization of metallic materials and defect geometry, is performed (Tian et al., 2016). ...
Purpose
Detecting the orientation of cracks is a major challenge in the development of eddy current nondestructive testing probes. Eddy current-based techniques are limited in their ability to detect cracks that are not perpendicular to induced current flows. This study aims to investigate the application of the rotating electromagnetic field method to detect arbitrary orientation defects in conductive nonferrous parts. This method significantly improves the detection of cracks of any orientation.
Design/methodology/approach
A new rotating uniform eddy current (RUEC) probe is presented. Two exciting pairs consisting of similar square-shaped coils are arranged orthogonally at the same lifting point, thus avoiding further adjustment of the excitation system to generate a rotating electromagnetic field, eliminating any need for mechanical rotation and focusing this field with high density. A circular detection coil serving as a receiver is mounted in the middle of the excitation system.
Findings
A simulation model of the rotating electromagnetic field system is performed to determine the rules and characteristics of the electromagnetic signal distribution in the defect area. Referring to the experimental results aimed to detect artificial cracks at arbitrary angles in underwater structures using the rotating alternating current field measurement (RACFM) system in Li et al. (2016), the model proposed in this paper is validated.
Originality/value
CEDRAT FLUX 3D simulation results showed that the proposed probe can detect cracks with any orientation, maintaining the same sensitivity, which demonstrates its effectiveness. Furthermore, the proposed RUEC probe, associated with the exploitation procedure, allows us to provide a full characterization of the crack, namely, its length, depth and orientation in a one-pass scan, by analyzing the magnetic induction signal.
... As a noncontact and nonintrusive temperature-measuring technique, infrared thermography is able to monitor all components of the whole equipment by intuitively observing temperature variations of abnormal parts. It has wide applications in machinery defect diagnosis [7][8][9], building monitoring [10], medical inspection [11][12][13], and nondestructive testing [14][15][16]. Younus et al. proposed a two-dimensional discrete wavelet transformation-based diagnosis system, to diagnose machinery using infrared images [17]. To detect motor rotors, Eftekhari et al. presented a method using infrared images' features taken from the hottest region of the motor surface [18]. ...
Rotating machinery has a complicated structure and interaction of multiple components, which usually results in coupling faults with complex dynamic characteristics. Fault diagnosis methods based on vibration signals have been widely used, however, these methods are intricate when identifying coupling faults, especially in the situation where coupling faults share similar patterns. As a noncontact and nonintrusive temperature-measuring technique, methods by infrared images can recognize multiple faults through temperature variations; however, it is not effective if the faults are temperature-insensitive. In this paper, an improved machinery fault diagnosis technique based on information fusion of infrared images and vibration signals is studied, to have better utilization of multisource sensors and to solve the problems when one single type of data is separately used. Firstly, data enhancement for infrared images and data visualization for vibration are performed on the dataset by using the principle of graphics and Short-Term Fourier Transform, which increases the diversity of the dataset and enhances the generalization ability of the model. Then, a multichannel convolution neural network-based method is constructed to achieve data-level information fusion and improve the fault diagnosis accuracy. The effectiveness of the presented method is validated by the experimental studies on a rotor test stand, the results illustrate that the coupling faults can be effectively identified by the information fusion method, and the fault diagnosis accuracy is higher in comparison with the method by a signal from single-source sensors.
... The most widely used non-destructive testing (NDT) methodologies include X-ray radiography, ultrasonic testing, eddy current testing and acoustic emission [1,2]. Apart from the conventional NDT techniques, various optical NDT techniques have also been developed, viz., optical fiber NDT, infrared thermography, laser interferometry-based speckle NDT, endoscopic NDT and terahertz imaging [2][3][4]. Though the optical NDT techniques are effective for surface and slightly sub-surface defects, the primary advantages of these techniques are wide-area monitoring capability, high detection sensitivity, possibility of enhanced detection using signal processing and relative freedom from electromagnetic interference [2]. Tian et al. [5] proposed the use of Helmholtz coil and ferrite-yoke-based excitation methods for material characterization and non-destructive evaluation of metallic components using eddy current pulsed thermography. ...
The defect detection sensitivity of magnetic nanoemulsions (MNEs) stabilized with different functional moieties such as anionic surfactant, co-polymer and a weak polyelectrolyte is reported here. The visually discernible colour contrast over the defective regions and the corresponding Bragg’s reflection, originating from the linear chain-like structures formed by the leakage magnetic flux are experimentally measured and compared with the theoretically obtained profiles. The linear chain-like structures, formed by the MNEs, are also visualized using atomic force and optical phase contrast microscopy studies. Defect detection studies are carried out on carbon steel samples with artificially made defects (rectangular slots) and the variations in defect detection sensitivity (colour contrast) are assessed under different stabilizing moieties. It is found that the electrostatically stabilized MNEs exhibited superior defect detection sensitivity as compared to the polymeric stabilizers. The microscopic origin for sensitivity variations, is studied by measuring the inter-droplet forces and hydrodynamic diameter. The inter-droplet force measurements show that the lower decay length is better for improving the defect detection sensitivity. Through image processing and intensity profiling, the defect widths are accurately estimated, which were in good agreements with the actual defect dimensions. The intensity profiles are found to vary linearly with the defect depth for the shallower defects. These results are useful to tailor MNEs with superior defect detection sensitivity and long-term stability towards development of MNE-based thin film sensors for automated and superior defect detection strategies.
... The researchers [15,36] investigated the failures of steel ropes and defect of ferromagnetic specimens by means of thermovision. In [15], since the measurements required extremely sensitive thermovision technology, the method can detect the tight of ropes at certain conditions. ...
The lifetime of wire rope is crucial in industry manufacturing, mining, and so on. The damage can be detected by using appropriate nondestructive testing techniques or destructive tests by cutting the part. For broken wires classification problems, this work is aimed at improving the recognition accuracy. Facing the defects at the exterior of the rope, a novel method for recognition of broken wires is firstly developed based on magnetic and infrared information fusion. A denoising method, which is adopted for magnetic signal, is proposed for eliminating baseline signal and wave strand. An image segmentation method is employed for parting the defects of infrared images. Characteristic vectors are extracted from magnetic images and infrared images, then kernel extreme learning machine network is applied to implement recognition of broken wires. Experimental results show that the denoising method and image segmentation are effective and the information fusion can improve the classification accuracy, which can provide useful information for estimating the residual lifetime of wire rope.
... Mabrouki et al. [10] investigated the vibrothermography for detection of fatigue cracks in steel compact tension specimen. Lahiri et al. [11] proposed the active IRT based technique for detecting defects in ferromagnetic specimens using low frequency alternating magnetic field induced heating. The authors observed an increase in the surface temperature using an infrared camera due to induced eddy current leading to joules heating. ...
This paper concerns the development of methodology for use of Infrared thermography (IRT) for online prediction of mechanical structural vibration behaviour; given that it has extensively been applied in non-destructive technique for evaluation of surface cracks through the observation of thermal imaging of the vibration-induced crack heat generation. To achieve this, AISI 304 steel cantilever beam coupled with a slipping friction rod was subjected to a forced excitations with an infrared camera capturing the thermal profile at the friction interface. The analysis of thermal image data recorded (radiometric) for the frictional temperature time domain waveform using a MATLAB FFT algorithm in conjunction to IR camera frequency resolution of 120Hz and the use of the heat conduction equation with the help of a finite difference approach successfully identified the structural vibration characteristics in terms of frequency and displacement, the maximum relative errors being 0.09% and 5.85% for frequencies and displacements, respectively. These findings are particularly useful in overcoming many limitations inherent in some of the current vibration measuring techniques in harsh and remote environments. Keywords: Structural health monitoring, Frictional temperature evolution, Online monitoring, Thermal imaging
... Infrared small target detection (ISTD) is a critical technique in both civil and military domains, such as leak and defect inspection [13,19], cell counting for medicine analysis [8], early-warning systems [12,32,40] and so on. Taking the early-warning system for an Huan Wang wanghuanphd@foxmail.com example, it is required to be able to detect the incoming targets as early as possible. ...
Infrared small target detection (ISTD) is a critical technique in both civil and military applications such as leak and defect inspection, cell segmentation for medicine analysis, early-warning systems and so on. Over the last decade, numerous ISTD methods have been proposed, such as methods based on image denoising, visual saliency detection, low-rank matrix recovery and traditional machine learning, but training an end-to-end deep model to detect small targets has not been fully investigated. In this regard, the paper proposes a novel deep model called UCAN for ISTD which concatenates two context aggregation networks and connects them using U-skip connections. A Missed-detection-and-False-alarm Combination(MFC) loss function, which is based on the Neyman-Pearson decision theory, is proposed to train the model and can well balance the detection rate and the false alarm rate. In addition, a two-stage detection scheme which involves a cascade of two UCANs is proposed to further improve the overall detection performance of ISTD. Extensive experiments on real infrared sequences and a single-frame image set and the comparison with state-of-the-art methods demonstrate the superiority of the proposed model.
... In addition to this, there are studies in which AMR [17], GMR [18], Magnetometer [3], Gaussmeter [7], GMI [19], and Magneto-optic [5] sensors were used. There are also studies seeking to determine the defects in the shape of cavity [3,10,16,[20][21][22][23][24][25]. This may be explained with the fact that it is not possible to change the parameters such as length, depth and width in actual cracks even if the actual cracks are found and examined. ...
Magnetic flux leakage (MFL) method is used frequently in researches on cracks on ferromagnetic materials. Recent studies on this method focused on the improvement of low power consumption and sensor sensitivity. Generally, it was determined as to how the changing characteristics of MFL signals collected through magnetic sensor and the size of amplitude value of signal were changed based on the physical properties of crack on the ferromagnetic material (width of crack, depth of crack, etc.). As different from literature, primary purpose of our study was determining how this change occurred based on the type and physical properties of an artificial crack that were with known physical properties and that were formed with M5 directed steel layers; and the secondary purpose of our study was to develop an artificial neural network estimating the type and physical properties of a crack with unknown physical properties in the light of the data obtained. Accordingly in our study, firstly a magnetic measurement system was produced consisting of a mechanical scanning system to ensure three-dimensional movement of sensor, of a data collection module to process the data from sensor and to send the same to the computer, and of a computer software to evaluate the data from computer and to record the same. Then, artificial crack samples of different types and physical properties were prepared from M5 samples in the shape of a plate. These artificial crack samples were magnetized by placing on a core that was converted into electromagnets using 50 kHz AC signal; and the surface of material was scanned one-dimensionally with position controlled fluxgate sensors. The sensors created in fluxgate sensor based on the position were examined in terms of harmonics with DSP Lock-in Amplifier; and the amplitude values of harmonics showing the biggest change were included in the computer. Following the determination of changing graphics based on the scanning lengths of MFL signals, the mathematical curves and formulas best suiting to the characteristics of such change were determined. The changes of variables in such mathematical curve formulas were analyzed based on the type and physical properties of crack. Lastly, 4 different BRANNs (Bayesian regulated artificial neural networks) were developed estimating the type and physical properties of crack that were using the MFL signals of artificial crack samples with known physical properties and that were trained accordingly and that had unknown physical properties. First of those four was used to determine the type of crack and the other three were used to find the depth, width, lower and upper sound thickness values of crack based on the type of crack. Accuracy degrees were obtained from those BRANNs that were obtained during the training stage, respectively as R = 0.998, R = 0.959 and R = 0.964. The BRANNs trained provided results corresponding to the actual for artificial crack models with unknown crack types and physical properties.
... where e m and e d are respectively the thermal effusivity of solid material Table 4 A summary of most practiced excitation methods in active IRT for detection of corrosion/crack defects in the recent literature (2013 to present) [307][308][309][310][311][312][313][314][315][316][317][318][319][320][321][322][323][324][325][326]250,271,276,277,253,254,263,267,268,279,255,269,273,258,261,262,264,274]. and defect. ...
Corrosion is considered a destructive phenomenon that affects almost all metals. There is a variety of corrosion monitoring and measurement techniques being deployed across industries. However, very few techniques are ideally characterised with non-contact, non-intrusive, on-line and direct features for measuring the accurate corrosion rate or actual metal loss. Infrared Thermography (IRT) allows the recording of electromagnetic waves emitted from objects by using an infrared imaging system, such as an infrared camera. IRT is an online method of Non-Destructive Testing (NDT) meaning the delays in receiving results from a laboratory experienced in many NDT techniques can be eliminated. It is non-intrusive which means no process disruption and downtime will be imposed to the production line. It is also a non-contact method which mitigates the hazard occurrence and need for highly experienced personnel.
The work presented here constitutes an overview on the applications of infrared thermography for the detection and characterisation of general metal loss in metallic materials. It reviews the fundamentals and represents the advances of thermography applications specifically in metal loss/thickness variation measurement along the recent literature.
... Thus, significant works have been conducted in the optimization of inductor shape and excitation parameters [25]. Lahiri et al. reported low frequency alternating magnetic field for thermographic NDE [26]. Shen et al. studied the effects of the heating parameters, such as the lift-off distance, the exciting current, the frequency and the turns of the coil on the temperature histories [27]. ...
Nondestructive inspection for fatigue cracks is a critical and challenge task in both science and industry fields. This paper investigates the sensing effect of region electromagnetic performance as well as thermal intensity and uniformity on weld crack detection. The uniformity variation caused by vertical and horizontal lift-off distance between sensing and defect has been studied. In particular, a new ΔT metric has been proposed to present the thermal contrast and evaluate the detectability for weld natural cracks. This has been conducted by detail interpreting the region sensing for electromagnetic and thermal fields. Results have shown that the crack can be detected with a higher thermal contrast as it lies in a region sensing with relatively high uniformity and eddy current intensity. IEEE
... It has been observed that imperfections created in almost all of the studies done are artificial imperfections with sharp shapes many of the defects are in the form of rectangular prisms [52][53][54][74][75][76][77][84][85][86][87][88]. There are also studies where gouge shape defects are used [68,70,73,83,89]. ...
Today’s main energy sources; natural gas, petrol and petroleum products are transported via pipelines that are safe at long distances. Most of these pipelines are buried and their integrity is highly important. Deformations like corrosions, dents and cracks destruct the integrity of pipeline and they can cause highly dangerous damaging results. Loss of lives, economical losses and environmental pollution can be given as an example of the problems that may occur. Prevention of such adversities before they occur is possible by inspection of pipelines at specific intervals. In recent years, the devices named “Pipeline Inspection Gauge (PIG)” and designed according to Non-destructive Evaluation (NDE) techniques are used for inspection without destructing pipelines. In this study, the importance of pipeline inspection is firstly emphasized and the studies about the inspection of pipelines at literature are examined. In addition, the usage purposes of PIGs, the basics of Non-destructive Evaluation technologies and the samples of applications at pipelines are examined. According to data obtained from the study, suggestions are made about pipeline inspection.
... Among various techniques being used for accurate and reliable measurement of subject temperature, infrared thermography is a comparatively new methodology that has become popular because of its noncontact, noninvasive, and real-time temperature measurement capability [5,6]. Although infrared thermography is routinely used for nondestructive evaluation and condition monitoring studies [5][6][7][8][9], its application in the bio-medical field is huge and rapidly growing [10][11][12][13][14][15][16]. Numerous applications of infrared thermography in the medical sciences have been reported in the last few decades. ...
Body temperature is a significant indicator of illness and hence is a useful parameter for clinical diagnosis. Among various techniques available for accurate and reliable measurement of subject temperature, infrared thermography is a relatively new methodology. However, it has become popular because of its noncontact, noninvasive, and real-time temperature measurement capability. During the last few decades, numerous applications of infrared thermography are reported in the field of medical sciences, which are rapidly growing. Diabetes is a metabolic disorder associated with high blood sugar levels over prolonged duration. One in every 11 adult population of the world is affected by diabetes and for every 6 s, one person dies from diabetes-induced complications. Therefore, a worldwide dedicated effort to prevent diabetic complications by early detection is important. Studies so far reveal that infrared thermography is capable of detecting subtle changes in skin temperature distribution in diabetic-at-risk foot and is capable of early detection diabetic-related peripheral neuropathy and vascular disorders. This chapter attempts to highlight the applications of infrared thermography in the early detection of diabetic neuropathy and vascular disorder. The basics of infrared thermography, classification of medical thermography techniques, details of infrared camera, ideal experimental conditions, data analysis, etc. along with typical case studies are discussed in detail.
... However, the problems of in-homogenous heating, limited heating area and blocking effect of coil [24][25][26] in reflection mode ECPT are still challenging the accurate material and defect quantitative characterization. Lahiri et al. 27 reported low frequency alternating magnetic field for thermographic NDE of defect with large area. Jäckel et al. 28 proposed an electromagnet yoke for external magnetic field to enhance the crack detection contrast by induction thermography. ...
Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF).
... The radiance received by the infrared detector is converted into an electrical signal and the object temperature is measured using suitable calibration curves [29]. IRT is routinely used in the field of non-destructive evaluation [29][30][31], condition monitoring [32] and bio-medical applications [33][34][35]. Though the application of IRT during MFH experiments has been reported in a few studies [27,28,[36][37][38][39], the temperature is not directly measured on the magnetic fluid samples. ...
... All of the above thermography based NDT & E require signal processing to perform defects detection or material characterization. In thermal testing, several thermal transient response features have been used as an indicator of defect status, which is critical for acceptance/rejection decisions for maintenance and lifetime prediction [26]. Thermographic signal reconstruction (TSR) is a processing technique that improves spatial and temporal resolution of a thermogram sequence [27]. ...
Eddy Current Pulsed Thermography (ECPT) is an emerging Non-Destructive Testing (NDT) technology and has an increasing span of application with capabilities of rapid contactless and large surface area detection. The close process loop of ECPT that contains pre-processing, post-processing and objective quantitative assessment is rarely presented. This work proposed a complete strategy aims to perform pre- and post- processing for surface crack detection based on ECPT platform. In addition, the quantitative evaluation is involved to objectively evaluate detectability. Specially, a new post image segmentation algorithm is proposed which based on the idea of grouping histogram and iterative adaption approach that leads to better performance for quantitatively identifying and sizing the defect. Experimental tests on man-made metal and natural defects have been conducted to show the reliability of the proposed strategy. The work can be further applied for other types of defects detection, quantitative evaluation, and aid in the development of machine vision industry for automated visual inspection.
... All of the above thermography based NDT & E require signal processing to perform defects detection or material characterization. In thermal testing, several thermal transient response features have been used as an indicator of defect status, which is critical for acceptance/rejection decisions for maintenance and lifetime prediction [26]. Thermographic signal reconstruction (TSR) is a processing technique that improves spatial and temporal resolution of a thermogram sequence [27]. ...
... All of the above thermography based NDT & E require signal processing to perform defects detection or material characterization. In thermal testing, several thermal transient response features have been used as an indicator of defect status, which is critical for acceptance/rejection decisions for maintenance and lifetime prediction [26]. Thermographic signal reconstruction (TSR) is a processing technique that improves spatial and temporal resolution of a thermogram sequence [27]. ...
... All of the above thermography based NDT&E require signal processing to perform defects detection or material characterization. In thermal testing, several thermal transient response features have been used as an indicator of defect status, which is critical for acceptance/rejection decisions for maintenance and lifetime prediction [26]. Thermographic signal reconstruction (TSR) is a processing technique that improves spatial and temporal resolution of a thermogram sequence [27]. ...
Thermography is an established technique in Non-Destructive Testing and Evaluation (NDT&E) for detecting and visualizing defects. The acquired thermal image sequences contain valuable information in the spatial, time and frequency domains. Many thermal feature extraction methods have been previously proposed to detect and quantify defects. However, the quantitative assessment and error analysis remain as challenges. In the present work, a quantitative analysis strategy is proposed for validating detection performance of various thermal feature extraction techniques based on Eddy Current Stimulated Thermography. F-score is adopted as a global quantitative evaluation indicator to assess the crack detectability. The quantitative validation is carried out based on a large number of simulations and experiments for cracks on the nonferromagnetic material. The detectability in relation to the variations in crack size and the different thermal feature extraction methods have been critically analyzed. The insights obtained from the present findings can serve as guidelines to other types of thermal-based NDT&E to improve the defect visibility and detectability.
... Mabrouki et al. [8] investigated the vibrothermography for detection of fatigue cracks in steel compact tension specimen. Lahiri et al. [9] proposed the active IRT based technique for detecting defects in ferromagnetic specimens using low frequency alternating magnetic field induced heating. The authors observed an increase in the surface temperature using an infrared camera due to induced eddy current leading to joule heating. ...
Infrared thermography (IRT) has matured and is now widely accepted as a condition monitoring tool where temperature is measured in a non-contact way. Since the late 1970s, it has been extensively used in vibrothermography (Sonic IR) non-destructive technique for the evaluation of surface cracks through the observation of thermal imaging of the vibration-induced crack heat generation. However, it has not received research attention on prediction of structural vibration behaviour, hence; the concept to date is not understood. Therefore, this paper explores its ability to fill the existing knowledge gap. To achieve this, two cantilever beam-like structures couple with a friction rod subjected to a forced excitations while infrared cameras capturing the thermal images on the friction interfaces. The analysed frictional temperature evolution using the Matlab Fast Fourier Transform (FFT) algorithm and the use of the heat conduction equation in conjunction with a finite difference approach successfully identifies the structural vibration characteristics; with maximum error of 0.28 and 20.71 for frequencies and displacements, respectively. These findings are particularly useful in overcoming many limitations inherent in some of the current vibration measuring techniques applied in structural integrity management such as strain gauge failures due to fatigue.
... Mabrouki et al. [8] investigated the vibrothermography for detection of fatigue cracks in steel compact tension specimen. Lahiri et al. [9] proposed the active IRT based technique for detecting defects in ferromagnetic specimens using low frequency alternating magnetic field induced heating. The authors observed an increase in the surface temperature using an infrared camera due to induced eddy current leading to joule heating. ...
... Radiance received by the infrared detector is converted to an electrical signal and the object temperature is measured using suitable calibration curves [27]. IRT is a remote temperature measurement methodology which is routinely used for non-destructive evaluation, condition monitoring [27][28][29] and in the rapidly developing field of medical thermography [30][31][32]. Boldor et al. [33] used IRT for measuring average temperature rise of multi-walled carbon nanotubes during selective photo-thermal hyperthermia using a near infrared laser radiation where the samples were placed on a custom made brass stage and then irradiated with laser. ...
... Although rail multiple cracks and blade natural edge defects have well detected and verified the capabilities of differently configured ECPTs, quantitative NDE needs further consideration and processing due to the geometric superimposition on the heating pattern [23,25,26]. Their inspection limitations of electro-conductive materials only, constant lift-off, and the requirement of sample scanning need to be further addressed. ...
This paper reviews recent developments of eddy current pulsed thermography (ECPT) for material characterization and nondestructive evaluation (NDE). Due to the fact that line-coil-based ECPT, with the limitation of non-uniform heating and a restricted view, is not suitable for complex geometry structures evaluation, Helmholtz coils and ferrite-yoke-based excitation configurations of ECPT are proposed and compared. Simulations and experiments of new ECPT configurations considering the multi-physical-phenomenon of hysteresis losses, stray losses, and eddy current heating in conjunction with uniform induction magnetic field have been conducted and implemented for ferromagnetic and non-ferromagnetic materials. These configurations of ECPT for metallic material and defect characterization are discussed and compared with conventional line-coil configuration. The results indicate that the proposed ECPT excitation configurations can be applied for different shapes of samples such as turbine blade edges and rail tracks.
... Each class of test objects requires special training of the network. In thermal testing, several thermal transient response features have been used as an indicator of defect status, which is critical for acceptance/rejection decisions for maintenance and lifetime prediction 23 . To enhance the flaw contrast and improve noise rejection qualities, pattern based image enhancement has been conducted by introducing the raw data upon a set of orthogonal basis functions. ...
Electromagnetic mechanism of Joule heating and thermal conduction on conductive material characterization broadens their scope for implementation in real thermography based Nondestructive testing and evaluation (NDT&E) systems by imparting sensitivity, conformability and allowing fast and imaging detection, which is necessary for efficiency. The issue of automatic material evaluation has not been fully addressed by researchers and it marks a crucial first step to analyzing the structural health of the material, which in turn sheds light on understanding the production of the defects mechanisms. In this study, we bridge the gap between the physics world and mathematical modeling world. We generate physics-mathematical modeling and mining route in the spatial-, time-, frequency-, and sparse-pattern domains. This is a significant step towards realizing the deeper insight in electromagnetic thermography (EMT) and automatic defect identification. This renders the EMT a promising candidate for the highly efficient and yet flexible NDT&E.
... Infrared thermography (IRT) is proved to be an excellent tool for non-invasive and real time monitoring of dynamic temperature variations. IRT has been widely used in the field of non-destructive evaluation [10][11][12][13], condition monitoring [14,15] and bio-medical applications [16,17] like breast cancer monitoring [18], diabetic neuropathy and vascular disorder [19], fever screening [20] etc. Due to its non-contact and dynamic temperature measurement capability, IRT is the most appropriate tool for monitoring thermoregulation induced subtle changes on skin temperature where other contact probes (like thermocouples or platinum resistance thermometers) may miss the localized dynamic temperature changes. Additional advantage of using IRT is that it provides a visual image of the surface temperature distribution over the region of interest which aids in temperature monitoring. ...
... Among these works, ECPT is widely and in-depth researched by Tian's group and several signal processing methods were used to improve the defect detectability [16][17][18]. What is more, a new ECT based technique is proposed for defect detection in ferromagnetic specimens using a low frequency alternating magnetic field induced heating [19]. However, the contemporary research has a great missdistance with quantitatively evaluation. ...
... Infrared thermography (IRT) is a non-contact temperature measurement methodology, which is extensively used in the fields of NDE [9][10][11][12][13][14] and condition monitoring [15][16][17] . In IRT, the infrared rays (wavelength: 0.75-1000 µm) emitted by an object under investigation are detected using a suitable infrared camera and the temperature of the object is determined from the intensity of the emitted infrared rays using Stefan-Boltzmann's Law, which is described below [9] : Here, q, A, ε, σ and T are the rate of energy emission (W), area of the emitting surface (m 2 ), emissivity of the surface, StefanBoltzmann's constant (σ = 5.676 × 10-8 Wm-2 K-4 ) and absolute temperature (K) of the object under investigation, respectively. ...
Non-destructive evaluation is essential for the safe and uninterrupted operation of pressure vessels. This study reports on infrared thermography-based online hydrotesting of three AISI type 304 stainless steel pressure vessels with simulated
defects of 1.8 mm, 2.2 mm and 2.5 mm depths. The surface temperature rise of the defect and defect-free regions are remotely monitored using an infrared camera. It is observed that the temperature rise of the defect region is much higher compared to that of the defect-free regions and the normalised temperature difference monotonically increases with defect depth due to the higher stress concentration-induced faster rate of deformation. The rate of increase of the normalised temperature difference rapidly increases with defect depth and the rate is found to be linearly correlated with the normalised stress difference between the defect and defect-free regions. The ring-like hot-spot observed in the defect regions of the infrared images, prior to failure, corresponds to the circular morphology of the fabricated defects, and the circumference of the circular defects is identified as the most probable location for crack initiation. Contrast enhancement of the acquired infrared images is achieved using image processing algorithms. This study shows that infrared thermography can be effectively used for online monitoring of growing defects during hydrotesting of pressure vessels.
... During analysis of the acquired infrared images, a region of interest was selected for each frame and the average temperature of the pixels in the region was used for further analysis. This technique essentially reduces the experimental variations as temperature is measured over a large number of pixels simultaneously in real time and the average temperature is also computed in real time using Altair software [24,25]. ...
Acoustic emission (AE) and infrared thermography technique (IRT) have been used to study the tensile behavior of AISI type 316 stainless steel. Strain rates of tensile testing were varied from 1.4 × 10−3 s−1 to 1.4 × 10−2 s−1. AE root mean square voltage increases with increase in strain rate due to the increase in source activation. Dominant frequency of the AE signals generated during different regions of tensile deformation has also been used to compare the results for different strain rates. The dominant frequency increases from elastic region to around 590 kHz during work hardening and 710 kHz around ultimate tensile strength (UTS) for all the strain rates. Temperature changes during different regions of deformation are monitored using infrared thermography. The temperature rise in the work hardening
region is found to approximately increase linearly with time and from the slopes of the linear regression analyses the rate of temperature rise in the work-hardening region is obtained which is found to be very sensitive to strain rates. From the experimental results an empirical equation that relates the rate of temperature increase with strain rate and thermal hardening coefficient is obtained. The correlation between the variation of AE dominant frequency and temperature rise during different deformation regions provided better insight into the tensile behavior of AISI type 316 SS for different strain rates.
... Detailed discussions on various IRTbased experimental techniques and data analysis procedures can be found elsewhere [23,24] . Infrared thermography is routinely used in the field of non-destructive testing [24][25][26] , the detection of weld defects [27] and condition monitoring [28] . IRT is an excellent tool for real-time non-contact monitoring of tool temperature during various types of milling processes. ...
Tool temperature is one of the major life-limiting factors for micro-end cutting tools. Therefore, monitoring of the cutting tool temperature during the milling process is very useful. Here, we use infrared thermography for online monitoring of the cutting tool temperature during the
micro-end milling of two different workpieces, aluminium alloy Al6061 and AISI 4340 steel, and the effects of milling parameters such as spindle speed, feed rate and depth of cut on the tool temperature are systematically studied. Our study shows that the tool temperature increases with increasing
spindle speed and feed rate because of a larger amount of frictional heat generated at the interface between the tool and the workpiece. The maximum increase in tool temperature in the case of the aluminium alloy workpiece is found to be 1.18 times lower than that of the steel workpiece, which
is attributed to the larger thermal diffusivity of the aluminium alloy and the reduced frictional heat generation due to the lower hardness and shear strength compared to the steel workpiece. Two-way analysis of variance is used to evaluate the relative importance of the various milling parameters
in tool temperature increase. It is observed that spindle speed is the most significant factor that influences the tool temperature, whereas feed rate is found to have a less significant influence. The workpiece temperature is simultaneously measured using a K-type thermocouple and a calibration
curve between the tool and the workpiece temperatures is obtained, which is used for estimation of the workpiece temperature using infrared thermography. The material removal rate is calculated for various process input conditions, which will be useful to increase the material removal rate
and to avoid temperature-induced tool damage. The advantage of using infrared thermography is that the temperature distribution of the micro-end milling tool and workpiece can be mapped.
Metal surfaces on industrial equipment are susceptible to fracture when subjected to extreme pressure and speed conditions. The safety of the parts is at risk and their service life is decreased by these fractures. One of the primary difficulties in developing eddy current non-destructive testing (NDT) sensors is locating fractures in any direction. The limitation is that fractures that are not perpendicular to the current flows produced cannot be detected by eddy current-based approaches. To locate arbitrary orientation fractures in conductive non-ferrous materials, this work explores the use of a rotating electromagnetic field technique and provides a novel rotating uniform eddy current (RUEC) system. This novel approach has greatly improved the detection of fractures in any orientation. The impedance signature of the fracture is investigated using a three-dimensional finite element (FE) simulation model of the new RUEC system. The rotating alternating current field measurement (RACFM) approach, which was designed to detect artificial cracks at any angle in underwater structures, is used in [1] to validate the model proposed in this study. The efficacy of the RUEC system and its potential in the detection of different fracture orientations in the aluminium specimen are demonstrated by the simulation results.
In-line inspection (ILI) technology is a crucial tool for maintaining pipeline integrity. However, it faces considerable challenges such as adaptability in identifying various types of faults. In this paper, a new type of ILI system based on electromagnetic induction and magnetization is proposed. Firstly, a novel magnetic ring structure (MRS) is developed which can generate axial magnetic flux leakage and a circumferential uniform alternating current field; secondly, the magnet structure’s configuration is modified and extended so that the pipe wall’s penetrating ability and magnetic flux are strengthened. This improves the detection capability for shallow surface defects as well as deeper hidden faults while ensuring trafficability and overcoming the detection performance constraint of single detection technology. To evaluate the feasibility of the proposed MRS system, an actual pulling test was performed. The proposed method’s detection rate and penetration capabilities are verified by finite element modeling and experiments.
A two-coil magnetic core inductor that works under a low-frequency alternating current is proposed to increase the detection area of SECT (Stepped Eddy Current Thermography). As the amplitude of the alternating current is small, the heating problem of the coil is ignored. And the cooling equipment is reduced that decreases the cost of the detection system. Additionally, the split structure inductor is studied, which confirms this structure is suitable for SECT and provides a reference for the design of an adjustable exciting inductor. The detection system for detecting subsurface defects is established in numerical models and experiments. The results indicate this detection system is suitable for detecting large-sized subsurface defects in a large area. Conclusions of the amplitude contrast in the heating process and the phase contrast in the cooling process suitable for defect depth analysis are obtained through the post-processing of thermal data.
Thermographic inspection is a popular nondestructive testing (NdT) technique that provides images of temperature distribution over large areas at surfaces of tested workpieces. Detecting delaminations between metallic layers is the matter here. Simulation of these inspections indeed helps to complement experimental studies, evaluate performance in terms of detection and support model-based algorithms. A semi-analytical model based on a truncated region eigenfunction expansion for simulation of thermographic inspection is focused onto. The problem is solved in the Laplace domain w.r.t time, and the temperature distribution approximated by expanding it on a tensor product basis. Considered sources are lamps providing thermal excitation but may also be eddy current sources (leading to a coupled electromagnetic and heat problem). The description of the delaminations as thin air gaps between the workpiece layers proves to be equivalent with introduction of a surface resistance to the heat flow, enabling treatment via the applied modal approach without additional discretisation. Complementary computations by industry (Finite Element Method) and in-house (Finite Integration Technique) codes confirm the accuracy of the developments. Then, much attention is put on imaging and detection. A two-step procedure is devised, first denoising of raw signals and detection of any possible defect using a thermographic signal reconstruction leading to high spatial and temporal resolution in the transverse plane, completed by proper edge detection, second an iterative optimization being employed, with results of the first step used for regularization of a least-square scheme to characterize thicknesses and depths. All the above is illustrated by comprehensive numerical simulations in conditions close to practice.
Eddy current pulse thermography (ECPT) is an active thermography technology in the nondestructive testing field. The inductor of ECPT is an important component that influences detection quality and efficiency. In this paper, a two-coil magnetic core inductor is proposed for ECPT, which characteristics are investigated by numerical simulation methods. This new structure enlarges the detectable area for ECPT and increases the view field for infrared cameras. Research results show that the uniformity of temperature distribution is improved significantly. At the same time, the geometric parameters and working parameters of the proposed inductor, including the coil turns, the coil height, the leg length of the magnetic core, the lift-off distance, the working frequency, are researched.
Eddy current thermography (ECT) plays an important role in the field of nondestructive testing (NDT). In this study, a moving detection mode of ECT is used for crack detection and the temperature distribution near the crack in this mode is studied. Firstly, the numerical simulation is used to analyze the eddy current distribution on the specimen surface. And then the experimental studies are carried out and thermal images are obtained in the experiments. The surface temperature distribution of the specimen is analyzed, and the fitted curve of the temperature decline trend is given. The curve is helpful to determine the best detection area. The temperature distribution characteristics near the crack are analyzed and the position of the largest temperature difference on the specimen surface is determined. Finally, a new method for determination of crack opening size based on edge detection technology is proposed, and the size of the crack opening is obtained.
This paper investigates the comparison of infrared thermography (IRT) and miniature Deltatron accelerometer sensors in measuring structural vibration characteristics in terms of frequency and displacement, given that of age IRT has fully grown for temperature condition monitoring. In addition, IRT has been extensively applied in non-destructive techniques for evaluation of surface cracks through the observation of thermal imaging of vibration-induced crack frictional heat generation. Therefore, in order to conduct this study, both single and dual cantilever beam-like structures (AISI 304 steel) coupled with a slipping frictional rod (lacing wire) were subjected to forced excitations with an infrared camera capturing the thermal profile emanating from beam-lacing wire frictional interface. Concurrently, miniature Deltatron accelerometer sensors were attached to the beam surface next to the frictional interface focused by IR camera. The thermally analyst vibration characteristics parameters were compared against those acquired by accelerometers. The comparison of results exhibited a maximum relative difference of 0.28% and 14.88% for frequencies and displacements, respectively. This shows that IRT is more reliable in measuring structural vibration frequency than displacements. The finding is particularly useful in overcoming many limitations inherent in some of the current vibration measuring techniques such strain gauges failure due to fatigue.
As a noncontact and non-intrusive technique, infrared image analysis becomes promising for machinery defect diagnosis. However, the insignificant information and strong noise in infrared image limit its performance. To address this issue, this paper presents an image segmentation approach to enhance the feature extraction in infrared image analysis. A region selection criterion named dispersion degree is also formulated to discriminate fault representative regions from unrelated background information. Feature extraction and fusion methods are then applied to obtain features from selected regions for further diagnosis. Experimental studies on a rotor fault simulator demonstrate that the presented segmented feature enhancement approach outperforms the one from the original image using both Naïve Bayes classifier and support vector machine.
There is a large interest to find reliable and automatic methods for crack detection and quantification in the railway bogie frame. The non-destructive inspection of railway bogie frame has been performed by ultrasonic and magnetic particle testing in general inspection. The magnetic particle method has been utilized in the defect inspection of the bogie frame but the grinding process is required before inspection and the dust is developed resulting from the processing. The objective of this paper is to apply the inspection method of bogie frame using infra-red thermography. The infra-red thermography system using the excitation of eddy current was performed for the defect evaluation of weld specimen inserted artificial defects. The result shows that the infra-red thermography method can detect the surface and inner defects in weld specimen for bogie frame.
Eddy current pulsed thermography(ECPT) is an emerging Non-destructive testing and evaluation(NDT & E) technique, which uses hybrid eddy current and thermography NDT & E techniques that enhances the detectability from their compensation. Currently, this technique is limited by the manual selection of proper contrast frames and the issue of improving the efficiency of defect detection of complex structure samples remains a challenge. In order to select a specific frame from transient thermal image sequences to maximize the contrast of thermal variation and defect pattern from complex structure samples, an energy driven approach to compute the coefficient energy of wavelet transform is proposed which has the potential of automatically selecting both optimal transient frame and spatial scale for defect detection using ECPT. According to analysis of the variation of different frequency component and the comparison study of the detection performance of different scale and wavelets, the frame at the end of heating phase is automatically selected as an optimal transient frame for defect detection. In addition, the detection capabilities of the complex structure samples can be enhanced through proper spatial scale and wavelet selection. The proposed method has successfully been applied to low speed impact damage detection of carbon fibre reinforced polymer(CFRP) composite as well as providing the guidance to improve the detectability of ECPT technique.
Magnetic materials were investigated by induction thermography at induction frequencies of 80–300 kHz. The influence of an external magnetic field on the thermal crack contrast was studied. With proper orientation of the external field, the contrast increased by a factor more than three. Numerical simulations of the static and high-frequency magnetic fields and the temperature distribution were performed. Using a stationary induction field and a modulated external field in the frequency range of 0.28–36.5 Hz, lock-in thermography was realised, which shows cracks with good contrast. The technique was applied to crack detection in ferritic steel profiles.
This letter proposed an eddy current pulsed phase thermography technique combing eddy current excitation, infrared imaging, and phase analysis. One steel sample is selected as the material under test to avoid the influence of skin depth, which provides subsurface defects with different depths. The experimental results show that this proposed method can eliminate non-uniform heating and improve defect detectability. Several features are extracted from differential phase spectra and the preliminary linear relationships are built to measure these subsurface defects' depth.
Pulsed eddy current testing of wall-thinning through cladding and insulation was studied from both theoretical and experimental aspects. The analytical solution was derived for a simplified four-layered structure and was used to conduct simulations to ascertain the feasibility of this method. A pulsed eddy current testing probe consisting of a circular excitation coil and an AMR-sensor-embedded differential detector was fabricated to measure the time-varying magnetic field signals on the axisymmetric excitation coil’s axis. The measurement system was able to measure magnetic field down to a few hundred micro-Gausses in an unshielded environment. Simulation and test results showed that over a certain time after turning off the excitation current the magnetic field signal’s decay behavior is almost merely relevant to the pipe’s wall thickness. Future development of a carbon steel pipe’s wall-thinning can be evaluated by using decay coefficients estimated from previously obtained test data.
The detection of flaws in steel pipes using Magnetic Flux Leakage (MFL) consists in detecting magnetic flux leaks outside the pipe, either with a magnetic sensor or with an induction coil, while the pipe is rotating. In the Vallourec group, many NDT units use MFL for testing
ferromagnetic pipes. In order to improve the performances of flaw detection, CEA LIST and the Vallourec Research Aulnoye (VRA) group are collaborating on MFL modelling. The aim is to be able to perform parametric studies thanks to a fast 3D numerical model dedicated to MFL systems. A simplified 2D geometry has already been derived for the development of first simulation tools. When considering the B-H curve of ferromagnetic materials, the non-linear magnetostatic problem can be solved with the generalized boundary element method (BEMG), which comes to the evaluation of two equivalent scalar potentials: the surface charge density and the volume charge density. When applying the Galerkin method for the discretization of integral equations, the particularity of this numerical model lies in the implementation of high order basis functions for the interpolation of the scalar unknowns. This paper presents some first numerical results for the numerical validation of the semi-analytical model.
The dipole model of a crack (DMC) is applied for a first time assuming that the distribution of the surface density of magnetic charge at the crack walls m along the depth of a surface crack is not constant, but is described by a second order polynomial. New analytical expression is derived for the z-component of the intensity of the leakage magnetic field (ZILMF) in this case. DMC inversion is performed using Hall sensor measurements of ZILMF by varying the coefficients of the second order polynomial which leads to determining the depth distribution of m. Additional inversions are performed assuming correspondingly constant and linear depth distribution of m and the results and the accuracies of the different inversions are compared. It is shown that m is significantly larger at the tip of the crack with respect to its mouth which indicates that the depth distribution of m should not be considered to be constant. Instead, the distribution of the surface density of magnetic charge at the crack walls m along the depth of the crack can be represented by a polynomial of first or second order, and the distribution of the corresponding ZILMF is described by the new analytical expression. These developments might make DMC inversions a viable alternative of Eddy-current inversions. .
Thermographic inspection with eddy current (EC) excitation is an emerging integrative NDT&E method with the ability to inspect for defects over large areas. The resultant surface heat distribution from direct EC heating and diffused heat can be obtained easily with a thermal camera, but techniques for the determination of heating mechanisms around a particular defect for quantitative defect characterisation are required. In this paper, numerical modelling and experimental studies are applied to understand EC stimulated thermography on simple discontinuity defects, including transient EC distribution and heating propagation for slots and notches. This fundamental understanding of transient EC distribution and heating propagation will aid in the development of feature extraction and pattern recognition techniques for the quantitative analysis of EC thermography images and defect characterisation.
Eddy current thermography is a new NDT-technique for the detection of cracks in electroconductive materials. It combines the well established inspection techniques eddy current testing and thermography. The advantage of this method is to use the high performance of eddy current testing without the known problem of the edge effect. Especially for components of complex geometry this is an important factor which may overcome the increased expense for inspection set-up.The principle of this technique and an algorithm to increase the sensitivity for small defects are described. Some inspection examples on aero engines parts are presented which show the potential of eddy current thermography.
The eddy current Thermography is an evolving non-contact, non-destructive evaluation method with applications especially in aircraft industries. It involves two approaches (a) the volumetric heating (skin depth much greater than the thickness) of the specimen and the observation of additional heating at defect locations due to Joule heating (called eddy-therm) and (b) the use of high-frequency eddy current bursts (skin depth is smaller than the thickness) for the transient surface/near surface heating of the objects and sensing the propagation of a “thermal wave” using a high-sensitivity infrared (IR) camera (tone burst eddy-current thermography (TBET)). In this paper, a study on the optimum frequency of eddy current excitation that will give a maximum temperature rise for a given thickness has been conducted using both modeling and experimental techniques. COMSOL 3.2 was used to solve the coupled equations of electromagnetic induction and heat transfer. The dependency of this optimum frequency (peak frequency) on thickness, electrical conductivity, and thermal response of the sample are studied. The relation between defect size and the coil inner radius is considered. The thermal responses of defective samples obtained by simulation are compared with experimental results.
We have developed a simple sensor for imaging internal defects in materials using a magnetically polarizable nanoemulsion. The gradient in the magnetic flux lines around the defective region leads to the formation of one-dimensional nanodroplet arrays along the field direction, which incredibly diffract the incident white light to produce bright colors. As the diffracted wavelength has a direct correlation with the defect features, this approach enable visual inspection of ferromagnetic components and has several advantages over existing flux leakage sensors in terms of cost, re-usability and complexity.
An investigation into the effect of size on the quantitative estimation of defect depth in a steel specimen has been undertaken using lock-in thermography. Phase contrast measurements over circular defects of varying diameter and depth are presented for a range of excitation frequencies. It was found that the diameter of a defect had an appreciable effect on the observed phase angle which consequently has significant implications with regard to estimating defect depth. Phase contrast measurements for a range of defects in a 10 mm steel specimen indicate that an excitation frequency of 0.02 Hz is the optimal frequency for defect detection. Results obtained with an excitation frequency of 0.02 Hz are used to discuss the limitations of determining the size and depth of defects. A finite element analysis was found to have good correlation with experimental data and thus demonstrates potential in providing improved estimates of defect depth.
A surface crack close to a spot heated by a laser beam impedes lateral heat flow and produces alterations to the shape of the thermal image of the spot that can be monitored by thermography. A full 3D simulation has been developed to simulate heat flow from a laser heated spot in the proximity of a crack. The modelling provided an understanding of the ways that different parameters affect the thermal images of laser heated spots. It also assisted in the development of an efficient image processing strategy for extracting the scanned cracks. Experimental results show that scanning pulsed laser spot thermography has considerable potential as a remote, non-contact crack imaging technique.
The thermographic images of laser heated spots or lines are perturbed by nearby cracks, providing NDE techniques for crack detection. Scanning with a laser line, rather than a laser spot, results in a substantial reduction in inspection time. 3D finite difference modelling results are presented that show the sensitivity of the laser line thermography technique to cracks of varying lengths, depths and openings. A novel crack imaging technique is presented that is based on assembling second spatial derivative thermal images of a scanned laser line. Experimental results show the new technique to image cracks with openings as small as a few micrometres. The scanning time of the laser line thermography technique is shown to be over an order of magnitude smaller than that of the laser spot thermography technique whilst producing crack images of similar quality.
A set of 2D steady state finite element numerical simulations of electromagnetic fields, eddy currents distribution and induction heating pattern was performed for different heights of a metal workpiece. Comparison between the calculation results show the height of the workpiece body with respect to the induction coil has a marked effect on the electromagnetic field distribution, eddy currents profile, heating structure and coil efficiency in the system. If the workpiece height is equal to or less than the coil height, then overheating at the workpiece ends is high and makes a nonuniform heating pattern along the workpiece wall.
Magnetic materials were investigated by induction thermography at induction frequencies of 80 - 300 kHz. The influence of an external magnetic field on the thermal crack contrast was studied. With proper orientation of the external field, the contrast increased by a factor more than three. Numerical simulations of the static and high-frequency magnetic fields and the temperature distribution were performed. Using a stationary induction field and a modulated external field in the frequency range of 0.28 to 36.5 Hz, lock-in thermography was realized, which shows cracks with good contrast. The technique was applied to crack detection in ferritic steel profiles.
Over two centuries passed since the first stone posed by Herschel in the foundation of the infrared radiation world. For many years, infrared thermography IRT had been a subject of dispute and investigation with great enthusiasm and wide scepticism.Today, the usefulness of infrared thermography has been amply demonstrated leading to a proliferation of infrared devices of different sizes and different performances to fulfil the requirements of the multitude of users in the vast variety of applications.
Eddy-current induced thermography (induction thermography, hereon referred to as eddytherm) is an active thermographic method which is capable of rapid and non-contacting detection of out-of-plane cracks in electrically conductive parts. In an eddytherm inspection, the part is induction heated; cracks cause localised changes in the induced eddy-current flow and the associated Joule heating is imaged at the surface of the part with an infrared camera. In this study the detectability of fatigue cracks in steel, titanium and Waspaloy is quantified by novel but simple image processing routines which are specifically applicable to eddytherm inspection. The quantitative detection data is then input into a cumulative log-normal probability of detection model to estimate the probability of detecting the fatigue cracks as a function of crack length. a90,95 (i.e., the crack length which can be detected 90% of the time with 95% confidence) is found to be 0.60 mm for steel, 0.78 mm for titanium and 1.50 mm for Waspaloy (a nickel-based superalloy), showing eddytherm to be an extremely sensitive method.
No other book on the market today can match the 30-year success of
Halliday, Resnick and Walker's Fundamentals of Physics! In a breezy,
easy-to-understand style the book offers a solid understanding of
fundamental physics concepts, and helps readers apply this conceptual
understanding to quantitative problem solving. This book offers a unique
combination of authoritative content and stimulating applications.
Magnetic flux leakage tools are widely used for the inspection of large diameter, transmission, gas pipeline where the pipe condition, with regard to outside diameter corrosion, is of interest. In seeking to extend the inspection capability of such tools to the detection and characterization of other pipe conditions such as mechanical damage and stress corrosion
cracking, it has become clear that much more needs to be known about both the magnetic characteristics of the materials constituting the inspection tool, as well as the specific pipeline
material condition to be determined. This paper gives an overview of magnetic flux leakage inspection tools and describes recent developments in tool modeling and signal processing which are aimed at extending the detection limits of existing equipment and which highlight the need for improved knowledge of material behavior in the vicinity of stress corrosion
cracking and mechanical damage.
Ruthenium(III) complex catalyzed oxidation of aliphatic amines with bromamine-T under alkaline condition proceeds efficiently to afford carboxylic acids in high conversion. Hexa-coordinated ruthenium(III) complex of the type [RuCl2(PPh3)(L)] (L, tridentate ligand derived by the condensation of o-phenylene diamine with salicylaldehyde) has been synthesized and it was used as a catalyst for the oxidative conversion of amines to carboxylic acids. The detailed mechanistic and kinetic investigations have been made for the oxidation reactions. Under similar experimental conditions all the amines proceed with a common oxidation mechanism and follows an identical kinetics with first-order dependence each on [Oxidant]o and [Amine]o, and fractional order with respect to [Catalyst] and [OH−]. To understand the detailed kinetics and mechanism of the reactions, the reactions have been subjected to changes in (i) dielectric permittivity, (ii) primary salt effect, (iii) halide ions and (v) temperature. The reactions were carried out at different temperature and the activation parameters have been calculated. From enthalpy–entropy relationships and Exner correlations, the isokinetic temperature (β) of 382 K, calculated is much higher than the experimental temperature (313 K), indicating that, the enthalpy factor controls the rate. The observed results have been explained by a plausible mechanism and the related rate law has been deduced. The present method developed for the oxidation of amines to carboxylic acids by bromamine-T offers several advantages including high conversion, short reaction times, and stable, cost effective and relatively non-toxic reagents which make the reaction process simple and smooth.
We report a methodology to visualize defects by naked eye using magnetically polarizable nanoemulsions stabilized with different surface active species. The response of the nanoemulsions to the leaked magnetic flux from a defective region is exploited to locate the defect. In the presence of leaked magnetic flux, the nanofluid shows a visually perceivable color change due to the changes in the interparticle spacing within the self-assembled nano-arrays. We discuss the methodologies to detect defect
morphologies and the underlying physics. The detection methodologies to quantify the defect shape, location and dimensions are validated in specimens with simulated defects of different geometries. The notable advantage of this technique is that it is simple, user friendly (does not need any processing of electronic data), fast and ideal for inspection of large area surfaces rapidly. This technique is ideal for the detection of surface and subsurface defects such as voids, cracks and inclusions in ferromagnetic materials.
A versatile computerised magnetic surface inspection system utilising magneto-resistive (MR) sensors has been developed. An unbiased 1 mm MR element sensor mounted to a computer controlled X-Y table stage is raster scanned across the sample surface. Domain patterns and surface scribed defects have been mapped by measuring the vertical component of the stray fields present on various ferromagnetic surfaces.
During thermo-inductive inspection, an eddy current of high intensity is induced into the inspected material and the thermal response is detected using an infrared camera. Anomalies in the surface temperature during and after inductive heating correspond to inhomogeneities in the material. A finite element simulation of the surface crack detection process using active thermography with inductive heating has been developed. The simulation tool was tested and used for investigations on austenitic steel components with different longitudinal orientated cracks. The shape of the crack varies in the crack opening and the depth. The simulation model was based on the finite element programming software ANSYS. The suitability of the developed simulation of the inductive excited thermography for crack detection will be demonstrated by calculations and experiments. This paper focuses on longitudinal orientated cracks in austenitic steel, which are opened to the surface. The results show that depending on the shape of the crack the temperature distribution of the material under test made of austenitic steel is different. It will be shown how the crack size affects the temperature difference between the crack and the surrounding surface.
No other book on the market today can match the success of Halliday, Resnick and Walker's Fundamentals of Physics! In a breezy, easy-to-understand style the book offers a solid understanding of fundamental physics concepts, and helps readers apply this conceptual understanding to quantitative problem solving.
A simple sensor for magnetic flux leakage methods of detecting cracks on the surfaces of ferromagnetic pipes is proposed. We show that the crack position can be determined by the Fourier coefficients of the leakage magnetic flux density on a circle inside the pipe in the pipe cross-sectional plane. Coils that directly output the Fourier cosine and sine coefficients were made. The experimental results showed that, using only these two coils rather than dozens of magnetic sensors, the center position of a crack on the inside/outside surface of the pipe could be localized.
Attention is given to electrical and magnetic methods of nondestructive testing, with emphasis on the widely used eddy current and magnetic flux leakage methods (including particle inspection). Other techniques, such as MW and AC field applications, are also examined. Theoretical analyses relating to the various methods are discussed, with emphasis on electrical conductivity and resistivity, dielectric materials, electromagnetism, circuit networks, ferromagnetic materials, and electromagnetic radiation. Consideration is also given to eddy current principles and methods, as well as MW methods of testing.
Longitudinally submerged arc welded pipes for gas and oil transportation are subject to the most severe safety requirements. To further enhance the NDT process, EUROPIPE as a manufacturer of large diameter pipes for the oil and gas industry has invested in the digital X-ray inspection technology and herewith completely replaces the X-ray film. The new installation consists of two separate X-ray chambers in order to keep up with the production flow. In each chamber two digital detector arrays and two X-ray tubes are installed. This installation replaces three old X-ray chambers with twelve X-ray tubes. The installation is the result of long-term research and development in the field of X-ray testing. The installation is one of the first implementing this technology in an automated serial production of large diameter pipes.
In this paper, we present the details of a new optical technique to detect the defects present in a ferromagnetic material or component, using a ferrofluid emulsion. This new flux leakage probe consists of monodispersed ferrofluid confined between two thin transparent glass slides or in a cuvette and a white light source for illumination. By employing ferrofluid droplets of suitable size and surfactant concentration, one can qualitatively identify the region where the defect is located in the test specimen by visually observing a color change in the ferrofluid cell, in the vicinity of a crack or defect in the test specimen. The origin of this color change in the back scattering direction is due to Bragg scattering from the droplet chains, formed by the leaked magnetic flux in the presence of a defect. We discuss in detail the procedure, the merits and potential uses of this new technique for non-destructive testing and evaluation (NDT and E) applications.
The magnetic flux leakage (MFL) method is commonly used as an inspection technique in the petrochemical, transportation, energy and metal industries. This paper shows how the finite element method techniques can be utilized to model a MFL system. It compares the predicted MFL signals from 2D and 3D models and shows that a signal obtained from 2D models is much larger than 3D models, which is attributed to higher saturation level in the area of the defect in 2D models. This paper also presents the modeled leakage flux profile along the direction of the axial length of the excitation yoke length. It is considered that this technique will help in the calibration of the sensors that are used in MFL sensing systems.
The effect of corrosion under coatings on carbon steel is a complex mix of many factors, including electrical conductivity, magnetic permeability, surface roughness, and coating thickness variations, which all have to be taken into account when analysing the pulsed eddy current (PEC) response from corrosion. In this paper, the PEC nondestructive evaluation method has been applied to a set of mild steel plates with varying levels of corrosion and various surface preparations. The panels are exposed outdoors for the same time-period and then the surfaces prepared in different ways, resulting in four different corrosion grades in accordance with the surface preparation standards of the society for protective coatings. Using principal component analysis (PCA) on nonnormalized and normalized PEC response waveforms, the most dominant features are extracted and used to classify and characterize the samples. Normalization has been done in an attempt to mitigate the effects of magnetic permeability and lift-off variations across the samples. The distribution of the first principal component coefficients are then compared against other time-domain features of the PEC waveform to provide a physical explanation, and relate the changes to differences in the corrosion grade and other properties of the samples. Despite the complex nature of the samples, the results show that with the application of normalization and PCA, it is able to classify the samples into different corrosion grades.
This paper describes the induction-lockin-thermography (ILT) in non-destructive testing (NDT). The defect can be localised and its depth estimated by the phase and the module of the temperature in synchronic regime. Various sources of external energy can be used to excite the heat flux in examined object. In this work the electromagnetic induction is employed to heat the specimen. The interaction of the specimen with the induction stimulation is studied by using the axisymmetric magnetothermal model, which is solved by the finite element method (FEM). This study aims to detect the eventual defect by choosing both parameters, electromagnetic and thermal frequencies.
Magnetic flux leakage (MFL) test technology has been applied to the inspection of aboveground storage tank (AST) bottoms since the late 1980s, when it was demonstrated that corrosion in flat carbon steel tank floor plates up to 10 mm (0.4 in.) thick could be detected using MFL techniques. This article will discuss a method that combines eddy current and MFL methods into one test probe design. This design not only detects discontinuities on the top and bottom sides of the tank bottom, but also discriminates between them.
High‐precision magnetic field sensors are of increasing interest in non destructive testing (NDT). In particular GMR‐sensors (giant magneto resistance) are qualified because of their high sensitivity, high signal‐to‐noise ratio and high spatial resolution. With a GMR‐gradiometer and a 3D‐GMR‐magnetometer we performed magnetic flux leakage measurements of artificial cracks and cracks of a depth of
≤50 μ
m
still could be dissolved with a sufficient high signal‐to‐noise ratio. A semi‐analytic magnetic dipole model that allows realistic GMR
sensor characteristics to be incorporated is used for swiftly predicting magnetic stray fields. The reliable reconstruction based on measurements of artificial rectangular‐shaped defects is demonstrated.
The magnetic flux leakage (MFL) technique is proposed for condition monitoring of 64 mm-diameter steel track rope used for transporting coal. In this technique, two saddle coils are used for magnetisation of the rope and the tangential component of leakage magnetic flux from flaws is detected using a giant magnetoresistive (GMR) sensor and amplified selectively. The capability of this technique has been evaluated by detecting local flaws (LFs) and loss of metallic cross-sectional area (LMA) type defects introduced on the track rope. The technique is able to detect 2 mm-deep flaws with good signal-to-noise ratio and resolve flaws separated by more than 3.2 mm. Using the amplitude and full width at half maximum of the MFL signals, it is possible to classify axial and circumferential flaws in the track rope.
In the case of thermo-inductive testing the material is heated by induced eddy currents and the emission from the material surface is detected by an infrared camera. Anomalies in the surface temperature correspond to in-homogeneities in the material. Experiments show that for magnetic steel the edges of surface cracks become visible through higher temperatures. In contrast, in non-magnetic materials one observes lower temperatures around a surface crack. An analytical and a semi-analytical model are presented to calculate the eddy current distribution and the temperature distribution for different cases. Results for magnetic and non-magnetic materials are compared, showing how the temperature depends on the material parameters, on the penetration depth of the eddy current and on the crack depth. The comparison of the calculated and measured results shows a very good agreement. Additionally, some applications are presented, where the thermo-inductive testing method has been used in laboratory and in industrial environment.
A surface crack, close to a small, well-defined heated spot, impedes lateral heat flow and produces alterations in the shape of the thermal spot image that can be monitored by thermography. Spot heating has been achieved using both cw and pulsed laser beam illumination on stainless steel and titanium samples and the technique has been found to be successful for determining the location of fatigue cracks. When using a pulsed laser beam one can also simultaneously generate wideband ultrasonic signals in the sample; this can be used to detect the presence of surface and sub-surface defects in the sample. Results are presented that have been obtained using a fixed camera and cw laser beam position with the sample being moved through the field of view of the camera. Results are also presented using a fixed camera and sample, with a raster scanned cw or pulsed lasers beam moving across the sample. A demonstration of how a non-contact ultrasonic measurement can be performed simultaneously is presented. Thermal imaging results obtained using cw laser beam heating close to a surface crack are compared with predictions made using a preliminary 2D numerical model.
An analytical model was developed to determine the length of a surface-breaking defect along the direction of the applied field when using the magnetic flux leakage (MFL) non-destructive technique. The theoretical model fits the experimental MFL results from simulated defects. The extreme positions of the normal magnetic leakage field component were subsequently used for a quantitative evaluation of the defect length. Permeability variations were neglected by employing a flux density close to sample saturation. Four different defect geometries were experimentally investigated and the validity of the analytical model was verified. Good agreement between theoretical and experimental results suggests that this method can be used as an inverse MFL data interpretation technique.
Infrared thermography transforms the thermal energy, emitted by objects in the infrared band of the electromagnetic spectrum, into a visible image. This feature represents a great potentiality to be exploited in many fields, but this technique is still not adequately enclosed in industrial instrumentation because of a lack of adequate knowledge; at first sight, it seems too expensive and difficult to use. The aim of the present paper is to shortly overview existing work and to describe the most relevant experiences devoted to the use of infrared thermography in three main fields, i.e. thermo-fluid dynamics, technology and cultural heritage, which have been performed in the department the authors belong to. Results may be regarded from two points of view, either as validating infrared thermography as a full measurement instrument, or as presenting infrared thermography as a novel technique able to deal with several requirements, which are difficult to perform with other techniques. This study is also an attempt to give indications for a synergic use of the different thermographic methods and sharing experiences in the different fields.
Active (lock-in and pulsed) thermography technique is used to quantify defect features in specimens of glass fiber reinforced polymer, high density rubber, low density rubber and aluminum bonded low density rubber with artificially produced defects. The relationship between phase contrast and thermal contrast with defect features are examined. Using lock-in approach, the optimal frequencies for different specimens are determined experimentally. It is observed that with increasing defect depth, the phase contrast increases while the thermal contrast decreases. Defects with radius to depth ratio greater than 1.0 are found to be discernible. The phase difference between sound and defective region as a function of square root of excitation frequency for glass fiber reinforced polymer specimen is found to be in good agreement with the predictions of Bennet and Patty model [1]. Further, using pulsed thermography, the defects depth could be measured accurately for glass fiber reinforced polymer specimen from the thermal contrast using the analytical approach of Balageas et al. [2].
The article shows the digital image analysis of X-ray and neutron radiography (NR) ad hoc developed for the inspection and monitoring of nuclear samples, used in several experiments at the High Flux Reactor of the Institute for Energy (JRC-Petten). This application is valuable not only in the characterization of the sample and of the experimental assembly, but also in acquiring information on the sample behaviour during and after the irradiation.The inspection foresees the X-ray radiography of the sample in order to detect the eventual presence of fabrication defects. During and/or after the irradiation, NR helps to understand the sample behaviour under irradiation (such as swelling, disintegration). NR can also be performed before the irradiation for comparison with NR during the irradiation and with the X-ray.The image analysis is used for acquiring qualitative and quantitative information from these inspection techniques at a high level of accuracy.
Lock-in thermography, an active IR thermography technique for NDT, is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. In this paper, thermal wave image sequences were sampled by a Cedip JADE MWIR 550 FPA infrared camera. Thermal wave signal processing algorithms are investigated to obtain information on subsurface defects. The Fourier transform, four-point correlation, and digital lock-in correlation algorithms are applied to extract the amplitude and phase of thermal wave’s harmonic component. A novel method called the time constant method (TCM) is proposed to analyze subsurface defects by using lock-in thermography. The experimental results confirm the thermal wave signal processing algorithms’ efficiency on subsurface defect detection.
This work presents a new method for indirect identification of sectors with high current density concentration in planar microwaves devices. The method consists in the use of infrared thermography (IRT) to determine the superficial two-dimensional temperature field of the device. The results agree well with those obtained with the method that makes use of electromagnetic (EM) simulation using commercial software of numerical analysis.
Surface‐breaking tight fatigue cracks in mild steel have been examined with laser‐generated ultrasonic pulses. Before the arrival of transmitted Rayleigh waves arriving at the detector, evidence is presented of a fast skimming longitudinal pulse which is also transmitted through the crack. Additionally, another ultrasonic feature is consistent with a longitudinal wave which is mode converted to a diffracted shear pulse by the tip of the fatigue crack. Such an interaction mechanism can form the basis of laser‐based fatigue crack depth measurements.
India has a moderate uranium reserve and a large thorium reserve. The primary energy resource for electricity generation in the country is coal. The potential of other resources like gas, oil, wind, solar and biomass is very limited. The only viable and sustainable resource is the nuclear energy. Presently, Pressurised Heavy Water Reactors utilizing natural uranium are in operation/under construction and the plutonium generated from these reactors will be multiplied through breeding in fast breeder reactors. The successful construction, commissioning and operation of Fast Breeder Test Reactor at Kalpakkam has given confidence to embark on the construction of the Prototype Fast Breeder Reactor (PFBR). This paper describes the salient design features of PFBR including the design of the reactor core, reactor assembly, main heat transport systems, component handling, steam water system, electrical power systems, instrumentation and control, plant layout, safety and research and development.
Non-contact ultrasonic measurements have been made on ferritic and austenitic steel specimens as a function of temperature from ambient to 1200°C, using a pulsed laser to generate and a reference beam laser interferometer to receive the ultrasound. The generation efficiency is found to remain surprisingly constant in both thermoelastic and ablation regimes over a wide temperature range. The sensitivity of the laser interferometer is also found to be temperature independent to a first approximation. However, it is typically reduced by 3–6 dB by convection currents above ∼ 900°C. Both the compression and shear velocities decrease with rising temperature. The former is measured with a precision of 1 in 103, the latter rather less accurately with the present configuration. Compression wave attenuation increases steadily below 600°C in both materials. There is a peak in attenuation in ferritic steel between 600 and 750°C, which is absent in austenitic steel. It coincides with a steeper decrease in ultrasonic velocity and is believed to be due to the martensitic structural phase transformation.The attenuation rose more rapidly in both materials as 1000°C was approached. The material attenuation varied with heat treatment, a value in the range 1–1.5 dB cm−1 being recorded at 1000°C. Complicated effects were observed during heat treatments at 1000°C and above. Both attenuation and forward scattering data were consistent with some annealing out of sub-structure, in addition to austenitic grain growth. Finally, there was evidence of lattice softening at the highest temperatures investigated. The data suggest that thicknesses of steel in the range 100–250 mm should be inspectable with a scaled-up system, depending upon various factors such as the presence of oxide scale, provided high power lasers are employed for generation and reception and an optimum bandwidth is chosen.
In this paper, fundamental theory of the pulsed phase thermography (PPT) processing method is presented including notes on thermal waves, pulsed thermography and lockin thermography. Moreover, advances in signal inversion for PPT using wavelets are included along with discussions about pulse shaping and polynomial fitting for signal improvement (synthetic data). Results are presented as well.
In this paper we present a study of case of determination of material properties using information from the surface temperature distribution obtained by infrared thermography. Two samples are used for the study: one in gypsum plaster and another with a hidden included steel cylinder. Both samples are heated to 120 °C and their surface temperature distributions are recorded while they are left to be cooled by natural convection in a 30 °C ambient. A simple numerical model is used in order to simulate the transient phenomenon. The parameters are determined by minimizing the deviation between the numerical and experimental results. First the parameters of the gypsum plasterboard are obtained from the information of the plain gypsum plaster sample and after the parameters of the steel inclusion are obtained from the data from the sample with the hidden inclusion. The following parameters are obtained: thermal conductivity and thermal capacity of the gypsum plaster; thermal capacity, radius, position and height of the steel cylinder. During all the presentation we discuss extensively on the particularities of the method when used in this chosen pair of materials. The last section is devoted to summarize the results and discussions.
Theory and Practice of Infrared Technology for Nondestructive Testing
- X Maldague
X. Maldague, Theory and Practice of Infrared Technology for Nondestructive
Testing, 1st ed., Wiley Interscience, 2001.
Tone burst eddy current thermography (TBET) for NDE applications
- C V Krishnamurthy
- K Balasubramaniam
- N Biju
- M Arafat
- N Ganesan
C.V. Krishnamurthy, K. Balasubramaniam, N. Biju, M. Arafat, N. Ganesan, Tone
burst eddy current thermography (TBET) for NDE applications, in: National
Seminar & Exhibition on Non-Destructive Evaluation, Trichy, India, 2009, pp.
328-335.
Nondestructive inspection by the method of magnetic flux leakage fields
- F Forster
F. Forster, Nondestructive inspection by the method of magnetic flux leakage
fields, Defektoskopia 11 (1982) 3-25.