Absolute Probe Research Articles

Effect of Metallic Coating Thickness on Stainless Steel and Carbon Steel Welded Plate Using Eddy Current Testing

Over the last few decades, steel has seen a sharp increase in utilisation. Non-destructive testing (NDT) methods still face difficulties when attempting to identify corrosion behind coatings. One of these difficulties is the lift-off that complex structures bring. Because of the structure’s obstruction, corrosion goes undetected and can cause catastrophic breakdown. Additionally, lift-off effects lessen the sensitivity. On this paper the effect of coating thickness was measure by using metallic coating at carbon steel and stainless steel plates. The effect of coating thickness being identify based on measurement changes with different layer of coating thickness. From here the absolute and differential probe were used in measuring the lift-off because of coating thickness and the defect value. According on the result show that the Length of the crack at Toe, Root and Heat Affected Zone (HAZ) will reduce from 2.6% until 38.5% for carbon steel and 2.6% until 48.7% for stainless steel when the thickness of coating was increased. It different with Datum measurement where on carbon steel it increases from 0% until 11.5% and stainless steel 0.7% until 6%. Lastly the effect of coating thickness more effecting on defect measurement either carbon steel or stainless steel and artificial intelligent should be apply on each measurement for finding the right data getting in measurement as recommended.

Eddy Current Testing Methods and Design for Pipeline Inspection System: A Review

Non-destructive testing and complex systems integration are commonly used in transportation, aircraft, automotive, manufacturing, petrochemical, and defence. Eddy current testing (ECT) is a common non-destructive evaluation technique, especially in the coating, nuclear, and oil and gas industries. However, the eddy current testing method must continue to focus on the probe’s construction and application. It ascribed noisy data to inadequate detection and a severe false alarm problem. Nonetheless, only few academics have elaborated on the intelligent ECT crack detection method. This study provides an overview of the eddy current testing technique and the probe structure design elements that influence fracture detection accuracy. The first section describes the Eddy current testing by encircling coil system for a differential probe (ECDP) and an encircling coil for an absolute probe design (ECDP). The explanations focus mostly on the probe’s creation and detection in Rotating electromagnetic field eddy current (RoFEC). The advantages and disadvantages of eddy current testing surrounding probes are analysed. In addition, a summary of prior studies investigating testing samples of ferromagnetic pipe, steel rod, and wire rope is presented. The second segment focuses on Eddy current testing employing a Giant Magnetoresistance (GMR) sensor system, with a particular emphasis on sensor arrays, GMR, and conventional eddy current coils for crack identification. Finally, a comprehensive overview of eddy current testing methods and design for non-destructive pipeline inspection systems is presented.

Effect of Single and Multi-Direction Coil for Differential Probe on Depth Crack Defect Measurement with Different Excitation Frequency Selection in Eddy Current Inspection

In recent years, a number of studies in Non-Destructive Evaluation (NDE) have been conducted on the sensitivity of probes in assessing the depth of cracks based on input stimulation. Range frequency and crack depth have been suggested as relevant features for input excitation waveform forms. The construction of an encircling coil for a differential probe (ECDP) and an encircling coil for an absolute probe (ECAP) was discussed in this paper. For the defect, the Multi-Frequency (MF) measuring method was used to compare ECDP with single direction and multi-direction turn coil growth. The measurement method was based on the coupling of ECDP and ECAP. By comparing the resulting signal between the probes, it is clear that the ECDP (with longitudinal and transverse coils) is very effective in measuring the various types of defects in the frequency ranges. The ideal excitation frequencies for inspection testing are 30kHz and 60kHz.

Non-Destructive Testing Using Eddy Current Sensors for Defect Detection in Additively Manufactured Titanium and Stainless-Steel Parts.

In this study, different eddy-current based probe designs (absolute and commercial reflection) are used to detect artificial defects with different sizes and at different depths in parts composed of stainless-steel (316) and titanium (TI-64) made by Laser Additive Manufacturing (LAM). The measured defect signal value using the probes is in the range of (20–200) millivolts. Both probes can detect subsurface defects on stainless-steel samples with average surface roughness of 11.6 µm and titanium samples with average surface roughness of 8.7 µm. It is found the signal reading can be improved by adding a coating layer made of thin paper to the bottom of the probes. The layer will decrease the surface roughness effect and smooth out the detected defect signal from any ripples. The smallest subsurface artificial defect size detected by both probes is an artificially made notch with 0.07 mm width and 25 mm length. In addition, both probes detected subsurface artificial blind holes in the range of 0.17 mm–0.3 mm radius. Results show that the absolute probe is more suitable to detect cracks and incomplete fusion holes, whereas the reflection probe is more suitable to detect small diameter blind holes. The setup can be used for defect detection during the additive manufacturing process once the melt pool is solidified.

Simulation Analysis of Eddy Current Testing Parameters for Surface and Subsurface Defect Detection of Aviation Aluminum Alloy Plate

In the process of eddy current testing (ECT) of surface and subsurface defects of aviation aluminum alloy plates, the setting of parameters is important to the test results. Inappropriate test parameters can cause false detection or even missed detection of defects. To address this problem, the effects of probe type, coil size, and excitation frequency on the accurate identification and quantitative evaluation of surface and subsurface defect detection were studied and analyzed in this study to determine the best testing parameters. The experimental results show that the absolute probe with an outer radius of 3.3 mm has better detection performance for aviation aluminum alloy plate defects. There are different optimal excitation frequency ranges for the surface and subsurface defects. An excitation frequency of 80 kHz to 90 kHz can be used for the detection of unknown defects.

Detection of delamination defects inside carbon fiber reinforced plastic laminates by measuring eddy-current loss

Carbon fiber reinforced plastics are likely to experience delamination due to the heterogeneity and anisotropy of the materials. However, the through-thickness conductivity of CFRPs is low, resulting in a weak output signal and large amounts of noise interference of eddy current testing in the detection of delamination. Based on the eddy-current loss theory, a method is proposed to detect delamination inside CFRPs. The method consists of an absolute probe with an 8-shaped coil and a unique signal extraction technique using eddy-current loss. The 8-shaped coil of the proposed probe enables the probe to generate a sufficiently strong vertical eddy-current component at its geometric center. The eddy-current loss on CFRPs is extracted by the parallel inductor-capacitor resonance circuit and micro-power detection module. The experiments show that the sensitivity of the vertical 8-shaped probe to the delamination detection is higher than that of the circular and square probes. Compared with ECT, the proposed method by measuring eddy-current loss for delamination has a lower frequency and less noise. In addition, this paper further explores the application of the proposed method in automatic defect detection. The results show that the proposed method can be effectively applied to the automatic detection and visualization of delamination inside CFRPs.

Correlation of eddy current signals obtained from EDM notches and fatigue cracks

For calibration of eddy current testing, artificial defects are commonly used by virtue of its simple production and ease control of geometric parameters. However, such defects are significantly different in terms of geometric aspects from real ones, even with a precise control of the manufacturing process. To ensure reliable calibration results, it is mandatory to establish a relationship between the signals from artificial (machined) and real defects. This work exposes a detailed study correlating eddy current signals from electrical discharge machine notch (EDM notch) and fatigue cracks. To perform the tests an absolute pencil probe was used. Although there is a significant difference between the signals of EDM notch and fatigue cracks, the results show that it is possible to use artificial defects to represent fatigue cracks reliably if a proper correction is implemented.

Control of Probe Density at DNA Biosensor Surfaces Using Poly(l-lysine) with Appended Reactive Groups.

Biosensors and materials for biomedical applications generally require chemical functionalization to bestow their surfaces with desired properties, such as specific molecular recognition and antifouling properties. The use of modified poly(l-lysine) (PLL) polymers with appended oligo(ethylene glycol) (OEG) and thiol-reactive maleimide (Mal) moieties (PLL-OEG-Mal) offers control over the presentation of functional groups. These reactive groups can readily be conjugated to, for example, probes for DNA detection. Here we demonstrate the reliable conjugation of thiol-functionalized peptide nucleic acid (PNA) probes onto predeposited layers of PLL-OEG-Mal and the control over their surface density in the preceding synthetic step of the PLL modification with Mal groups. By monitoring the quartz crystal microbalance (QCM) frequency shifts of the binding of complementary DNA versus the density of Mal moieties grafted to the PLL, a linear relationship between probe density and PLL grafting density was found. Cyclic voltammetry experiments using Methylene Blue-functionalized DNA were performed to establish the absolute probe density values at the biosensor surfaces. These data provided a density of 1.2 × 1012 probes per cm2 per % of grafted Mal, thus confirming the validity of the density control in the synthetic PLL modification step without the need of further surface characterization.

A Novel Eddy Current Testing Error Compensation Technique Based on Mamdani-Type Fuzzy Coupled Differential and Absolute Probes.

Eddy current testing (ECT) is an accurate, widely used and well-understood inspection technique, particularly in the aircraft and nuclear industries. The coating thickness or lift-off will influence the measurement of defect depth on pipes or plates. It will be an uncertain decision condition whether the defects on a workpiece are cracks or scratches. This problem can lead to the occurrence of pipe leakages, besides causing the degradation of a company’s productivity and most importantly risking the safety of workers. In this paper, a novel eddy current testing error compensation technique based on Mamdani-type fuzzy coupled differential and absolute probes was proposed. The general descriptions of the proposed ECT technique include details of the system design, intelligent fuzzy logic design and Simulink block development design. The detailed description of the proposed probe selection, design and instrumentation of the error compensation of eddy current testing (ECECT) along with the absolute probe and differential probe relevant to the present research work are presented. The ECECT simulation and hardware design are proposed, using the fuzzy logic technique for the development of the new methodology. The depths of the defect coefficients of the probe’s lift-off caused by the coating thickness were measured by using a designed setup. In this result, the ECECT gives an optimum correction for the lift-off, in which the reduction of error is only within 0.1% of its all-out value. Finally, the ECECT is used to measure lift-off in a range of approximately 1 mm to 5 mm, and the performance of the proposed method in non-linear cracks is assessed.

A portable embedded contactless system for the measurement of metallic material conductivity and lift-off

This paper describes the development, implementation and characterization of a portable embedded measurement system for the contactless estimation of a metallic material conductivity and of the lift-off between the system probe and the metallic material surface. The system consists on an absolute probe with compensation and is capable of measuring the in-phase and in-quadrature components of the probe output voltage using as a reference the probe stimulus voltage. The stimulus module includes a direct digital synthesizer (DDS) to set the measurement frequency, while the acquisition module includes analog voltage amplification and analog-to-digital conversion. A microcontroller is used to control the measurement, process the acquired voltage samples, estimate the desired parameters and perform USB communication. The final dimensions of the pen-like system, its capability of communication with a smartphone and its ability to power the system from the smartphone make it highly portable and especially suited for non-destructive testing (NDT) and field measurements.

Is carbonyl index a quantitative probe to monitor polypropylene photodegradation?

For several decades, authors relied upon the carbonyl index to monitor the photo-oxidation of polypropylene and to account for the degradation of the mechanical properties. This paper starts from one question: is the carbonyl band at 1712 cm−1 in infrared spectroscopy really appropriate to quantitatively measure the extent of oxidation of polypropylene? This article brings a negative answer to this question, and the results given in this paper suggest that carbonyl detection by infrared spectroscopy, despite it has been used for years, is not the absolute probe to monitor the photooxidation of polypropylene. Hence, the article aims to provide new relevant and quantitative criteria. These criteria allow the photo-oxidation of PP to be correlated with properties degradation, the one of interest in this case being the gloss loss, which reflects the loss of the surface mechanical properties. These criteria give an early warning of the degradation and permit anticipating the loss of polypropylene functional properties. There are various criteria that can be proposed, the methyl band at 1456 cm−1 being the easiest way to measure the oxidation. It is shown that the modifications of the methyl absorbance fit quite well the increase of crystallinity, molecular weight, and it quite-well reflects the micro-hardness, this last parameter being well correlated to the loss of gloss.

Optimisation of pulsed eddy current probe for detection of sub-surface defects in stainless steel plates

Pulsed eddy current (PEC) technique is used for the detection of sub-surface defects in electrically conducting materials. In order to extend the application of PEC technique for the detection of defects in thick non-magnetic materials, the detection sensitivity of the probe need to be enhanced. Detection sensitivity of the probe mainly depends on the probe configuration. In view of this, optimisation of probe configuration for deeper penetration of magnetic field in the material is carried out through finite element modelling. Present study focuses on model based design optimisation of PEC probe for the detection of sub-surface defects located more than 4mm from surface in a 8mm thick AISI type 316 stainless steel plate. The performance of ferrite cored absolute probe, ferrite cored send-receive probe and ferrite cored send-receive probe with outer shielding has been compared and optimised probe has been fabricated. The detection sensitivity of the optimised probe has been studied using machined notches introduced at different depths.

Evaluating the III-Posedness of Inverse Problem to Size Flaws from Eddy Current NDT Signals Obtained with an Absolute Type Probe

This study discusses the applicability of eddy current testing to the non-destructive evaluation of the depth of a flaw. Three-dimensional finite element simulations are carried out to calculate eddy current signals due to a flaw, and subsequent calculations correlate the difference between signals due to two flaws with the difference between the depths of the flaws. Standard deviation of the difference between the depths of the flaws is used to discuss the ill-posedness of the problem. A flaw is modeled as a sufficiently long rectangular region with a constant width and uniform electrical conductivity; an absolute pancake probe is considered. This study reveals that lift-off and coil diameter do not have a large effect on the ill-posedness, which supports that it is reasonable to decide parameters in actual inspections so that signal-to-noise ratio is maximized. The results obtained also indicate the difficulty in evaluating the depth of a flaw deeper than 1 mm using the signals obtained using an absolute pancake probe.

Near electrical resonance signal enhancement (NERSE) in eddy-current crack detection

An investigation was performed into the effects of operating an absolute eddy-current testing (ECT) probe at frequencies close to its electrical resonance. A previously undocumented defect signal enhancement phenomenon, resulting from associated shifts in electrical resonant frequency, was observed and characterized. Experimental validation was performed on three notch defects on a typical aerospace superalloy, Titanium 6Al–4V. A conventional absolute ECT probe was operated by sweeping through a frequency range about the electrical resonance of the system (1−5MHz). The phenomenon results in signal-to-noise ratio (SNR) peak enhancements by a factor of up to 3.7, at frequencies approaching resonance, compared to those measured at 1MHz. The defect signal enhancement peaks are shown to be a result of resonant frequency shifts of the system due to the presence of defects within the material. A simple, operational approach for raising the sensitivity of conventional industrial eddy-current testing is proposed, based on the principles of the observed near electrical resonance signal enhancement (NERSE) phenomenon. The simple procedural change of operating within the NERSE frequency band does not require complex probe design, data analysis or, necessarily, identical coils. Therefore, it is a valuable technique for improving sensitivity, which complements other ECT methods.

Evaluation of the electromagnetic characteristics of type 316L stainless steel welds from the viewpoint of eddy current inspections

This study evaluated the electromagnetic characteristics of austenitic stainless steel welds from the viewpoint of eddy current testing. Seven welded plate specimens, which were welded using JIS Z3221:2010 YS316L welding metals, were prepared. Two welding metals and several welding conditions were adopted to discuss the generality. The results of eddy current examination of the specimens using three different types of eddy current probes, that is, an absolute pancake probe, a differential plus-point probe, and a uniform eddy current probe, confirmed that the welds cause a large noise especially when the absolute pancake probe was used. The analysis of the signals through finite element simulations revealed that the magnetic property of the welds is not negligible from the viewpoint of eddy current testing. Complementary experiments were conducted using a vibrating sample magnetometer to validate the results.

Model Based Capability Assessment of an Automated Eddy Current Inspection Procedure on Flat Surfaces

The probability of detection (POD) of a well-controlled, automated eddy current (EC) procedure is evaluated in a numerical model and compared with experiments. The procedure is applied in laboratory environment with a single absolute probe which is positioned for raster scan over flat surfaces containing fatigue cracks. The variability of the signal amplitude, due to small fatigue cracks in the Titanium alloy Ti-6Al-4 V, is expected to mainly originate from crack characteristics and the index distance of the raster scan. The POD model is based on the signal versus crack size ( versus a) result. The presented procedure provides a well-defined basis for a comparison between a simulated and an experimentally based POD assessment. Finite element analysis is used to model the EC method. A simplified fatigue crack model is first introduced and evaluated experimentally. Numerical computations are then used to build the corresponding model-based POD curve which shows good agreement with the experimental result. The model-based POD curve is generated both by means of a parametric and a nonparametric approach. Differences between model-based and experimental POD are discussed as well as the delta POD approach using transfer functions.

A LabVIEW-based virtual instrument for simulation and analysis of SECM approach curves

We have developed a LabVIEW virtual instrument (PAC_Fit.vi) for efficient simulation and analysis of probe approach curve data from a scanning electrochemical microscope (SECM). The virtual instrument (VI) is available for free download and can be used to determine absolute probe height above a substrate, measure rate constants for irreversible electron transfer at a substrate, and perform simulations of SECM approach curves. We anticipate the VI will be of use for educational purposes as well, perhaps as a classroom tool for introducing the principles of SECM. We have applied the VI to an analysis of the dynamic nature of an aluminum alloy (AA2024-T3) substrate immersed in acid solution in which the activity of the substrate increases over time due to dissolution of the passive oxide layer. The value of kapparent is observed to increase by a factor of 40 over an immersion time of approximately 1 h.

Absolute Probe of Surface Chirality Based on Focused Circularly Polarized Light

We present a new nonlinear optical technique to probe chirality, i.e., lack of reflection symmetry, of surfaces and thin molecular films. The technique is based on second-harmonic generation and focusing of circularly polarized light at normal incidence on the sample. Because of the high symmetry of the experimental arrangement, the technique provides an unambiguous probe of chirality in the sense that it avoids false chiral signatures arising from possible in-plane anisotropy of the sample. The technique is verified by using two Langmuir−Blodgett thin films, one chiral and anisotropic, the other achiral and anisotropic, where the latter acted as a reference. Due to the focusing condition, the technique is also naturally applicable to nonlinear chiral microscopy of surfaces and interfaces.

A coupled fictitious electric circuit's method for impedance of a sensor with ferromagnetic core calculation. Application to eddy currents non destructive testing

The eddy current testing method is widely used to evaluate conductive pieces. This method requires an adequate mathematical model which is able to describe the complicated interactions between the source and induced currents, primary and secondary, the fields and the flaws in materials. This paper describes a model which predicts the apparent changes in the impedance of an absolute ferrite-cored probe in axially symmetric non destructive testing (NDT) configurations. Originally, this model is based on coupled electromagnetic quantities principle. To include the contribution of the magnetic environment, the state variable chosen is the current because the magnetic magnetization is replaced by the fictional equivalent currents. The obtained modelling results are validated by comparison to finite element computations. Once validated, the suggested model is not only applied to calculation of probe's impedance in the presence of a defect inside the load but it is also applied to determine geometrical and physical characteristics of the eddy current non destructive testing (ECNDT) device. This half-numerical technique with a very weak time of simulation can be used for the design of new probes and offers a simple solution to the inversion problem. The model is implemented within a software tool (CECM: coupling electromagnetic circuits method) developed in MATLAB environment.

Local Tuning of Conductivity in Amorphous Titanium Oxide Films by Selective Electron Beam Irradiation

Amorphous TiO2 (a-TiO2) films electrodeposited on steel substrates have recently been found highly e-beam sensitive, allowing for reduction and crystallization with high lateral resolution. We here report on the strong correlation between the e-beam-induced changes in oxidation state and film structure, as observed by transmission electron microscopy and Micro-Raman spectroscopy, and the local film conductivity (σ), measured by conductive atomic force microscopy (c-AFM). c-AFM at constant applied potentials reveals a low σ of 1.9 × 10-4 Ω-1 cm-1 for a-TiO2 and a further decrease of σ by up to a factor 5.5 × 10-3 at locally reduced spots, rather than an enhancement in conductivity consistently reported in literature upon reduction of crystalline TiO2. However, σ significantly rises with the first appearance of anatase phase in micro-Raman spectra, and makes a second large jump coinciding with the formation of TiO, with σ being 2 × 10+4 times higher than in the surrounding a-TiO2. We further observe a rectifying effect due to the presence of micrometer-sized anatase/steel Schottky barrier diodes at locally crystallized spots. The absolute probe current rather than the current density is found responsible for e-beam-induced crystallization, underlining the thermal nature of crystallization at electron energies disqualifying atomic displacement. Structural changes are strictly limited to the irradiated area with anatase nanocrystals being extended nearly throughout the 60 nm thick film, not showing preferential orientation. The results demonstrate the possibility of e-beam-induced confined tuning of σ in the amorphous oxide film in both directions. This observation is novel and will allow for high-resolution patterning of electrical properties in amorphous semiconducting oxides.