Reduction of Coil-Crack Angle Sensitivity Effect Using a Novel Flux Feature of ACFM Technique

Alternating current field measurement (ACFM) testing is one of the promising techniques in the field of non-destructive testing with advantages of the non-contact capability and the reduction of lift-off effects. In this paper, a novel crack detection approach was proposed to reduce the effect of the angled crack (cack orientation) by using rotated ACFM techniques. The sensor probe is composed of an excitation coil and two receiving coils. Two receiving coils are orthogonally placed in the center of the excitation coil where the magnetic field is measured. It was found that the change of the x component and the peak value of the z component of the magnetic field when the sensor probe rotates around a crack followed a sine wave shape. A customized accelerated finite element method solver programmed in MATLAB was adopted to simulate the performance of the designed sensor probe which could significantly improve the computation efficiency due to the small crack perturbation. The experiments were also carried out to validate the simulations. It was found that the ratio between the z and x components of the magnetic field remained stable under various rotation angles. It showed the potential to estimate the depth of the crack from the ratio detected by combining the magnetic fields from both receiving coils (i.e., the x and z components of the magnetic field) using the rotated ACFM technique

Advances in Potential Drop Techniques for Non-Destructive Testing

In the field of Non-Destructive Testing, Potential Drop (PD) techniques have been used for decades, especially in the petrochemical and power generation industries, for monitoring crack growth and wall thickness variations due to corrosion and/or erosion in pipes, pressure vessels and other structures. Inspection is carried out by injecting currents in the specimen to be tested and measuring the arising electrical potential di erence between two or more electrodes placed on its surface. The presence of a defect generally increases the resistance and hence the measured voltage drop; inversion of these data can give information on the size and shape of the defect. However, while the principle underlying these techniques is relatively simple, some di culties have been encountered in their practical applications. Many commercial systems based on PD methods, for instance, require the injection of very large currents in order to obtain su ciently large signals; doubts have been raised on the stability of these methods to variations in the contact resistance between the electrodes and the inspected material. The present work aims to show that some of these problems can be easily overcome, and to evaluate the capabilities of PD techniques for crack sizing and corrosion mapping. After a brief review of the advantages, disadvantages and applications of the main electromagnetic methods for Non-Destructive Testing, an experimental setup for Potential Drop measurements which was developed for this work and which uses small alternating currents (AC) is described. The setup is benchmarked against existing PD systems and then used to validate a model that allows AC PD simulations to be run with a commercial Finite Element code. The results of both numerical simulations and experimental measurements are used to investigate the possibility of sizing defects of complex geometry by repeating the analysis at several di erent frequencies over a broad range, and of reconstructing the depth pro le of surfacebreaking defects without the need for assumptions on their shape. Subsequently, the accuracy to which it is possible to obtain maps of corrosion/erosion on the far surface of an inspected structure is discussed, and results obtained with an array probe that employs a novel arrangement of electrodes are presented. Finally, conclusions are drawn and suggestions for further research are made

Challenges in improving the performance of eddy current testing: Review

Eddy current testing plays an important role in numerous industries, particularly in material coating, nuclear and oil and gas. However, the eddy current testing technique still needs to focus on the details of probe structure and its application. This paper presents an overview of eddy current testing technique and the probe structure design factors that affect the accuracy of crack detection. The first part focuses on the development of different types of eddy current testing probes and their advantages and disadvantages. A review of previous studies that examined testing samples, eddy current testing probe structures and a review of factors contributing to eddy current signals is also presented. The second part mainly comprised an in-depth discussion of the lift-off effect with particular consideration of ensuring that defects are correctly measured, and the eddy current testing probes are optimized. Finally, a comprehensive review of previous studies on the application of intelligent eddy current testing crack detection in non destructive eddy current testing is presented

Investigation into the detection and classification of defect colonies using ACFM Technology

A research project was undertaken to provide insight into the use of Alternating Current Field Measurement (ACFM) technology for the detection and classification of transgranular stress corrosion cracking (TGSCC) plaguing Canada's oil and natural gas transmission pipelines. Work was conducted using a series of machined defects and natural TGSCC samples. The results suggest that ACFM warrants further investigation in a larger scale project. Guidelines for future endeavors are provided. -- Of the 63 machined defects, used in 21 colony configurations, visual inspection identified all of the defects and an automated computer algorithm missed only one. The data set was not large enough to develop a sizing algorithm but provided valuable insight into defect signal interactions. -- Present ACFM technology is capable of detecting natural SCC colonies, but more work is required before individual crack classification can be achieved when the cracks appear in clusters

A Feasibility Study on Advanced Nondestructive Evaluation (NDE) Methods to Characterize Weld Defects in Railroad Tank Cars

DTFR53-11-D-00008LUnder the sponsorship and support of the Federal Railroad Administration (FRA), Transportation Technology Center, Inc. (TTCI), with participation from the original equipment manufacturer (OEM) of advanced nondestructive evaluation (NDE) equipment, NDE service providers, and other research institutions, conducted a feasibility study of applying advanced NDE methods to detect and characterize weld defects in railroad tank cars. Researchers evaluated the performance/capability of various state-of-the-art advanced NDE techniques for fatigue crack detection and characterization in railroad tank car butt welds and fillet welds. The team determined that advanced NDE methods could detect toe fatigue cracks with acceptable signal-to-noise ratio (SNR) while demonstrating challenges with accurate flaw sizing. Further, based on the false positive results obtained from this study, the team found that detailed attention and efforts are required to reduce the false positive rat

Investigation of wireless power transfer-based eddy current non-destructive testing and evaluation

PhD ThesisEddy current testing (ECT) is a non-contact inspection widely used as non-destructive testing and evaluation (NDT&E) of pipeline and rail lines due to its high sensitivity to surface and subsurface defects, cheap operating cost, tolerance to harsh environments, and capability of a customisable probe for complex geometric surfaces. However, the remote field of transmitter-receiver (Tx-Rx) ECT depends on the Tx-Rx coils gap, orientation, and lift-off distance, despite each coil responding to the effect of sample parameters according to its liftoff distance. They bring challenges to accurate defect detection and characterisation by weakening the ECT probe’s transfer response, affecting sensitivity to the defect, distorting the amplitude of the extracted features, and responding with fewer feature points at non-efficient energy transfer. Therefore, this study proposed a magnetically-coupled resonant wireless power transfer (WPT)-based ECT (WPTECT) concept to build the relationship between Tx-Rx coil at maximum energy transfer response, including shifting and splitting (resonance) frequency behaviour. The proposed WPTECT system was investigated in three different studies viz., (1) investigated the multiple resonance point features for detection and characterisation of slots on two different aluminium samples using a series-series (SS) topology of WPTECT; (2) mapped and scanned pipeline with a natural dent defect using a flexible printed coil (FPC) array probe based on the parallel-parallel (PP) topology of WPTECT; and (3) evaluated five different WPTECT topologies for optimal response and extracted features and characterised entire parameters of inclined angular Rolling Contact Fatigue (RCF) cracks in a rail-line material via an optimised topology. Multiple feature extraction, selection, and fusion were evaluated for the defect profile and compared in the study, unattainable by other ECT methods. The first study's contribution investigated multiple resonances and principal component analysis (PCA) features of the transfer response from scanning (eight) slots on two aluminium samples. The results have shown the potential of the multiple features for slot depth and width characterisation and demonstrated that the eddy-current density is highest at two points proportionate to the slot width. The second study's contribution provided a larger area scanning capability in a single probe amenable to complex geometrical structures like curvature surfaces. Among the extracted individual and fused features for defect reconstruction, the multi-layer feed-forward Deep learning-based multiple feature fusion has better 3D defect reconstruction, whilst the second resonances feature provided better local information than the first one for investigating pipeline dent area. The third study's contribution optimised WPTECT topology for multiple feature points capability and its optimal features extraction at the desired lift-off conditions. The PP and combined PP and SS (PS-PS) WPTECT topologies responded with multiple resonances compared to the other three topologies, with single resonance, under the same experimental situation. However, the extracted features from PS-PS topology provided the lowest sensitivity to lift-off distances and reconstructed depth, width, and inclined angle of RCF cracks with a maximum correlation, R2 -value of 96.4%, 93.1%, and 79.1%, respectively, and root-mean-square-error of 0.05mm, 0.08mm, and 6.60 , respectively. The demonstrated magnetically-coupled resonant WPTECT Tx-Rx probe characterised defects in oil and gas pipelines and rail lines through multiple features for multiple parameters information. Further work can investigate the phase of the transfer response as expected to offer robust features for material characterisation. The WPTECT system can be miniaturised using WPT IC chips as portable systems to characterise multiple layers parameters. It can further evaluate the thickness and gap between two concentric conductive tubes; pressure tube encircled by calandria tube in nuclear reactor fuel channels.PTDF Nigeri

Alternating current potential drop and eddy current methods for nondestructive evaluation of case depth

Case hardening treatments offer a means of enhancing the strength and wear properties of parts made from steels. Generally applied to near-finished components, the processes impart a high-hardness wear-resistant surface which, with sufficient depth, can also improve fatigue strength. Applications range from simple mild steel pressings to heavy-duty alloy-steel transmission components. The characteristics of case hardening are the surface hardness, effective case depth, and depth profile of the residual stress. The specified case depth varies for different applications. It is useful to be able to measure the case depth nondestructively to ensure the specification is met.;In the work outlined in this dissertation, the aim is to evaluate the properties of case hardened parts nondestructively. The case hardening process produces a change in the electromagnetic properties of the steel components in the near surface region. Consequently, the electrical conductivity and magnetic permeability have different values near the surface compared with those of the substrate. It is assumed that the conductivity and permeability variation with depth is indicative of the hardness profile allowing the case depth to be estimated from electromagnetic measurements. A two-layer model is adopted to approximate the case hardened steel parts as a homogeneous substrate layer surrounded by a homogeneous surface layer with uniform thickness. Alternating current potential drop (ACPD) theoretical calculations have been performed and compared with experimental measurements for both case hardened cylindrical rods and homogeneous metal plates. Driver and pick-up coils have been used for eddy current induction measurements on the cylindrical rod specimens. The multi-frequency measurement data are used to estimate the case depth by model-based inversion. The measured case depth is in reasonable agreement with the effective case depth from the measured hardness profile. Excellent agreement is observed between the measurement data and the theoretical calculation on homogeneous metal plates