Gaussian process for interpreting pulsed eddy current signals for ferromagnetic pipe profiling

© 2014 IEEE. This paper describes a Gaussian Process based machine learning technique to estimate the remaining volume of cast iron in ageing water pipes. The method utilizes time domain signals produced by a commercially available pulsed Eddy current sensor. Data produced by the sensor are used to train a Gaussian Process model and perform inference of the remaining metal volume. The Gaussian Process model was learned using sensor data obtained from cast iron calibration plates of various thicknesses. Results produced by the Gaussian Process model were validated against the remaining wall thickness acquired using a high resolution laser scanner after the pipes were sandblasted to remove corrosion. The evaluation shows agreement between model outputs and ground truth. The paper concludes by discussing the implications or results and how the proposed method can potentially advance the current technological setup by facilitating real time pipe profiling

Non-destructive evaluation of ferromagnetic material thickness using Pulsed Eddy Current sensor detector coil voltage decay rate

© 2018 Elsevier Ltd A ferromagnetic material thickness quantification method based on the decay rate of the Pulsed Eddy Current sensor detector coil voltage is proposed. An expression for the decay rate is derived and the relationship between the decay rate and material thickness is established. Pipe wall thickness estimation is done with a developed circular sensor incorporating the proposed method, and results are evaluated through destructive testing. The decay rate feature has a unique attribute of being lowly dependent on properties such as sensor shape and size, and lift-off, enabling the method to be usable with any detector coil-based sensor. A case study on using the proposed method with a commercial sensor is also presented to demonstrate its versatility

Review of Pulsed Eddy Current Signal Feature Extraction Methods for Conductive Ferromagnetic Material Thickness Quantification

Thickness quantification of conductive ferromagnetic materials has become a common necessity in present-day structural health monitoring and infrastructure maintenance. Recent research has found Pulsed Eddy Current (PEC) sensing, especially the detector-coil-based PEC sensor architecture, to effectively serve as a nondestructive sensing technique for this purpose. As a result, several methods of varying complexity have been proposed in recent years to extract PEC signal features, against which conductive ferromagnetic material thickness behaves as a function, in return enabling thickness quantification owing to functional behaviours. It can be seen that almost all features specifically proposed in the literature for the purpose of conductive ferromagnetic material-thickness quantification are in some way related to the diffusion time constant of eddy currents. This paper examines the relevant feature-extraction methods through a controlled experiment in which the methods are applied to a single set of experimentally captured PEC signals, and provides a review by discussing the quality of the extractable features, and their functional behaviours for thickness quantification, along with computational time taken for feature extraction. Along with this paper, the set of PEC signals and some MATLAB codes for feature extraction are provided as supplementary materials for interested readers

A pulsed eddy current sensor for UAV deployed pipe thickness measurement

The necessity to inspect essential infrastructure such as oil and gas pipelines for wear, and deterioration highlights the critical role of enhancing Non-Destructive Testing (NDT) methods. Routine inspection for wall thinning is essential for monitoring the structural integrity of these assets and preventing serious accidents. Given the challenges of manned access to these assets, Unmanned Aerial Vehicles (UAVs) equipped with high-resolution cameras are increasingly being adopted as a safer and more efficient alternative for remote inspections. However, their inability to detect sub-surface defects or assess thickness under coatings restricts their applicability. Pulsed Eddy Current (PEC) technology provides a promising solution, capable of assessing thickness beneath coatings and addressing the shortcomings of camera-based inspections. Traditional PEC systems are effective but bulky and difficult to incorporate within mobile platforms, limiting their versatility and ease of deplorability. This paper presents a novel, compact PEC sensor system to address these challenges, enhancing PEC inspections for mobile platforms. The system can be effectively mounted on a crawler-hybrid UAV, facilitating detailed 360-degree inspections of pipe surfaces. Findings detail the autonomous deployment of this PEC system via a UAV for the non-intrusive assessment of wall thickness. Finite element analysis was used for the design and performance evaluation of the PEC system. Integrated with a multirotor-crawler UAV engineered for navigating through complex pipeline environments, this mobile PEC system can conduct thorough evaluations of steel pipeline wall thinning. The system delivers a sensing method that achieves accurate thickness measurements, with errors under 4.8%, facilitating reliable and comprehensive asset inspections

Advances in applications of non-destructive testing (NDT): a review

Manufacturing defects and discontinuities in a product are anomalies which can lead to severe damages which may sometimes involve loss of life. These defects must be examined and corrected before the product goes into service. There are two methods of testing a product for defects and discontinuities viz. Destructive Testing and Non-Destructive Testing. Destructive Testing entails subjecting the product to conditions that leads to failure of the product whereas Non-Destructive Testing (NDT) is the process of examining the products for defects in a way in which it retains its usefulness for future service. This paper discusses various methods involved in NDT such as Visual Testing, Magnetic Particle Inspection, Penetrant Testing, Ultrasonic Testing, Radiographic Testing, Acoustic Emission and Eddy Current Testing with a major focus on  advances in the applications of NDT

Current deflection NDE for pipe inspection and monitoring

The detection of corrosion on insulated and/or coated pipes in the oil and gas industry remains a challenge. Routine inspection, which is commonly achieved with in-line tools known as "pigs", is not possible where there is any risk of the pig becoming stuck. There are thousands of kilometers of pipe worldwide deemed ``unpiggable'' whose safety must be ensured using Non-Destructive Evaluation (NDE) external to the pipe if potentially catastrophic failure is to be avoided. Many NDE techniques lack sufficient sensitivity due to the coating thickness producing a high standoff distance between the pipe and the sensor and therefore require costly and time-consuming removal of the coating. A method capable of detecting and/or monitoring of defects (e.g. one-third-wall depth corrosion) while leaving the insulation/coating intact would be highly attractive. This thesis documents the development of a technique in which a low-frequency AC current is directly injected into the pipe at distant locations, and perturbations in the magnetic field caused by "current deflection" around defects are measured using solid-state magnetic sensors. Two methods of applying this novel technique were investigated. Firstly, scanning the sensors to measure perturbations in the field and screen for defects, and secondly, permanently installing sensors outside the pipe for Structural Health Monitoring (SHM). A Finite Element (FE) model has been developed and used to investigate the practical challenges that are faced by the technique and how these may be overcome. The sensitivity of the technique for defect detection by external pipe scanning in a practical scenario has then been evaluated using a model-assisted Probability of Detection (POD) framework that combines the measurements of the signal from an undamaged pipe with synthetic damage profiles and contributions from general corrosion and sensor misalignment. The results indicate that good performance is expected for damage detection by scanning above a typical insulation thickness with just a few amps of injected current. A similar framework has then been used to evaluate the sensitivity of the technique as an SHM solution which suggests excellent corrosion detection performance with the permanent installation of inexpensive magnetic sensors. The technique has potential advantages over competing methods in both scanning and monitoring modes and there are many opportunities for future development.Open Acces

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

Coupled Finite Element Modelling and Transduction Analysis of a Novel EMAT Configuration Operating on Pipe Steel Materials

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonElectromagnetic Acoustic Transducers (EMATs) are advanced ultrasonic transducers that generate and detect acoustic waves in an electrically conducting material without making physical contact with the material unlike its counterpart, the piezoelectric transducers (PZT). The conventional EMAT consists of copper coil that generates the dynamic field when excited with a sinusoidal current, a permanent or electromagnet that provides the bias field and the conducting material specimen. The complex interaction between the bias field and the Eddy current induced within the skin depth of the conducting material by the dynamic field gives rise to the acoustic wave that then propagates within the surface of the material. Within the research a finite element EMAT model was developed using commercial software Comsol Multiphysics, to study and compare the Eddy current density and Lorentz force density generated by three EMAT configurations: The Meander-line, Spiral and Key Type EMAT configuration respectively. It was observed that apart from the ease of fabrication and simplicity of connectivity when stacked in layers, the Key Type coil EMAT showed a high tendency to generate higher amplitude of Eddy current and Lorentz force test materials especially when stacked in layers. Also, the effect of varying some key EMAT parameters was investigated to determine the optimal performance of Key Type EMAT configuration on CS70 pipe steel plate. The research further developed a coupled finite element model using the same software, Comsol Multiphysics to account for the generation, propagation and detection of acoustic wave by the Key Type EMAT configuration on CS70 grade of pipe steel. The model can solve the magnetostatic, electrodynamic and elastic equations that give rise to acoustic wave generation, propagation and detection on the test material. The developed coupled finite element model was validated both analytically and experimentally to establish the validity of the finite element model. The analytical and experimental results obtained were consistent with the numerical result with an average discrepancy less than 9 % percent. Finally, the research developed a novel modelling strategy to decouple and quantify the various transduction forces in operation when normally-biased EMAT and magnetostrictive EMAT configurations are used on various grades of pipe steel materials. The strategy established the value of the critical excitation current beyond which acoustic wave is generated solely by the dynamic Lorentz force mechanism. The critical excitation currents when Magnetostrictive EMAT configurations are used to generate acoustic wave was found to be; 268A, 274A, 279A, 290A and 305A for CS70, L80SS, L80A, TN80Cr3 and J55 respectively. While for Normally-Biased EMAT configurations, the critical excitation current was found to be 190A, 205A, 240A, 160A and 200A respectively. This work also compared the critical excitation current of the two EMAT configurations studied and established that normally-biased EMATs are more efficient in the generation of acoustic waves than their magnetostrictive counterpart due to their lower value of critical excitation current.Petroleum Technology Development Fund (PTDF) Nigeri