Depth of penetration effects in eddy current testing

The simple depth of penetration equation used for most eddy current calculations does not take into account the effect of the size of the coil or the effect of flaw morphology. The work described in this paper describes use of the CIVA eddy current model to investigate this effect and some experimental investigations. Knowledge of this effect is important in examination of thin sections with eddy currents. Two examples of this are the small sections required to be inspected in laser metal deposition, and welds in thin sections joining dissimilar metals such as copper and aluminium for electrical connections

Modelling of pulsed eddy current testing of wall thinning of carbon steel pipes through insulation and cladding

Conventional eddy current techniques have been used to a great extent for detection of surface breaking defects in conductive materials. Pulsed Eddy Current (PEC) techniques excite the probe’s driving coil with a repetitive broadband pulse, usually a square wave, instead of sinusoidal wave. The resulting transient current through the coil induces transient eddy currents in the test piece, these pulses consist of a broad frequency spectrum, and the reflected signal contains important depth information. Surface pancake type pulsed eddy current probes have been used for wall thinning and corrosion detection but these methods can be slow. In order to increase the scanned area, an encircling coil has been proposed, with a view to inspect a complete circumference with a single pulse. The work presented in this paper employs COMSOL Multiphysics finite element (FE) modelling software, to further investigate the behaviour of an encircling probe design as a part of the development work. This work involves modelling of an encircling coil around a steel pipe with insulation and cladding of different materials. Pulsed eddy current testing of wall‐thinning through cladding and insulation was studied for various wall thinning situations. The simulation results show the capability of this system in pipe wall thinning detection

A pulsed eddy current system for flaw detection using an encircling coil on a steel pipe

Conventional eddy current techniques have been used to a great extent for detection of surface breaking defects in conductive materials. However, detection of sub-surface defects is limited due to skin effect phenomena and material properties. Pulsed Eddy Current (PEC) techniques excite the probe’s driving coil with a repetitive broadband pulse, usually a square wave. The resulting transient current through the coil induces transient eddy currents in the test piece, these pulses consist of a broad frequency spectrum, and the reflected signal contains important depth information. The work in this paper employs COMSOL Multiphysics, the finite element (FE) modelling software, to investigate the behaviour of a new encircling probe design. This work involves modelling of an encircling coil around a steel pipe with high lift-off to simulate insulation. The 3D modelling of the coil wrapped around a steel pipe was employed and surface breaking discontinuities were modelled. The simulation of these scenarios provided essential information about the behaviour of this probe design

Reliability Improvement of Magnetic Corrosion Monitor for Long-Term Applications

Electromagnetic techniques are widely employed for corrosion detection, and their performance for inspection of corrosion is well established. However, limited work is carried out on the development and reliability of smart corrosion monitoring devices for tracking internal or buried thickness loss due to corrosion remotely. A novel smart magnetic corrosion transducer is developed for long-term monitoring of thickness loss due to corrosion at critical locations. The reliability of the transducer is enhanced by using a dissimilar active redundancy approach. The improved corrosion monitor has been tested in the ambient environment for seven months to evaluate the stability against environmental factors and degradation. The monitor is found to show great sensitivity to detect defects due to corrosion. Detection of anomalous patterns in the time series data received from the monitors is accomplished by using Pearson’s correlation coefficient. The critical component of the monitor is identified at the end of the test. Research findings reveal that, compared to the existing corrosion monitoring techniques in the industry, the detection and isolation of faulty sensor features introduced in this study can contribute to reliable monitoring of thickness loss due to corrosion in ferromagnetic structures over an extended period of tim

Development of Permanently Installed Magnetic Eddy Current Sensor for Corrosion Monitoring of Ferromagnetic Pipelines

Permanently installed sensors are a cost-effective solution for corrosion monitoring due to their advantages, such as less human interference and continuous data acquisition. Some of the most widely used permanently installed corrosion sensors are ultrasonic thickness (UT) gauges. However, UT sensors are limited by the need for coupling agents between pipe surfaces and sensors. The magnetic eddy current (MEC) method, on the other hand, does not require couplant and can be used over insulations. With the development of powerful rare earth magnets, MEC sensors with low power consumption are possible, and there is the prospect of using them as permanently installed sensors. A novel wireless magnetic eddy current sensor has been designed and optimized using finite element simulation. Sensitivity studies of the sensors reveal that the excitation frequency is a critical parameter for the detection of corrosion defects. An in-depth explanation of the relationship between the sensitivity of the sensor and the excitation frequency is presented in this paper. The results of an accelerated corrosion test, conducted to simulate the service environment of the sensor, are also discussed. It was observed that the sensor signals are very sensitive to corrosion defects and show no subtle differences due to temperature and humidity changes

A numerical study of the depth of penetration of eddy currents

The simple standard depth of penetration equation used for most eddy current calculations does not take into account the effects of the size and type of the coil, the lift-off or the specimen thickness. The work described in this paper includes a study of the depth of penetration of eddy currents for different coil sizes including surface and encircling type coils by taking advantage of the sophisticated finite element modelling software COMSOL. Knowledge of these effects plays an important role in designing eddy current coils and examinations of conductive materials with the eddy current technique. This paper includes a study of the effects of all the dimensions of a surface coil, encircling coil, lift-off and specimen thickness at several excitation frequencies. It is demonstrated from the results obtained from these numerical studies that the coil parameters affect the depth of penetration at different frequencies

Investigation of an encircling pulsed eddy current probe for corrosion detection

Pulsed Eddy Current (PEC) is an emerging nondestructive testing and evaluation (NDT & E) technique and has been used for a wide range of conductive materials. Existing Pulsed Eddy Current probes use surface type probes on pipes. For this type of probes, it is assumed that the diameter of the pipe is significantly larger than that of the excitation coil and the pipe wall is assumed as a plate. In this work, a new encircling pulsed eddy current probe is proposed. The system aims to increase the scanned area by taking advantage of an encircling coil to scan the complete circumference of a pipe with a single pulse. The proposed system consists of an encircling driver coil, Giant magnetoresistance (GMR) magnetic field sensors, a conditioning circuit, a data acquisition card connected to a computer with Matlab software for signal processing and presentation.TWI ltd and School of Engineering and Design of Brunel Universit

It Looks Good, but What is it Like to Live There? Exploring the Impact of Innovative Housing Design on Crime

This paper reports on the findings of a collaborative project (funded by the Home Office and managed by the Commission for Architecture and the Built Environment - CABE) which was conducted in late 2009 and early 2010. The project set out to strengthen and update the evidence base on the impact of design on a range of crime types – with a specific focus upon housing developments acclaimed for their innovative design and award winning architecture. This paper presents the findings of an in-depth assessment of the impact of housing design features on crime. Utilising a comprehensive data collection exercise, the specific design features of thousands of homes were collated and assessed against police recorded crime data. The design features were based upon the key elements of Crime Prevention Through Environmental Design (CPTED) including road layout, house design, surveillance, territoriality, car parking, communal space, management and maintenance and physical security. The unique and painstaking methodology not only provided an excellent dataset for analysis, but also highlighted the need both for greater conceptual clarity within CPTED and for crime-risk assessments to be based on the careful operationalisation and measurement of CPTED factors. As well as assessing the impact of specific (and combined) design features upon crime, the research also resulted in the production of a new data collection tool designed to address the weaknesses of existing checklists in assessing innovative contemporary developments, which are often unconventional in nature. The paper explores the degree of conflict and/or synergy between the traditional principles of CPTED and contemporary directions in architecture and design. Finally the paper considers the extent to which traditional CPTED principles remain relevant within contemporary residential developments and explores whether areas of revision are required