Eddy Current Technology Research Articles

Performance Estimation of a Remote Field Eddy Current Method for the Inspection of Water Distribution Pipes

Remote Field Eddy Current (RFEC) technology allows the in situ inspection of metallic water distribution pipes. RFEC tools provide the location and magnitude of corrosion defects on the inspected pipes. The capacity of an RFEC tool to detect corrosion defects is evaluated in this paper by comparing its results with those obtained from the analysis of computed tomography (CT) scan images of the inspected pipes. Localization and characteristics of defects identified with the RFEC tool and from the CT scan images were compared for six cast iron pipes. An original method is proposed for the analysis of the CT scan images from which wall thickness losses were estimated by using the basic principle that the attenuation coefficient of X-rays in a homogenous material is a linear function of its density. The results show that the RFEC tool is able to localize most of the defects identified from the analysis of CT scan images. These findings reveal that the tested RFEC probe provided reliable information on the main corrosion defects, and thus on the general structural integrity of the inspected pipes.

Accurate thickness testing via phase-sensitive eddy current

Phase-sensitive eddy current technology provides an excellent option to metal finishers for measurement of many application combinations. With phase-sensitive eddy current systems available for about $6,000, the eddy current method provides a relatively inexpensive alternative for accurately determining coating thickness. Eddy current systems are easy to operate with menu-driven, prompting software, so even non-technical operators can make instantaneous, accurate and repeatable thickness measurements directly on the process line for improved through-put, quality control and fewer rejections. Many of the largest volume platers use eddy current systems at the end of the plating line for direct process control and incorporate X-Ray in the quality lab for final inspection. Using this combination of technologies ensures the most efficient method to achieve conformance to thickness specifications

Thickness Measurement of Composite Material Using Eddy Current Testing

Composite materials have some obvious advantages such as high specific strength 、high specific modulus 、corrosion resistant 、abrasion resistant and so on, it is believed to be highly competitive compare to other materials. Advanced composite materials have been used more and more widely in defense industry, among them carbon fiber reinforced resin base composite material is most representative [1] ,there has great value for the study of carbon fiber composite materials. Eddy current is a nondestructive testing technology widely used on metal materials, the using of eddy current technology in aviation domain has a long history, but there is few reports on composite material with eddy current NDT. Experiments show that eddy current used on composite material is feasible, and the result is satisfactory. The thickness measurements of carbon fiber advanced composite materials have been done in two different ways.

Use of Eddy Current Technology to Assist in the Evaluation of the Fatigue Damage of Electrical Conductors

The article deals with the evaluation of fatigue damage on overhead conductors which have been in service for a period exceeding 50 years. Under wind excitation, electrical transmission lines are subjected to aeolian vibrations that may induce wire fatigue of conductor at the exit of supporting equipment. This fatigue phenomenon is a fretting fatigue problem which is located at contact points between wires belonging to adjacent wire layers or between external layer wire and the supporting equipment. This article reports the methodology followed: 1) in selecting wires with the more severe damaged contact point using eddy current technology and 2) in comparing, through a metallographic examination, the contact points of those selected wires coming from in situ worn conductors and from laboratory fatigue tested virgin conductors used as reference.

Electrostatic wear monitoring of rolling element bearings

Research and development work at the University of Southampton using an electrostatic condition monitoring system developed by Smiths Aerospace Information Systems has shown that electrostatic charge signals can be used to detect the onset of wear in lubricated tribo-contacts. Preliminary investigations have already demonstrated the viability of this system when tested on a laboratory-based pin-on-disc rig, a reciprocating laboratory wear rig and in an FZG gear scuffing rig. These preliminary experiments have indicated several charging mechanisms may be involved, namely—tribo-charging, localised surface charge variations, exo-emissions and debris generation. The electrostatic monitoring system has now been implemented on a taper-roller bearing test rig. The electrostatic system employed comprises three wear-site sensors (WSS) and an oil-line sensor (OLS). The WSS are mounted close to the bearing in order to monitor the earliest stages of component surface breakdown and wear, whereas the OLS is placed in the re-circulation oil-line to monitor debris generated and transported from the deteriorating component. For the present tests, taper-roller bearing wear was monitored using electrostatic sensors as well as vibration and lubricant temperature measurements; also two additional oil-line monitoring devices, supplied by Macom Technology Ltd., using Eddy current technology and ferromagnetism to sense debris entrained in the lubricant recirculating system were employed. The experimental data shows that the electrostatic monitoring systems detected bearing deterioration up to 4 h prior to complete failure (seizure) during a seeded fault test. The electrostatic wear-site and oil-line sensors detected changes in charge that coincided with increases in vibration, temperature and debris generation detected by the two Macom units.

Confirming plant integrity by specialised NDE inspections

The UK power industry is going through a difficult period, trying to balance the demand for electricity with conforming to the new environmental regulations. Because of overcapacity, it is no longer an attractive proposition to build new power stations but, instead, it makes economic sense to keep older power stations running beyond their design life. Structural integrity is increasingly demanding greater accuracy and repeatability from NDE inspections; new equipment and technology has been developed predominantly based on ultrasonic and eddy current technology. The development of information technology has been crucial for the improvement of ultrasonic imaging techniques. Advanced specialist inspections including phased array, time-of-flight diffraction and advanced eddy current, have been developed for evaluation of steam pipework, generator end-rings, steam chests, blade roots, rotor bore and rotor discs and many other plant items. The latest phased array techniques bring considerable benefits to the inspection of complex geometries. Ultrasonic inspections on components with complex geometries can give rise to confusing signal patterns which influence the speed and integrity of inspections. Additionally, access restrictions often limit probe movement, further affecting test integrity. The development and utilisation of phased array ultrasonic hardware and analysis software, has enabled high-integrity high-speed scanning and imaging of complex components. 'Sweep Scanning' can be carried out from a static position allowing coverage where access is restricted; the data can then be stored for future interrogation if required. The phased array probe contains multiple elements, and scanning can be mechanical (probe movement), electronic (pulsed beam sweep), or a combination of both. Component drawings and geometries can be overlaid on the phased array images, enabling both inspection design and ease of analysis. Advantages are gained through scanning complex geometries quickly with high integrity. Focusing of the optimal inspection angle gives improved defect detection and electronic data storage enables an auditable inspection fingerprint. This paper concentrates on three main applications: phased array and time-of-flight diffraction applications, rotor bore applications and generator retaining ring (end-ring) applications.

The use of eddy current arrays as a replacement for dye-penetrant inspection of generator and exciter end-rings

With reduced inspection time and recoverable inspection data, eddy current array technology is the future of surface crack detection on power station components. Generator and exciter end-rings will soon reap the benefits of accurate surface crack detection using eddy current array solutions from RWE npower. Accurate defect mapping, quick and complete data recovery, relative defect size information and rapid data acquisition are just a few of the drivers behind the switch away from fluorescent dye-penetrant inspections.

The potential for friction stir weld inspection using transient eddy currents

The development of a growing range of new welding methods for high-strength alloys requires a method of monitoring the full weld profile to assist at both the development and production stages. The aim of this project was to investigate the potential for using transient eddy currents for friction stir weld (FSW) process monitoring and defect detection. As a result, transient eddy-current technology has proved to be remarkably well suited to FSW inspection for on-line process monitoring, being able to penetrate deep into the weld and produce a cross-sectional profile of a parameter related to the electrical conductivity. This is sufficient to indicate the 3D location of any changes in conductivity, as shown by scanning specimens with known conductivity changes at various depths. Comparison with high-frequency surface conductivity measurements has also shown good agreement. A model-based inversion to give a more accurate profile of conductivity is also thought to be possible and work has commenced on this. Further work is required to link electrical conductivity to the microstructure and important material properties of the weld. Better understanding of these relationships will considerably enhance the advantages of using transient eddy currents to monitor the friction stir weld process.

Transient eddy currents – are they here to stay?

Details of transient eddy-current inspection were first published over ten years ago, however the ideas that led to this technique date back much further to a programme of basic research into eddy-current imaging. The spin-off from this programme has led to several developments in eddy-current technology underlining the essential role of fundamental research as a means of gaining insight into the solution of practical inspection problems. The conceptual development of transient eddy-current inspection is reviewed and evaluated here in order to determine whether or not this technique has the potential to make a significant contribution to NDE.

Eddy Current Separation of Fine Non‐Ferrous Particles from Bulk Streams

Recovery of fine non‐ferrous metals from waste streams is a notoriously difficult problem in eddy current separation technology. Existing processes either have a low capacity or an incomplete recovery for particle sizes below 5 mm. In a new process, the particles are fed slightly wet to make them stick to the surface of the conveyor belt. The action of the magnet rotor makes the non‐ferrous particles tumble, so that they break loose from the belt and end up in front of the rotor. The new process combines a relatively high capacity with an almost complete recovery, even for heavy and poorly conducting non‐ferrous metals.

Pulsed Eddy Current Technology: Characterizing Material Loss with Gap and Lift-off Variations

Ownership costs of operational aircraft have increased steadily over the years. One of the major cost drivers is structural deterioration due to corrosion. Beyond the economics, finding and characterizing corrosion is essential for the continued airworthiness of aircraft fleets. To this end, the pulsed eddy current technique holds the potential of becoming the primary means of detecting corrosion in multilayered structures. Its wide-band frequency spectrum allows the determination of a large number of parameters, such as defect size and location. Pulsed eddy current is still considered an experimental nondestructive technique because of realistic inspection problems (e.g., probe tilting, protrusion of rivets, and thickness variations in adhesive and paint) have not been addressed in the past. Recent advances change this situation and allow pulsed eddy current to be a credible field technique.

Pulsed Eddy Current Technology: Characterizing Material Loss with Gap and Lift-off Variations

Pulsed Eddy Current Technology: Characterizing Material Loss with Gap and Lift-off Variations

Pulsed Eddy Current Technology: Characterizing Material Loss with Gap and Lift-off Variations

Pulsed Eddy Current Technology: Characterizing Material Loss with Gap and Lift-off Variations

The Investigation of Separability of Particles Smaller Than 5 mmby Eddy Current Separation Technology. Part I: Rotating Type EddyCurrent Separators

Owing to the growing emergence of the end‐of‐life electrical and electronic products with complex material structures and an ever‐diminishing particle size of the valuable metals involved, development of eddy current separators (ECS) has been targeting selective separation of small non‐ferrous metal particles smaller than 5 mm. Separability of various materials smaller than 5 mm, including fine copper wires, has been investigated using ECS with various design concepts. The present research work is divided into two parts, with Part focusing on the rotating type ECS which are today common in practice, and with Part II dedicated to the ECS with novel concepts such as wet ECS technology. In Part I, three rotating belted‐drum ECS were employed, which are manufactured by Bakker Magnetics, the Netherlands, Huron Valley Steel Co., US, and Eriez Magnetics, UK respectively. It is found that the belted‐drum ECS are effective for separating materials below 5 mm if the magnetic drum rotates in opposite direction to the conveyor belt. The separation principle, particularly the "backward phenomenon" of the rotating type ECS for small particles has been unravelled in the present study. Moreover, separation of AI from the 0–10 mm fraction of electronic scrap has been conducted. The results obtained demonstrate that the belted‐drum ECS with appropriate design may be applicable for separation of small aluminum particles from electronic scrap.

Pipeline simulation facilities for the development of in-line inspection technologies for gas transmission pipelines: Nestleroth, J.B.; Bubenik, T.A.; Haines, H.H. Materials Evaluation, Vol. 53, No. 4, pp. 484–487 (Apr. 1995)

In the US the major components of the natural gas system include nearly 450,000 km of transmission pipelines, 145,000 km of gathering lines, 1,345,000 km of distribution mains, and 450,000 km of service lines. In-line inspections are one important tool being used by pipeline operators of their pipeline systems. In-line inspection of gas pipelines is accomplished by instrumented vehicles commonly referred to by the pipeline industry as pigs. These instrumented vehicles must be self-contained with data recorders and power to operate sensors and store nondestructive measurements. Ultrasonic, magnetic flux leakage, and eddy current technologies have been successfully applied for various pipeline inspection applications. The vehicle is propelled through the pipeline by the flow of the product (oil, natural gas, etc). The Pipeline Simulation Facility was built to advance the state of the art of gas pipeline inspection technology. The facility consists of four elements. The first is a Non-destructive Evaluation Laboratory and a linear test rig. This laboratory allows detailed analytical modeling and carefully controlled experiments for studying basic technology effects. The second element is an outdoor pull rig. The pull rig consists of four 91.4 m lengths of pipe with diameters of 305, 610, 762, 914 mm. Test bedmore » vehicles or inspection tools can be pulled through these pipe lengths, which contain carefully controlled defects. The third element is a flow loop, a 1,433 m long, 610 mm diameter pipeline where both pressure and flow can be controlled. The last element is a set of test bed vehicles. These vehicles are modular systems upon which inspection equipment can be mounted and used in the pull rig or flow loop. The facilities have been designed to accommodate research that extends from detailed analyses of defects in flat plates under idealized conditions to the same types and sizes of defects in a pressurized pipeline operating under flowing gas conditions.« less

Tracking of cracks in sheet steel specimens under cyclic loading

In this report a non‐contact gauging system based on eddy current technology is presented which permits unproblematic detection and tracking of cracks initiated by cyclic loading in sheet steel specimens. In comparison with other measuring methods the automatic pilot unit developed displays distinct advantages thanks to its highly accurate measuring results. This measuring unit is suitable for the examination of thin sheet steels (< 2 mm) and has been successfully used for studying ductile materials. Some results of such investigations are therefore illustrated.

A review of eddy current system technology : 38824 McNab, A. British Journal of Nondestructive Testing, Vol. 30, No. 4, pp. 249–256 (Jul. 1988)

A review of eddy current system technology : 38824 McNab, A. British Journal of Nondestructive Testing, Vol. 30, No. 4, pp. 249–256 (Jul. 1988)

A review of eddy current system technology 38824 McNab, A. British Journal of Nondestructive Testing, Vol. 30, No. 4, pp. 249–256 (Jul. 1988)

A review of eddy current system technology 38824 McNab, A. British Journal of Nondestructive Testing, Vol. 30, No. 4, pp. 249–256 (Jul. 1988)

A review of eddy current system technology : 38824 McNab, A. British Journal of Nondestructive Testing, Vol. 30, No. 4, pp. 249–256 (Jul. 1988)

A review of eddy current system technology : 38824 McNab, A. British Journal of Nondestructive Testing, Vol. 30, No. 4, pp. 249–256 (Jul. 1988)

Phased array eddy current inspection of expansion transition zones in steam generator tubing : Eddy current technology incorporated, Virginia Beach, Virginia (United States), R8605, 16pp. (1986)

Phased array eddy current inspection of expansion transition zones in steam generator tubing : Eddy current technology incorporated, Virginia Beach, Virginia (United States), R8605, 16pp. (1986)