Eddy current method

Determining Residual Austenite with the Eddy Current Method. 

The eddy current method is used for the quantitative evaluation of residual austenite contents in the martensite struaure. 

The principle physical phenomenon of applying the eddy current method for evaluating the amount of residual austenite in the structure of quenched steel is magnetic induction, involving the influence of the changeable magnetic field on the studied area, found under the probe. 

The detection of residual austenite in fact requires average frequency, however for comparison reasons (reference) with a different recognized method, it is recommended to use high frequency, as with high frequency of eddy currents the penetration depth is comparable in the diffraction method and eddy current method. 

Nondestructive Cracks and Corrosion Testing by Eddy Current Method. 

The realized experiments have shown the large possibilities of analysis by the eddy currents method. They allow, besides the verification of the coating and the determination of its thickness, to give an overview on the percentage of the main chemical components of the controlled samples coating by a deepened processing. 

Abstract An Eddy current method applying a High Temperature Superconductor ( HTS ) DC SQUID sensor operating at Uquid nitrogen temperature (77K) is presented. The method is developed for the detection of surface or surface near defects. We compare the performance of the SQUID system with the performance gained from a commercial Eddy current system, while using identical probes. The experimental data are obtained on defects in gas turbine blades. The advantage of planar conformable probes for the use with the SQUID is discussed. 

Remote Field Eddy Current (RFEC) technology is a variation of the conventional eddy-current method, developed for detecting flaws at any point in the walls of (particularly) ferromagnetic (Fe) tubes and pipes from the inside diameter. 

There are difficulties of detecting defects in axial canal because of solid sediment layer of 1. 2 mm thick on the canal surface. When using known defectoscope devices a preliminary labor-intensive mechanical treatment of the axial canal surface is needed. The experience of application of different methods of rotor axial canal control in multifunction automatic device ROTOR - K has pointed to the fact that the most effective method is eddy current one [1]. All the dangerous cracks were just detected by the eddy current method, the part of the cracks were not... 

This work presents two procedures of quantitative evaluation of the material discontinuities, using the eddy current method. One of the procedures concerns the long surface or subsurface crack-type discontinuities in a flat conductive body. The second procedure allows a quantitative evaluation of short discontinuities, such as voids, inclusions etc. 

The eddy current method allows to evalute the state of stress in ferromagnetic material. The given method is used for determining own stress as well as that formed in effect of outside load. With regard to physical principles of own stress analysis, the dependence between the magnetic permeability and the distance between atomic surfaces is utilized. 

Dybiec Cz. Eddy current method for defecting intercrystalline corrossion Materials XXIII KKBN, Szczyrk 1994. 

Czeslaw Dybiec, Ste n Jankowski, Sylwia Wloarczyk, Control of stress and structural changes using the eddy current method. Materials XXX KKBN Szczyrk 1996. 

At present, all over the world the X-ray television systems, instruments based on magnetic heat and eddy-current methods are used to check the air-passengers luggage and to check staff when entering the hazardous objects. In banks, security services and etc. the optic-television and endoscopic technical vision systems are widely used. 

Eddy-Current Methods This is one of the earliest NDT methods and is still used Basically, this method reveals any differences tn electrical impedance between parts to be tested and a reference sample. Parts to be examined are passed through a coil or explored with a probe, and a trace appears on a CRT, Since magnetic and electrical characteristics are closely related to metallurgical quantities, a trace position or pattern or a meter reading clearly shows variations in metal hardness and composition, as well as defects. Both ferrous and nonferrous parts can be tested, and various coils, probes, and detector lips are available,... 

In association with all the above methodologies, the thickness of exposed pipes is controlled with high precision by using magnetic or eddy current methods that can provide a fast and precise identification of internal, external corrosion or blistering inside the metal thickness. 

Liquid penetrant method Magnetic particle method Eddy current method Microwave method Radiography, including... 

Some examples of the application of eddy current method are discussed in the literature,49,50 and are given below in order to illustrate the relevance of the method in the industrial context. 

Inclusions Processing (weldments) Ferrous and nonferrous Radiographic method Eddy current method is used in thin-wall welded tubing coupled with reference standards... 

Inclusions Processing Ferrous and nonferrous wrought samples Ultrasonics for wrought samples Magnetic particle method for machined sample surface Eddy current method for thin wall tubing and rods of small diameter... 

Lack of penetration Processing Ferrous and nonferrous weldments Radiography, ultrasonics confined to specific cases Eddy current method used for nonferrous samples Magnetic particle and liquid penetrant methods when back surface of weld is visible... 

Hydaulic tubing Processing and service Aluminum 6061-T6 Eddy current method... 

Intergranular corrosion Service Nonferrous Liquid penetrant method is primary choice, radiography, eddy current method and ultrasonics may be used with some limitations... 

Non-Destructive Evaluation of Carbon Fibre-Reinforced Structures using High Frequency Eddy Current Methods... 

Lange, R., and Mook. G. (1994), Structural analysis of CFRP using eddy current methods, NDT E Iniernalionut. 27, 5, 241-248,... 

Owston, C. N. (1976), Eddy current methods for the examination of carbon fibre reinforced epoxy resins. Materials Evaluation. Nov. 1976. 34. 11, 237-244, 250. 

Dingwall, P. F., and Mead, D. L. (1976), Non-destructive inspection and volume fraction determination of CFRP using an eddy current method, June 1976, Dept, of Defence, Report RAE-TR-76078. 

A surface examination should be made to confirm the presence of or to dehneate surface or near-surface flaws. It may be conducted by a magnetic particle method, liquid penetrant method, eddy current method or electrical contact method. 

Degoeje MP, Wapenaar KED, Non-destructive inspection of carbon fiber reinforced plastics using eddy current methods. Composites, 23(3), 147-157, 1992. 

There are a number of techniques in the field of SHM for analyzing structural integrity of bonded composite joints. Most of the conventional monitoring systems, such as microscopic failme analysis, ultrasonic. X-ray, thermography and eddy current method are off-line techniques [10, 11], i.e., it s not possible to monitor real time during the service life. But for adhesively bonded joints, real time in-situ monitoring is required. SHM techniques which enable the possibility of in-situ monitoring include acoustic emission, carbon nanotubes network, active vibration method and backface strain based technique. 

Second, the eddy current method [8] is generally used to monitor the thickness of metal film, such as Cu film and W film. In this method, deposition amount is measured based on the amount of the eddy current generated in the film to be polished. Then, the deposition amount is compensated by the above-mentioned profile control by the carrier. 

Davies, R.M. and Thomas, WJ. (1937) The determination of specific heats by an eddy-current method. Part 1. Theoretical. Philos. Mag. Ser. VII. 24, 600-633. 

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