Showing papers on "Eddy-current testing published in 1979"

Digitally controlled multifrequency eddy current test apparatus and method

Abstract: Digitally controlled eddy current test apparatus for detecting flaws, their extent and location. The apparatus provides absolute and differential measurements. The apparatus employs multi-frequencies with the signals from the test coils mixed in a predetermined manner to reduce unwanted signals such as may be introduced by wobble (lift-off) and support plates.

The Application of Finite Element Method Analysis to Eddy Current NDE

Abstract: The Finite Element Method for the computation of eddy current fields is presented The method is described for geometries with a one component eddy current field The use of the method for the calculation of the impedance of eddy current sensors in the vicinity of defects is shown An example is given of the method applied to a C-magnet type sensor positioned over a crack in a plane conducting material INTRODUCTION Eddy current NDE techniques detect defects in a conducting material by using a sensor which induces currents in the material, and then observing the changes in the impedance of the sensor in the vicinity of the defect The theoretical analysis of the relation between the defect properties and the impedance change requires the solution of Maxwell's equations to determine the current fields in the material For most practical problems, the geometry is too difficult for closed form analytic solutions, and numerical solutions are required The most promising numerical technique for computation of eddy current fields is the Finite Element Method This method has long been used in stress analysis and heat flow problems (Ref 1), and in recent years has been applied to the computation of eddy current fields in electrical machines (Ref 2) The method has also been used to investigate a problem in magnetostatic NDE (Ref 3), but has not been applied to eddy current NDE, which is a time varying field problem In this paper, the Finite Element Method for the computation of eddy current fields is presented The method is described for geometries with one component eddy current field, for which the problem reduces to the solution of the two-dimensional diffusion equation The use of the method for the calculation of the impedance of eddy current sensors is explained An application of the technique to the case of a C-magnet type sensor over a crack in a plane conducting material is shown Derivation of the Diffusion Equation for OneComponent Vector Potentials In eddy current testing, the frequencies are usually low enough that the displacement current term in Maxwell's equations is negligible Under this assumption, Maxwell's equations become

Eddy currents probe for the inspection of pipes

Abstract: A probe (1) for eddy current inspection of tubes has between a conically tapering guide head (34) and a cylindrical coil bobbin (2) a radially flexible sheath (16, 17) which is under a uniformly outwardly acting bias voltage and a larger diameter having, as the bobbin (2). It is fastened with a quick coupling (41) to a thrust hose. The new probe is used in particular for testing the tubes of steam generators in nuclear power plants (Fig. 1).

Multifrequency Eddy Current Inspection with Continuous Wave Methods

Abstract: This paper describes the application of continuous wave, rnultifrequency eddy current methods to nondestructive inspection of materials. A generalized description of the technology is included, follow~d by s~me ~esults o~t~ined in_mul~i~requency_examination of tubing. A major advantage of multifrequency ~nspect1on 1s the a~1~1ty to d1scr1m1nate aga1nst unwanted test parameters. The discrimination process 1s effected by comb1n1ng the data from individual frequencies in a manner similar to simultaneous solution of multiple equations. r~ultifrequency tests are described showing how discrimination has been achieved against parameters such as probe motion, tube support plates and magnetic surface deposits.

Optimization of eddy current transducers (surround coil)

Abstract: This paper provides a rational approach to the design of surround coil transducers for eddy current testing by maximizing the product of filling factor and empty coil Q. It is shown that reasonable criteria for coils whose inner diameter lies in the range from .1 cm to 11. cm are (assuming operation at a frequency below self resonance): coil length to ID ratio should be in the range of 1.5-2.5, wall thickness to ID ratio should be in the range .13-.20, and the wire size should be selected so that the coil losses at operating frequency are only a few percent above the dc resistance.

Investigating the computer analysis of eddy current NDT data

Abstract: The objective of this activity was to investigate and develop techniques for computer analysis of eddy current nondestructive testing (NDT) data. A single frequency commercial eddy current tester and a precision mechanical scanner were interfaced with a PDP-11/34 computer to obtain and analyze eddy current data from samples of 316 stainless steel tubing containing known discontinuities. Among the data analysis techniques investigated were: correlation, Fast Fourier Transforms (FFT), clustering, and Adaptive Learning Networks (ALN). The results were considered encouraging. ALN, for example, correctly identified 88% of the defects and non-defects from a group of 153 signal indications.