·Table of Contents
·Methods and Instrumentation
Eddy Current Inner Control of Amagnetic Pipes Using the Rotating Magnetic FieldR. Grimberg, A. Savin,S. Chifan
National Institute of R&D for Technical Physics, 47 Mangeron Blvd, 6600, Iasi, ROMANIA
LESIR, ENS Cachan, 61 Av. du Président Wilson, 94235 Cachan Cedex, FRANCE
|Fig 1: The inside transducer with rotating magnetic field|
The axes of the emission coils are set 1200 apart in angle, the coils being star-connected and supplied by a three-phase current system. The rotating frequency of the magnetic field generated by vectorially composing the fields generated by each coil apart equals the angular frequency of the supply alternating currents. The interaction between the eddy currents and the possible material discontinuities from the tube wall is revealed by the reception coil system. The signal processing method is classical; the reception coils being interrogated sequentially.
Figure 2a presents the basic diagram of the control equipment, while its specific embodiment is given in Figure 2b.
|Fig 2: a) Basic diagram of the equipment b) Control installation picture|
|Fig 3: a) sample with outer channels b) sample simulating corrosion|
The transducer's responses to the discontinuities from the three samples are presented in Figure 4 a, b and c.
| Fig 4: a- transducer's response to the ASME standard sample|
b- transducer's response to the test sample with outer channels
c- transducer's response to the sample simulating corrosion
The symmetry of the problem imposes the utilization of a cylindrical coordinate system with the Oz axis coinciding with the axes of the inspected tube and that of the transducer's emission part. Three regions can be discerned here: the region W1 representing the tube interior with the transducer; the region W2 consisting of the tube wall, and the region W3 outside the tube.
Within the region W1 the following relations are valid
where represent the electric and magnetic fields created by the transducer's emission part and are given by the relations
with the dyadic Green's function in free space, the current density, the position vector of the measuring point, the position vector of a current point of the source; w the angular frequency of the three-phase current system,m=4p×10-7 H/m, and
are the fields created by the eddy currents induced in the tube wall, solutions of the differential equations
|Fig 5: Angular dependence of the Hr component of the magnetic field|
The good agreement between the theoretical model and the experimental measurements permits to solve in the future both the forward and the inverse problem.
This work has been partly supported by the International Atomic Energy Agency under the Contract no: 302-I3-ROM-11164
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