FINITE-ELEMENT MODELING OF CONDUCTING SHELLS FOR EDDY-CURRENT NDE PROBLEMS USING IMPEDANCE-TYPE INTERFACE CONDITIONS

A 3D finite element scheme is developed to calculate eddy current prob e responses (impedance or induced emf changes of coils) due to conduct ing shells in eddy current NDE (nondestructive evaluation) problems. T hese problems are related to the eddy current inspection of copper and magnetite deposit zones of steam generator tubing in PWR atomic power plants. The finite element scheme uses impedance interface conditions to model the deposit shells and calculates the probe responses by per forming integrals over the shell surfaces, thereby ensuring high accur acy even if the probe signal is very small, Two benchmark arrangements are investigated. One, which has an analytical solution, is a conduct ing thin plate,vith an impedance probe. The other is a stainless steel tube with a copper shell attached to its outer surface and scanned by a transmitter-receiver probe. In both problems, the calculated probe responses show good agreement with the analytical and experimental dat a.