Evaluation of Electromagnetic Inspection of Outer Side Defect on Small Diameter and Thick Steel Tube With Steel Support Using 3-D Nonlinear FEM

Steel tubes are used in the heat exchanger in the petrochemical plant. Since these steel tubes are grouped in a bundle by the support steel plate, it is necessary to inspect the existence of defects from the inside of each tube. In these steel tubes, the corrosion or the defects are generated by the friction with the support steel plate at the outer side of steel tube. In this paper, the electromagnetic inspection method using only ac magnetic field is proposed. The behavior of ac flux in the steel tube and support steel plate is examined using 3-D nonlinear finite element method taking account of eddy current. It is shown that the detection of outer side defect is possible without being influenced by the support steel plate with high permeability. The usefulness of this proposal inspection method is shown by verification experiment.