Proposal of Carburization Depth Inspection of Both Surface and Opposite Side on Steel Tube Using 3D Nonlinear FEM in Consideration of the Carbon Concentration

In the steel tube of a heating furnace inside an oil-refining plant, its both surface and opposite side is carburized. If these carburization depths are increased, the steel tube will be exploded suddenly and a big accident may occur. Therefore, the inspection of these carburization depths is important. The conductivity of the layer with carburization is larger than the layer without carburization in the steel, and its permeability is smaller than the layer without carburization. Therefore, the estimation of both carburization depths is possible by using the differences of these electromagnetic properties. In this paper, the new technique of measuring the both depths by using two kinds of alternating magnetic field is proposed. The both depths are obtained by evaluating the flux density in layers with and without carburization steel tube using the 3-D nonlinear FEM. It is shown that the inspection of both depths is possible by using the differential electromagnetic characteristics.