Numerical Simulation Of Probe Signal In Eddy Current Nondestructive Testing

Eddy current nondestructive testing (ECNDT) can quickly detect the flaw in metal materials. The main purpose of this dissertation is to research the numerical simulation of the probe signal in ECNDT. We focus the study on the axisymmetric defects and fine hole defects in tube.Axisymmetric defects detection of tube could be simplified as two-dimensional model. We study the axisymmetric defects by using ANSYS. The details of the process were discussed. In this model, the research has been done on investigating the influence on the probe signal by changing the parameters of coils and of flaws.A fine hole defection in the tube cannot be simplified as two-dimensional model. Since the size of the hole is often very small, computation of the eddy currents by means of the finite element method (FEM) is difficult due to a large number of unknowns and a complicated mesh. The volume integral equation (VIE) method needs meshes only in the flaw volume, thus is fit for the analysis of this problems. In this paper, the simulation of a fine hole in a steam generator tube wall was carried out. The ECT probe is of a pair of difference bobbin coils. The solution was divided into two parts. Firstly the eddy current caused by the coils in the tube wall without flaw was obtained by using analytical method. Then the flaw was regarded as an equivalent current source and the resulted perturbation to the eddy current was solved by using VIE method. The impedance changes of the probe were calculated.According to the result, using FEM could quickly get accurate result of the axisymmetric defects detection; while the VIE method is suitable for small size flaw. The conventional flaw detection simulation can be achieved by using the two methods.