Hong-En Chen

Sizing of Wall Thinning Defects Using Pulsed Eddy Current Testing Signals Based on a Hybrid Inverse Analysis Method

Quantitative non-destructive evaluation, especially sizing of piping wall thinning in nuclear power plants is still a difficult and urgent issue. In this paper, an inversion approach for PECT (pulsed eddy current testing) signals is developed based on ANN (artificial neural network) method at first for profile reconstruction of wall thinning, the sizing result of NN is then utilized as the initial value of the CG (conjugate gradient) inversion scheme to overcome the shortages of both the NN (accuracy problem) and CG (local minimum problem) methods. Several reconstruction examples using the proposed hybrid strategy indicate that the combination of NN and CG methods is rather effective for wall thinning reconstruction from PECT signals in view of both the robustness and sizing accuracy.

Evaluation of plastic deformation and characterization of electromagnetic properties using pulsed eddy current testing method

Plastic deformation, as a type of micro-damage caused by external loads such as earthquake, is necessary to be evaluated by using an efficient non-destructive evaluation technique in order to guarantee the structural safety. In this paper, the feasibility of the pulsed eddy current testing method for evaluating the plastic deformation in an austenitic stainless steel has been studied through experiments and simulations. Moreover, the electromagnetic property variations due toplastic deformation have also been investigated.

A study on influence of plastic deformation on the global conductivity and permeability of carbon steel

Non-destructive evaluation (NDE) techniques are indispensable for inspection of damage in structures of carbon steel, which is widely used in many industries. In this paper, experimental and numerical studies were conducted to investigate the electromagnetic property variations of carbon steel Q195 due to plastic strain by using the 4-probe potential drop method and ECT aiming at NDE applications. A series of specimens were fabricated and uniform global plastic strains of different levels were introduced to the specimens by tensile testing. 4-probe potential drop measurements were carried out to obtain the conductivity information at first. It is found that the macro conductivity is not affected significantly by the plastic strain once taking into account the influence of the cross-sectional area reduction of the specimens. Combining the results of numerical analysis using a code of Ar formulation with the measured ECT signals, the permeability of specimens with various plastic damages was evaluated through inverse analysis. It is proved that the ECT signal change due to plastic damages is mainly caused by the variation of permeability, which gives a good possibility to evaluate the plastic damage with a magnetic NDE method.

Comparisons of damage-induced magnetizations between austenitic stainless and carbon steel

To explore the mechanism of damage-induced magnetization for paramagnetic austenitic stainless steel, the differ- ences of damage-induced magnetizations between an austenitic stainless steel and a carbon steel are experimentally studied. Various plastic strains are introduced into the test-pieces of the austenitic stainless steel of 304 type and S185 carbon steel material. The residual plastic strains and the damage-induced magnetic fields nearby the test-pieces, the volume fraction of the damage-induced ferromagnetic martensitic phase in austenitic stainless steel test-pieces are measured. The relationships be- tween the residual plastic strain and the damage-induced magnetic field of two materials are investigated and their differences are compared. In addition, by establishing the relationships of the damage-induced magnetic field with the damage-induced martensitic phase, the effect of the phase transformation on the damage-induced magnetization of austenitic stainless steel is analyzed.

Numerical simulation of magnetic incremental permeability for ferromagnetic material

Magnetic Incremental Permeability (MIP) method practiced as a NDT technique to evaluate the material degradation is based on the eddy current testing in addition to a low frequency bias magnetic field generated by an electromagnetic magnet. To clarify the mechanism of MIP and to find optimal probe design, a numerical method to simulate MIP profile is important. In this paper, a simulation scheme and a numerical code are developed for MIP of ferromagnetic material based on the simulated polarization strategy and the reduced vector potential formulae. Experiments are also conducted for test-pieces of carbon steel to demonstrate the validity of the proposed scheme.