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Multilayered Tubular Structures (MTS) such as pipeline are widely employed in such industrial fields as nuclear energy, petroleum, etc. It is vital to non-destructively evaluate MTS periodically before catastrophic accidents take place. As one of the advanced Electromagnetic Nondestructive Evaluation (ENDE) techniques, Pulsed Eddy Current Testing (PECT) has been found advantageous over the other ENDE methods regarding evaluation of integrity of MTS. In this paper, a fast forward model of PECT inspection of MTS is proposed based on the analytical modeling, namely the Extended Truncated Region Eigenfunction Expansion (ETREE). The closed-form expressions of PECT signals of 3D magnetic field and coil Electromotive Force (EMF) have been formulated. The proposed model has been verified by Finite Element Modeling (FEM) and experiments. The advantages of the model in terms of high computational speed and accuracy have been identified.

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 A_r 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.

The purpose of this study is to characterize the features of magnetic flux density perturbation as a result of the variation of conductivity in an equivalent model of the stress-corrosion crack (SCC). By using numerical computation of A-𝜙 method, the magnetic field nearby the inspection target was simulated for an eddy current probe of large rectangular excitation coil and a conductor plate with a modeled SCC. A conductive notch was set in the center of the conductor plate as an equivalent crack model of a real SCC. Different conductivities and crack depths were varied into the equivalent SCC model for analyzing their influences to the distribution of magnetic flux density perturbation above the model plate. Numerical results showed that the distributions of magnetic flux density were suitable to distinguish the difference of the conductivities of the SCC between 0% and 20% of the base material for normal testing frequencies. In addition, it was also found that the profile of distributed conductivity along the crack length can be better represented with the field induced by the excitation current laterally to the crack length.

This paper presents numerical simulation results of eddy current signals to determine the appropriated dimensions of imitative stress-corrosion cracks (SCCs) in viewpoint of similar eddy current testing signals. The imitative SCCs were modelled as multiple tiny slits in three dimensions. A Finite Element and Boundary Element hybrid method (FEM-BEM) was utilized to simulate the eddy current signals in an impedance form of an absolute pancake coil. Equivalent conductivity ([Formula: see text]) of the imitative SCCs was estimated by using a uniform notch model at a fixed width of 0.2 mm, and adjusting the conductivity in the notch region. According to the numerical results, the impedance amplitude could be significantly used to quantify the [Formula: see text] of imitative SCCs. In addition, the variation of test frequency affecting to [Formula: see text] value was investigated. Finally, the appropriated imitative SCCs dimensions for the eddy current testing were quantitatively predicted by using a statistical methodology.