Characterisation of cylindrical hidden corrosion using 2D analytical modelling of the surface magnetic field
Eddy current testing, as a traditional electromagnetic non-destructive testing technique, has been unable to meet the current, increased requirements for defect detection. In order to study the physical relationship between a defect and the electromagnetic field in depth and provide additional methods for its quantitative assessment, an analytical solution for the surface magnetic field is presented in this paper. The magnetic vector potential equation between a conductive plate containing corrosion and a cylindrical coil is solved using the method of separation of variables. Using the truncated region eigenfunction expansion (TREE) method, the series expressions for the radical and axial magnetic induction intensity are obtained. The finite element simulation validates the analytical model of the surface magnetic field. The results obtained from the two calculating methods are almost identical. Based on the proposed model, the influences of size and hidden depth of cylindrical corrosion on the surface magnetic field are analysed. The two characteristics of transverse influence node and longitudinal influence area are extracted from a butterfly-shaped graph to quantitatively analyse and evaluate the cylindrical corrosion. The influence node gradually moves backwards in the radial direction as the corrosion radius increases. Together, the thickness and hidden depth of the corrosion determine the longitudinal distribution of the surface magnetic field. The thicker the corrosion, the larger the influence area becomes, whereas the deeper the corrosion, the smaller the influence area becomes. The analytical model is used to formulate the theory of eddy current testing and provides a reference for the detection and characterisation of defects in practice.
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Document Type: Research Article
Publication date: September 1, 2018
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- Official Journal of The British Institute of Non-Destructive Testing - includes original research and devlopment papers, technical and scientific reviews and case studies in the fields of NDT and CM.
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