A New Magnetic Testing Technology Based On Magnetic Gradient Tensor Theory

The magnetic testing technique is generally considered to be an efficient and effective non-destructive testing (NDT) method and has been widely used in the ferromagnetic materials inspection industry. Interpreting magnetic signals and quantitatively evaluating defect geometry constitute the overall goal of the magnetic inspection procedure. In this paper, magnetic gradient tensor (MGT) theory is applied to detect and interpret pipe defects as a preliminary attempt at developing a new magnetic NDT method. The defect location and equivalent magnetic moment calculation formulae are derived from the MGT theory and the configuration of the MGT measurement system is optimised by defect location tests. The inspection experiment for pipe defects indicates that different types of defect have different equivalent dipole moment characteristics and the equivalent dipole moment gets larger as the defect volume increases. So, equivalent dipole moments calculated from the MGT can be used to quantitatively evaluate defect geometry and assess defect severity.