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This article is based on the associated linearity of magnetic flux leakage signal eigenvalues and detection status information, proposing a methodology that applies multiple magnetic flux leakage signal eigenvalues to evaluate defects and goes a step further in conforming the limitation of the traditional evaluation system, which merely uses signal peak values. In response to the situation that magnetic flux leakage testing signal peak values have been applied as the main parameters to evaluate defects and carry out various related research, we find that the single magnetic flux leakage testing signal peak values cannot exactly represent the leakage magnetic field and reflect the information of the defects. So we attempt to come up with a new way of defects evaluation to better and more accurately evaluate defects. By means of simulation analysis in simulation software ANSYS and experimental verification, the linear relationships between multiple magnetic flux leakage signal eigenvalues and defect parameters through which we can exactly evaluate the defects are obtained, respectively. Finally, the validity of this evaluation system is firmly demonstrated by a practical defect. [ABSTRACT FROM AUTHOR]

Magnetic flux leakage (MFL) non-destructive testing technology is widely used. The MFL of a defect first increases with an increase in the magnetic excitation and is then thought to remain constant after magnetically saturating the ferromagnetic objects being tested. This trend is in agreement with the B-H curve. In this work, the change trends of the MFL are assessed by further deriving and analysing the MFL signal description, and a reduction of the MFL is found when the component is subject to strong magnetic fields. Later, using simulations from finite element models with various notch sizes and test conditions, the change trends of the MFL are further described and verified. Furthermore, the reduction of the MFL is also modified by reducing the primary origin of the magnetic compression effect. The work mentioned above elucidates scenarios involving increasing MFL and provides further knowledge about MFL mechanisms. [ABSTRACT FROM AUTHOR]

In magnetic flux leakage (MFL) testing technology, the MFL signals are thought to result from all defects and are used in their evaluation. The tested defects include two types of defects, concave and bump-shaped features, and recently described mechanisms in the MFL method indicate that the former defects produce positive MFL because of magnetic refraction and the latter ones produce negative magnetic fields because of self-magnetization regulation; consequently, these defects result in raised test signal waves and sunken test signal waves, respectively. Thereby, a new methodology for accurately identifying the defect type based on the mapping relation between the signal features and defect types is proposed. Both simulations and experiments with three representative defects (i.e., notch, protrusion and combination) were conducted to confirm their identification using this new methodology. Combined with MFL standards such as American Society for Testing and Materials (ASTM) E570-09 (Standard Practice for Flux Leakage Examination of Ferromagnetic Steel Tubular Products, ) and British Standards (BS) EN 10246-4 (Non-destructive Testing of Steel Tubes-Part 4: Automatic Full Peripheral Magnetic Transducer/Flux Leakage Testing of Seamless Ferromagnetic Steel Tubes for the Detection of Transverse Imperfections, ), suggestions for standard specimens with reference defects that consist of both types of defects are provided. [ABSTRACT FROM AUTHOR]