Investigation of the role of a nonmagnetic spacer in local wall thinning inspection

Detectability of an artificial slot, placed at the bottom of a steel plate was investigated by the method of Magnetic adaptive testing (MAT), when the measurement was performed through another steel plate. Influence of an air gap (or of a nonmagnetic spacer) located either between the magnetizing yoke and the top plate surface or between the two plates was explored. It was found that if the thickness of the nonmagnetic spacer was not larger than 0.15 mm, it had no influence on the detectability of the slot in the given geometry. This result shows an excellent applicability of MAT, and it is encouraging for possible future practical applications. The empirical data were compared with results of an electromagnetic simulation, and the outcome was interpreted and explained.